Need some advice here. I have a 2000 scram 400 that is fouling plugs. It all started after the throttle cable came off. at least thats when I started noticing that it wasn't running up to par. Its the wife's bike so I don't get on it much unless to fix it. My question is I have had it for about two summers is that enough use to require a top-end rebuild. and if so what compression should I look for on it when doing a compression check. It actually runs okay at my elevation (Las Vegas) but when I run it up in
Utah thats when I run into the plug fouling. could top end cause fouling?
It ran fine up in Utah when I first bought it I never had to jet it for the elevation. but now its not. So whats up?? Any ideas? Could the carb be dirty? Wouldnt that cause a lean condition? (clogged jets?) any ideas would be greatly appreciated before I tear into it Thanks Jay

 

The engine wil be running much richer at a higher altitude, and foul plugs. What is the altitude where you were riding in Utah? My Scrambler 400 will foul plugs every other ride or so when I go from 7000 feet to 10,000 feet in altitude. It is jetted correctly for 7,000 feet, but that 3,000 foot difference makes a big difference in jetting...

Good luck,
Lorrin

 

I am almost positive that the 400's are oil injected. If that is the case then the throttle cable most likely operates the oil injecter pump. You say something happened with the throttle cable. I think something happend when you fixed the cable and your injector is pumping to much oil to the carb making it run rich.

 

Leel I am running 2500' here to Utahs 6500'. But when the bike was new it didnt make that big a difference in performance. I know I should probably jet for the altitude. But could there be something else wrong with it. Does anybody know what kind of compression I should be looking for? 2000scramblrman yes it is oil injected but all that happened was the ball end of the cable came out of the slide end of the carb. Im not real sure how the the oil injector works off the cable but I will have to check that out also. Thanks for the replys If anybody else has any ideas I would appreciate hearing them. Thanks again Jay

 

The throttle cable splits below the handlebars, one side to the carb, the other to the oil injection pump.

You didn't describe how the plug is fouled, dry and black, or oil soaked.
The change in altitude will make a difference, especially if you didn't rejet for Las Vegas from the sea level factory jetting.
The oil injection is run STRICTLY off of the throttle, altitude has no effect on the oil injection system.
On a stock 400, look for about 130 psi cranking with the throttle wide open, with a minimum of 100 psi. Do the compression test with the engine warm.

 

Thanks CaptNemo I'm going to tear into it tommorrow. Just trying to get some ideas of what would cause the plug to start fouling when I have changed nothing. Its stock and has ran well up to now. The plug is a dry caking black? I think Im going to throw a fresh top-end on it for the heck of it. Its probably time anyways. and then go from there. Thanks for all the replys Jay

 

You have to check the oil pump operation. It should not need a top end yet. Pull the cover off of the injection pump and check its adjustment and make sure it moves with the throttle. I think it may be way rich since your repair. The owners manual tells you how to set it.

 

Depending on the hours and the way it was ridden, you should have quite a few more years on a stock 400 SC engine. If you took care of it, it should like new inside. Work with the jetting, it sounds like it's running a bit rich due to the altitude. A couple of spark plugs and some jets are a bunch less expensive than a piston and a bore job.