Idle speed control

[stig]

Am having trouble with idle speed (stuck at 1200rpm) on my Demon carb. The butterflies seem to be sticking open. Even if I back the idle screw right off so that it's not even touching the mechanism, they won't fully close?

Also, I noticed on these butterflies that they have a bleed hole drilled in them - don't remember that on the GTR. Is it common?

[steve_d]

These carbs have linkages all over them so the opportunity to bind is high. Had similar with my Holley and had to go round until I found a burr on one of the arms. A quick tickle with a needle file soon fixed it.

Steve

Edit. have seen the drilling mentioned before as a tuning mod. can't remember what it was supposed to do for you.

Edited by steve_d on Saturday 15th July 21:58

[stig]

steve_d said:

These carbs have linkages all over them so the opportunity to bind is high. Had similar with my Holley and had to go round until I found a burr on one of the arms. A quick tickle with a needle file soon fixed it.

Steve

Edit. have seen the drilling mentioned before as a tuning mod. can't remember what it was supposed to do for you.

Edited by steve_d on Saturday 15th July 21:58

Thanks Steve. I've seen drilled butterflies before too. You'd normally do it to help idle characteristics, but in my case, it seems to be doing more harm than good.

Will strip it tomorrow and have a better look.

[eliot]

Also check that the butterflies are centered on the shaft. My throttle body plates were slighty offset causing a bind. Just release the screws a little (they are usually locktighted or burred over) and allow it to centralise and retighten.

[stig]

Just a quickie.

Seemed to have fixed my idle speed problem, so you may want to try this if you're suffering.

I never knew how much the float level affected the idle - until now! I backed my floats off to the recommended settings (both primary and secondary bowls were both too high), tinkered with the 4 idle mix screws and voila - one fixed idle The air/fuel meter jiggles between slightly rich and stochiometric which is just right I reckon. You can stand directly behind the car now without a gas mask - not even a hint of a tear

Now, when the engine's nice and hot, it idles at a rock steady 800rpm

The float levels directly affect the idle metering circuits so give it a try, you might be surprised at the results.

PS. The new louvres are doing their job admirably too!!!!