1990 xt 350 problems

[kx250rider90]

i bought the bike last night the guys said it needs rings and has a valve tap but when i rode it by him it ran alright carb is gunna need to be cleaned. when i got it home i took it down the road and i got it up to 55mph and the bike just died wouldnt jump start. it still has compression and i know its not seized. any ideas?

[bobtbkr]

Well, you need fuel, air and spark to make a motor go basically..

have you verified you have a good battery? good stator? all connections nice and firm?

how do you KNOW you have good compresion? did you test it with a compression tester?

if the spark plug is black and fouled looking, its not firing right and must be replaced.

[jsnmid]

Unless you can confirm the Intake Boots are new, buy a new set. They are the #1 issue with the XT350. After that, pull the petcock to make sure the screens are OK and clean. Then clean the carb really well.

Don't worry about the battery. It doesn't have to have a charge. Mine's been dead for 20 years.

[maim]

xt350's are not usually e-start. check for spark and might want to replace the plug while you are there. otherwiae do what jsnmid and bob said. might be easyer to pull start it than kick it over. might want to do a compression test with decompressor disconnected incase rings are stuck in the groves on the piston..

[kx250rider90]

i brought it to my buddys house and took the spark plug out and it was smashed it looks like the piston hit it but the bike didnt lock up or anything. the only thing that could hit the plug is the piston and what would make it come up that far? im going to take the top end apart today and see what it looks like.

[jsnmid]

Wrong spark plug, Or really trashed wrist pin or crank bearings. The wrist pin or bearings would have knocked like crazy before hand.

[Psycho18th]

Hopefully it's just the wrong length plug. Otherwise, there probably would have been some warning it was about to go ahead of time. Can't remember the plug size offhand...

Psycho

[kx250rider90]

alright it didnt have compression my buddy was wrong about that i pulled it apart and a valve went through the piston

[kx250rider90]

the head is pretty scratched up but i was told that as long as the new valves seat im alright. is this true?

[jsnmid]

Should be ok. smooth out the scratches with some sand paper.

Make sure you get all the pieces out of the cases.

[William1]

Cam chain tensioner failed.

Cam chain skipped a tooth. Bent valves, trashed the piston, possibly bent the rod. Shame you did not tend to the bikes problems before you tried to run it hard.

Send the head to WilliamsMotoWerx ot Engine Dynamics, see if it can be salvaged. You'll need to incpect the rod for true.

[kx250rider90]

i found a head for an 84 xt350 would that fit my 1990 xt 350?

[jsnmid]

i found a head for an 84 xt350 would that fit my 1990 xt 350?

They didn't make an XT350 in 84. '85 was the first year.

If it is a xt350 head and they just got the year wrong, it will fit. 1985-2000 heads are all the same.

Don't buy it unless it comes with the cams and caps. After they break in, they become a matched set.

The 1984 XT250 head looks like the 350 head, but I don't know if there are were any changes.

[Yamaguy55]

The heads are sort of the same between the 250 and 350, but the gasket surface would become part of the combustion chamber if used on a 350, if I recall right (wife has a SRX250, basically the XT 350 with electric start) I'd go after a 350 head, there's a ton of them out there.

If you try and reuse your head, can't have any small metal projections into the combustion chamber or you will beat the engine to death from detonation. (pinging: caused by sliver of aluminum head glowing and acting like a spark plug)

Whatever head you use, get new valve seals installed, and be sure to have the valves cleaned up and relapped. Can't grind these, once through the hard coating, they wear instantly, have to buy new. But a bit of 400 grit Clover compound and a light relap will do wonders. With the head upside down, and a spark plug installed, you should be able to fill the combustion chamber with gas (outside please) and not see any liquid in the ports after five minutes. If so, it's valve job time. Worth every penny if you want to really use the bike. That stupid cam chain tensioner got you (sadly) good. Check both of the cam chain tensioner rubber arms for wear and replace if suspect. Sudco sell a lot of stuff like that. I just told another post here about some other XT 350 stuff, go read it so I don't need to repeat.

Good luck.