miss at wot

[rmuscle]

havent ben this stumped in a while. getting a miss at wot ,up around 13000 rpm , which is also causing me not to climb up my rpm to about 14 where it should run. here is what i have changed so far (did one at a time) changed plug , plug boot , swaped stage six ignition from other bike , replaced ring on piston , checked reeds no cracks or brake, changed silencer on pipe (was also having a little over heating issue thought could have been this ). gone up and down from 115 to 130 main , i think thats it. the only thing i havent tried yet was disconnecting my teather , im gonna try a differnt carb , andf i havent checked crank seals, . this motor was just built and only has been raced once . runs like a raped ape untill like i said hits up around 12,800 to 13, 000 rpm and starts missing , any ideas ?

[Coley'sdad#8]

put a pressure test on it, that will tell you if you have a leak from the intake to the crankcase. what color is your plug???
check your grounds, kind and size of carb?? what size motor??
water or trash in fuel?? if there is just a little piece it will suck up and lean out @ wot. You mentioned overheating issue,, this goes hand in hand with a lean run condition, always start your jetting fat and work backwards.

[nitrofish]

I would check your kill tether like you plan. Ground would be my next thought. You could look for an intake leak. If you did not have a problem before any change go back to those parts you changed or the wrenching you have done to make them. One other thought, adequate fuel to carb during wot? We had a gas cap breathing issue once, it was a brand new one. I would still lean towards electrical. Matt.

[rmuscle]

Originally posted by Coley'sdad#8
put a pressure test on it, that will tell you if you have a leak from the intake to the crankcase. what color is your plug???
check your grounds, kind and size of carb?? what size motor??
water or trash in fuel?? if there is just a little piece it will suck up and lean out @ wot. You mentioned overheating issue,, this goes hand in hand with a lean run condition, always start your jetting fat and work backwards. plug seems normal acctually it doesn't really seem to change no matter which way I go. 70 motor 28 mm carb. Haven't checked fuel yet but was planning on it to see if any water in it

[Coley'sdad#8]

I always assume that the person has already checked what I consider the simple or obvious but yes check fuel delivery from hose, plugged vent hose, kill switch elimination, crank up in dark and see if wire arcking anywhere. Unresponsive jetting changes are also another sign of unstable cranckcase pressure / air leak so pressure check it. just because you dont have a problem down low rpms isnt an indicator because pressure and vacuum change drastically in the upper rpm's. Is this a new setup or did it just start this on an existing setup?????

[rummel]

IF THE PLUG ISNT GAPPED RIGHT IT WILL BREAK UP. FOR EXAMPLE WE RUN A 90CC DRR I HAD IT GAPPED .028. BIKE WAS BREAKING UP ON TOP END HAD TO GAP DOWN TO .025 AND FIXED THE PROBLEM. JUST FROM THE SIMPLE GAPPING THE BIKE WOULDNT RUN RIGHT.

[Coley'sdad#8]

thats probably with the stock ignition but with the stage-6 ignition
he is running it will shoot a lightening bolt out the end of the plug that will look something like a bad thunderstorm:rolleyes: :rolleyes: :rolleyes:
:rolleyes: :rolleyes: :rolleyes:
:rolleyes: :rolleyes: :rolleyes:
all I can say is dont get your hand wedged down around the plug with it running or you will never make fun of somebody for wetting their pants again:cool:

[rmuscle]

Originally posted by Coley'sdad#8
I always assume that the person has already checked what I consider the simple or obvious but yes check fuel delivery from hose, plugged vent hose, kill switch elimination, crank up in dark and see if wire arcking anywhere. Unresponsive jetting changes are also another sign of unstable cranckcase pressure / air leak so pressure check it. just because you dont have a problem down low rpms isnt an indicator because pressure and vacuum change drastically in the upper rpm's. Is this a new setup or did it just start this on an existing setup????? its new set up. Guess its time for me to make a leak down tester. Checked fuel flow already looks good. U may be on right track with crank pressure. Will test it see what happens what's the norm 6 lbs

[edwardsp&b]

Id keep going back to grounds. Dumb question, but you do have an extra ground from frame to case right?
Bryan

[Coley'sdad#8]

6 to 8# for 10 mins

[quadrider79]

From what you have said. I feel a 130 main is too small, with a 28mm carb. That sounds to me like you would be running a 24mm carb. GO UP!!!!!!!

[rmuscle]

ok so i checked fuel no water , swaped carb , and bypassed teather still nothing . will try bigger main tomorrow . put it on the stand and ran it wide open and really held it ther for a bit got rpms up to 14000 and didnt miss a beat , put it on the ground and starts missing near 13000 , so what would cause this when it has a load on it ,

[Ryki3r]

I just went threw the same thing with my son's 50. I pulled the cylinder and found part of the base gasket was leaking. I also put dielectic grease on all of the connections. I don't know if it was both or just one or the other.
I hope this helps.

[hotquads1]

what exhaust is this that you are trying to run at 14000? could it be that the pipe is signing off, not many pipes out there that are operating in that range. A bike will usually turn more rpm on the stand with no load than on the ground, so this would be common .