Fast idle on occasion after WOT runs. Cause?

[69427]

I noticed a problem with my 850DP Holley on occasion. I put it on after a problem with my 780VS when it (the 780) seemed to have injested some crap, and I haven't gotten around to fixing it yet.

Back to the 850. The idle doesn't return to normal quite often. If I blip the throttle a touch it comes right down. I've got dual return springs on the primary linkage so I don't think it's a weakness on the spring's part, and I don't necessarily suspect stuck advance springs in the distributor. I'm working under the car primarily at the moment, but once I get back to the engine stuff what should I look for? I'm assuming it's possible that the secondaries aren't closing all the way due to some linkage slop or shaft bind. Until I get back to the carb what are some suggestions for what to look for?

Thanks.

 

[mrvette]

Choke setting, classic, winter is coming, so cooler weather demands a less rich setting on the closure....I remember that from 1/2 a century ago on every carb I ever ran, especially with electric chokes....

:hissyfit:

 

[69427]

Choke setting, classic, winter is coming, so cooler weather demands a less rich setting on the closure.????????...I remember that from 1/2 a century ago on every carb I ever ran, especially with electric chokes....

:hissyfit:

What?????

There's no choke, and the problem happens on a hot engine too, frequently after coming off the track.

 

[mrvette]

Choke setting, classic, winter is coming, so cooler weather demands a less rich setting on the closure.????????...I remember that from 1/2 a century ago on every carb I ever ran, especially with electric chokes....

:hissyfit:

What?????

There's no choke, and the problem happens on a hot engine too, frequently after coming off the track.

sorry man, lost the title when reading the post, I"m outta here...


:friends::crutches:

 

[SmokinBBC]

I don't know squat about holleys, but maybe throttle cable sticking due to angle? Blades hanging up slghtly due to linkage problems?

 

[mrvette]

Dizzy centrifugal advance weights not coming back....rust? and wear...

never did see the studs on a old Pontiac dizzy wear out, but seen it on a Chebby HEI just recently...caused all sorts of strange operations....had to punch them out and replace with Poncho parts...works fine NOW....

:crutches:

 

[BBShark]

Are the return springs on the cable side or in front of the throttle plate? I had an idle problem with a carb where the springs were behind the throttle plate. The pull (in the same direction) on the throttle shaft from the spring and the cable caused problems that were corrected by putting the spring in front so that the force was pulling directly on the cable, not the throttle shaft.

 

[larrywalk]

I agree - putting a pair of throttle return springs in front of the throttle is a better configuration.

In addition, check the distributor flyweights for freedom of movement; also check the vacuum advance canister for freedom of action by applying a vacuum and then releasing it, letting it return to the static position. Vacuum diaphragms do get old and stiff and may not fully return to the correct positions.

 

[69427]

Dizzy centrifugal advance weights not coming back....rust? and wear...

never did see the studs on a old Pontiac dizzy wear out, but seen it on a Chebby HEI just recently...caused all sorts of strange operations....had to punch them out and replace with Poncho parts...works fine NOW....

:crutches:

Gene, I luv ya man, but do you even read my posts before you reply? I mentioned in the original post that I don't think it's the weights. I had the distributor out and apart a year ago (for lubing and endplay adjustment) when I put the new engine in, and the problem only popped up recently when I put the 850 carb on.

 

[69427]

Are the return springs on the cable side or in front of the throttle plate? I had an idle problem with a carb where the springs were behind the throttle plate. The pull (in the same direction) on the throttle shaft from the spring and the cable caused problems that were corrected by putting the spring in front so that the force was pulling directly on the cable, not the throttle shaft.

Unfortunately the springs are on the cable side. I originally wanted to put them on the front to balance the forces on the linkage and hopefully minimize the force/wear on the butterfly shaft bore but the air filter base sits so stinking low I couldn't package the springs in there. However, while I've got the base removed to check out the carb linkage I'll kick around how much rework/welding it would take to modify the base shape to allow clearance for the front-placed springs.

Thanks for getting me to think about this spring placement issue again. :thumbs: