77 OMC 235 backfiring above 1500 rpm

[Gunsanddaisys]

It's about time I make a post instead of just lurking around.

I'm working on getting my family's 77 cobalt bow rider back into shape and I'm currently at a bit of an impasse. The motor is a 351w based 235 with selectrim. It's idle seems perfect sitting at about 575 rpm from what the tach tells me. The problem arises when trying to throttle up. Once it reaches an indicated 1500ish rpm, the motor hits a hard cliff and starts to die until the throttle is backed off. If the throttle is moved quickly, it backfires through the carb, but can be returned to an idle if back off quick enough. I'm leaning towards it being carb based since it sounds like the secondaries are opening when it hesitates. Any help would be appreciated.

 

[Scott Danforth]

Most likely a "lean sneeze". Go thru the carb

 

[Bondo]

Ayuh,..... Welcome Aboard,.... I agree with Scott, ya got a fuel delivery issue, probably the carb itself,.....

 

[Gunsanddaisys]

Carb is in the process of being rebuilt for a second time, I guess skipping the compressed air wasn't a great idea. Hopefully this alleviates the issue. Thanks for the advice!

 

[Gunsanddaisys]

Somehow, I looked over a pretty critical system when redoing my ignition components. Turns out, my advance curve is nonexistent. Up to the point at which it stalls out/ backfires the timing remains steady at 10?. Makes sense as to why the base timing was initially set to 22? with no signs of pre-ignition. Hopefully the advance head will be salvageable.

 

[Bondo]

Turns out, my advance curve is nonexistent.

Ayuh,.... What are, the fly-weights seized,..??

What distributor is it,..?? still got Points,..??

 

[Scott Danforth]

Run a piece of fising line thru all the carb circuits

As bondo said. Check to see if the fly weights are rusted in place in your dizzy

 

[Gunsanddaisys]

Sorry for the wait. Suspense was probably killing you.... The cam assembly that rotates with the fly weights was seized to the lower drive shaft. Weights were nice and free, but they weren't allowed to rotate the rotor any. After fashioning a small puller out of a steering wheel puller, I got the cam/ rotor piece off and sanded the lower drive shaft. Cleaned out the inner bore of the rotor piece with a firearm barrel brush. After some molly grease, the rotor can now advance beautifully! Motor now revs flawlessly!