1980 85 HP evinrude good compression, timing and spark and fuel, only backfires.

[SparkieBoat]

I have a 1980 85 hp evinrude, I got it in a horse trade. I figured it had something wrong with it but it has great compression, good spark on all 4, timing seems to be right according to the number 1 cylinder and the markings on the flywheel. the previous owner was not a genius, a 2 inch big hole is cut in the exhaust housing I assume in an effort to get more HP. also I noticed that the intake manifold and linkage are not the original. So I am not sure what is going on. maybe they messed up the reeds or left them out all together?? When I try to start the motor it spins over good until it starts getting fuel, then it starts to strain to crank and will do a loud pop (backfire) which comes out of the exhaust. . that is all I can get it to do. any ideas?

 

[racerone]

??????----With no reed valves it could not run at all.-----Check the flywheel key.----Inspect the starter motor.

 

[SparkieBoat]

it does not run at all. only a loud back fire. I have more information, apparently the midsection came with a 140 and is where the 1984 140 block that came with the trade came from. (same model number). so someone put this 1980 85HP head onto this midsection, could this be the problem?

 

[Chinewalker]

No, not likely the problem as the mids are pretty much the same. Backfires usually indicate a timing issue. Could be the plug wires are reversed? You said you checked it, but how did you do that without the motor running?

 

[SparkieBoat]

It turned out to be the flywheel key, I checked the timing while cranking the engine, it appeared to be hitting at 4 BTDC on the #1 cyl. but the sun was out and maybe i just could not tell. thanks a lot for your help guys, i really appreciate it.. engine is running like a champ now. turns out that the 140 block that i have came off of this midsection, I am thinking about tearing it down and checking it out. evidently something is wrong with it..maybe just a hole in a piston.

 

[emdsapmgr]

You said the compression was good when you purchased it. Unlikely there is a hole in the piston if your numbers look good. Not sure what you are trying to say. It supposedly runs like a champ, why would you want to tear it down? Additional info would be helpful

 

[SparkieBoat]

sorry i was not clear on that emdsamgr. What I got in a recent trade was a complete 85 hp outboard and a 140 hp powerhead. evidently something is wrong with the 140 powerhead and they pulled it off of the midsection and put this 85 hp power head on it. the 85hp head is running great now, it was the one with the sheared flywheel key. the 140 head is the one i suspect has maybe a bad piston or something.