I posted this in the General Dirt section and in the Yamaha 2 stroke section but I still cant source the issue with the bike. so I thought I would ask the motor/jetting experts.

I just finished rebuilding my 96 Yz 250... ran great before I took it apart! Dont know if it matters or not but the bike has the long rod kit installed that was very popular in that era. Had the PV matched to the exhaust port and now the bike falls on its face when the PV should open like its not operating properly but it is operating correctly but I get nothing when I get to about 1/2 - 2/3 throttle it just cuts out... BAD! Ive been though the carb a million times already, installed a rebuild kit, new clean jets, and checked the float level over and over again to no avail and theres no way that jetting that was once good just suddenly went bad. So I bought a JD kit and installed it with the same issues, contacted him with the problem and he said that with the jetting recommendations that he gave there is no way the bike would run that poorly and insists that it is not a carb issue. His recommendation was 175 main, red needle 3rd clip pos, 42 pilot. What do you guys make of this?

Here is a vid of what the bike is doing. Throttle is being held wide open in both vids.




Its 10x worse under load. Ive done a leak down and compression test and both are great. Tested resistance in all electrical components and all tested within spec when cold obviously with the exception of the CDI. Not sure what else to look towards before I just start blowing money and replacing the electronics piece by piece until I find the problem. Ive already tried a different coil as well. Cleaned all grounding elements and made sure there was a good metal to metal surface. I hate to repeat threads but Im VERY desperate at this point since I have a riding trip scheduled for SC on the 15th of April. Ive been through this bike so many times it makes me sick!

Thanks for any possible advice, Brian

Edited by BDubb106, 27 March 2012 - 04:27 AM.

im sure you already probably checked but is it possible theres an air leak somwhere

Yes thats one of the first things I did was a leak down test... 6psi over 7 mins was lost.

Edited by BDubb106, 27 March 2012 - 04:42 AM.

i meant like a bad carb boot or something but after reading your other thread it seems like weak spark actually. did blackwoodz lend you his electronics and did you test them out yet. It reminds me of what happens when a coil is starting to go bad but you said you swapped coils with no change so i was thinking maybe the stator but you also said you checked that.

Yes I checked carb boot with the wd-40 trick, I dont think its bad. Im thinking electrical. I tried the coil off my 03 but I havnt even started the thing in 2 or 3 years so IDK what kind of condition its in if any moisture got in there. I checked everything electrical with the Ohm meter but the bike seems to rev better until it starts to warm up. Theres really no way to test them when the bike is warm. Im leaning that way but was really hoping someone would have an idea of where to start or another test I could run to double check. Blackwoodz has been really busy lately and hasnt gotten to the bike yet, but Im running out of time before my trip. I just dont want to blow a bunch of unnecessary money on parts and have that not even be the cause of my problem. Those damn electrical components arent cheap

Figured I would give the thread a few days and if I didnt get any help by the first Ill almost have to start buying parts if I want to ride on the trip since the race bike is in pieces  for grease and maint. to get it ready for the upcomming season.

yeah i hear ya. when coils go bad thats when you see it though, when they get hot and when the motor is under load with alot of air moving. you also said that it seemed to start sputtering when the pv started to open so that kinda points towards coil too. its hard to believe that two different coils would do the exact same thing though.

I agree but all symptoms point towards the coil or stator and the coil is obviously the cheaper of the two to replace. Even for an aftermarket coil your talking $60-70. Not to mention I still need a new pipe and silencer.

A stator on E Bay right now for $95 . If you end up replacing parts. This one said 100% guaranteed to work.One for a 98 for $59.99 with free shipping if that would work.

Edited by VinceDC, 27 March 2012 - 06:30 AM.

yea I saw both of those on there and they are on my watch list. Thanks!

te4250, on 27 March 2012 - 05:14 AM, said:

I hated to send him parts when my YZ is also having very similar symptoms as his sincee my new top end.......but I really think both are bikes have carb issues...I have a guy bringing me a KX PWK   to test tomorrow.

Hopefully yours is a carb issue! Would make things very simple. I wish the 03 carb would have fixed my issue.

So I got around to messing with the bike more... tested the coil and stator again. Stator tested perfect, the weird thing is that the primary winding in the coil tested higher than it should. The manual states it should test between 0.2 and 0.3 ohm and that it might read 0 depending on the quality of the ohm meter. It tested at like 1.3-1.4 ohm... and that was the lowest reading, there were others that read quite a bit higher depending on where I contacted the testing points.

Any idea whats up with that? Does that mean there is too much resistance in the primary winding of the coil? Ie... bad coil? 0 would mean that it is an open circuit but the high reading is throwing me through a loop.

New coil should be here any day now, and hopefully I can get it on the bike and wont have to replace the CDI... but Id like to make sense of how these readings work so I have an idea what Im dealing with.

Well my luck is just excellent! Got the bike running right... it was indeed the coil. Got it replaced and fired it up, rev's forever! Now my only problem is my truck. Loaded the bike up and was heading to the track and heard a loud pop! So I pull over on the side of the highway and this is what I found





Leaf spring right through the bottom of my truck bed. GREAT

did you happen to be in a baja run last weekend to break a leaf spring? lol i would weld that and drive it !

Haha no baja for me... this truck has never seen an unpaved surface. I cant believe the bracket just snapped like that. I just heard a loud pop and couldnt believe my eyes when I saw that. Im just gonna replace the bracket and call it a day. Probably replace both while Im under there.