Backfire Help

Plugs gapped at .040

 

Or you can pull the intake & heads & leave the motor in. Looks like you have some room to work

You might have a cooked intake gasket at the center exhaust heat (riser) passage.

That's the first thing I eliminate when I get heads rebuilt. On my Olds, they've been filled with an old piston

 

A Vortec can get you thrown off the HAMB! LOL
Just my opinion, but if it were me I would take the distributer and have it checked. Then move, on to removing the intake and checking the gasket if the dist checks out good.
Thats two simple and cheap things that will alleviate a lot of what if's.

 

oh well maybe I'll scratch the Vortec, lol
Do I still need to have the dizzy checked if I'm seeing the spark at cylinder 1?

 

If we thinking its the intake I'll grab a fresh gasket on the way home and start taking it apart. :-/

 

If you have good compression on #1, observe valves/rockers moving properly and a nice blue spark from #1 plug wire on a new plug grounded to block, then only likely issue is bad intake gasket at #1 int port. Pull the intake

 

If you had vacuum in the engine and you did the test as prescribed there is a problem with the gasket.
I don't like using the blue gaskets I think they are to hard for a alum intake.

 

I agree with Saltflats-never had much luck with blue gaskets and aluminum intakes.

 

I agree with what was said here. I think there's more than one issue (leaking intake gasket), but I think what he's saying is important to why half your cylinders are potentially dead. After you change intake gaskets and get it running again, if you still have this problem, put the carb on backwards so it's feeding the opposite sides of the engine that it would normally. Now which cylinders are dead?

 

I think grabbing gaskets and checking is what I'd do
It will probably take less than 2 hrs even if you screw around a lot.

If you want to eliminate the distributor as a culprit ...
That would be easy enough to do- rotate the distributor body the amount of 1 terminal on the cap. (360*/8 = 45*) then walk the plug wires back 1 terminal where they were in relation to the engine block & rotor then Retime it.

What this does is move the working reference of the distributor to another cylinder.

What you are looking for is the problem to move to the next cylinder in the firing order. If problem does move, the distributor is to blame. If problem doesn't move you can put a mark of GOOD on the distributor and quit worrying about it.

 

If leak was at #1 presumably because of the oil on the plug, and the manifold is true split it would also effect 467 only by being lean. I don't know if the edelbrock air gap is a true split or if its a common plenum.

 

I can't believe I've never heard of this diagnostic trick before. It's simple, it's perfectly logical, and best of all it's FREE! You don't run into that combination nearly often enough!

Thanks, 31Vicky!

 

I was thinking that about 8 seconds after I posted. I'm pretty sure Air Gap is true split. Good call on the distrubutor, too! I would not have thought of that.

 

Don't mind me I'm just an asshole, ask ironbutt.
He will tell you.

 

I'll agree Edelbrock is a good manifold,but i got a bad one years ago out of Summit when Edelbrock manifolds were coming out of Mexico,all comps.have stuff get by Quality Control

 

I have the intake off and I see the valves are carboned up but they do (especially #1) open and close as I turn the crank by hand.

Is there anything else I need to check while I have the intake off?

also what do I do about the perforated cutout in the middle of the gasket?
do I leave it plugged or cut it out?

Is there any way I can clean the valves?
Pour Tranny fluid on them?

 

These match my thoughts too. Depending on what has been done to the block and heads as far as surface milling goes, it can alter the fit of the intake. I like to glue the intake gaskets to the heads with 3M weatherstrip adhesive so they don't move. If sealing becomes a problem, you can glue both sides but it will be more difficult to remove. Sometimes the surface of the aluminum intake is too smooth for the gasket to seal properly and you need to roughen it up a little.

 

Seafoam will clean the valves.
What do the intake runners look like ? Oily on 1467?

 

Actually they didn't look that bad, the only oily one was #1.
what about the cutout on the gasket?
do I leave it plugged or cut it out?

 

That's an exhaust riser, it heats the manifold and prevents cold weather icing of the carb. Daily driver I'd open it. HP hotrod fair weather I'd close it up. Most have a steel insert ?

 

yep it does have the insert

 

That intake has no exhaust heat passage.

Did the gasket looked burned or broken near the heat riser opening? How does the gasket area of the manifold look?

I'm not so crazy about intake gaskets with that metal insert. It's thicker than the gasket itself

You would be better off blocking the hole with a piece of cast iron or something

 

The gasket didn't show any signs of being burned or broken, but on the manifold you can tell there was heat/burn spot at the heat riser opening. I have the manifold on now I'm headed to bed, I'll finish connecting everything tomorrow after work and test is out.

 

Air gap - duhh

 

OK so while putting things back together I decided to mount my coil on the firewall vertically instead of horizontal on the intake. Well when I did that it wouldn't start. I shook it and layed it on its side and it started. The #1 Cyl is now hot and running as it should, but now on 2,5,8 the exhaust are not hot and it seems the problem has switched sides.
Could this all be related to the coil?
Would a defective coil give these symptoms.
The vacuum gauge is showing a more steady reading but still has some slight movement.
I should be able to mount the coil in a vertical manor right?

 

Maybe. Normally a coil doesn't know which cylinder it's firing but a marginal coil may only fire the cylinders with the least resistance. Also typically a weak coil will misfire under load, the opposite of what you had originally. Still since you've changed the symptoms by moving the coil around it sounds like your problem may be ignition related. Got another coil? Are you sure your coil and/or ballast resistor and plugs/wires matches the resistance specified by your electronic ignition?

 

I don't have another coil but will buy one first thing in the morning.

I'll get one of those high voltage coils.

Posted using the Full Custom H.A.M.B. App!

 

Yeah, the coil could be low on oil & overheating. I've heard when they are tilted they can act up.

 

Did you cancel 2,3,5,8 and experience no change the same as you did earlier on 1,4,6,7?
Still backfiring?
Did you do the same test for crankcase vacuum?
Does the other side now have a vacuum leak?
Did you follow manifold torq down procedure?

Is your vacuum gauge reading higher also?

The coil- moving the coil and loosing spark could be in the wiring to the coil or the coil itself.

 

When you get another coil make sure it is the correct reistance for the pertronic system.