idle problem

[92CamaroRS]

i have a 79 bronco, 300 I-6, fresh rebuild, offy 4bbl intake, 600 cfm edelbrock carb, about 100 miles on it, it ran fine, but lacked alot of bottom end, and poped back through the exhaust, i bumped the timing up some, got rid of the pop back and gave it alot more bottom end. but now it wont sit there and idle, i have to keep giving it gas to keep it running, if it dies it will fire right back up but its annoying and shouldnt be happening. i played with the idel screw and to keep it running i would have to have the idle set at 1500-1600 rpm. any ideas?

[rixGAphx]

Originally posted by 92CamaroRS
i have a 79 bronco, ....any ideas?
Well, you've got spark and air/fuel, so you're doing better than a lot of folks with re-builds!! :eek:

Have you actually had a timing light on it?

From a fresh re-build, and the fact that advancing the distributor helped, I'd make an initial *guess* that the distributor gear was inserted wrong by one tooth. This is quite common in rebuilds.
You've adjusted it to the max, and that eliminated the 'pop', but you still aren't getting decent idle.
So, withdraw the dist gear (battery disconnected, of course), re-insert by advancing one tooth (careful that you don't retard by one tooth), then fiddle with the fine adjustment again.

Failing the above, I would still be looking at the valve train, since you have air/fuel and spark, just not at the right time apparently.
The rebuilder *might* have mis-set the cam-to-crank timing with the timing chain.
Before tearing into this, I'd remove the valve cover and verify cam timing (by checking opening/closing positions of valves of #1, and comparing to distributor rotor position).

Another direction would be the Exhaust Gas Recirculation (EGR)system. Many aftermarket intake set-ups delete this emissions feature. The problem is that the head still has an exhaust recirc passage (usually from the rear-most exhaust valve, across to the intake manifold).
Idealy, one would keep the EGR. For performance only, it's often desirable to delete this, but sometimes attention is necessary at the head to coordinate with the new manifold.
I dunno if deleting the EGR would cause your symptoms.

Good luck.
-Rick

[4kQuad]

I'm going for something simpler, you say it ran for 100 miles. But was week, so you turned up the idle screw. What about the fuel/air mixture screw.

Sounds to me more like it is off.......Or the Old Carb had to many small backfires through it.

Carbs don't like that. Also check to make sure the choke is fully opening, messing up the air/fuel mixture.

Oh yes, grab a little carb cleaner and sray around the base. Somethimes the thick gaskets that goes between the carb and the intake settles so to speak and a carfully done retorking of the seat screws may help.

Turing the timming up advances the spark and in a way changing the fuel mixture as it now fires at a differnt point, so the mixture is compressed different when the spark plug fires.

[92CamaroRS]

It idled before i advanced it, I have messed with the mixture screws as per Edelbrocks recomendations. Haven't had a timing light on it, im starting to think i advanced it too much? it starts fine when cold and hot tho :???:

[4kQuad]

I don't know what your book is saying, but the old rule of thumb after rebuilding a carb. Trun all the screws in all the way, with it being a 4 bbl I would guess there is at least 3 or 4 screws.

Then turn each out 1 and 1/2 turns, meaning put your screw driver in the screw slot, a 1/2 turn it just that. so 1 and 1/2 turns would be 3 halfs. Yes I'm sure you can do fractions. It's just hard to be clear typing somethimes.

With them all set that way fire it up and see what you get.

!!!!!!!Count each turn of the screws and write it down while you try this if you do, that way you can put it back to where it was before you started. Write it down...well doing so much stuff you won't have to second guess yourself putting it back.

You can ear time it with out a light. let it idle for a sec, then punch it ( the gas ) and let out. The motor should pick up as soon as you press the gas, if it pings or studders it's to advanced, if it Rums alive then dies down fast only to slowly climb back up. It's retarded. So a well timmed motor reacts to the gas the moment it is pressed, not when the motor decises to.

Hope you get some help out of this some where.
did you check ther mounting nuts to make sure they are still tight and your not sucking air by the gasket??