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250 Help!--Pre-mix or What???


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Good evening folks:So I fired up my 94 Yz 250 for the first time with the new Top-end. My Top-end rebuild went pretty smooth-Fired up on the 3rd kick.

Your basic water leaks//loose clamps easy!

I have A few re-builds under my belt-but nothing with this much power

Now-for the problem. I am running a gal of new 32-1 way to thick--should be 40-50 max to 1 ,now when i start it -it way smokes and does not have a crisp throttle.I run it thru the gears a couple of times --gets better.After it gets to temp no smoke at idle or thru the gears.------It sputters thru 1st and 1/2 way thru 2nd and then hold on for dear life thru 5th!

Bike has basic mods-Pipe-Reeds 38 slide bore with big bowl kit-No air/idle screw that i can find.

Can you point me in the direction on this low end problem?

Thanks-Ray.

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I would do the break in cycle with 32:1, then 40:1 and rejet for conditions ect. My bike was reall loaded up,after the break in cycle. In first - second, really boggish and then it cleard up, and sounds crisp. When you go from 32:1 to 40:1, its not going to affect anything intil you rejet it for that ratio if it was meant for 32:1

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I am having the same problem after a full rebuild i thought i read to mix 24:1 in the book, but seems way too rich, this is my first yamaha and full rebuild but it seems boggy and hard to start at first, i leaned the mixture screw but still not getting the responce needed, it is a 89 and it driving me crazy as once you get on a good strait and cleans out it halls balls.

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Running more oil in the fuel causes a lean condition, not a rich one. Bottom-end, midrange, and top-end have nothing to do with what gear you are in, they are simply monikers for RPM ranges...

Does the bike bog at low rpm, mid, or high rpm? If you put the bike in 4th gear at about 5 mph and roll on the throttle taking it up through the rpms slowly does it clear out as you get moving and pull really well on top?

If what I am describing is the case, you need to lean your pilot jet and needle position. But you really need to check to see that your float level is correct first, it will affect your jetting on all circuits. Where is your air-screw at currently? have you tried turning it all the way in, then bringing it back out 1-1.5 turns?

There are some really great jetting threads on this board already, search them out and follow the advice of the pro's.

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Hey afternoon:Thanks for the replys.Im a HVAC Tech-on-call tech this weekend.

Ok DJ- good point,it bogs at low RPMS in 1st and 1/2 thru 2nd.My power-band is already up 3rd thru 5th. It sounds like im having Carb issues ,makes sense,this bike was in boxes for two years in the corner of the guy's shed.

So -Im taking it off-apart.I tried to get some info about this Carb,but alot of dead ends.My Ktm buddy said that since my engine Mods are all Top-End H.P He said that I have to mess with the jets and float height. Ok but heres the deal the only thing that I know about this Carb is that it is a Mikuni TM.There is no air/idle screw ???.My Oldest Sons RM 125 has about the same Carb,but smaller-It has an air/idle screw on the left side,runs great -Pro-Circit pipe-Any weather any time run's great.Back to the YZ-Can someone go to my Pics and tell me what this Carb is ?? and How to set it up for better low end Performance ???. And last but least"Power Valve" This was a thorn in my side from Day 1!. Im sure if it was in wrong it would have flyed,but is there any adjusting on this ? Thanks-Ray. http://www.s754photobucket.com/albums/prostreetray

Edited by prostreetray
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Cool -Im going to tear it down after the Nascar race tommorow.Im out on the West-Coast.We have a few good sand areas to ride.My bike had a mount for a flag IE Required

for sand dunes. Low-end was really not an issue.From what i learned about the mods on my YZ -It is all about the Top-end H.P-----Im Too old and Scared-Ha!-Ha! to go that fast or jump too high ---I want Low-end-My youngest Sons YZ-80 Smokes me out of the hole-Tx for the reply.

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