The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: wally on 13.06. 2025 05:03
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Hi All,
I started my 51 Golden Flash after 2 years storage. I had drained the fuel from the tank & carb.... Fresh fuel, checked spark, started 2nd kick. Ran well at idle, blipped the throttle, the Monoblock's slide stuck open & she revved hard for a second before I could stop it. Have tried to start it since after oiling the slide... not even a kick. Took the valve covers off, the valves are opening and closing. Any ideas why she won't fire?
Wal
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Maybe something to do with the points. Check spark and ignition timing?
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There shouldn't be any oil in the carb. Has some run down and blocked the pilot jet?
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been sitting for 2 years ?
have you drained the crankcase ?
has the oil you put in the slide fouled the plug ?
does the carb slide bottom out in the bore ?
is the spark plug wet , and still sparking ?
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Thanks Sean, Ted & Cheeser,
Yes, fresh oil, & only a smear of oil on slide & it now bottoms out. The plug is wet & sparking.
I think the problem is timing, perhaps killing the engine abruptly whilst at high revs has caused slippage.
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Stripped ATD gear?
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The previous owner of my Venom over-revved it when he missed a gear, and the valves tangled.
The "tilted" valve head wasn't obvious until the valve was removed though.
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Thanks Sean, Ted & Cheeser,
Yes, fresh oil, & only a smear of oil on slide & it now bottoms out. The plug is wet & sparking.
I think the problem is timing, perhaps killing the engine abruptly whilst at high revs has caused slippage.
Checking ignition timing with a stick takes about 5 minutes.
Correcting it takes longer!
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If a valve has kissed a piston a compression/leak down check should tell you, quick and easy to do.
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Thanks Bago & Triton, those tests are todays mission.
Wal
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Hi All,
Thanks for your advise.
I checked the timing, (several times) using the cigarette paper method; spot on.
Tried the thumb test for compression; it has some.
I've borrowed a screw-in tester; the instructions say warm the engine up; I wish.
My question is...what could be the acceptable reading difference be between hot test & cold?
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Do a test on the difference between the cylinders… choke off throttle wide open
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Thanks Sean,
I'll find out at least the cold engine values.
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On a cold engine I get a maximum reading of 110 psi
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Thanks Morris...................Wal
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I’ve got the same problem, only a very weak spark sometimes no spark….
Was going to return magneto for check under warranty…
Did you find the solution Wally 👍
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Hi Mikey,
I opened up the plug gap from the normal 18 to 36ish & the spark was OK.
The compression when tested was low so have removed the head, ground the valves & obtained a head gasket.
Now; I've had the bike for over 60 years & each time, in the past, when removing the head I've had to give it a belt with mallet to free it.
This time the head, the gasket, & the gasket to block floated free.
I think I may have hydraulic the engine which would account for the non start & compression.
Time will tell.
Will let you know
Cheers,
Wally