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Poor compression - 15T

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Poor compression - 15T

Post  fulmar88 on Thu Jun 23, 2016 7:35 pm

I've always thought my Fulmar 88 is a bit under powered but have nothing to compare it to. It kicks over really easily so I did a quick cold comparison with my 10E Falcon which had a rebore and new piston 1200 miles ago. The Falcon recorded 135 psi, the Fulmar 95psi. Has anyone a feeling as to whether this low reading would seriously affect performance? I have a secondary issue of an occasional slipping clutch when kick starting so obviously a new piston will only make this worse.

Steve.
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compression

Post  john87 on Thu Jun 23, 2016 8:16 pm

Squirt a little engine oil in the plug hole, just enough to make the rings seal, and then try it then.. See if there is much of a difference..

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Re: Poor compression - 15T

Post  fulmar88 on Fri Jun 24, 2016 12:05 pm

Thank you John, I will try that. I'm sure I have an issue as I have to paddle away from rest on inclines and even on the flat I struggle to get going and the engine is trying to stall.
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Re: Poor compression - 15T

Post  fulmar88 on Fri Jun 24, 2016 6:43 pm

A squirt of oil improved matters to 110 psi from 95 without. I've no idea whether the oil had moved around the whole periphery of the piston but it made a difference at least. I shall have to contemplate stripping to see what piston is fitted. I think it's standard but it's been 13 years since I last had it apart.
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Compression

Post  john87 on Fri Jun 24, 2016 8:45 pm

Hmm, rings stuck perhaps.... but all the same I am very sure that there is very much more too it than that.. Timing retarded?? Does it ever spit back through the carb?? Does it run hot?? Exhaust is not blocked is it???? That would be my first thought...

john...

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Re: Poor compression - 15T

Post  fulmar88 on Fri Jun 24, 2016 9:50 pm

I stopped using it 5 years ago because it started to miss and backfire under load, uphill etc. Since I got it out again last week (and it was still doing it) ive had the exhaust off and it is completely clean and a nice dark brown colour inside, as is the plug. Ive checked the timing and reset the points to 18 thou (spec) from around 12. This has improved the backfire considerably. It only did it once in 60 miles and that was at sustained wide throttle opening. I've checked fuel delivery and it's fine. I've ordered new points and condenser as this was suggested as a reason for the misfire/backfire but don't really want to remove the flywheel unless I have to as the crank end is very weak on the 15T and prone to shearing off.
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Re: Poor compression - 15T

Post  fulmar88 on Sat Jun 25, 2016 4:20 pm

Another 50 miles today with no misfire/backfiring so the points gap change seems to have solved that? I'm sure what power there is though reduces with miles. Early in the run I can easily achieve 55 downhill etc. Later on I can't get above 50 no matter how hard I try. Brakes aren't binding so I'm at a loss to explain it.
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missfire

Post  kerabo on Sat Jun 25, 2016 7:48 pm

If setting the points wider cured your problem I would put money when it hot the cases and the main bearing have movement in excess of the gap your points were set at. I have had the same problem on a 1H  and villiers industrial engines. It's no big deal just keep the points a little wider . Try a fraction more and see if it gives your power back.
Only happens when hot. So a hard run has this effect.
Regards Ken
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