i have comp #'s happy memorial day

junior1113

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have a 68 6hp mercury that runs great for the first 10-15 min then loses 1/2 power. let it sit for 10 min then runs great for 10-15 is there a mechanism for overheat that would cause this or any suggestions not to familiar with these old little motors thanks for any input paul
 

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Re: old 6hp question

Re: old 6hp question

Not much to those oldies, electrically speaking so probably not stalling out due to electrical issues, unless you have a short somewhere that only appears after 10 minutes. You may be dropping a cylinder (spark) though I suppose, which would result in 1/2 power.

A bunch of questions....

Does it run okay for those 10 minutes, no peculiar behavior?

Feel exceptionally hot on the exhaust side of the block?

Does that model have a telltale water output, and if it does it is hot?

Have you done a compression check yet?

There is an inspection cover on the intake side, which can be easily removed to see the condition of the piston skirts & rings, and some of the cylinder walls.

I'm assuming you start it with the choke, and then you remove the choke after a few minutes and it still runs okay?

Vent open on the fuel tank?



.
 

junior1113

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Re: old 6hp question

Re: old 6hp question

runs great when running those 10 min at a time then when loses power it just acts like a 2 hp let sit for 10 min then run great for ten min that time it sits i would imagine its cooling down then fine not sure. ican run it in the barrel and never have this problem. water pump is working great the whole time it's new fuel vent is open, dont think its losing a cylinder because it wont rev up when its runing weak it seams more like its losing rpms at these times
 

junior1113

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Re: old 6hp question

Re: old 6hp question

appreciate all input, my fellow boaters
 

junior1113

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Re: old 6hp question

Re: old 6hp question

wish it was an evinrude i would have answers a lot sooner maybe i should post this in evinrude section
 

junior1113

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Re: old 6hp question

Re: old 6hp question

any input there????
 

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Re: old 6hp question

Re: old 6hp question

Have you done a compression check yet?

There is an inspection cover on the intake side, which can be easily removed to see the condition of the piston skirts & rings, and some of the cylinder walls.
 

junior1113

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Re: old 6hp question

Re: old 6hp question

Havent Done Comp Check Yet Will If U Think This May Tell Me Something
 

junior1113

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need help please before i take to a dealer

need help please before i take to a dealer

comp test isnt going to tell me anything about this intermitin power loss or is it dont make no sense in this matter
 

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Re: old 6hp question

Re: old 6hp question

One theory is that it may be getting hot, and piston skirt is dragging thus resulting on power loss. I was hoping to determine the health of the motor (compression check) before moving on to suggestions to pull the flywheel to investigate electrical items (losing spark on one cylinder), or rebuild fuel pump, hoses & carbs (starving for fuel) etc.
 

junior1113

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Re: old 6hp question

Re: old 6hp question

oh i see u own a couple of these i got a 72 9.8 thunderbolt also it is tougher than the 15 evin. that i got just caught up on this stuburn 6hp will get comp test reults for u amd ,appreiate your knowledge on these old things, one thing i tried pulling one plug at a time when this was happening and i could'nt get it to run on bottom cylinder alone but top would run alone?????? will have test result in 1 hr
 

junior1113

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Re: old 6hp question comp #'s

Re: old 6hp question comp #'s

compression test result are 93psi in each cylinder whats next??
 

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Re: i have comp #'s happy memorial day

Compression values are a little low, but at least they're even. You're using a rope start, so I wouldn't expect huge numbers especially from a 40 yr old motor. Compression is probably okay.

Your latest cylinder drop test yielded results which may suggest your bottom cylinder has a weak spark, or no spark. That may lead you to your issue, and would certainly result in low rpm and low power. Could be intermittent, and more noticeable under load rather than on muffs or in a tank.

I'd investigate the condition of the spark plug wires and plugs, and only then move onward to pull the flywheel to review the ignition components. Try running that motor at night if you can to see if you can see any arching wires, especially on that bottom cylinder.

To check for spark strength, you can use a bolt in the spark plug boot while pull starting. Spark should be bright white/blue and be able to jump approx 3/8" to ground on the block. Might need an assistant for that test.

Many ignition parts for that motor are a bit pricey, but there is a good probability you need a new coil, breaker points, and/or condenser.

That flywheel can be removed with a three point puller, using 1/4" or 5/16" bolts in the flywheel (poor memory). Shaft is tapered, keyed. Loosen the flywheel nut a few turns, then tighten the puller, then tap lightly but firmly on the end of the puller and the flywheel should pop free (hopefully).
 

junior1113

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Re: i have comp #'s happy memorial day

cant even fire it now pull cord recoil in done, pulled 100 times and only a poof
so try replacing plugs and wires then go to coils the points then condenser
 

jimg984

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Re: i have comp #'s happy memorial day

sounds like something my brother did to my engine, he didnt realize it was a two cycle and required a 50:1 oil mixture. it acted the same way
 

junior1113

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Re: i have comp #'s happy memorial day

wish that was my problem 10th 2 stroke outboard
 
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