LPG Idle Ajustment GT40

[rossl]

On our GT40 engine there seems to be 3 different ajustments on the Impco LPG Carb cone shaped bit and body, as the idle is a bit lumpy i thought i would try and smooth it out.

1) Idle screw in middle of cone diaphram bit. (Says Idle)
2) Power tap on top of cone, set mostly towards R. (Says Power)
3) Spring loaded screw on side of intake, not on diaphram bit. (Seems to effect idle)

Looking on the net point 2) seems to only be for full throttle mixture ajustment, so i'll leave that.

Question is whats the difference between 1) and 3) ?

Cheers
Rossl

[saltwater_cowboy]

What mixer do you have?

Idle adjustment on impco mixers are extremely sensitive. Just a 1/4 turn either way can upset it and will cause incorrect mixture throughout the throttle range, not just at idle.

The idle is also controlled by the engine ECU via the air idle bypass so you need to figure that in when setting it up too.

Check for any vacuum leaks on hoses or the mixer. These will make the idle lumpy too.

[rossl]

Thanks for the info saltwater, have been doing some reading up on the air idle bypass valve you mentioned and the symptoms of a bad one seem to match what i'm seeing, lumpy idle, surging at idle, occasional stalling when put into gear.

Cheers
Rossl

[saltwater_cowboy]

If your suspecting the idle bypass then its worth removing it and cleaning it. They tend to get gummed up over time.

[rossl]

Took off the idle bypass and cleaned it with carb cleaner, lots of black muck came out, was a bit better than before, but after 4 hours or so started to act up again.

Reading on the net it seems it is only used for quick warm up cold starts and running air con or high drain accessorys, both of which does not effect us, would it be worth unplugging it and see what it runs like then, do i really need it?

Cheers
rossl

[saltwater_cowboy]

Its used to control the idle speed by allowing air to bypass the throttle plates. Simply unplugging it is unlikely to solve the problem.

It works by using a servo motor to open and shut a valve. If you unplug it with the valve in the wrong position you'll never get a smooth idle, it will either be too low and lumpy or too high.

If it ran ok for a while then played up again check the PCV lines to see if they are allowing excess oil to foul it up.