'00 WR400 Overheating/Lack of power

I've been asked to have a look at a friends WR400 that has suddenly become low on power and is overheating. He's changed the plug and said that it was white. Having looked at this site a few times previous I was guessing that the woodruff key on the crank had stripped due to a loose nut. This was tight. It's not losing coolant or pressurising the system. Compression is good and it seems to start ok. Any ideas before I strip the carb? It does tend to run better with the choke out. Are there any concerns with the cam timing going out of sync? Any help would be gratefully received, cheers.

Sounds like its a bit lean. Bump the main jet up a size and turn the fuel screw out some and see if it runs any better.

It's obviously very lean. If it happened suddenly you should look for dirt in the carb jets or maybe even a broken needle clip. It could also be an air leak after the carb, maybe a tear in the rubber boot between the carb and the head. Was anything done to the bike just before the problem arose?

Cheers for the advice folks, I will check this out later. As far as I'm aware nothing had been changed on the bike but I won't take that as gospel. I had it running yesterday and it didn't actually sound too bad but was definitely more responsive on choke so theres a good chance there is something in the carb. It's running standard can etc. so I'll check it out. Many thanks.

the bike is running too lean.. ideal jeting shud give the spark plug brownish or tanned in colour..definately it's a jetting issues coz running the bike lean means ur engine is running hotter n dis is the cause of ur bike overheating..

get ur bike rejet a.s.a.p. coz running lean can damage ur engine.. :thumbsup:

Cleaned the carb out twice now. One jet definitely had something partially blocking it. Refitted, took ages to get going. Popping in pipe when spinning on decompressor. Ran it without airfilter. Power definitely back. Washed out air filter and reoiled. Non start again. No popping, appears to have lost spark. Anyone have resistance readings for the coil? Possibly kill switch playing up. It'll be a box of matches at this rate!!!!

did u check the float level ..:thumbsup:

Did you change that white plug?

Yeah plug was changed and I've since swapped it for another known good plug. I haven't checked float level but I know it holds a lot of fuel (takes a while to drain out the bottom) and it doesn't flood. I have now definitely lost spark and will work back through. This could have been two faults from the start. Thanks for the replies guys, this site is excellent!!!

At long last!! I've put another CDI unit on and it seems to have cleared up the fault!! Hopefully that will be it! Time to fix all the other bits now!!!

This bike is a nightmare!!! Although the CDI was secondhand, after only 6 or 7 rides the problem has come back!! No power, red hot exhaust, popping back through on deceleration. It's had a new camchain, removed all wiring, stripped carb again, checked resistances of coil (slightly out), stator coils, TPS. I have another coil coming now but I won't hold my breath. I don't mind buying a new CDI unit but I don't want it to get frazzled by something on the bike!! Checked the voltage at the lights, appears to be 30 volts!!!! New regulator, exactly the same!!! Disconnect the capacitor and voltage goes right down!! I'm supposed to be a mechanic but this is really p**sing me off!!

It's a great bike to ride but it's doing my head in at the moment! Think I'll stick with the Bombardier, never lets me down!!

I had a similar problem just recently and it about drove me nuts and I was really beginning to question my ability to work on my own bike but I was able to find the problem when I had tore the carb apart to check what jetting was in the carb and to clean up the carb after it had set for a while I put the carb slide plate in upside down :thumbsup: put it in right the bike ran like beforemy mistake for not paying attention putting it back together.

Out of interest, do you guys in America have a capacitor fitted by the headlamp? My Yamaha dealer doesn't have one listed and the online parts fiche doesn't show one! Whats going on with this bike?????????????????

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