RB30, potential auto choke issue?

[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.

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/forum...711#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.

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