C15S Won't Start

[C15S]

The continuing saga of the 1962 C15S Scrambler I rescued after 25 years in a CONEX box.  When I got it the inner cover on the right side was off with the gears and shifter plate out.  I got that all put back together, and it shifts fine.  Before I put the cover back on, I verified the timing marks were aligned.  There is a pin prick on the cam gear, and you can just barely see the top (behind the lock washer) of what I think is the corresponding tick mark on the pinion gear.  Everything was lined up per Rupert page 74, Illus 8.2-8.5.

However, when I vigorously kick start vaporized fuel is blown OUT of the carburetor.  To me that means to piston is coming up while the intake valve is open, and the valve timing must be off.  Right? 

[V500]

I'd say so.

[rhyatt]

sounds like the valve timing is adrift
BUT
the scrambles bikes had the Energy Transfer ignition system - which if weak could also contribute to this
weak spark - slow burn - still burning when inlet opens -----

https://1drv.ms/b/c/77b24d882b9c7950/EbxhZF5qGJ1GtrqpVwhf4DIBUdX9cvmSgebhqB0nBxvU9w?e=weXPcq

and of course incorrect procedure when adjusting the valve clearances - the procedure isnt difficult , just needs care and a degree of precision


try this link

[JulianS]

See the valve timing on service sheet 428 on the above link- the inlet valve does close after bottom dead centre on the compression stroke, most 4 strokes are similar, I think to do with the gas velocity. So you may not have a valve timing problem?

[C15S]

Thanks for the replies.  The link to the service sheets confirmed my valve timing is correct.  I marked up the nut that holds the alternator in place with TDC and BDC, then measured to degrees from each when the intake and exhaust valves are suppose to open and close.  All good per Service Sheets 427 and 428.

It dawns on me that for a motor that is supposed to have a 10:1 compression ratio that it turns over too easy, even when I don't do a partial open of the exhaust port. I know think the rings and valves may be the culprit.  Not enough compression to draw in and compress the fuel.  What do you think?

[rhyatt]

Easy to verify using a wet and dry compression check.

Screw your compression gauge in to the plug hole.
Wide open throttle
Kick over a few times , check readings , around 150 psi would be nice.

If not near that , squirt a bit of oil into top of piston crown and kick over again.

If readings improve the rings or bore suspect.
If no improvement the pressure leaking past valves.
Have you checked valve clearances ?

[Rupert]

Have you checked the pushrods are the right way round? Outer to inlet. Just a thought...

[C15S]

Did the test.  You think 40 psi is to low   Hopefully its just rings and valves, and that cylinder is OK.  As always, thanks to everyone that responded.   

[rhyatt]

40 psi is not too good -
try the squirt of oil to saturate the top ring and momentarily seal it
if compresssion jumps up then barrell off and look at ring gaps and bore

if no change then compression is leaking upwards --- check the valve clearances though anyway

[Barnsey]

Rupert beat me to it.  On my bike the push rods got reversed by accident as I reassembled the bike. It confused the hell out of me until I realised my mistake.