Truck is running but not right.

[Redneckedness]

Whats up guys? So I got my sons truck put back together and running. With the exception of a few issues like it overheating (will be replacing the radiator) and fuel tank not fitting quite right. The big problem is i cant get it to run smooth. If i advance the timing the upper rpms are fast and runs like a raped ape but it wont idle well, tries to die when you give it a little gas. If i retard the timing it idles better but during acceleration under load it back fires and hesitates. Seems like a fuel delivery issue but not sure. Didnt rebuild the edelbrock 1406. The set screw on the passenger side seems to affect it when i turn it but the one on the drivers side doesnt seem to have any affect. Ive only got 4 psi fuel from the pump but seems to be enough when the timing is advanced so i figured its fine.

[85lebaront2]

Ok, one idle mixture not working could be either a plugged idle jet in that side cluster, or an air leak killing 4 cylinders.

Ignition, what distributor are you using? If a regular DS-II I would check the advance mechanism and make sure it is fully functional.

[Gary Lewis]

If one of the idle air/fuel mix screws doesn't make a difference then you have a plugged passage in the carb.  I've been successful pulling the screw out and squirting compressed air in there.  Used my rubber-tipped nozzle and hit it with 120 psi.  That cleaned out whatever passage was clogged.

I wouldn't do this on a Holley or Motorcraft as there are diaphragms in there you could hurt.  But it didn't hurt the Edelbrock as there are no diaphragms.

And 4 psi should be plenty except maybe at high RPM.

[Redneckedness]

Im using the duraspark II with a crane kit in it. When i put the timing light to it and open the throttle it advances the timing so im assuming its working but i guess that doesnt mean its working right. If i drive it gently it wont backfire. Its when i try to accelerate moderately that it does.

[85lebaront2]

Do you know when the advance starts, what rpm? If it is below your normal idle speed it will be very hard to (a) set the timing and (b) get a stable idle. Automatic transmissions can be loads of fun sometimes with advance kits.

[Redneckedness]

Ill definitely give it a try. Cant hurt.

[Redneckedness]

Its a manual trans and im not 100% sure but I think it starts in a little later than that. When i had it advanced it ran so well i couldnt believe it but the idle wasnt right. Im hoping that its that screw. How do i check for vacuum leak. I have a vacuum leak tester.

[Frank Wyatt]

Make for sure that you have the firing order correct. It's very easy to get one crossed. Especially a 302/351 as there are two different firing orders for them. The firing order must match the camshaft being used. That can sometimes cause some odd symptoms.

[ArdWrknTrk]

Are you sure the marks on the harmonic damper actually correlate to TDC #1?

460's can get inductive misfire between #'s 7&8.
It's recommended not to run these wires right next to one another.

When you say "backfire" is it an explosion in the exhaust, or is the engine spitting up through the carb?
If the latter, you'd better go check all the vacuum lines and caps.
It's very easy to pop one of those, especially on the back of the carb spacer where you won't see it's broken.

[85lebaront2]

Jim is correct, the old firing order 302s (actually clear back as far as my 1964 260 V8 Falcon) said to run the wires in the sequence 7,5,6,8 through the guides, 460s and FE engines were 5,7,6,8.

As to the balancer, mine came apart, not catastrophically, but enough that I changed it. Look for signs that the rubber bonding the two pieces together hasn't allowed one piece to slip.

[Redneckedness]

It was in the exhaust. What I'm thinking is that it was so retarded that maybe it was firing as the exhaust valve was opening. That would explain the sudden slow down at the same time the engine backfired. Problem is I'm new to this so i don't have much experience. I realized I was making a rookie mistake because I wasn't disconnecting the vacuum advance when i was trying to set the timing.

[Gary Lewis]

Depends on the source of vacuum to the advance.  Some are "timed", which means that there's none when the throttle is closed, and some are "manifold", which means it is there all the time.  If manifold then your timing will be way off if you set it with the vacuum attached.

[Redneckedness]

I think its vacuum. Ill try it tomorrow with the vacuum disconnected and see what happens. As well as it ran, the only thing that makes sense is the carb at idle wasnt giving it enough fuel on one side. Makes sense since its a dual plane intake.  As soon as i goosed the throttle it would come back to life, running strong.

[Gary Lewis]

Both idle circuits have to work for it to run properly at idle.  Have you tried blowing it out with compressed air?

[Redneckedness]

Will do that tomorrow. Can i use carb cleaner when i do it?

[Gary Lewis]

You can try carb cleaner, but compressed air is much better.