Hi all,

Last year I purchased a 1993 Baja 32 Magnum with twin 502 magnums. It has been in storage for a while, was my wife's uncle's boat bought new one owner. All orginal. Has the weber carbs which I went through both on the off season with rebuld sets and set to correct specs. The port engine runs great. The starboard engine will backfire through carb if I push throttles too hard on launch. If I ease into throttle it is fine. Both ends run perfect at steady RPM including right up to 5000rpm. The only time I get the backfire is on quick throttle. The timing is advancing as expected. I thought about slightly advancing it has as a test. Other things I need to check

1) Make sure the accelerator pump has 2 nice shots on throttle advance
2) Make sure the coil purple wire is getting full 12v and there is not a voltage loss somewhere
3) Try slight timing advance to see if any difference
4) Swap carbs to see if problem moves to the other engine

Any other ideas or thoughts on what is might be? Definitely only on transition, and only though the carb which I think means a lean condition

Thanks!!

Kevin

Backfire thru carb is typically, but not limited to, being too lean when advancing the throttles. It is not always a pump shot issue.

Bad plug or two, wires, cap, rotor, etc can do it also.

If timing is correct, don't touch it. It's something else.

Run into this with aftermarket billet Holley style carburetors a ton since they seem to be more prone to have issues from non use over the winter.

Accelerator pump most likely culprit.

Thanks. The old caps and plugs are under a seat in the cabin so I know those were replaced at some point. I have not yet removed the plugs because it looks like a lot of fun to get at the middle ones on these twins. If I had a bad plug or two would the engine still idle perfect and also run 5k at WOT with no issues?

Ayuh,.... There would be Other symptoms,....

Like noted above, it's goin' lean causin' the backfire,....

Maybe ya missed something durin' the carb rebuild,..??

Pull spark arrestor and watch the accelerator pump squirt, or lack thereof. These carbs have accelerator pump issues.

Thanks, sounds like the accelerator pump is first thing to check. I put new ones in both carbs and bench tested them but that was last fall. I need to confirm it still works, perhaps adjust it for a bigger pump shot...

Make sure the acc pump plunger seals in the bore and does not get stuck going down and/or up. New parts do not guarantee proper operation of this circuit.


GAWD I love my Holley's.