RB30, potential auto choke issue?

[Throbbinhood]

Hey guys, have a bit of a weird one that I haven't been able to quite sus out...

Every now and then (3x in the last year), when I'm driving in very cold conditions (late last night, in the snow the time before that), I'll be driving and while partial throttle will be ok, anything past half throttle results in the car bogging down and losing power. If I clutch in and try to give it a bootful, she'll bog down and wont get past 3k rpm. If I clutch in without revving it, she sits around 1500rpm, higher than her usual 800-900rpm idle. By the time I pull over to whip the top of the airbox off to have a look, the issue seems to resolve itself. Last night, I just pulled over for a minute and let it idle, and it was all good.

Would I be right in thinking it could be improper operation of the automatic choke? That basically, on the freeway last night, intake temps were so low it caused the choke to kick back in, and so when I'd put the foot down she'd run rich because she wasn't getting enough air? Would also explain the high idle?

Is there an adjustment for when the automatic choke kicks in, or can I disable it somehow?

[mudnut]

It sounds like the
second stage of
the carby sticking.

[Throbbinhood]

It sounds like the
second stage of
the carby sticking.

Nah, I checked that, it all moves quite free, vac operation is all fine.
I spoke to a carby shop. They said that because I've plugged the air heater thing (the heatshield over exhaust into airbox section) that it could be causing the whole thing to be too cold.

I can't surely be the only one that's plugged this? Otherwise we'd all have water in engine at any crossing...

Does anyone know how the automatic choke is activated? Is there a thermostat somewhere for it?

[mudnut]

Check that the choke break
diaphragm ( top rear of carby)
isn't holed
or split. Its job is to
pull the choke off and
keep it there.
And/or unblock the
pre-heat flap for the cold
weather.

[Throbbinhood]

Check that the choke break
diaphragm ( top rear of carby)
isn't holed
or split. Its job is to
pull the choke off and
keep it there.
And/or unblock the
pre-heat flap for the cold
weather.

I'll check the choke break.. The preheat flap was all stuffed, and it's not a sealed thing.. Can carbies not operate cold at all? What difference does the cold air make once the car is running and at temperature?

[Patrol'n]

Nah, I checked that, it all moves quite free, vac operation is all fine.
I spoke to a carby shop. They said that because I've plugged the air heater thing (the heatshield over exhaust into airbox section) that it could be causing the whole thing to be too cold.

I can't surely be the only one that's plugged this? Otherwise we'd all have water in engine at any crossing...

Does anyone know how the automatic choke is activated? Is there a thermostat somewhere for it?

You're definitely not the only one with the stove/ heater pipe plugged mate.

I've had mine plugged for ages without issue. (Had a different issue recently with idle but I believe completely unrelated), likely to be dirty fuel in the idle circuit. I have not found any adverse affects from plugging the pipe many months ago, no affect on choke operation at all.

[mudnut]

I re-read your post
and it really does
sound like the second stage
binding while cold.
As the revs rise to 1500.
It is almost a carbon
copy scenario of what
happened to mine.
Also check the screws
inside the carby.

[dom14]

Nah, I checked that, it all moves quite free, vac operation is all fine.
I spoke to a carby shop. They said that because I've plugged the air heater thing (the heatshield over exhaust into airbox section) that it could be causing the whole thing to be too cold.

I can't surely be the only one that's plugged this? Otherwise we'd all have water in engine at any crossing...

Does anyone know how the automatic choke is activated? Is there a thermostat somewhere for it?

I removed the exhaust manifold shroud ages ago. The foil hose that connects the exhaust hot air to the air cleaner was never connected. So, plugging the hose shouldn't cause any dramas. Mine's going fine without any of it.
choke thermostat is a bimetal spring inside the auto choke housing. As the engine warms up the spring absorbs the heat and expands, which effectively open the choke flaps to make the mixture leaner.

Your issue is not likely caused by the auto choke closing the flaps by cold air intake when the engine is already warm.
It's more likely WOT circuit issue, rather than the idle circuit issue.

If you look at the picture, there are three screws that you can loosen and then turn the auto choke clockwise or anticlockwise to make it lean or rich. There's a mark on the plastic and the carby body to align it. Normally you don't need to touch this at all. In my experience, the bimetal spring rarely wears out or fails. But, whether the flaps or the shaft get stuck inside from gunk is another issue, and it is a possibility, but not common. Even though if that's the case, running bit too rich shouldn't rev limit & bog down the way you described it. Having said that, make sure the electrical connections to the auto choke is not loose or disconnrcted somewhere. I don't think the auto choke is the issue, but it's worth checking it anyway.

If the carby has never been rebuilt, then it's time for a one.
In the meantime, get a carby cleaner and spray generous amounts of it while revving the engine(warm engine).
Spray into the throttle as well as choke flaps. Hopefully that will clear up any blockage and friction and solve the problem.

Not sure how the depressing of the clutch makes the revs jump from 800 to 1500(I'm guessing on neutral). Somebody might be able to explain it.

[dom14]

It sounds like the
second stage of
the carby sticking.

Yeah, I think that's the case.

[Throbbinhood]

The rev's aren't jumping from 800 to 1500... My normal idle is 800rpm when the car is warm... So, driving down the freeway normally, car fully warm, idle's at 1500.. Until I'd been driving down the freeway for a fair whack of time and then I experience the 'bog down' issue, and I press the clutch in, my idle is 1500 - same as when the choke is operating and the engine is cold.. Hence my train of thought of a choke issue..

WOT with car warm/day weather and car hauls ass. It's only after a long freeway run late at night, and a snow drive that I've had these issues.

I double checked the secondary butterflies, moving freely, no sticky spots on the carby, it's operating correctly.

Spoke to another carb specialist about the stove pipe, he said it shouldn't make a difference in vic temps.

[dom14]

Yes, stove pipe thing shouldn't make any difference in VIC temperatures. But, dunno about sub zero alpine temperatures though, which can depend on your carby condition and tuning. Mine doesn't have the stove pipe or the shroud at all. Drives just ok in high altitude, but fairly gutless. I think the moist air doesn't help and even though the cold air does help for more boost in theory. The solution is to make the air/fuel mixture rich, which I'm not too sure the job of the auto choke.
It's not too hard to find out whether the auto choke is working ok, but an intermittent problem can be pretty tricky to locate.
Sticky throttle shafts can be intermittent issue, or may not show during your typical throttle test.

You can also try what I suggested above, which is adjusting the choke lean/rich setting.

I would first give the carby a good carby cleaner spray clean while revving high.
IF that doesn't help, pull the carby out and tighten the three bolts that holds the throttle body to the float.
Since the gaskets aren't available on their own, you might have to cut the gaskets using gasket paper or spend $78 and get a rebuild kit.
If you do rebuild it, take time and do it properly. Plenty of carby cleaner to clean the interior passages and plenty of high pressure air to clean the gunk.
Be careful with the plunger boot, as it can break easily. Don't loose any springs or balls inside the float, 'cos springs aren't included in the typical rebuild kit.

[Bigcol]

I think you will find it will either be the Needle and seat in the carby
or
a blockage in the fuel line

works fine
except when cold late night

check the connectors to the fuel pump at your tank

[dom14]

Just to be sure, check the fuel pressure, fuel filter(change it) and check and clean the gauze filter.
Intermittent fuel pressure problem due to a faulty fuel pump connection or fuel pump fault issue can be hard to diagnose.

[Bigcol]

Just to be sure, check the fuel pressure, fuel filter(change it) and check and clean the gauze filter.
Intermittent fuel pressure problem due to a faulty fuel pump connection or fuel pump fault issue can be hard to diagnose.

it IS hard to diagnose
long laborious headache
yes, check all filters, lines etc - maybe filter is partially blocked - with cold weather it is blocking the feed in
make sure there is no leaks from any of the lines - while under pressure
check all wiring & connectors - anything that looks dodgy - replace

last 2 ports of call
carby kit - or professionally serviced exchange
pull out tank and clean tank and filter in pump

however,
not revving is fuel starvation - which could be blocked filters
or
the Needle and seat is not opening - the spring maybe cactii - or the rubber tip may be on its way to being cactii

[dom14]

tank pump failure is rare in RB30 s. But, bad electrical connections can create havoc.
Checking fuel pressure can rule out fuel pump/blockage issue. Better to do it while revving the engine high and low, to make sure the pressure is enough for both idling & WOT.

[Throbbinhood]

Turned out to be a hole in one of the vac lines - or so I believe - replaced the line but haven't had any cold enough weather.

Silly me, I didn't mark the choke's original position before I adjusted it. Does anyone know what the factory or ideal setting is for these?

[Throbbinhood]

Any ideas?

[dom14]

Any ideas?

There are marks on the choke bimetal piece and the choke body. Normally two marks need to be aligned with each other to be optimum.
But, in some cases you might have to turn clockwise or anticlockwise to make it rich or leaner, depending on the seasons or the climate.

Ideally, when cold starting, the choke flaps should totally close the passage.
But, mine never did that, but the vehicle was starting fine without it. It was kinda slightly open even when freezing cold, allowing some air to pass through.
I'm yet to experiment with it to see whether it helps to adjust the choke to close the flaps completely during the winter.

[Throbbinhood]

Thanks Dom. Looks like the one in the picture is adjusted a bit off haha! I'll line it back up and see how we go! Still starts alright with it off, but coughs and splutters a bit more than I'd like.

[dom14]

Thanks Dom. Looks like the one in the picture is adjusted a bit off haha! I'll line it back up and see how we go! Still starts alright with it off, but coughs and splutters a bit more than I'd like.

Hi Chris,
No problemo. The choke flaps are slightly opened in mine(cold starting) when the choke alignment marks are lined up. Only way to close the choke flaps completely when cold was to turn the choke bimetal assembly anticlockwise. For some reason, I didn't feel right about it, so I left the factory setting of them lined up. What you see in the picture is when I was fiddling with it.
Let me know, if yours is the same, and don't be afraid to experiment with it. Bimetal spring is pretty strong. You can't break it unless you turn it 180 degrees or something.
Cheers
Dom

[dom14]

BTW, vacuum leaks are PITA. The only way to find and diagnose vacuum problems for sure is to use a vacuum tester. It's around $20 or so on ebay. Too cheap to not to have a one.

[Throbbinhood]

Hey Dom (or anyone else),

Is the cold idle speed set by the choke opening/closing, or is there something else that controls the cold (fast) idle speed? And if so, is it adjustable, and how?

[dom14]

Hey Dom (or anyone else),

Is the cold idle speed set by the choke opening/closing, or is there something else that controls the cold (fast) idle speed? And if so, is it adjustable, and how?

Fast idle cam(the white plastic half moon thing) has three "steps" on it that sits on the throttle lever to keep the cold idle high enough during a cold start. Other than that, there's a fast idle screw that adjusts the idle speed. It basically pushes on the idle lever to control/adjust the idle speed. Turn it clockwise to increase the idle speed and vice versa. Idle mixture screw is on the throttle body, which you probably don't wanna touch at this stage. Adjust the fast idle screw if your cold idle speed is too low. But, make sure you don' get it mixed with the idle mixture screw. Idle mixture screw is at the bottom, in the middle of the throttle body & the fast idle screw is above it towards the left, just above throttle lever.

To give a direct answer to your question, I would have to say yes and no.
No, 'cos choke is not directly connected to the fast idle, but yes 'cos choke is indirectly connected to the fast idle cam.

What is the problem you're having atm?

I'm also fixing my carby atm. Right now, I'm trying to determine on how to definitively test the bimetal spring of the auto choke. When I find the proper way to do it, I'll post it on my other carby thread.
I have the Gregory's manual carby pages. I'll scan it when I get a chance and post it on "RB30 facts..." thread.
This time, by the time I'm done, I'm hoping to be an RB30 Nikki carby specialist. :D

Check this with your carby. Open up the air filter and let the engine run and warm up.
Once it's fully warmed up, see whether the choke flaps are fully opened(flaps in the middle) or partially opened.
Let me know what you find.

I'll post some pictures tomorrow morning to accompany my description above.

Cheers
Dom

[Throbbinhood]

Thanks for the reply Dom.

It's sort of hard to describe.. The car always seems to have a high idle - 1000-1200rpm. When first started, she's usually higher, around 1800rpm. It seems to take an age for it to come down to 1200.

Adjusting that fast idle screw seems to make no difference when the car is cold. After a long highway drive the other day (lots of hills), I readjusted the idle to 750 and it was beautiful. But low and behold, when I took it for a drive a few hours later, the idle was back up to 1000-1200. It's acting as if it's not getting warm enough to stop the 'cold start' mixture or whatever it is, and so it affects my idling as if the motor is cold.

I'll take the lid off on a cold start, see where the choke flap is, then drive it around until she's warm and check again and report back.

I'm trying to avoid a carby rebuild as money is tight with a few other priorities coming up.

[dom14]

Hi Chris,
First of all, I might have to take back what I've previously posted about your choke circuit being ok. I'm no longer certain about that. I just opened this thread to ascertain the choke is working without any issues and to understand bit more about it's correct functionality.

http://www.nissanpatrol.com.au/forums/showthread.php?35137-Auto-choke-test-help&p=632711#post632711

Also, I should mention, when cold, the choke flaps only completely close for a fraction of a second when you crank. When the engine's running, the flaps are slightly open via the Choke Breaker vacuum mechanism. It's on the top of the carby with a small vacuum diaphragm and lever attached to the choke shaft.
As the engine warms up, the flaps should move towards the middle and fully open(I'm guessing it should be fully open on a normal warm day, unless it's freezing cold or something). Mine doesn't fully open atm, and when I manually force it to open fully when warm(by turning the choke assembly clockwise), the engine appears to be running better, as far as I can see and hear. So, I'm wondering whether the choke gets bit crooked from years of use. Leaving the choke assembly turned clockwise to lean the mixture is ok when warm, but not so when it's cold, so it's not a solution.

About rebuilding the carby, carby rebuild kit is around $78. But, you don't necessarily have to buy that.
You can tear apart the carby and rebuild it by cleaning it properly. You can cut the gaskets using gasket paper, normal thick cardboard(same thing basically). If the old gasket is not damaged and usable, apply bit of white lithium grease to help it seat better. Cutting the float bowl gasket is not as easy as the bottom end gaskets, but perfectly doable. You will need a ute knife, a leather hole puncher that you use to cut holes on waist belts, etc. Rather than outlining the gasket layout using the old one, I use acrylic paint to stamp the gasket layout using the carby float compartment. That way you get the tiny holes in the middle of the carby accurately placed on the paper, so there's no chance of them coming out of alignment. Once you get hold of the technique, it's fun, especially if you enjoy desk tech jobs. :)
Even with a new paper gasket, whether you cut it yourself with paper or whether you bought it, it's good to apply a thin layer of white lithium grease to help it seat better as well as to help on reusing the same gasket again. Lithium grease has no clogging effect on carby passages.

So, I say go for the rebuild job and take plenty of time. Follow my previous carby threads. I'll scan the Gregory's carby pages in the meantime and post here on the "RB30 facts....." thread soon.
If you don't have a compressor and blow gun, dip the carby parts in petrol or other solvent for a half a day or so. But, make sure you remove the parts with rubber diaphragms, or else they will get damaged by any solvents.
In case if you don't have an air compressor setup, or a mate nearby with a one, you can use mine at my joint.
Let me know if you need help with that.

So, I say, go for it and rebuild it yourself. It's obviously long overdue for a rebuild. Since it's a petrol only engine, I bet your carby is in far better condition than mine. All it need may be a good clean inside and out.

[dom14]

To add further bit more, it's more than likely that your carby issues are nothing more than clogged passages, needle sticking or throttle valve sticking, etc. A good, careful clean should fix it.
If the plunger boot is in good condition(or even not), make sure to be super gentle if you have to remove it. The rubber boot can easily break when you try to take it off or even worse when you try to put it back in. I managed to break the brand new one, and had to use superglue to fix it(not a good thing). Applying bit of grease to the plunger boot hole & the plunger rubber boot should help with the installation.
So, the patience it s good virtue when it comes to rookie carby building jobs. Take plenty of time with carby rebuilding, unless you've done it plenty of times before.

[Throbbinhood]

Last time I had a crack at pulling it apart, I only ended up getting a bit of it apart before I realized I was out of my depths :P

I'll check the choke operation when cold, and see if she opens fully when hot and go from there.

For what it's worth, when I had the choke adjusted all the way off the other week, she was idling at 750-800 perfectly - she was just hard to start. Hopefully I can play with the choke adjustment and find a happier medium.

Thanks for the advice too. :)

[dom14]

You probably answered this question million times so far. In anyway,
have you checked to see there are no vacuum leaks at all?
Only way to confirm vacuum leaks is to use a vacuum tester, which is a cheap tool.
You can use water spray, soap water spray, WD40 spray etc etc on suspected areas, but doesn't give a result as good as the vacuum tester.

[Throbbinhood]

Yeah, been through that as well haha. No leaks.

[dom14]

Yep, you would have to rebuild the carby. Get over your carbyphobia and take a crack at it.
You can do it! Tear apart the bastard and fix it. :D

P.S. If any screws are too tight to undo, give a gentle tap on it with the screw driver & a small hammer.

[dom14]

I would love to help you out with your carby, man, but I'm up to my butt with my own carby drama, as well as other work I've been trying to finish on the car. :)

[Throbbinhood]

Haha thanks man, yeah I've got a trip on this weekend, so I'll deal with it for the moment. After that though, it's going to be a while until I'm headed anywhere, so should have some time to hopefully pull it apart and go from there. Does the carby rebuild kit come with replacement jets and things?

And what other things are you doing to your rig? How'd you go with the 35's?

[dom14]

No 35"s yet. I reckon i stay with 33" for the time being. I will consider 35"s when I turbo it in future.
I'm fool proofing the rig with overheat sensor alarm, oil pressure sensor, centerlocking, A/C system fix and regas, have both carbies fixed and ready, have the spare dizzy fixed and tuned for gas, bike rack project, dual battery project, have some plumbing done for a third gas tank and redo the plumbing to be able remove the auxiliary tanks when ever I need it, etc etc.
Yeah, quite a load of shite to go. Not sure I get all done, but I'm doing my best. Ah....of course, the windscreeen rubber needs replacing as well, and I dunno whether the water leaks have screwed up the metal edges of the body on the windscreen rubber area. I'll find out soon. Ah......of course, I got side steps that needs attaching as well. So, it's a crap load of work to do, only friggin 24 hours for a day. :)

Carby kit comes with needle, needle seat, balls, washers, all the gaskets, accelerator plunger and the rubber boot, but no jets AFAIK. I wish the kit comes with jets. But, who knows. Look around, you might be able to find a kit with jets. I had no luck so far. If there's a kit that comes with jets, I would buy another kit for sure.
May be the jets need sourcing separately. I'm not sure. I'll look into it.

I'm pretty confident, your carby only needs a good, careful clean only(low kms & not on LPG). You will need compressed gas for sure to clean it properly. Just have to make sure all the flying parts like balls, plugs, etc are removed before you do that, otherwise they fly into orbit to be never seen again. I'm loving carby repairs('cos they are desk tech jobs. :) ), but some blokes can't stand that kind of work. See how you go, and keep me updated. By the time I'm finished with the two carbies, I will know a lot about this RB30 Nikki carby.

Cheers
Dom

[Throbbinhood]

Well, as an interim measure (as I had to drive it long distance over the weekend and couldn't pull the whole thing apart for a clean), I had a bit of a play with the automatic choke adjustment.

Found a happy spot, where it's a fair way closed for starting, but seems to open up fully much more quickly. Long story short, she starts first time - will idle at around 1200 for 20 seconds before starting to lower. First minute of operation is a bit lumpy while the carby warms up, but that's fine as I normally leave it sit for a few minutes anyway. Very happy!

[dom14]

Well, as an interim measure (as I had to drive it long distance over the weekend and couldn't pull the whole thing apart for a clean), I had a bit of a play with the automatic choke adjustment.

Found a happy spot, where it's a fair way closed for starting, but seems to open up fully much more quickly. Long story short, she starts first time - will idle at around 1200 for 20 seconds before starting to lower. First minute of operation is a bit lumpy while the carby warms up, but that's fine as I normally leave it sit for a few minutes anyway. Very happy!

That sounds pretty good. If it stays that way, you don't need to worry about anything more.

[Throbbinhood]

That sounds pretty good. If it stays that way, you don't need to worry about anything more.

Yeah so far should do the trick. Coming into summer shouldn't matter so much. Potentially look into it when it starts getting cool again :P

[garett]

i choke with my right foot... i know its not quite the same but it works where i live .

[Patrol'n]

Hey mate, sorry to be off topic here, but I see you run 33's on your GQ, how do you find them with a Carbie RB30, does she still drive ok?

[Throbbinhood]

That's for you Dom. FWIW, I run 35's, and I find it fine. Cruising at 100 I got better economy in 4th, as she labours a bit in 5th with 35's. 110-120 and I pop it into 5th.
That said, I don't mind revving her out to 4k to get up to speed, but honestly, I'm pretty happy with it.

Dom14 will be better placed to answer re: 33's.

[Patrol'n]

That's for you Dom. FWIW, I run 35's, and I find it fine. Cruising at 100 I got better economy in 4th, as she labours a bit in 5th with 35's. 110-120 and I pop it into 5th.
That said, I don't mind revving her out to 4k to get up to speed, but honestly, I'm pretty happy with it.

Dom14 will be better placed to answer re: 33's.

Thanks for that, I have thought about 35's but I always thought they were a touch too big for my engine, although your experience with it being ok is interesting, I may get a set of 33's and wish I'd gone 35's. Do you find any serious negatives, acceleration, braking, fuel economy and crawl speed in low range?

[Throbbinhood]

Thanks for that, I have thought about 35's but I always thought they were a touch too big for my engine, although your experience with it being ok is interesting, I may get a set of 33's and wish I'd gone 35's. Do you find any serious negatives, acceleration, braking, fuel economy and crawl speed in low range?

I don't drive it like a race car, but acceleration still seems fine to me for a big car. Braking I certainly noticed a difference, but that just required a slight driving style adjustment. She still pulls up if I really put the foot down. Fuel economy, on the highway I get 15-17L/100km, depending on the area (hilly hwy/vs flat). She sucks at keeping 100 up the hills, but she sucked on 31's too. I find if I gear back to 3rd and hold her at 3500 she'll sit on 90 up most biggish hills. Crawl speed in low range can be a little sucky. I'm still running the std 4.3s. Being a manual, going up steep hills, and trying to do it really slowly, isn't too ideal - especially with the rb30's tendency to stall in the steep stuff. That said, I've done a fair bit of high country stuff and it hasn't been an issue. Steep downhills are a bit more of a pain, but having just tinkered with my choke stuff bringing my idle back down to a normal level, I'm hoping I get a bit more control at lower revs.

Haven't had this rig on 33's, but love the 35's and the positives, in my eyes, far outweigh the negatives.

[dom14]

Hey mate, sorry to be off topic here, but I see you run 33's on your GQ, how do you find them with a Carbie RB30, does she still drive ok?

It's ok, the take off was bit sluggish previously, but now since I've put two carbies together to come up with an overall better carby, it's got bit more grunt. Since the carby base directional cup thing has been removed(broke off), it looks like there's a bit of improvement as well. Also, since I fixed the auto choke, the flaps are fully opening when warm now, so that gives a bit more grunt as well. I'm yet to remove the carby base plate heater grid thing, so I'm hoping there will be more improvement after that. Only thing is that I feel less in control of the car in terms of stability, but I reckon that feeling will go away after I'm used to drive on higher wheels. :)

And yeah of course the braking experience may be different as well, you may feel sudden braking seem to take bit longer to come to a complete stop.

[CaptainNewman]

Hey fellas, sorry for the dig, can start a new thread if needed...?

Have had a similar problem to the OP for the last 4 years. Driving in cold weather, whether in a long highway run or a pop to the shops, the RB30 sometimes seems to lose power, like it's rev-limited. On a night highway run once, I ended up foot to the floor and slowly went from 110 to 100...90...80... Pulling over for a minute or two usually fixes the problem for about half an hour, before it occurs again.

Have had the carby rebuilt twice, new fuel pump, vac hoses, filters etc. etc. The vacuum operated flap for the (non-existant) pre-heat/stove-pipe thing over the exhaust manifold works OK. Had a tune in Summer this year, ran & idled great, but now in the cold weather idles a bit poorly until things warm up.

The problem shows up on my permanantly-installed (in the cab) vacuum gauge. In normal running, 'foot to the floor' (FTF) on the acclerator causes manifold vacuum to go to 0mm/Hg (e.g. atmospheric pressure), indicating open throttle. When the 'losing power' problem occurs in the cold, FTF only causes vacuum to go to 5mm/Hg, or even 10mm/Hg, and *feels* like its only on half-throttle or something (even tho FTF!).

If you keep driving with FTF (say in 4th gear at 100km/hr), the vacuum will slowly creep up from 5mm/Hg, to 10, to 15. This corresponds to a loss of power and before you know it, your doing 60km/hr along the freeway.

Pulling over and leaving the engine idling for a few minutes fixes the issue. This made me think it could be the carby icing up, but the issue occurs even over short drives...

Anyone's ideas to the rescue ?

[mudnut]

When you rebuilt the carby, did you have a go at making the second stage bore nice and smooth, with wet and dry paper?

I use a piece of vacuum hose blocked with a small ball bearing on the pre -heat diaphragm in the warmer months. In winter I swap out the blocked hose so the pre-heat works.

I also fitted a manual choke cable. After doing all of the above, the cold weather problems have thankfully disappeared.

The mechanic who built the engine for me also made the idle mixture a bit richer.

[CaptainNewman]

When you rebuilt the carby, did you have a go at making the second stage bore nice and smooth, with wet and dry paper?

I use a piece of vacuum hose blocked with a small ball bearing on the pre -heat diaphragm in the warmer months. In winter I swap out the blocked hose so the pre-heat works.

I also fitted a manual choke cable. After doing all of the above, the cold weather problems have thankfully disappeared.

The mechanic who built the engine for me also made the idle mixture a bit richer.

Thanks Mudnut. By pre-heat diaphragm do you mean the vacuum-operated flap on the air intake that opens above the exhaust manifold? Mine works but is missing the original sheet metal that would have funneled warm air from the manifold into the airbox via the flap.

Exhaust tip is sooty so probably running fairly rich as it is... Might have to look at fitting a manual choke. Did you find it difficult to fit etc?

Had a 10°C day in Adelaide today, on the short cold/rainy run uphill tonight home from work, the poor old Patrol barely made it up. Ended up in 1st gear doing 20km/hr, foot to the floor. Pulled over at the top and after a few minutes idling everything was back to full power and off I went. Very strange !

[mudnut]

Do you mean the tin shroud and the corrugated hose are missing? When I first had the headers fitted, I used a bit of exhaust pipe welded to a u bolt to anchor the hose to a pipe.

I eventually modified the shroud to go over the headers.

There is a hole drilled into the metal dash level with the hand throttle, on the P/S of the steering wheel. That is a convenient point to fit a choke cable kit.

I removed the autochoke housing and made a sheetmetal bracket to fit the choke cable to the butterfly lever. It works quite well with a bit of fiddling to set it up.

I bought a used hand throttle, gutted it and modified it to fit a cheap cable kit, which gives it the ability to be locked at any position.

To fit the cable I drilled a small hole in the hand throttle shaft, so I could thread the cable through to anchor it.

[CaptainNewman]

Do you mean the tin shroud and the corrugated hose are missing? When I first had the headers fitted, I used a bit of exhaust pipe welded to a u bolt to anchor the hose to a pipe.

Yes my tin shroud and corrugated hose went missing long ago - someone must have decided it wasn't necessary ! Do you think it makes much difference to cold weather carby performance ?

[CaptainNewman]

When you rebuilt the carby, did you have a go at making the second stage bore nice and smooth, with wet and dry paper?


Hmmm, after trawling through the forums perhaps sticking secondaries might be the culprit after all ? Would it make sense for them to stick more in colder weather, and for the problem to go away once the car is left idling for a few minutes?

I had a look into the top of the carby today. Could operate the secondary throttle linkage by hand with the airbox off, and see the secondary butterfly move in the bore. But couldn't manage to move the linkage/butterfly by hand when the engine was running... Gave it a rev to well over 4000rpm and the secondary butterfly didn't seem to move at all...

Should I be able to see movement of the secondary butterfly when revving the engine ?

Thanks for your help fellas

[mudnut]

Definitely made a difference to my Trol. The 2nd stage butterfly wears a groove in the carby bore. When it is cold the bore shrinks onto the butterfly. The couple of minutes sitting on a warm engine is enough to free it up. Having the pre-heat sped up that process.