Carburettor questions

[Seanm1ecy]

Hi all, winter over, so back to helping Chris with Project Zil

Ive stripped and rebuilt the carb, but have some questions.

1, what is the purpose of the large black spring loaded drive that has what looks loke a flexible drive pushing an arm down onto the throttle linkage?

2, there is a diaphragm on the left hand side of the carb that appears to be part of a vacuum operated rev limiter, the spring inside this linkage appears to hold thenthrottle open slightly, which makes setting idle speed impossible, does anyone have a picture of this linkage on a vehicle that has a decent idle set up?

3, what sort of idle speed should I be aiming for, normally on a big V8 I would be looking for around 600 rpm, is this the same for the Zil?

Cheers
Sean

[Calfdozer99]

Answer to no 1 is: It's the governor umbilical that comes from the step up ratio box on the under bumper mounted generator, it should back the engine revs off to 1000rpm whilst giving 3000rpm at the genny... Only when pto engaged though..

[Seanm1ecy]

Ah, that makes sense, and also suggests a way of setting it back up - I do not think it really worked properly from the first time we tried it.

More to do

[Calfdozer99]

Is yours the K135 carb?

I've been and investigated mine around the area you mention in question 2.

It is indeed the max engine rpm governor which I believe was designed to limit the damage of young Soviet conscription soldiers just pulling the hand throttle fully out, blowing it to bits and evading a bit of duty.

However, mine has been disconnected where the vertical rod meets the throttle arm..
It's definitely not needed by us enthusiastic types as we care for and listen to our engines..

It will be alot easier to set up an idle, generally tune without it.

I don't think mine has ever come close to over-revving and I've trundled about the country a fair bit now..

Scott

[Abrs]

Hi. On these carbs the rev limiting mechanism should not interfere with the carbs operation during normal operating ranges, it will only intervene once a valve opens when the maximum governed engine speed is exceeded, this valve spins with the engine and is a centrifugally operated spring and weight type, when a certain speed is achieved the forces acting on the weight open the valve and allow vacuum to operate the diaphragm located in the housing on the side of the carb, this in turn pulls the throttle closed until engine speed reduces, the rest of the time the mechanism has no effect on the carb as there is no vacuum present, if you are having an issue setting the tickover then there might be another reason. Regards

[Seanm1ecy]

I think the rev limiter is actually holding the throttle open a little, the spring that opposes the diaphragm is quite short, and shows signs of previous abuse.

I could really do with a picture of the spring and linkage from another carb woild answer some questions - does anyone have a carb laying around that they would be happy with popping the cover off for a look?

Otherwise the carb works quite well, if I manually hold the throttle against the throttle stop the engine idles sweetly at around 600 rpm

Cheers
Sean

[Abrs]

That's right the spring should be trying to pull the throttle open, it's countered by a constant (low level) vacuum which is present the whole time the engine is running, only when the centrifugal valve closes is there enough vacuum to operate the diaphragm fully which in turn pulls the linkage enough to reduces engine speed. I am sorry as I've just noticed in my last post I said valve 'opens' I meant closes, just to add to your confusion ;) . Anyway it sounds to me like you have a vacuum leak somewhere if the spring is not being countered, is the diaphragm in the top ok? There are also two drillings with jets going into the carb chokes, you might have a blockage there possibly, you can see them when the complete speed limiter housing is removed from the side of the carb. Also check for a poor seal between the housing and carb, or cracks in the casting itself, being located where they are means they can become damaged if say someone puts weight on it for some reason.

[Seanm1ecy]

Thanks for the info, makes a lot more sense now.

I have some more to go on now, but I think I will have to get shot of this particular bit of protection, it is provimg to ne a real pain in the bum!

Cheers
sean

[Abrs]

You can remove it, firstly you would need to remove that spring and uncouple the linkage from the end of the throttle spindle, secondly on the opposite side of the carb at the other end of the spindle there is a mechanism that gives the limiter 'free travel' in order to reduce the engine speed, this basically alows the spindle to rotate and close the throttle even if you still have your foot flat down on the accelerator pedal, this linkage arrangement would have to be locked so you have a direct effect on the throttle spindle.

On the other hand the limiter is not a bad thing to have working, and I'll bet it probably only needs a basic fiddle to fix it, like I've said you need a slight vacuum to work against the spring and hold it against the mechanism at the other side of the carb, without this idle speed is impossible. Just start looking for places where vacuum could be lost, the diaphragm in the top is the most obvious place to start, check it for perforations.

I'll try and get some pics of one of these in pieces for you, it'll make what I'm saying make more sense

[moose7576]

Anyone thought of replacing the original carb in the Gaz 66 with a more efficient alternative? Thinking that according to the threads it might offer slightly better performance and fuel economy to boot.

[Grommet1]

There's a thread here somewhere discussing webers I think
Regards
John