Has anyone had a pcv valve stick or fail on an A12 GX. I've got an uncontrollably high idle - running twin SU's - and even with the butterflies fully closed it idles at 2000.

There has to be an air leak somewhere and the PCV valve seems most likely.

I'm going to try blocking it temporarily just to see what happens.

Can't you just block the PCV valve premently? I know the EPA doesn't like this kind of thing but wouldn't it take the problem out of the equation.

If it is faulty I'll block it and run crack case ventilation to a dedicated filter somewhere else.

It's no issue in Australia - but if I can keep it and if it is working it is a more elegant solution that a seperate filter.

Blocking the PCV valve should drop your idle speed a little bit -- if it is working correctly. But a stock A12/A14 will idle smoothly at 600 rpm with it connected.

You can usually clean the PCV valve with spray carburetor cleaner. If the spring is broken, replace it.

I'm unable to test the motor running as I am currently w/out radiator.

But - I removed the pcv valve and when I shake it the internals move around freely.

If I suck through the bottom of it (simulating negative pressure at the manifold side) air comes in freely - If I blow through the bottom (simulating neg pressure at the crank side) no air moves as the inner part of the pcv valve moves and closes.

Surely if the pcv valve were in working order the spring inside it would at least restrict movement of its internals enough to prevent opening or inlet of air unless the crank case needed to vent.

I assume that seeing as I could freely suck through it then my motor has a huge air leak on the inlet manifold.

Perhaps if I plug the manifold where the pcv valve was then the motor may run a whole lot better.

I think I'll just filter the crank case via the main air filters on the carb by tapping into the air filter backing plate. Seeing as this is a point far higher than the cyl block I don't expect to get any fluids pushing up and out there.

Seeing as the pcv valve doesn't come apart does anyone have any idea how to replace the spring.

From my experiance the PCV is only there to release the pressure built up in the rocker cover.

If you disconnect it from the aircleaner whislt running it should hiss :)

I cannot see how it can change the idle speed.

So i think that must be in your tunning or something :)

Is it a 1200 GX with round top carbs, or the later type with square top carbs? The later types have more plumbing & more places to leak air plus a couple of air bypass adjustments, If you have the latter type then try to get a 180B SSS workshop manual as the twin carb setup is pretty much the same & the adjustments will be right there in print. If everything is OK then procede to plan "B" below

If you have the early stuff like mine, then just pop the hose off the valve & put your thumb over it with the engine running. If the idle returns to normal, you have your answer. This valve is the same as the stock 1200 one, & the last time i bought one, they were not expensive.

Removing one permanantly from a perfectly good street engine is what loosers do.

They have NO negative impact on performance, & anyone who has the faintest idea how they work would know that. They also help keep your engine clean, both inside & out.

I somehow suspect that you have a gasket [or other] leak into the manifold.
Good luck
Chris

could also be the carbs are not in sync with each other, could lead to high idle and very rough running engine, you may be able to check by running engine and look at air valve height through front of carb if one is higher than the other that carb is flowing more air
Bob

It did have flat top twin carbs on it but they were knackered so we've started with a twin 1 1/2" SU conversion (really similar carbs).

Both butterflies are closing the same amount. The rear carb has it's piston way higher than the front one and is definitely flowing more air.

I intend to keep the pcv valve if I can find a replacement.

I wonder if there could be a leak between inlet and exhaust somewhere on the manifolds.

I would dissconect the linkage between each carb and adjust the carb idle screws untill flow is same with both carbs, need to check with flow meter, if you don't have one you can use a piece of 3/4 inch heater hose hold one end to front of each carb and other to your ear you should be able to get them close. if you you had a leak at the manifold it would run very lean and not pull air though the carbs