The spark plug on my '82 Dr 250 is fouling very badly. I'm no expert but thought that this must have to do with carby. I have stripped carby and adjusted it so many times but with no success. I have checked airbox for rags! washed the air filter element and finally removed it all together. Still no improvement. Finally I took the carby off my '85 road DR and again still fouling plug. I changed froma D8EA to a hotter plug D7EA and this gave me a little improvement (30 miles before fouling so badly the motor started misfiring. I stripped the motor down last year and didn't do anything to it as it was in quite good nick.

------------------

I would appreciate any help you can find. To further complicate matters, I put the samemotor into my road DR 250 and it ran perfectly! The only thing that I have done to it is to replace the cam chain so I am wondering whether the bike could run well (besides the fouling although perhaps a little down in power) if the cam chain was one notch out? Or could tappet settings cause the problem?

------------------

Roger, we need some accurate history here!

You stripped the engine down - when did it start fouling? IMMEDIATELY after?

You put the same engine in another bike and it ran fine - BUT sounds like you replaced the cam chain, therefore a fairly significant dismantle - I'd guess you fixed the original error.

Also you don't say if it's oil fouled or gas fouled.

If the cam chain was one tooth out it could have run ok, but yes somewhat down on power. Tappet settings - can't think how that could have caused fouling.


------------------
Grant Johnson

Share the Dream!
at: www.HorizonsUnlimited.com

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

Thanks Grant and Old Road Toad. My 85 SF needed a rebore so I took the motor out and replaced it with an 82SZ (same motor). It ran very well except for a rattly cam chain. When the SFmotor came back I replaced it and took the 82SZ and put it back into its frame. This was a bike I had just bought for NZ$100 and hadn't had it out yet. Apart from the cam chain the motor was good so stripped it down and got it checked with the decision being made that a cam chain was all that was needed. Rebuilt the motor with new cam chain and wasn't perfectly happy that the cam chain was at one oclock. Tried it one tooth either side and that seemed far worse so put it together. Motor started third kick and ran sweetly. But off road after 15kms it started missing. Checked the plug and it was oiled very very badly. Cleaned it and she (or should that be he?) went for another 15 kms before plug fouled again. Tried a hotter plug (D7EA instead of standard D8EA) and it now ran for 40 kms before fouling. I have done about 400kms since the problem started and although it feels down in power at the top end of the rev range it is going well. The regular spark plug cleaning breaks give me time to admire the awesome scenery. If it was aweal spark wouldn't it break down under power? And if it was a weak spark would it be magneto, CDI or coil and how could I tell?

Hi Roger,

That makes it all much clearer! (BTW all three of your posts made it, you just need to force a refresh (hold down shift key and click refresh, or if that fails go to the address bar and delete the "www." from the address and press enter. That WILL get the latest page. Web server caches cause this problem frequently. I deleted the extras - you can too if this happens again.)

Re your problem, with this information I suspect you have a broken oil ring, or some similar problem, perhaps a bad o-ring sealing the cam tower from the combusion chamber, bad head gasket, or a cracked or incorrectly installed valve stem oil seal (intake, as it is getting into the combustion chamber, although the exhaust could also be bad) or something like that.

If it's definitly oil-fouled it's not ignition or carburetion causing the problem - assuming it really is OIL-fouled. A compression test may show low numbers which would point to rings, but if it's a broken or incorrectly installed oil ring the numbers will be fine, as the compression rings are probably fine. I think you just need to take it apart again.

I'd also talk to your dealer to clarify the cam chain positioning question, although I suspect you got it right.

Good luck!

------------------
Grant Johnson

Share the Dream!
at: www.HorizonsUnlimited.com

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

Grant it was that litle smiley face and capital OIL that caught my attention so I emailed a riding mate who used to have a Yamaha dealership and he said that there is no smoke out the back and plug is definitely not oil fouled! How do you know my bike better than I do? No, don't answer that. Okay, so does that help the matter?

No! Rats!

I had it all sussed out, grumble grumble.

If it's NOT oil for sure, and no smoke, it's probably NOT rings valves etc., OR carburetor - it should be smoking BLACK smoke if it's so rich that it fouls the plug in that short a distance, or BLUE smoke if it's oil.

Given that, the only thing left is ignition. Weak/bad coil, or who knows what else. I don't even know if your bike has points or electronic ignition or what. But I would start by swapping bits from the other bike and see what fixes it. Start with a BRAND NEW spark plug, then the coil, then any black boxes. Once you have substituted one item, don't swap it back out - leave the new components in until you have replaced everything and it is fixed - or not! It could be two related components!

Good luck,

------------------
Grant Johnson

Share the Dream!
at: www.HorizonsUnlimited.com

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

Thanks Grant. My plan is this: seeing that the troublesome motor has been in the road bike and performed well I will assume that the magneto is not the problem. Seeing also that I have tried two new plugs and have replaced the spark plug cap I will put those possibilities aside. That leaves CDI and coil. So the coil will go onto the road bike and I will have an answer on that in a few days and a few more if I have to try the CDI. Watch this space for developments!

------------------

Put suspect coil on and engine started cutting out at low revs. Took it to an auto electrician and he said it checked out fine! Checked myself for spark onto the engine and very good spark. So put suspect coil back onto road bike to recheck but further trouble when I went to start off from the traffic lights - guaranteed to get the adrelaine running! So will go hunting for a second hand coil. Thanks for all your help.


------------------