03 250f surging

OK first post and the reason I joined this forum in the first place. I do mostly trails and hill climbs but lately my bike has been acting up almost like it has a power band, it sputters quite a bit when in the lower rpms but when you get it up there it tends to be OK. I need that low to mid range power that I'm not getting right now can anyone help me out? I've tried just about everything I could think of... Bike has FMF jet kit with FMF powerbomb header and power core 4 slip on, k&n air filter. I also do regular maintenance after ever ride including oil change.

I'd start by cleaning the carb, especially the PJ. Maybe even just replace it. Check your vent hoses aren't clogged too. Air filter clean?

I've done all of that, carb is freshly rebuilt and air filter cleaned and oiled with k&n products after every ride, I usually do everything "by the book" but I just can't figure this out, on the other hand the bike does burn oil I'm not sure if its a significant amount, could a complication from that be causing the problem? Also engine is rebuilt with less than 100 hours on it, new valves, springs and crank because the crank was seized.

Also under load like say at the middle to top of a hill climb the throttle likes to give out and its not like a regular bogg its too low, also it likes to do it when hole shot at the bottom of the hill until the rmps ramp up, I've messed with the carb before and a lot, but I must be missing something, should I just keep trying my jetting and needle clip?

Burns oil? Have you checked the spark plug, might be getting fouled.

That was my cruising problem last week, I couldn't get steady throttle out of it replaced the black carbon built plug and that solved it, I'll check it when I get home but I'm pretty sure it should still be new

The carbon build up on the plug and in the exhaust makes me lean more towards the bike burning oil

If it's burning oil it's getting in there through either the valves or the rings. Low compression maybe?

It seems like the compression is good, for example if i used my hand I would probly break my wrist lol, valves are pretty fresh but in need of shimming which I'm doing tonight, so what I'm thinking is the piston rings because I have all new valves and springs but the piston and rings I'm almost positive are still stock from 03 , if that's the case would I still get a Saturday of riding for my last season ride? Or should I put it away and start my winter engine work?

Judgment call. How many hours are on the piston/rings? Is the cam chain original too? Jumping time could cost a bunch.

Maybe you should check the valve timing to make sure it hasn't jumped a tooth already.

Could it be this?

From the JD Jetting website:

Yamaha WR250/WR450F Stutter Condition-

This is an ignition problem that Yamaha has designed into the bike to make the motor run cooler at light throttle and medium speeds. The stutter is VERY COMMON, and can sometimes be reduced by disconnecting the TPS electrical lead from your carburetor. The condition is most common on flat roads at light throttle positions, when producing under 10hp at the rear wheel. The stutter is harmless and will not affect the power under acceleration, if it is not too annoying, leave the bike as-is and just ride it. The problem is mostly noticed when riders want to do road riding with their bikes.

Try disconnecting the TPS lead and see if it helps your condition. The other alternative is to try running either clip position #2 or #4 on the Red marked needle. This is a work-around that forces you to use more throttle than normal and lightens the stutter, but the bike will make less power when accelerating.

See- http://www.pbase.com/jdjetting1/image/96130587 and http://www.pbase.com/jdjetting1/image/99387782 and with replacement CDI and no jetting changes-


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Mine was doing this pretty frequently while on the road--really bad after I installed the 290 kit. I disconnected the TPS and it has since stopped.

I've checked timing is good and not exactly sure about the piston and rings, and murph it does affect my accel it stutters hard when beginning to climb a hill.

Well I think its between piston and rings or carburetion because there are 4 or 5 jets I think, and either of which could be the wrong one for the flow I need, I'll have to do a fine tuning on the carb and if symptoms persist I'll have to check piston

Have you adjusted the fuel screw lately? It's been quite a bit cooler these days.


Let us know what you find out and good luck!

Doing my valves right now and for some reason I can't get my intake valves out with a magnet I got the exhaust out just fine, is there another way to release the intake valves without harming the buckets?

Sorry, discard that last one, i found the problem, the &%$#@! who I paid to do my valves tightened the cam cap on the intake side down too much and it bent the soft aluminum slightly over the bucket thus sort of locking them on there, is there a way I can file that down without harming anything and getting shavings in my valve train ?

Yikes! I dunno about removing the squished material, but be careful not to gouge the buckets. How do the cam journal surfaces look? I wonder if being over torqued can make the clearances out of whack? I'd try and put it back together and torque it correctly and remeasure the clearances.

OK so got the job done, I had to go in with a razor and dental tools to scrape the bucket free of the aluminum trapping it in there, it was a very little amount but just enough to mess some stuff up, valves are back in spec as well and bike runs very nice now, I haven't done a climb yet gotta wait til Saturday. I think my problem should just be carb if its even there anymore... just a future reference to anybody with a 4 stroke, never have other people do the work, they will never work on the bike like its their own, to some (especially the guys who did my engine) bike mechanics its just another job anyway and they can't wait to get home so they WILL cut corners . I'm not really talking about mechanics in general but mostly the guys I dealt with lol

Thanks for helping guys! I'm sure I'll have some problems in the near future but hopefully none as odd as I just encountered.

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