SOHC.co.uk Forums > CB500/550

It won't start!

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matthewmosse:
Ok, an old chesnut, got good compression and valve timing now as per manual ( last owner had it out by a lot but valves survived somehow.) I've set the points as per factory manual and carbs came off a running engine on the bench. New air filter fitted, fresh fuel, good spark. tried re setting points several times. However when engine turns over it won't fire and there's air/fuel blowing back into the airbox... the compression tester shows normal compression on all 4 cylinders. Is there normally air movement in the 'wrong' direction? ??? :'( >:(
this bike has it in for me at the moment...... I've run my 500/4 for years as a commuter but recent gearbox problems meant switching to a spare 550 lump from a breakers until time allows a rebuild of the original motor.

Dave M:
Plug leads on the right plugs?

matthewmosse:
yes they are, gessing that I'm no good at setting points............... but It should have fired at least.

SteveD CB500K0:
Even with the points/timing out, I'd expect it to pop and fart!

You have to be systematic:

1. Is there a spark on the plug?
2. Is there fuel (are plugs wet)?

Answer those first.

matthewmosse:
Ok the mystery deepens;- cylinders 2&3 suck air in the normal way (though weakly) and have damp plugs.
1&4 appear dryer and blow air quite stongly back thru the carbs putting lots of fuel in the airbox, like great clouds of it. The engine is something of a curiosity in itself by the way. It has no stamped number in the usual place, and a number has not been erased either, what it has instead is a silver sticker nearby which says 'honda assighned engine no.'
I'd be expecting all 4 cylinders to suck air from the carbs with equal enthusiasm, not blow air out of the inlet. Could it be possible that  I've ended up with an odd shaped crank or camshaft? the valves are all opening and closing fully. 
I've rebuilt 550 engine's in the past and never seen anything like it, Not that Ive checked if cylinders are blowing air bach thru the inlet...
Seems the engine is a bit of an odity to me. It simply isn't possible to put in any parts the wrong way appart from valve timing which I've checked. The camshaft cut out faces foreward and is flush with head top face when 1&4 tdc timing (T) mark is is lined up. However there is no knowing what a past owner may have done. Could be a case of full engine strip down........... Damn
Anyway Thanks All for the advice. Ps anyone know of the origins of an engine with no stamped number? could it be a warrantee replacement set of cases or something?

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