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Discussion Starter #1
hi all i have a 1989 yamaha exciter 570cc water cooled. has twin carbs. sled runs great at slower speeds under 40mph. anything past half therattol the motor stalls out. adding choke makes it worse. i think running to rich on full therattol. lower needles on the pistons that act as the butterfly? or am i missing something simple?
 

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Did you clean the carbs at the begining of the season? What do the plugs look like? How much oil are you useing?
 

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Discussion Starter #4
yes cleaned carbs last month. just picked up this sled so it is new to me. someone has played with the carburetors before i got my hands on it. i cleaned carbs, replaced plugs. one plug was brownish one plug slightly blackened but not covered in suit. runs with no misses at beginning idle to 1/2 pedal great. i can climb hills and accelerate right up to 40mph. but anything over 1/2 pedal the motor falls on its face. and it is instant too. adding choke makes it worse. i do have another stator on hand but with it running so smooth at lower rpm it is making me think carbs high speed jetting is off? i did find the carbs were badly out of sink. one was half way up before the other started lifting. i sinked the cables to pull equally. is the piston in the carburetor, essentially the butterfly, is it supposed to be even with the ventury when pulled to full theratol? i found one was pulling a good 3/4" past the opening of the carb venture. but after adjusting i have had no high end gain. more power at low speed though.
 

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Check compression first, once you know the mechanical parts are good you can move on.

Good idea to check spark as said above.

Chances are the engine is too rich or too lean over half throttle. Some people thing putting bigger main jets in will give you more power, if the previous owner was monkeying with the carbs you will have to verify the jet numbers with your dealer.

Pull the fuel lines off the carbs and pull the engine over to verify the fuel pump is working.
 

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Discussion Starter #7
ok compression is good 110#'s each. spark appears very solid. i lowered the needles for the pilot jets leaning the high end. it picked up another 30mph and had more power but still is not coming alive like it should. lower end rpms and theratol are great. a 570cc water cooled exciter should do more than 75mph. the plugs are brownish but then it isnt ran under full theratol for the whole ride. running mid theratol the sled runs good and the plugs show that more than just the high end rpm's where it is faulting. the needles are lowered to their max now. i am thinking of dropping a size on my pilot jets.
 

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Ok, you have the engine running well, now it's time to look at the drive train.
Do the sharpie test.
Remove the belt and mark a straight line from the center to the outside edge of both clutch units.
Put the belt back on and make some runs.
Remove belt and see how much of the marker line is worn off. This will tell you if the clutches are shifting out properly.
 

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At 110 your rings are gone, your compression is Not good! 125 would be ok!
Do a top end and then drop a gear on the top gear of the chain case!
 

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OK sry to bring this back up..but I to have a 89 exciter :) and its doing the same thing..
last year it ran like a ..well ,it was sweet . now this year same as above but mine is at like 3/4 throttle then it falls flat, BUT if i hold it there (wot) after about 3ish seconds it wakes up and keeps pulling like CrAzY.. up to 3/4 throttle it seams fine, after it just bogs out for a few . i pulled the carbs and cleaned them good(even left them in a carb dip tank for about 4 hrs thinking i missed something . but :-( no good. i did replace all fuel lines,vacuum lines and oil lines. (primed the oil lines) new plugs Br9es. new gas 92oct and semi synth 2 stroke Lucas oil . Thought it was a gas cap causing a vacuum in the tank,nope.carb needles are set in the center. tried to lower and raise them and that made it worse. HEEELLLPPPP PLEASE
 

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edgex800ves
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SteveB Id say clean and service your clutches, Im betting your primary needs some work with those symptoms! Rollers, center bushing, weight bushings in your primary would be my suspects for sure.

now this year same as above but mine is at like 3/4 throttle then it falls flat, BUT if i hold it there (wot) after about 3ish seconds it wakes up and keeps pulling like CrAzY.. up to 3/4 throttle it seams fine, after it just bogs out for a few
Sounds like you have something binding in there! Perhaps even a good cleaning is all it needs but look for worn parts while your scrubbing away grime and belt dust!


Chilly4x4
is the piston in the carburetor, essentially the butterfly, is it supposed to be even with the ventury when pulled to full theratol?
Its not a piston its a slide, and they should both be opening the full height of the venture at wot! you can see how to set your slides in the how to section, but I agree with RJ do the sharpie test! lotsa people try to tweak carbs chasing a clutch problem!
And 110 compression is low like Kc said but you may have a tester that reads low, try using your tester on a known engine before you rebuild it due to a low reading tester!
 

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Discussion Starter #14
why is it always the clutch?

lol i would say someone has had some clutch issues before. but another thing to check is the reeds.
 

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lol it just seams like it shouldn't be the clutch. (now this is in my mind) but
off the line if i hold at 3/4 throttle i'll hit 70-80mph then at that speed i'll go wot and it acts like someone shut off the gas for a few seconds and ill slow down to 65ish then the front end almost comes off the ground when it comes back . that to me is the carbs , but again this is my first sled and im an backyard auto mechanic and dont know this stuff .
geme a small block Chevy 67-97 and i can help you . this stuff, i feel like homer Simpson doing brain surgery :dunno:
 

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edgex800ves
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I still say clean and service your clutches! from 3/4 throttle to wot your needles coming out of your main jet, your main jet isnt plugged if you can do 3/4, your other jet, the pilot jet would destroy your ability to idle if it was plugged. Your issue sounds exactly like a binding clutch. Clean them and inspect them to rule it out then go back to dialing in your carb.
off the line if i hold at 3/4 throttle i'll hit 70-80mph then at that speed i'll go wot and it acts like someone shut off the gas for a few seconds and ill slow down to 65ish then the front end almost comes off the ground when it comes back
This would happen because your clutch is binding and not shifting out, then letting loose, it will get worse!
 
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