High RMP Backfire

[propless]

The problem appears to have been either the rotor or the distributor cap - will take the boat out tommorrow and put it under load.
FYI - I did order a new carb from TPC Racing so I'll soon have a Holley 800cfm double pumper available.
Thanks to each of you for your thoughts and ideas- this place is great!

[Craig]

A lot of good suggestions. One thing that hasn't been asked, when you put a timing light on the motor and rev it, does the mark move up balancer smoothly? It should cease moving up the wheel at about 3000 rpm (depending on your curve) but it should hold steady if the rpm is steady. If it jumps around a little, you might be getting into some timing chain slop. Friend had a Baja with a 502 Mag. Had a bunch of hours on it. Every once in a while it'd pop like yours. When we finally pulled it apart he did have a lobe that was wore down noticably.
Craig

[propless]

Craig -
Good question. I did watch for this movement because I had I had experinced this problem in the past on a 455. Pointing this out to others will hopefully help with trouble shooting motor issues - thanks!

[Craig]

No problem hey a 455, Old, Ponitac or Buick?
Craig

[Bahner tunnel]

Double check you accelerator pump for proper fuction i.e broken diaphram , linkage ect .... Good luck.

[shockwaveharry]

Propless, Is it fixed???

[propless]

Yes and No.
Yes - It appeared that after replacing the distributor cap, rotor and rotating the motor to the #1 cylinder, then setting my timing from scratch has given me the ability to take the RPM's from a consistent 4000 - 4200 to 5200 - 5400 RPM's. What a difference, it is truly sweet.
No - I still have the ocassional backfire through the carb only at the top end of the RPM's (above 5000) though. I have ordered a new carb from TPC and should have it installed in about two weeks, hopefully the bacfire issues disappears after that.