My XS 400 only goes 25 mph.

[only]

Er, if this is a sohc XS then it doesn't have shims, just good old fashioned tappet adjusters.

eek, did not know that. i have yet to open an xs400 up. makes it easier, though.

 

[Jamin Smitchger]

I did a compression test on the engine, and to do the test I squirted a bunch of oil in the spark plug hole. I did the test wrong so I decided to run the bike a little while in order to get the oil out. I ran the bike at least ten minutes with absolutely no problems. I am not really sure what is going on. With oil in the cylinder, the compression was running at 150 psi. I will test it without oil after I run it more tomorrow.

 

[only]

ride it around and try to burn off the oil. a good compression check with oil in the cyl AFTER a bad compression check means your rings are toast.

chances are, the bike if fine, the black smoke was carbon coming from the one dead cyl that you recently got to light off. black smoke usually equals fuel, unless it wreaked like burnt popcorn, which would indicate carbon. id say run it, ride it, beat on it, then redo the compression check without oil. be sure you disconnect the fuel feed first. record the numbers, and the cyls should be within 10-15% or eachother. if one or both is lower than say 150, add an ounce or so of oil and retest.

 

[Jamin Smitchger]

All right, I am getting this bike figured out. I went out for a ride on the bike and took it up to 60 mph no problem. Anyways, I did the compression check and the readings are
Cylinder 1: Dry=140, Wet 250
Cylinder 2: Dry=138, Wet 230

I guess the actual numbers are not as important as the fact that the two cylinders are very similar to each other. I believe the large spike after adding the oil may have been because I added too much oil (incompressability of liquids). So I don't think I have worn piston rings, but rather busted valve seals. What do you guys think about my reasoning?

 

[drewpy]

those compression figures are OK, so long as they are within 10% of each other. It is maybe about 10% down from 150psi.

Try adjusting the valves first!

 

[Travis]

.... So I don't think I have worn piston rings, but rather busted valve seals. What do you guys think about my reasoning?

Yep.. if it's still spitting oil out the exhaust, or burning a ton of it.. then it's got to be valve seals. Is there blue smoke? Does it look like a two stoke going down the road? If it's not too bad, I would just run it like it is for a while. Maybe the old dried out seals will get a little better after some heat cycles and lubrication.

 

[only]

seals would puff blue start up, and a constant faint blue/white while riding. along with smelling like the exxon-valdez. i commend you for taking my advice and doing a compression check. all good news here!

 

[Jamin Smitchger]

I will order new valve seals today from www.bikebandit.com . Does anyone know of anyplace to get them cheaper.

 

[Travis]

I find that bike bandit usually has decent prices.. You can find stuff cheaper if you search around but sometimes it's not worth your time.

 

[drewpy]

I got those viton seals as the "new" ones I got with the gasket set lasted 200 miles.

I must admit the viton ones are fantastic

 

[only]

viton rules. ive used viton on every application ive ever had the head(s) off of. it is superb for a valve seal material.