RB30, potential auto choke issue?

[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.