any ideas on exactly what happened??

LAYNFRM · Post by **LAYNFRM** » March 25th, 2009, 9:58 pm

here's the info. 05 CR250, jetted for trails, and the plug had been in there for over a year of trail riding and it ran perfect and never had a problem whatsoever. i put my motard wheels on it and was driving it around town all day with some motard buddies. it wouldn't pull 5th gear (15/39 gearing) past 85ish, but i figured that was because it was geared so tall since it pulled hard like usual in every other gear. i've done a lot of research about turning a 2 stroke street legal, and i know not to keep the RPM steady by cruising and letting it lean out that way. i don't cut the throttle off without pulling in the clutch so that it won't get starved of lubrication. my only real guess so far about what happened is that it leaned out on top and was burning a hole in the piston when the prong on the spark plug actually melted. i guess i got lucky since it didn't burn all the way through, and i didn't get metal all in the bottom end.

i put a new piston in it today, cranked it and whatnot, but i wanted to post up on here and see if anyone had any ideas on what the problem could be before i go and run it on the road again.

the right is the exhaust side

_joshua_ · Post by **_joshua_** » March 26th, 2009, 1:27 am

Too hot.... Jetting problem... The spark plug must be also too "white"....

racein01 · Post by **racein01** » March 26th, 2009, 2:38 am

Bad fuel batch??

fastkart · Post by **fastkart** » March 26th, 2009, 7:08 am

Lean.

hoofarted · Post by **hoofarted** » March 26th, 2009, 7:56 am

Lean. Try a colder plug, too.

100hp honda · Post by **100hp honda** » March 26th, 2009, 8:37 am

i have a question for anybody/everybody. over the last couple years i been on various sites, ive seen pistons that look like someone took a hammer and chisel to the top of it. in my own mind im thinking, wouldnt you hear a huge banging and rattling sound well before it got to the point of destruction ?? not busting anyones balls, im just real curious

fastkart · Post by **fastkart** » March 26th, 2009, 8:41 am

When i burned the piston below and it also shattered the sleeve on the intake side from the bottom 1/3 or the reed box ( I didn't find a piece any bigger than a pencil lead, and it was stuck in the dome of the piston) I heard nothing but the motor shutting down, and on the kart the motor sits right beside me and a foot below my right ear.

100hp honda · Post by **100hp honda** » March 26th, 2009, 8:44 am

you heard nothing? i was reading on another site that guys when they run alcohol use a different plug so it melts the ground strap before the piston melts. i was reading about alcohol and i guess it makes a very loud nocking sound when things start to go bad

fastkart · Post by **fastkart** » March 26th, 2009, 8:53 am

All I heard what the engine shutting down... doesn't hardly seem possible. I got back to the trailer, dropped it back in gear, tried turning it over and she was locked up tight. PUlled the plug and it was white. The top end didn't seize, but there were tiny peices of sleeve that locked up the main bearings and wedged around the crank. Here's the jug minus the piece of missing sleeve. Oh... also, it was my top end, but a friends bottom end. I borrowed it because my bottom end shattered a main bearing earlier that year.

100hp honda · Post by **100hp honda** » March 26th, 2009, 9:23 am

damn thats alot of damage. between you, brit or Pstoffers im not sure whos harder on equipment

south central hoon · March 26th, 2009, 11:10 am

LAYNFRM wrote:05 CR250, jetted for trails

WTF does that mean? jet for elevation, temperature, humidity, porting, etc.

that fucker is LEAN.

two stroke motocross bikes were never intended to be ridden on the street, they were designed to blast into corners, power out over doubles, slam on the brakes and repeat.

having said that....
if you want to ride a two stroke on the street, jet it fat as hell for your elevation, temp, etc. and hope for the best....and chop the throttle on straights.

LAYNFRM · Post by **LAYNFRM** » March 26th, 2009, 10:08 pm

i upped the main today from a 390 to a 430 (mikuni hex jets). gonna try that to begin with and test it tomorrow. when i said the bike was jetted for trails, i meant it wasn't too fat on top since i lug the motor and don't rev the crap out of it like it would be on a MX track. should i adjust the needle in any way to account for riding it on the street?

i also went from a 9 series plug to a BR8ECM. gonna put the iridium version in when this one fouls since no one had them in stock and i had to order a couple. i'm going to run castor 927 at 32:1, which i normally do, but at 40:1 when i trail ride.

hoofarted · Post by **hoofarted** » March 26th, 2009, 11:38 pm

Thats a big jump in main size! That thing will spooge - watch. My 01 250 runs a 390 main, 44:1 927 mix...but then again - its not WFO on the street either. My needle is in the center position as well. IIRC lower numbers on the plug mean hotter, no?

kkvslayer · Post by **kkvslayer** » March 27th, 2009, 1:05 am

hoofarted wrote: IIRC lower numbers on the plug mean hotter, no?

yup,he went from hot to hotter but not sure how it would run on a 10 series, a 9 series should be fine if its jetted proper for street use

100hp honda · Post by **100hp honda** » March 27th, 2009, 3:44 pm

anyone have the powervalve get clogged with 927 ? i think 927 is only 25% castor but just wondered if that was enough to cause problems. im using R50 in my two fiddy

BannedCR500Riders.com

any ideas on exactly what happened??

any ideas on exactly what happened??

Re: any ideas on exactly what happened??