Mercruiser 233 ford 351 W coil voltage

[Lancer76]

I've been having intermittent issues with my 1976 ford 351 W mercruiser 233. Compression is good in all cylinders and swell and timing are right on, but after the engine warms it can run rough, die a at idle, backfire occasionally, etc. All fuel filters changed and runs great on the hose. Timing and dwell are spot on. One thing I measured is that the voltage to the coil increases with Temp and RPM. A cold engine running will deliver 9.9v to the plus side of the coil. As the engine warms, the voltage will creep up to 10.2 v at idle. When at 1700 RPM the voltage goes up to 11.2 v and 11.7 V at 2700 RPM. I measured this on the hose and am wondering if the resistance wire might from the choke to the coil is bad and loses resistance with increased temp. First, is this possible? And second would a pertronix ignitor II with flame thrower coil be a reasonable approach? Reviews seem mixed on these units. Any other thoughts welcome.

 

[Scott Danforth]

Its not your coil

Backfiring is fuel related. Look at your carb

 

[Lancer76]

Thank you, I will do that. I have a rebuild kit - I suppose I ought to use it.

 

[Lancer76]

I cleaned and rebuilt the carb. It looks very good! Two questions
1. Is it a requirement that it is repainted before install?

2. I adjusted the idle mixture needle screws out 2 turns. When I get it in the water for fine tuning, the.manual says to adjust the so as to maximize manifold vacuum. Where do I measure that from on this engine (ford 351w)?

thanks.

 

[Lancer76]

Want to give a BIG thank you to Scott and others on this site that provide sound advice from experience. In my case, the rebuilding of the carb was the medicine that was needed. Motor runs smoothly and without any hesitation or intermittent missing. Like a new motor, yet its 42 years old.

Hats off to the pros that know!