Spark plug breakdown

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Posts: 29
Joined: Sun Jan 14, 2007 6:41 pm
Location: Brisbane, Australia

Spark plug breakdown

Post by DaveDare »

Hi guys. I have posted on a different topic previously with the same problem but I am still to no avail. Let me outline the problem:

I have a 900S2 '83 model. Just back on the road after a minor refurb.

Pickup wires are replaced with Steve's good stuff.

New coils.

New regulator.

New plugs (about a dozen so far)

New Inlet manifold gaskets.

The Story:::

I can take the bike for a run say 20 to 50 klms/miles and the bike runs very well. after a while it cools and then the front plug breaks down. Seems like the ceramic is cracked. I am guessing it is running super lean.

Only happens on the front cylinder. I am now totally lost as to what might be the problem. I will list some of my thoughts which may or not be feasible.

• Somehow the carby is running too lean (maybe jetting???)

• The inlet manifold is still leaking

• (Not being a sparky), could the current be too high??? I don't think so.

• The cylinder head is leaking slightly.

• The jetting is not right?

• The 2 into one is not baffled correctly

• There is an alien force at hand...I have no idea!

Can somebody please help and shed some light. I am at a complete loss.

Thanks guys.


Parallel Twin
Posts: 144
Joined: Sun Jun 17, 2007 7:11 pm
Location: Cincinnati Ohio

Post by baddean »

Hey Dave,
Are you sure that the timing is correct? Are you sure that the plugs are the correct ones for your bike? Double check for intake leaks. Good fuel?
Gapped properly? Torqued properly?(too loose, Too tight) Too loose won't transfer heat, too tight stresses plug when going from hot to cool. Front carb jetted correctly?
I'm thinking that since it is only the front cylinder it would be related to timing, jetting, or intake leak since the plug in the rear cylinder does not do this.
Other than cracking ,how does the plug look? White, scorched, hot.
Does it look different than the rear plug?
When you replaced the intake manifold gaskets how tight did you make them? They should only be tight enough to seal. If you tighten them too tight it crushes them and they will leak.

Let us know how it goes,

Some useful plug info. ... index.html
Faster, faster until the thrill of speed overcomes the fear of death.
Hunter S Thompson RIP

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