302 back fire

I have a 1972 SeaRay with a 3

I have a 1972 SeaRay with a 302. I have moved the timing up and down and it does not stop the back fireing. The advance is functioning. The boat had sat for sometime before I bought the boat. It will not reach full RPM's. It will reach full RPM's when I first run the boat. For the first 5 or 10 minutes it runs okay. At this time is will reach 3800 to 4000 rpm. Later it will not break 3000 rpm. At this time it back fires and the rpm floats. (The rpm's go up and down.) What could it be??? An earlier owner marked the fly wheel at 20 BTC. Is that correct? The dwell is at 26. I have adjusted the carb using the rpm drop method. I have a book that has the time set with it in gear at 600 rpm. Help!!

" Clynn,
What condition

" Clynn,
What condition is ignition system in? You could be cross firing if your plug wires are old or you have carbon trails in your distributor cap.
Eddie "

" Eddie, Thanks

The cap is

" Eddie, Thanks

The cap is new. I will check the wires.

Clynn "

"Clynn, 20 degrees is too m

"Clynn, 20 degrees is too much initial advance. 5.0 liter H.O.'s have 14 degrees as a practical max, so I'd go for 8 to 12 in a marine engine. The mfr's manual for your engine might have the timing info. You may also want to set the #1 cylinder on TDC and check the accuracy of the timing marks and the distributor.

As for the backfiring, wires or the coil/ballast resistor may be the problem as resistance increases with heat. If the points & condensor are old, it's probably time to replace them or install a Pertronix pickup in your distributor.

"

Thanks croozertoo

That is

Thanks croozertoo

That is great info. The book I have tells me to set it at 8. When I did that it ran...poorly. Once I advanced it ran better. I will check the TDC and the coil/ballast resistor. I will check on the Pertronix system.

Clynn

" Clynn, check points and repl

" Clynn, check points and replace if in doubt, check vac & mechanical advance are working correctly (not siezed) set timing at 32 deg at 3000rpm (in nuetral) recheck at idle, should be around 12 deg. Use good fuel as lower octane ratings require less advance and therfore poorer performance. I run my std. 302w on optimax and easily reach 4800rpm (I dont recommend sustaining 4800) with settings as above. As eddie said, plug wires are often overlooked, even if they look o/k, replace every 2 year depending on usage. Resistance testing wires cannot simulate high rev and high temp running conditions. Your timing marks need to be accurate as this is your main reference for timing, replace harmonic balancer if in doubt. Aldo "

" Great info, Aldo. Now I hav

" Great info, Aldo. Now I have some things to look at and not guess what to do.

Clynn "

" Well, Now that you've be

" Well, Now that you've been through the Ignition System.......
Your problem is Lack of Fuel..... The motor is running Lean..... "

" Thank yo Bondo,

I will tu

" Thank yo Bondo,

I will turn the screw a little more.

Clynn "