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Dead-spot mid throttle

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I need some advice...2002 TTR 125. Had it for about a year and it has a flat spot on accelerating form mid-throttle to wide-open. So flat in fact that if the throttle is very suddenly opened from mid to wide-open it will stall!

I went through and cleaned the carb, tried lifting the needle (no difference) and in desperation bought a brand new carb. Still have the same problem. Changed spark plug and checked the valve timing (good) and set the valve clearance...still have the same problem.

Riding in altitude between 3500 and 7500 ft. Could it be an ignition problem (coil?)... Any ideas would be appreciated.

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Could be well read some of my posts lol sorry may need a compleat tear down.It may be the cam is wore check the cam for wear .All so check the cam chain may be stretched out to the max and no longer adjusting .Taking into concideration all the other things you have all ready checked and replaced .My first thought would of been the carb allso or air filter.

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Sometimes the jets wear out. If you get small particulates (fine sand) in the gas that are just bad enough not to score everything steel, but they can wear the softer brass.

You're throttle position is right at the point when the needle starts dropping off being the controller and the main is really picking up.

... look for an air leak between the head and carb, as well. Usually you'll get the sudden back fire, if it's too lean, if you catch it before it stalls.

-Kerry

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You say you got a new carb did you adjust the pilot .Because I keep thinking carb problem and I know my carb brand new was way lean on the pilot it was only out about a 1/4 -1/2 turn way lean. The main jet starts at about half throttle then takes over compleatly as you just about hit full throttle .Too lean ,and a motor will run some what dull and have a flat spot in the powerband . Lean the bike can cough and stall when you twist the throttle open , Lean it can cough and stall in slow turns ,Lean it can be hard to start it after a crash, Lean You'll have a hard time starting it when it's cold, Lean the bike will run hot and feel kinda slow and have flat spots in the power band when useing the throttle.If it's too rich the bike will have a sputter -surging because it tring to burn extra fuel.Rich Bike will start but won't like the twist of the throttle with out sputtering + it won't clean out at a higher RPM.

Did you clean out the gas tank may have dirt and it's getting in too the carb cloging up the jets

Do you have a after market exaust or have you done any airbox mods or by chanch has the head been ported or opened up? You may need a bigger main jet.The pilot jet and air screw controls the amount of fuel from closed throttle to about 1/4 throttle so basicly at slow enging speed or RPM. Then the needle From there the main jet starts to takes over .

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Raise the needle. Change one circut at a time, so you know what circut is the problem.........How much did the carb cost ya??

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Barra1967cuda - thanks for the quick reply - appreciated

I checked valve timing so I think the timing chain is OK. I am thinking that is is probably not the cam beacuse once you get past the flat spot and it recovers in wide-open throttle, it has good power.

It is possible that the cam is worn - I didn't check valve lift. However I would like to eliminte the easy (cheap) items first.

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Olalla7700 - Good idea...I originally thought it could be a vacuum leak between carb and head. I re-torqued the head bolts and checked for a leak, but nothing presented itself. Probably not worn jets though because the problem is exactly the same with the new carb

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readjw - Can't remember exactly what the new carb cost, I think it was right around $300

I was thinking that it could not be the jets or needle setting because they sell these bikes here with those settings and they seem to work.

On both carbs, I started with the pilot screw at 1 1/2 turns and tried 1/4 turn at a time in and out - still no solution.

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Olalla7700 - Good idea...I originally thought it could be a vacuum leak between carb and head. I re-torqued the head bolts and checked for a leak, but nothing presented itself. Probably not worn jets though because the problem is exactly the same with the new carb
Yeah, it was one of those "post first then re-read"... whoops. Now I see the confusion. I apologize for adding to it.

The flat spot and cam wear idea has me intrigued. The worn cam will usually affect the whole rev-range, either end, or both ends. The middle has me confused, unless carb adjustments were made to compensate, and that put the middle out of wack. Just another idea...

-Kerry

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Did you get it figured out yet $ 300 for a carb hope it wasn't a stock carb .Could of got a bbr or a bigger el cheapo off e-bay for that .

The reason for checking the cam is allso I figured you'd check the cam bearing sufaces and all so the rocker arms for wear .I had a stock cam on someone elses TTR I did a few years back that messed up in the middle of the rpm range it allso messed up the arms so I replaced bolth .So it may have been the cam or the arms or a combo of bolth.

Allso don't mean to sound like a broken record but the main drive shaft breaking some times dose that .When it happens sometimes you can't tell sometimes there is noise or fells like you skip a beat while on the throttle or when shifting.For a experiment one time I ran a motor for over forty hours hard a heck on it like I stole it all the time .That had a broken shaft checking it every 8 hr's of run time .While rideing it you couldn't even tell it was broke it didn't skip a beat. Bout the time it started to wear out the bearings to the point it was about to start on the case I stoped and fixed it all.

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