Need help with friends 250r!!!!

[NJ450rider]

I dont work on 250rs hardly at all. And im stumped as too why my friends 250r wont run. Heres the story:

A few weeks ago his top end took a crap and he put in a new piston/ring/ kit. the cylinder was inspected and told it was fine. Put it all together and it ran great. The next time he took it out within 30 minutes the lil elbow at the back of the cylinder poped while riding and antifreeze went flying everywhere. went home and got it to go back in. went ridng a few days later and it was fine. than following day went out and it did it again! LOL i dunno if its because theres something wrong or not. anyways he took the cylinder off and checked the headgasket to see if i was leaking at all. it wasnt and he put a new gasket on anyways.

Now today he said it started right up first kick. came out and rode around for 10 to 20 minutes. let it sit for a lil while. when he tried to start it it ran for a minute and than fouled a plug. We brought it home and put in a new plug and nothing still wouldnt run. took apart the carb and cleaned it. jets were fine and put it all back together. looked over all the wiring and found nothing really wrong. After it fouled it just wont run at all. Itll run for about a second with the gas off. as soon as you turn the gas on it dies. It has plenty of spark so i am completely stumped why it wont run.

I really need some pointers and things to look at because its really strange why it wont run for anything all of a sudden.

its an 86 or 87 250r

stock cylinder/ piston size
fmf pipe
k&n air filter with prefilter cover/no air box lid

thats all it has for engine mods and its been that way for many years.

Like i said its been great all until today. wierd that it fouls a plug and wont run but its got spark and fuel. any help will be huge!!

[TRXNICK]

Well I can help you with the elbow popping out of the head. I had the same problem with mine. First of all these bikes are 20+ years old and the heads and that elbow are made out of aluminum. That elbow is a press in fitting, If the head gasket is leaking it is causing pressure in the cooling system and thus blowing that elbow out of the head, because where that is pressed in is getting old and tired. I took my head off and had a friend at work weld the elbow permenetly in the head. Have your buddy take the head to a shop and have it checked to make sure it is perfectly flat. I have had mine done like this for 2 years and no problems. As for the other problem I'm sorry I can't help you guys out. There are plenty of guys on here that can help you out with the other problem.

[Dave83]

Was this engine broken in properly after re-doing the top end?The flooding problem could be several things.did he happen to check the reeds when he had them out?Could also be a sticky float,but he did clean the carb,so that may be a reach.Choke circuit may be hung open,or it may be as simple as a loose connection in the wiring.i would try starting it with the throttle wide open(I dont like to do it,but I do as a trouble shooting measure.)If it starts there,its more than likley in the carb.If not,break out the ohm meter and go over the wiring.

[rnr568]

that was my friend that posted that for me but im the one with the prblems lol i started it with the throttle wide open and it ran for about 10sec give or take than died