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Sluggish throttle, won't get max power unless cowling is off

E

EODJay

New member
Yesterday the motor (J90TSLECM) was very sluggish, had a hard time getting on plane and when it did it would barely get to 3800 RPM. Having just replaced ball and socket for timing advance rod, I thought it had popped out again. Nope. I left the cowling off to see if I could find anything and the motor came to life. All the power was back and it ran up to 4800 RPM with no hesitation. Put the cowling back on and it's a dog again. Did this a few times to confirm. same results. There are no obstructions in the intake tract, motor has great compression, 135 in all holes, and spark is great with a tester. Any ideas on what could cause this?
 
Plug wires are new this year and all checked out ok. Help me understand how a bad plug wire or wires would have any affect on the motor running sluggish with the cowling on versus it running great with it off. Not being a smartass. I want to learn everything I can.
 
I should have said the wires were new in the first post not just that spark was good. My fault there. At any rate, can you think of any reason this could happen? Also, I've agonized over the carburetors to make sure they good to go. All new jets, carbs cleaned thoroughly and floats adjusted meticulously to 15/16" drop and dead even with carb body upside down. The motor ran beautifully right before the timing adjustment ball and socket broke and I replaced that. I'm going to pull the flywheel to check the condition of the key this evening if the weather permits. Can you think of anything else right off the top? This one really has me scratching my head.
 
Racerone, I have to give you credit. I think you were dead nuts on with the wires. While I did check the resistance of the wires earlier, I did not check the wires for fine cracks. I should have. I just checked them and found one to have a very fine crack in the boot that you can't see unless you bend it. I've ordered new wires but in the mean time I wrapped the offending wire in electrical tape and will see if that is indeed the problem. Thanks for your input, it is valued. I'll keep yall posted on what I find out.
 
Racer is 100% correct on cowling install.. But like was said , hey old (force , us marine motors)
boobie said, not seen with johnrude . but it's a possible cause. Motor starves for fresh air.
 
Racerone was absolutely correct in it being the plug wires or in this case, one wire. The small crack that I found was letting it short to the latch like riopga above mentioned. I heavily wrapped the cracked boot in electrical tape and got it back on the water and everything is fine. New wires are inbound and I have a lesson learned.
 
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