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fast idle cam adjustment- Engine warm, air cleaner removed- open throttle and close choke by handto bring fast idle cam into position (fast step). close throttle and let choke valve return to open position. restart engine without touching accelerator and note RPM. 2,000 rpm is correct for 400 and 435 hp v8s. bend tang on fast idle level to adjust
fast idle cam adjustment- Engine warm, air cleaner removed- open throttle and close choke by handto bring fast idle cam into position (fast step). close throttle and let choke valve return to open position. restart engine without touching accelerator and note RPM. 2,000 rpm is correct for 400 and 435 hp v8s. bend tang on fast idle level to adjust
That's what I read in the vintage "How it works"-bulletin from Chevrolet. But I don't understand .
What does it mean: "bring fast idle cam into position (fast step)."? Which position is it?
BTW: 2.000 rpm at fast idle seems to be (much) to high .....
most people recommend a lower fast idle, 1,200 to 1,500 rpm, the 2,000 figure is probably related to emission regulations.
My problem is, that I can't get any "fast-idle". When starting the engine cold, rev stays about 650 rpm, increasing with warming up. Only the warm engine has an idle at 850 rpm (and 650 in gear).
I was used to have a start-idle at 1000+, what slows down, after a short step to the acc-pedal and regulates then at 850 rpm.
After my carb-change, there ist no more fast-idle when starting the cold engine. I try to understand the choke-system, but can't find out, what brings the engtine to the high idle-speed at start. The descend obviously comes from the "falling-down" of the idle-cam when pushing the acc-pedal and opening the throttle.
Can anyone explain to me, how the system works and where I have to look after?
Unfortunately my Corvette-mechanic passed away last fall. He was an absolute Corvette-specialist with customers all over Europe. But he always "forbid" me to work on my own car ("hands off - bring it to me!") .
Now I have to learn to help myself and to understand, how it works.
carb change or rebuild? if change, where is the old one? compare them. the choke turns a piece with steps on it that a second idle stop rests on. as choke opens the piece turns so the high part is not under the stop screw.
carb change or rebuild? if change, where is the old one? compare them. the choke turns a piece with steps on it that a second idle stop rests on. as choke opens the piece turns so the high part is not under the stop screw.
It is the original equipment. I know about that "step-part" (green plastic-part) and the "stopper" touches it on the second step (from lower edge) - what seems to be correct.
Still I don't know, what causes the idle to increase on cols start (and let it fall after short "throttle open". I realize, that "throttle open" will make the "step-part" fall down, but that has no obviously effect on the idle-speed.
you have a divorced choke coil on the intake manifold connected with a rod to the choke mechanism on the carburetor?
when fully cold does the choke completely close after one step and release of the gas pedal?
if it does, the rpm when fully closed is adjusted by bending the tab in your first picture.
you have a divorced choke coil on the intake manifold connected with a rod to the choke mechanism on the carburetor?
when fully cold does the choke completely close after one step and release of the gas pedal?
if it does, the rpm when fully closed is adjusted by bending the tab in your first picture.
As far, as I understand, the step limits the opening of the choke on cold-start. As it is adjustetd now, it will not totally close the choke but let a small gap.
But as I've written before: Even if I close the choke by hand on cold-idle or if I open it a bit more, on idling engine there ist no increasing in idle-speed at all.
What shall increase the idle-speed and let it fall after throttle-opening?
As far, as I understand, the step limits the opening of the choke on cold-start. As it is adjustetd now, it will not totally close the choke but let a small gap.
But as I've written before: Even if I close the choke by hand on cold-idle or if I open it a bit more, on idling engine there ist no increasing in idle-speed at all.
What shall increase the idle-speed and let it fall after throttle-opening?
GR
I explained this already. that small cam that rotates around with different steps on it- that will dictate speed. how many steps are there? 3? you need to be on the last one. the choke flap on top of the carb simply controls the amount of air entering the carb. the cam and the steps control how far the throttle gets stuck open above idle.
is your engine stock? does the engine run good other than the choke not working properly? I run a tri power on a 496 and I could never get my fast idle to work properly. the choke works correctly, but the rpms never increased like the service manuals say they should.
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