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yz 125 powerband problem...help

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hey guys i just bought a "new" 99 yz 125 for cheap, it didn't come running just needed a top end. got a new top end and the cylinder replated, it started, idles good, had good low end power but has absolutely no top end power, it hesitates like crazy, sounds like when its starting to come into powerband it starts to cough/hesitate,

it won't pull the front end up no matter what i do, ive gone through the carb, jetting is stock, float heights been adjusted, jets are clean, i have yet to inspect the reeds, but i heard they only affect low end power if there leaking... powervalves are clean/good actuating..

also it sploges like crazy, im begining to think maybe a crank seal? will this cause hesitation, like its not getting any fuel?

plugs good...running a br8es...any other suggestions before i tear this thing apart?

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Double check your main again... also a good idea to make sure the PV is opening all the way or if its even operating at all with the bike running, just pull the cover off and take a quick ride around the yard.

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the powervalve moves nice and freely, ill double check to be sure the governor gear isn't f***,both the main and pilot is stock (350, 35 i believe, i can't remeber if these are the right numbers but im positive i put it back to stock), i put it that way when i got it, the original jetting was far richer, and pretty sure i put the blue powerband in always do), ill do a couple plug chops to verify whether or not its runnning rich/lean, i don't think its to rich, cause it coughs, and it doesn't studder/stumble, which is why its confusing because of the amount of splouge. i haven't done the bottom end yet, the crank felt good though, not up/down play in the main bearings, had a little bit of side to side play, but well in spec.

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hey guys, just an update, fiqured out the top bolt, above the reed setup that joins the cases together has broken off, now its spit all the gasket out now theres a big air leak there, any suggestions on how to repair this without splitting the cases?

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Engine pressure test tools can be built really cheap

Take off the reed cage and use it for a bolt pattern template,

and a 1/4 aluminum plate can be made to fit.

Screw in, or press in rubber tire valves can then be put in the plate,

as welll as a cheap 10psi air pressure guage.

Use a rubber plug, something like a sink rubber plug,

with some fender washers and a nut and bolt,

to seal the exhaust flange.

Then plug the power valve oil overflow outlet on the left side of the motor,

and make sure the right side power valve mechanism cover is off, to see

if any air comes out of there. A spray bottle with water in it can be used to locate any leaks

There is some permatex motoseal available at some of the parts stores

that works great on engine cases.

If the cases are leaking above the reed cage, you might be able to

remove the reed cage, and brake clean the case half line, then smear

a tiny of bit sealant across the line from the inside, to seal it.

Bottom end pressure is'nt very much, probably less than 5psi when the engine is running

A brokem bolt can be removed if you get some copper or aluminum tube from a local hobby shop, that fits inside the hole to be used as a drill bit guide, then use an easy out, or a homemade easyout type tool can be made to remove the broken bolt

Edited by yamaha7442

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on my last bike i noticed the sump plug was all cracked and not tightening up properly but i really did not want to split the cases so i bought some of that abro steel paste stuff and stuck it in where the bolt would go and it worked perfect think you could try that ?

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