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Right hand plug fouling

Submitted by david_henshaw on Tuesday, 1 November, 2011 - 00:00
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Commando

Hi, please can I have some ideas on this problem, my '73 750 roadster keepsfouling the right hand plug, I am running a single carb amal mk 1 with a 250 main jet, needle in middle groove and the mixture seems about right, slightly rich but ok, the bit that is puzzling me is that it seems to be oil fouling on the right but there is not much smoke, none when revving and only sometimes on tickover, would this be enough? thanks for any thoughts. Ralph.

Submitted by tom_mortensen on Tuesday, 1 November, 2011 - 00:01

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The obvious answer would be different ignition timing between the two cylinders. Have you fitted electronic iginition or are you still using the old mechanical? Anyway start by checking ignition timing, and in particular if its the same for both cylinders. Valve clearances could be off on the offending cylinder. You could have oil flowing into the cumbustion chamber. Is the soot soft, moist and velvety? Then its oil bening burned. If its dry and black, excess fuel. You could have some kind inlet port obstruction, after the point where the manifold splits into two. Just a few things to consider, others may chime in with other suggestions.

Submitted by david_lord on Tuesday, 1 November, 2011 - 00:02

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Ralph

It could also be that the RHS inlet valve seal has come adrift, but I would expect blue smoke to be obvious from that side and not the other.

David

Submitted by david_henshaw on Wednesday, 2 November, 2011 - 00:00

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Thanks for the ideas, the bike is fitted with electronic ignition (pazon) the carb is new, initially Ihad BP7ES plugs fitted butreplaced them withBP6ES to see if a hotter plug would help, I think its time to check the valve guide seals, I haveheard somewhere that oil can pass down the outside of the valve guide is this true?, the other thing I have thought of is the oil ring on right hand piston passing oil, but I would have expected more smoke. Thanks again guys, Ralph.

Submitted by john_whiting on Wednesday, 2 November, 2011 - 00:03

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If oil is passing the outside of the guide it is loose in the head,requiring o/s guides and maybe reaming to cure.Its not uncommon with any type of ally head.The seals can be replaced without removing the head,but if you take the head off you can also check the bores.Regards John.

Submitted by david_henshaw on Monday, 7 November, 2011 - 00:00

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thanks for all the ideas, I stripped the head off at the weekend and found that the right hand inlet valve guide had broken off under the flange flush with the cylinder head allowing oil to run down the guide bypassing the seal completely, has anyone else had this occur,cheers Ralph.

 



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