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1984 Chrysler Sea King, 15hp. Lagging in forward gear

LoganB

Member
Hello. I recently purchased a 1984 Chrysler Sea King, 15hp. The engine runs great, starts first or second pull and shifts fine. Seems good in a tank but I recently mounted it on one of my boats to take it out for a test run. It idled well in neutral and will rev high with no issue in neutral. However, it seemed to lack power when I shifted into forward. It idles fine but would only give me about a third or so power when I cranked the throttle.
It moves, just won't plane out. The prop has a small chip but this shouldn't be causing such a problem, in my experience. The boat was only an 8 foot dinghy, the 15 HP should have shot that thing up and out without a problem.
When I got back to the house I threw the engine back in the tank and ran 2 treatments of sea foam then tweaked the throttle and carb screws a bit to bring it up to a higher rev in forward, although it still doesn't seem like it's much higher to me.
I have yet to check compression, check plug gap (if this were bad it shouldn't be running so well or revving so high in N, I think), RR carb.
I don't have a bunch of time to work on it and don't currently have a legal boat but I am able to do some things on weekends. I only say this as a warning that any responses from me might take a little while.
I appreciate any help or advice anyone has to give!
Thanks
 
Running past high idle in neutral tells you absolutely nothing and very harmful to the motor do not rev it up in neutral period. Any two cylinder engine will run good on one cylinder in neutral until you put it under a load. Do the compression and spark gap tests and go from there.
 
Thanks, will check that this weekend if I get a chance.
Would you be able to tell me what the gap should be or a close approximation?
Thanks again!!
 
Compression was about 120 on both. R&R the plugs. The old ones were pretty corroded on the outside, seized into the block. Exciting getting those out.. Once I pulled them they were pretty well oil soaked and the gap seemed a bit loose. So I gasped some new ones at the .03 the internet told me for this engine. Squeezed down one of the boots a bit so the plug snapped on tighter. Cranked her up and threw a couple hits of carb cleaner into the intake. Seems to be running perfect in the tank, it'll be a bit before I can lake test.
I've never experienced a possible weak spark causing such a problem, appreciate the advice of pulling and checking those. Can't lose with a couple new plugs.
 
A little history will help,when was last time engine was run Was old gas still in carb,Gummed up possibly, Fuel line conditions.Fuel tank cleaned recently? Do the 2 tests kimcrbr1 suggested first,then move on to fuel diagnostics.
 
Like I said in my latest post, pretty sure all's good now. But, if you'd like the info for knowledge sake.. I put new ethanol free gas and new2 cycle oil on new tank with new outside line. Possible that there was some old gummy fuel in the carb but the two sea foam treatments and most recent carb cleaner treatment ought to have fixed that. If any problems are left in the carb I'll know soon and do a rebuild. Last time I ram it was Sunday. The time before that was last weekend. Before that was the weekend before. There seems to be a pattern.. that's all the info I can give you on top of the already provided info, I believe
 
Keep an eye on the plugs if they come out powdery white you need to rebuild the carb. The insulators should be a toasty brown for the center electrode.
 
They were black and, like I said, oily. Had a neighbor (car mechanic) look at them and he said they're probably not throwing a very strong spark and he suggested I replace. I was already replacing so it worked out.
Thank you, I'll keep an eye on them
 
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