Author Topic: 91 lt250r wont start (Read 1195 times)

Jsmitty42 · « **on:** October 03, 2013, 01:39:09 pm »

ok so i just bought a 91 lt250r from a guy and he said he put a brand new wisco piston and rings in it and it needed carb work to run and i got it home bump started it and it makes a rattel nois from the engine and i dont know what it is... and it is really easy to kick it wont start by kick almost like there is not enough compression in the kicker to start it also when it is running it wont idel on its own and the idler screw is all the way in and one more thing the choke does not seem to work either... so someone please help me thanks

Chuckie25 · « **Reply #1 on:** October 03, 2013, 02:09:45 pm »

Step one: Conpression check

Buckeye513 · « **Reply #2 on:** October 03, 2013, 02:33:37 pm »

Check your crank seals this is what mine was doing when one of my crank seals was blown out. Compression tested fine 150-175psi but wasn't sucking a fuel charge cause of the vacuum leak out the crank seal.

Gillio · « **Reply #3 on:** October 03, 2013, 03:19:08 pm »

Pull your intake or exhaust and see how much the piston moves around in the bore. It MIGHT have the wrong size piston in it. Sounds like a shade tree mechanic scenario.

Jsmitty42 · « **Reply #4 on:** October 03, 2013, 04:44:04 pm »

ok pulled the head of and the piston wiggels side to side is it supposed to have play at all or is it supposed to be tight?

Rainman56 · « **Reply #5 on:** October 03, 2013, 05:30:23 pm »

How much wiggle?There will be some.Are there any numbers etched on the top of the piston?Pretty sure all Wisecos have numbers on the top.Won,t fix your problem but will give you an idea whether the guy was full of ****...For some reason almost every 2 stroke for sale seems to have a "just rebuilt,new top end".

Did you do a compression check?Also if the choke isn,t working it would make it tough to kick start.How do the reeds look?Basically gotta check all the basics,usually a good idea anyway when buy an older quad especially any of the performance oriented ones.They likely weren,t babied.Not trying to scare ya but I,ve yet to buy any vintage snowmobile,ATV,s,muscle cars that haven,t been messed up in some way.Likely lots of different hands been working on it for 20+ years.

Gillio · « **Reply #6 on:** October 03, 2013, 05:33:56 pm »

If the heads off, check for markings on the top of the piston. It has the size stamped into it. And you'll need a set of vernier calipers to measure the bore size. Your looking for roughly .06-.07mm difference on a forged piston, If your around .31mm range your prolly running a undersize piston. I've seen it happen and kinda run before.

Rainman56 · « **Reply #7 on:** October 03, 2013, 05:40:18 pm »

Think Wiseco uses part numbers on top not the typical .010,.020 but I could be wrong.Think the mark a part # on the top.

Gillio · « **Reply #8 on:** October 03, 2013, 06:07:58 pm »

The last 4 Digits of the part number should be your piston size.

BadMoonRacing500 · « **Reply #9 on:** October 03, 2013, 08:04:31 pm »

Quote from: Gillio on October 03, 2013, 06:07:58 pm

The last 4 Digits of the part number should be your piston size.

yes 6700= stock ,6750=.050mm over, 6800=.100 over and so on in increment's of .050mm. don't think .030 and .060 over thats in inchs.

Jsmitty42 · « **Reply #10 on:** October 06, 2013, 09:43:50 am »

talked to the guy i bought it from he said he think that the jug got "micked to much" and that i just need over sized rings ?will that work

Gillio · « **Reply #11 on:** October 06, 2013, 11:30:10 am »

Naaa. You need to remove the cyl and measure it and get a new oversized piston with a fresh bore job. Chances are that the bore is blown out and out of round. You need to start fresh.

BadMoonRacing500 · « **Reply #12 on:** October 06, 2013, 12:31:24 pm »

Find out what size piston is in it and buy (1) .050 size up, then take it to a good machine shop and have them bore and hone the cylinder to the size of that exact piston. The pistons can have slight varience in size.

Jsmitty42 · « **Reply #13 on:** October 06, 2013, 02:52:34 pm »

ok so took the cyl off and the crank arm moves side to side is that bad

BadMoonRacing500 · « **Reply #14 on:** October 06, 2013, 03:14:47 pm »

Are you talking about the rod or crank?

Jsmitty42 · « **Reply #15 on:** October 06, 2013, 04:35:29 pm »

yes the rod is it supposed to move ?

James Dandy · « **Reply #16 on:** October 06, 2013, 05:10:00 pm »

Yes it's supposed to move side to side at the rod bearing, but if you hold it centered on the bearing, then try and wiggle the piston side of the rod side to side, it shouldn't move much. There's a tolerance there. Not sure what it is.

Jsmitty42 · « **Reply #17 on:** October 06, 2013, 05:36:03 pm »

ok so just grab the piston and it shouldt move very much or r u saying the whole rod shouldnt move much ?

BadMoonRacing500 · « **Reply #18 on:** October 06, 2013, 06:21:27 pm »

The rod will move, the thrust washers on the piston pin everyone talks about keep it from moving during operation. When you rebuild it make sure to get the billet thrust washers and 99rm 250 pin bearing. The stock washers break, and will destroy your engine. The washers are availible in the store here or through motorgeek or chrisG.

Jsmitty42 · « **Reply #19 on:** October 06, 2013, 06:31:26 pm »

ok so now when i put a new piston in it dont i have to oil it what kind of oil do i use and were do i put it ?

BadMoonRacing500 · « **Reply #20 on:** October 06, 2013, 06:51:12 pm »

put a little good 2 stroke oil on the cylinder walls, and piston side's, piston pin and bearing and around the rings.

Jsmitty42 · « **Reply #21 on:** October 07, 2013, 03:03:45 pm »

do i even need a new piston if the rings that were stuck came off?

El Diablo · « **Reply #22 on:** October 07, 2013, 10:18:18 pm »

If you bore & hone your cylinder, then you will need a new piston.

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Author Topic: 91 lt250r wont start (Read 1195 times)

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