Help please,
Just put a "remanufactured" 2bbl carb from Champion Parts on my '69 F-100. (Actually 2 , the first one had a broken screw in choke attach hole, second also had some linkage problems.)

Now it backfires through the tail pipe. Did it twice on 3 mile drive.
My son drove to a fastfood restaurant and some busybody was going to call 911 because she thought she heard a gunshot.

Any Suggestions?

I also posted on carburation conference.

Richard

 

Correction-

I have a correction! after I put the third rebuilt carb on.( still had to rob a couple clips from #2) This is slightly different than the old one that was on when purchased 2 months ago..

The engine is backfiring through the carburetor not the exhaust.
It did not back fire with the old carb. just hung up and would not idle down. Why would changing the carb cause backfire??

I tried to check the timing and can NOT find any mark on the harmonic balancer. There is an indicator mounted overhanging it.

Thanks,
Richard

 

Don't know if you've already tried this, but try rubbing the harmonic balancer (or whatever its called where the timing marks should be present) with a yellow grease pencil. Sometimes those marks get covered up with rust, gunk etc and this helps a great deal. Good luck.

 

Thanks Dutchman,
Supposedly my teenage son is cleaning the harmonic balancer with greased lightning as we type.

Am going to shoot for 8 degrees BTC even though the plate on valve cover says 6.

Any ideas on why changing the carb. with start the backfire?

Richard

 

Need more carburetor help!

Thanks for the insight Lee,

The truck only on INITIAL ACCELERATION, hesitates, stalls and or backfires through the carb.

The truck ran ok, not great, for two months since purchased with only an occasional hesitation upon inital acceleration. The carb that was on it hung up on deceleration until the gas pedal was tapped. Then it would idle down.
So I replaced it with "remanufactured" autolite. The last two had slightly different configuration on the horizontal plate behind the carb opening- one is smooth and the other, as the one we ran for two months, has an indention about 1 1/2 inches in diameter.
Both cause the same symptoms.

I found the very faint timing marks after a thorough cleaning. Engine is now set at 8or9BTDC and advances to about 30BTDC upon acceleration when it doesn't stall out.

Hesitation/Backfire occurs only on the initial accelerator pump. There is at least some gas coming from the two pump jets.

I'm open to any suggestions.


Need more carb help!
Dutchman, Lee, Polkat and others- thanks

I found the very faint timing marks after a thorough cleaning. Set the engine at 8or 9 BTDC at idle of 700rpm.( that's as low as I could get it.) Shows about 30 BTDC when revved up, IF it doesn't stall out or backfire.

Engine now runs good at idle and cruise. Just can't get past the initial acceleration. Easing on to the pedal usually works but stomp on it will definitely backfire or stall.
There is SOME gas being pumped in with acceleration pump.

?? How can I adjust the accelerator pump throw or amount of gas squirted in? There are 2 holes in the arm and the pin is now in the hole furthest out.

? The remanufactured carbs have had two configurations on horizontal surface to the rear of the choke plate. One is smooth while the other has a 1 1/4 inch indention that is shaped like the outside of a vacuum diaphram. Both had the same symptoms. Both are Motorcraft. Does it make a difference?

Glad for more suggestions

 

Dutchman, Lee et al.
Thanks for the suggestions

I tried accelerating with the choke partially closed and it did not backfire. It backfired more as I opened the choke plate. Thus agreement that it was getting more air than fuel.


Investigated and found there is some adjustment on the acceleration pump rod. The end pin was in the 2nd of 5 small holes in the connection arm at the carburetor. I moved it out to the 5th or furthest from the pivot point. That I believe increased the stroke distance.

At the pump lever arm I moved the pin to the innermost of two holes and I think that started the pump earlier.

Now it does not seem to hesitate.
Will verify it on the road once I get the gears changing.

Thanks to all,
Richard