online170

Like the title says, it seems like a sticky throttle issue. Heres the description.

-1975 gen 1 SBC
-355ci
- Air gap manifold (no exhaust cross over).
- headers, (wrapped)
- 750 cfm holley double pumper (4150 series) with choke horn and choke plate, completely open.
- Mechanical secondaries.
- 1.25" drop base air cleaner.
- 3" tall air fliter, with a slight dome on the lid.
- There seems to be a slight vacuum leak, i can hear a whistling at idle to 1500 rpm.
- T56 transmission

If you need any other details let me know.

Behaviour:

I took the car on a 4 hour round trip yesterday (2 hours each way). Went through some rain and stuff, but i dont think that should matter. I like to run the car at 180* watertemp, measured at the intake manifold, next to the thermostat. However, because i was in 6th gear the entire way, i stayed below 1500 rpm the entire time. As a result, the temp was only 135ish. SO the car was running cool.

So after 2 hours of staying on the throttle at 1500 rpm, i put the clutch in, to shift gears, and it climbed up to 3000 rpm by itself, and stayed there. I had to blip the throttle quickly. It blipped up to 4000 and dropped back to idle (950rpm). Then i touched the gas again, to go in 2nd, and when i depressed the clutch pedal to go into third, it did the same thing. I had to blip again.... Did this a couple more times in between gears.

I noticed this problem shortly after the T56 install, but it didnt do it this badly before. It seems to get worse the longer i kept it under load, at a low rpm. It was only up to 2000 rpm before, and it would only do it sometimes, not between every gear, and not every time i touched the gas.

It also "holds the rpms high" when im braking in neutral, but thats a little different. It climbs to 1500rpm max from idle, (i think because the vacuum in the brake booster is low), and then the idle drops back down after ive stopped the car and no more vacuum is needed.

Now heres the wierd part. The car can pull its own weight, in any gear at 1300+ rpm. However, when the throttle was "sticking" it couldnt. not even at 2000 rpm. But as soon as i touched the throttle, it was like it got it's power back. (i dont know if that makes sense). But basically the rpms had climbed, but the power wasnt there, untill i touched the gas pedal.

I had opened the hood at our destination, and made sure the throttle spring was still there, and the carpt isnt blocking the gas pedal.

Also worth mentioning, the carb and timing need tuning, it is running fairly rich right now.

I dont think the "throttle" lever/linkage/pedal is actually sticking. I think its a carb issue related to vacuum. But i dont understand whats going on. Any ideas?

xpndbl3

iTrader: (5)

did you check the return spring? i would imagine they're not strong enough to snap the throttle back to idle. also too weak of dizzy springs can cause unstable timing at idle which chages idle rpm.

online170

Hmm i dont think its the throttle return spring, but it might be the distributor springs.

Thing is, ive had this car for 2 years now, and it had a q-jet on there before. Ive driven it quite a bit, and its only started doing this after the T56 swap.

The more i drive it under load at a low rpm, the worse it seems to get. But after the car has cooled down, its like a new slate, the problem is gone again until i subject it to long period of load.

jayk2k3

iTrader: (2)

maybe throttle cable is sticking between the gas pedal. ive seen it