power band problems

hi guys,
just wondering if any one can help me. I have a 2001 yz250 that got very lazy and it wouldnt hit power band, so i have done a top end rebuild including a barrel re-nickel, new boysen reeds, had the carb re-jetted, de-coke'ed the expansion chamber and repacked the muffler and had the stator rewound as it was burnt out.
it has plenty of torque but wont hit that high rev range.

any help would be much appreciated
thanks  

Welcome...I'm not sure what the problem is, but I'm sure someone will be able to help soon...just sit tight  
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"Only the desert has a fascination to ride alone in the sun in the forever unpossessed country away from man. That is a great temptation."
--D.H. Lawrence

Only thing i think it can be is that it's not properly jetted for your elevation. Was your bike re-jetted near where you are riding and was it just stock jetted?  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

hi,
it was done by a mate who is a bike mechanic.i had it rejetted for the pipe fitted.  he thought the stator was the problem but in formed him that it was re-wound, he said to get it re-checked which i did and it was ok.

thanks  

have you cleaned your power vavles lately? & are they set correctly?
DavidS  
i take a lot of pride in what i am

___________________
ride: 02yz426
local: north east Oregon

terrain type woods with lots of roots & rocks

hi,
yeah i cleaned every thing whil i had it apart for the rebuild, and once together with power band not working removed the power valve actuator cover to see if it was movind and it was. thats the thing thats got me and my mechanic scratchin our heads as it all works.

thanks  

triumph-daytona:
hi,
yeah i cleaned every thing whil i had it apart for the rebuild, and once together with power band not working removed the power valve actuator cover to see if it was movind and it was. thats the thing thats got me and my mechanic scratchin our heads as it all works.

thanks

If you pull the plug; how does it look?  What changes from stock jetting were done?  
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Dave H 2006 YZ250
(2008 YZ 125 son)

Can you give us a little more information on the bike?  Have you had it since '01?  Is this a new condition?  Was it a slow fading of the power or an immediate change?  How long has it been like this?  Were any mods done to cause it?

If we can get more details on the issue it would help us to get a better idea where your problem is.

Normally, the board here is thinking Fuel, Spark, Compression for the motor to run right.  It sounds like  you MUST have the latter 2 for all the work that's been done.  If it is fuel then it's just a gas tank to cylinder approach which we all can help with.  
2001 YZ250 [Todd]
2003 KX60 [Abby]

Even though the carb was re-jetted, it still may be off.  
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Stand in the place where you are, think about direction and wonder why you haven't
North Carolina

i picked the bike up in mid 06 after being off bikes for a while. it ran ok, had tourque and would hit power band, but got lazy after a while and had low compression and wouldnt hit power band, so decided to strip down and have a look,(broke my wrist while waiting for the barrel to come back so it was a very slow rebuild as i wasnt in a hurry) rings were worn and had scratched the *** out of the barrel. also found the hi rpm coil in the stator was burnt out, so had that rewound by a guy that was recomended by a local yamaha dealer.  had barell re surfaced, fitted new piston,rings,reeds and the rewound stator then off to bike mechanic to rejet the carb.  all back together and ran fine with plenty of power but no powerband, he said stator could be problem but it i told him it was rewound, but i pulled it back out to have it rechecked any way and it was fine. the only other thing it could be is the cdi but they either work or they dont as ive been told, (dont they?)

thanks  

My opinion is that the jetting is still off. The guy at the shop probably just jetted it to what their manuals say and called it good. Could be something else though. Are you running high octane fuel with a 32:1 fuel/oil ratio? Also put a compression tester on it and make sure something is not messed up, make sure it is actually getting enough compression. Who replated the cylinder? If you have a cylinder that is bored just a bit over stock and you have a stock piston it will not have the right compression either. A lot of the big companies that redue cylinders often request that you send a piston or buy one from them that way the replated cylinder is fitted to a specific piston size and type.  

I would definitely do a compression check on the bike.  On a new top end it should register 160-180 psi range.  Next, check for spark.  Pull the plug and touch the electrode to the cylinder head.  Spark should be a bright bluish white.  If both are in order I would check the condition of the plug.  Compare it against a plug chart online....generally looking for a nice tan color.  If goopy with oil or bare metal you are rich or lean.  If that's the case, I would start with the gas tank and work your way down.  Pull the fuel line from the carb and make sure you have a good steady stream to your float bowl.  If so, I would pull the carb and give it a good cleaning before attempting to rejet.  When cleaning the carb inspect the floats and tangs for good operation.  Inspect the fuel valve [pointy thing next to the jets on one side of the carb].  Make sure the valve operates and does not stick.  Make sure the spring is in good working order.  Remove all the jets and clean with carb cleaner and compressed air.  Replace jets and run a spark test again.  If it's not hitting the power it's likely your main jet or needle placement.  Would definitely not be the pilot.

There's plenty of information on jetting but I would basically start with the needle.  Move up a "clip" for a lean condition down a "clip" for a rich condition.  If that doesn't work move the clip back to stock and go up or down a size in the main according to what you condition you're experiencing.

So far as spark tests go there are plenty of entries that can give you an idea.  You'll basically ride the bike Full Throttle for a short period then simultaneously pull the clutch and hit the kill switch.  This is the test for the main jet.  You're basically sampling engine performance at WOT by shutting the engine down at WOT.

Lastly, one thing that hasn't been mentioned is a flywheel weight.  You said the bike hit the power pretty well previously so I hadn't mentioned that.  If you bought the bike used the previous owner may have had it set up for trail/woods riding and had a flywheel weight installed.  This shifts the power from high-end to low-midrange.  There is much less of a "hit" and a wider power curve throughout.  I doubt this is the case since it seems to have worked fine previously but it might be worth a look or a call to the previous owner.  
2001 YZ250 [Todd]
2003 KX60 [Abby]