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Merlin 53 Running and backfire

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Merlin 53 Running and backfire

Post  trickydicky on Mon Jul 18, 2016 6:41 pm

Hi,

JH I have got my merlin running with your new piston (thank you) and rebuilt using the crankcases that take the rubber seals. All seems to be running better now. However, I am getting a bit of backfiring from the exhaust and wondered whether this is due to the timing being out or is it more forgiving than that? I have set the carb needle to 2 13/32" as advised, thoroughly cleaned it out and don't believe I have any air leaks. The only thing I have noted is that the running is very sensitive to the strangler position. Open it just a tadd and she stops.

Timing is as per the book piston at TDC, then line up flywheel with the notch on the crankcase. However the flywheel may not be the original and I wondered whether there was much variance such that this might cause a problem? I was wondering whether retarding or advancing the the ignition might help? Your thoughts will be welcome.

Thanks TD
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trickydicky

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Join date : 2015-09-22
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TIMING

Post  piston 197 on Mon Jul 18, 2016 7:42 pm

Yes there will be variance from one flywheel marking to another, check that the points are just starting to break when the piston is 5/32" before TDC ( on the up stroke) this will check that the marks are accurate, if not set the timing as above and make a new mark on the flywheel for future reference.
Standard needle length below the slide should be 2.41" if it is too weak in this position ( and you cannot open the strangler when it is running) try reducing this length in stages to richen the mixture ( raising the needle)
JH
p.s. mine runs an absolute treat, but then again mine has a carb manifold from one side of an excelsior talisman twin and an Amal 375 monobloc carburettor !
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piston 197
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Re: Merlin 53 Running and backfire

Post  trickydicky on Mon Jul 18, 2016 7:47 pm

Thankyou for the information JH I'll try that this weekend and let you know how i get on.

Is the carburettor prone to problems given you have changed it?

TD
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trickydicky

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carburettor

Post  piston 197 on Mon Jul 18, 2016 8:08 pm

Mine is fitted to a James cadet competition with 125cc 10D engine, I bought the bike about 1990 in pieces from a numberplate dealer in Bristol, started to collect parts as some were missing, but around 1992 I was persuaded to sell it to a friend  ( Ian) in his 70's, he finished it off and fitted the carb manifold and carb as he had one to hand, I bought it back restored around 2000 when my friend now 80 was giving up riding Bikes, I had it a few more years and another friend ( Ron) in Cheltenham wanted a bike with lights as his trials Merlin had no lights and he kept getting caught in the dark coming back from VMCC runs,
Unfortunately he died about 18 months ago and I bought it back from his widow.
It has always ran well since being restored and has been left pretty well alone since
First purchase price in bits  £120 ( 1990)
second  restored £650 ( 2000)
third time £1000 (2014)
Perhaps a true reflection of the times ?
JH
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