backfire thru carb at 3000 RPM

[tiltbilt]

Crossfire? If pulling one plug wire at a time did not stop backfire, maybe it is more than one, or two cylinders crossfiring from blown head gasket between cylinders. Did you start torque procedure in the center and work your way to each end? Fire from adjacent cylinder can ignite the charge even without spark. Just a thought, can't seem to think of anything else that has not already been covered in discussion. Try pulling off 2 adjacent wires at a time. Don't know if it is possible to remove exhaust manifold if the manifolds are conjoined. You might find it by using an infrared heat gun to see if one or two cylinders drop temperature while backfiring. Shoot the intake runners also, temperatures could give you a clue. If it is a blown head gasket, it may or may not be bad enough to show up as lower compression on two adjoining cylinders. Pressurizing each cylinder with adjacent spark plug out might hiss enough to find it, piston at TDC with valves closed, listen at carb and adjacent cylinder. ?????????????? That's all I got.

Yes, I torqued head from center out as the manual states. I also have done a compression test and leak down test. Both ok.
Don't have tool to test temperature of runners.
Am I chasing something that is normal (wont backfire under load while driving cos vacuum would drop and power valve would open)?

[39CENT]

Yes, I torqued head from center out as the manual states. I also have done a compression test and leak down test. Both ok.
Don't have tool to test temperature of runners.
Am I chasing something that is normal (wont backfire under load while driving cos vacuum would drop and power valve would open)?

oh I thought you were not under load when testing.

[tiltbilt]

oh I thought you were not under load when testing.

Yes, everything has been done with no load.
I have not assembled the car enuf to drive yet.
Sorry if something I said misled you.

[39CENT]

here is a chart might help


http://roncrawfordsholleyrebuilds.co...eshooting.html

[Jenz38]

here is a chart might help


http://roncrawfordsholleyrebuilds.co...eshooting.html

yes ,this i a good idea to start from beginning on new. Maybe you have something oversight and obsessed into some thing.
Open a beer ,close the door behind you without telefon and start in quiet new...

[tiltbilt]

here is a chart might help


http://roncrawfordsholleyrebuilds.co...eshooting.html

Thanks for the chart. All ideas on chart have been covered. May be able to use chart in future tho.

[tiltbilt]

yes ,this i a good idea to start from beginning on new. Maybe you have something oversight and obsessed into some thing.
Open a beer ,close the door behind you without telefon and start in quiet new...

Have opened many a beer and started over at least four or five times. I have been doing this profession since 1969 and have been led astray many many times. Like tracing wiring for an open circuit and finding that your test light bulb was out. LOL

[tiltbilt]

Talked to a straight owner today, and he said his pops thru carb while driving and holding a steady speed. I think he may have a breaker plate sticking with the ***** binding in the dist. I shared an old post I found on this forum for him to check out.
I am thinking about drilling the jets out on my donor carb to see if my problem changes at all.

[Jenz38]

It must be to find ...

let us to continue ;-)...

You have your Valves correct grind in ? maybe they are stop sealing at higher revs ?

Internal manifold leaks ? If there has standing water under the carb for years maybe there is a rust thru ?

You have the washers under the intake valve springs ? (im think it was the intakes,not the exhausts..)

[tiltbilt]

It must be to find ...

let us to continue ;-)...

You have your Valves correct grind in ? maybe they are stop sealing at higher revs ?

Internal manifold leaks ? If there has standing water under the carb for years maybe there is a rust thru ?

You have the washers under the intake valve springs ? (im think it was the intakes,not the exhausts..)

Thank you for not giving up on me.
I believe valves are correctly ground. The machinist that did this job always does great work on all my builds.
Not been sitting with water in intake. always garaged.
Valve springs are properly shimmed with washers.