Carburator help please!

[dave`12]

I put a new Holly Demon on my 350cid last year. The carb ran good for the first 500 miles or so, but now I'm having several issues:

1. Idle always high after driving. For example I drive down the street and when I pull up to the stop sign, the idle will be high, no tach, guess maybe 1100RPM or so. I juke the gas and it will come down to normal. This happens every time. I've played with the electric choke, but nothing seems to help.

2. Sometimes, totally random from what I can tell, I get engine run on. But it's not normal, it manifests as one quick loud zoom, then it's done.

3. Now, the last two times I drove the truck, about 1-2 seconds after shutting it off, (no engine noise) boom, like a shotgun from the tailpipe.

I'm tempted to just dump this carb and get another (sorry, I'm not going FI).

Any help greatly appreciated.

p.s. timing is at 8 before. Plug wires, cap and rotor are almost new. Engine runs strong, starts good. Truck runs great other than these issues.

[geezer#99]

Sounds more like the weights are hanging up in the distributor.

[cadillac_al]

definitely have to get that idle down so it will shut off easier. could be a vacuum leak.

[Wrenchbender Ret]

Disconnect the throttle link from the carb & try it. You may be at the end of the travel & it will not let the throttle close all the way. Make sure the automatic choke is opening all the way & the fast idle cam is returning to the off position.
George

[garyd1961]

Originally Posted by geezer#99

Sounds more like the weights are hanging up in the distributor.

This was my first thought.

[dave`12]

thanx for the replies. I was out of town for my anniversary, just got back.

I looked at the weights, they appear to be good, springs as well. This is a cheap distributer I got off amazon, so you never know. Perhaps I should turn it off while it is idling high and see where they are? Man, I wish chevy had put the distributer in the front of the engine, it's quite difficult to remove the cap.

I sprayed carb cleaner looking for a vacuum leak, nothing moved my RPM's. I do have one spot where a little oil comes up??

I checked the throttle linkage and can rule that out.

The funny thing, is that every time I juke the throttle after stopping, the idle returns to normal. That would seem to point to the weights of the options you have given me here?

Do you guys think I should dump the cheap distributer a spend a few bucks for a better one? It's HEI.

[geezer#99]

Where’s your throttle return spring hooked up?

Check side to side movement of the throttle plates. They can hang up in the bore sometimes.

[PGSigns]

You may need to lean the choke. That flip you are doing is getting it off the last step on the fast idle cam. You can back off the fast idle screw a little so the last step on the fast idle does not run the rpm up at all. Thats how mine is set up. Also you may need to lean the idle air screws a tad.
Jimmy

[garyd1961]

When it's idled up get out and pull on the throttle linkage and see if it goes back down. If it does you may need a stronger throttle return spring or maybe relocate where it's hook up

[dave`12]

Finally got it figured out. Found a nasty vacuum leak at the manifold. Also had a mechanic look at the carb and he adjusted the accelerator pump. All the above issues are gone now. He talked me into setting the timing at 6B. Although the truck runs great, I do think it has less power.

Any opinions?

p.s. It's a mild 350cid from the mid 70's out of a Blazer. By the sound of the idle, it has a mild cam. Edelbrock performer manifold, Demon 600 carb. I've always thought 8-12 was the sweet spot.

Thanx again for all your help - Cadillac al nailed it.

[tdangle]

Originally Posted by dave`12

Finally got it figured out. Found a nasty vacuum leak at the manifold. Also had a mechanic look at the carb and he adjusted the accelerator pump. All the above issues are gone now. He talked me into setting the timing at 6B. Although the truck runs great, I do think it has less power.

Any opinions?

p.s. It's a mild 350cid from the mid 70's out of a Blazer. By the sound of the idle, it has a mild cam. Edelbrock performer manifold, Demon 600 carb. I've always thought 8-12 was the sweet spot.

Thanx again for all your help - Cadillac al nailed it.

I'd go ahead and bump up the timing to 10-12 BTDC, if it were me

[68 P.O.S.]

SBCs run best at ~36 degrees total timing. ~32 degrees if you have vortec heads. Initial timing depends on how much timing your distributor has in it. Vacuum advance needs to be restricted to 10-15 advance and hooked up to manifold vacuum.

[mattfranklin]

As long as your exhaust system is quiet enough for you to hear engine knock you can advance the timing a little. Experiment with the timing, do it back and forth a few times to make sure you really feel the difference.

Your mechanic may have just been being conservative to minimize risk of damage in case you weren't going to pay attention to your engine.

[tdangle]

Originally Posted by mattfranklin

As long as your exhaust system is quiet enough for you to hear engine knock you can advance the timing a little. Experiment with the timing, do it back and forth a few times to make sure you really feel the difference.

Your mechanic may have just been being conservative to minimize risk of damage in case you weren't going to pay attention to your engine.

I agree

[dave`12]

Good advice. I think I'm going to bump it up a few degrees and see how it feels.

thanx all

[Ziegelsteinfaust]

Originally Posted by 68 P.O.S.

SBCs run best at ~36 degrees total timing. ~32 degrees if you have vortec heads. Initial timing depends on how much timing your distributor has in it. Vacuum advance needs to be restricted to 10-15 advance and hooked up to manifold vacuum.

This

But I will only add traditional small block heads of aftermarket design like afr 32* is typically max too