Sayfoo

I recently replaced my intake manifold gaskets and ever since then, my '69 BB has been running a little differently.
I now have a random small popping/backfire through my Hooker side pipes, both at idle and on decelerating. Mostly on the pass. side. Nothing else changed.
Is it possible that I installed the distributor 1 tooth off?
I believe that I installed it with the rotor in the same position as when it was removed and the car does seem to run well, but it didn't backfire before.
Any ideas??

Tampa Jerry

Sounds like a vacuum leak, perhaps from an intake manifold gasket. Put a vacuum gauge on the engine and see how it reads. Jerry

4-vettes

You put the rotor back where it was. But the body of the distributor rotates to adjust timing. Did you put a light on it and re-time?

HeadsU.P.

"car does seem to run well . . . "
Sounds like timing is real close.

A backfire, like Tampa Jerry said, is usually a lean condition from too much air, not enough fuel, from a vacuum leak.

Tell us about your choice of Intake gasket, type of sealant and how much was applied.

Sayfoo

I used a FelPro gasket set and a thick bead of The Right Stuff silicone on both ends and a little around the coolant ports. Did not use the rubber end pieces. It does not externally leak oil or coolant.
I did re-time it.
So, I guess I'll check for vacuum leaks.
Spray brake cleaner all around the outside of the manifold and the carb base?
I think the "new", California approved brake cleaner is non flammable, so what to use?
Starting fluid (explosive??), carb cleaner, acetone, etc.??

4-vettes

Small propane torch unlit. Is what they teach at Harley Davidson university.

Bikespace

If the popping is in the sidepipes, the correct term is "afterfire". @lars has commented on several related threads about this, if you search for that. In my case, the 90% solution was moving my vac advance hose to a manifold vacuum port and adjusting idle mixture. What is your timing now?

HeadsU.P.

Sorry Sayfo, I see a do-over on the gasket.
Common error of installation, being shy on the sealant. I don't know why people are so stingy on the sealant.

You need to apply, coat, smear, brush, whatever, every square inch of that gasket. Not just a dab here and a dab there. And BOTH SIDES of the gasket too.
Notice how close the Intake ports are to each other. Just a thin wall of material. All ports are under vacuum but at different times of the engine's cycles. It is imperative that everything gets a coating of sealant even that narrow ridge.
Those built-in gasket seal rings such as Printo seal etc are not enough. Thats just a marketing gimmick.

Your best bet is to lay out some wax paper on your work bench. Place the "bottom side" of the gasket facing up on the paper. (I am assuming the heads were thoroughly cleaned with Acetone) Edelbrock makes an excellent sealant called Gasteniche. Apply with the brush inside the can and coat entire gasket. Wait a couple minutes to get tacky. While you are waiting, apply RTV around the heads water-ports. Lay gasket in place. Installed two bolts to hold it in place.
I like to wait a few hrs to dry. Now apply the the Gasteniche again to the exposed side of gasket, RTV water-ports again!
The Right Stuff on the china walls and you are good to go. RTV thread sealant on the bolts.

Just a note about spraying carb cleaner, propane and the likes looking for vacuum leaks. It seldom works unless you disable the fan belt.
Keep in mind, that test may only reveal a leak on the top side of the gasket. What about the bottom side where all the oil mist is at?

derekderek

the only real way to check an intake manifold gasket is to do an autopsy on it. remove carefully to see what you can see. as heads U.P. said, get new gasket attached to the head so that you know where it is and you know it will not shift when you drop the manifold on it. and i don't know why people think a big boobed blonde on her back with dress up and legs opened will help sell gasket sealer to men...

0311 jarhead

What he said. Printo seal is a gimmick. Sometimes it works and sometimes not so good. Found out the hard way

Sayfoo

I don't think the timing and the vac advance are the problem as I didn't have this problem before doing the gasket replacement, due to sucking in coolant.
But, if I remember, 12 initial and 36 total?? '69 with low compression (9.5) '71 heads.

Sayfoo

Yea, I think I'll re-do it.
As per gaskets, any preference as to FelPro or Mahle?

HeadsU.P.

FelPro are excellent. Make sure you get the 0.060 thick regardless of which port size.

Bikespace

Probably not, but how did you replace the intake gaskets without removing the dist and a bunch of vacuum hoses?

Sayfoo

I took a picture of the rotor and replaced the dist. with the rotor in the same place. Positioned the dist. aprox. where it belonged, started the engine, and then set timing.
Only 2 vac hoses.
I didn't have this afterfire problem before replacing the gaskets. As far as I can see, the only 2 things that it could be are the distributor (which I'm 99% sure is correct) or the gasket seal.
Since the gasket set is only $10 on amazon and I have the rest of the sealants that I'll need, it's no biggie to change it again. Should take +- 3 hrs..
Thanks everyone for the input.

hugie82

if you went to a very different intake and it’s popping a little, I would say your carb might need the mixture screw backed out a 1/2 of turn. It is odd that it’s only popping on one side, so it could be a vac leak between the head and manifold. Now since you have a few heat cycles on this intake, you can go back and retorque the intake bolts. Hopefully that will seal any vac leak. You said you marked the timing and that’s good to get the car running but there is a very slim chance your time is in the same spot. I would definitely put a timing light on it and set it. If all this fails, you may need to pull the intake and see where the vacuum leak is and redo it.