'94 YZ-125 hesitates and bogs at lower RPM

[AGrayson84]

Hey everyone, I picked up a stock '94 YZ-125 about 2 years ago. It was in need of a new jug and piston. I decided to freshen things up beyond that, and before I even got it running I did new bearings, new crank/rod, cleaned up the carb, slapped on a FMF pipe and muffler, had the jug bored to 56mm as well as nickel-plated and honed, had the jug ported for more mid-range power, had the head milled, aftermarket reeds, new spark plug, and popped in a Wiseco 56mm piston/ring.

Ever since I got the bike running it has no power down low. I'm using 93 octan gas and have done several different gas/oil mixtures after starting with the manufcaturer's recommendations. I've also tried a several different smaller and larger pilot jets, and have replaced the mixture screw.

The bike just hesitates and jerks around down low as you try to give it more throttle to get up to speed. I can keep it in first gear and try climbing a hill and it just simply will not do it without a bit of speed and momentum. If I were to try to stay under 10 mph it just won't do it without hestitation, bogging, and then dying out. Some people say this is typical of a 2-stroke bike like this, and I've never owned/ridden a 2 stroke dirtbike before but I beg to differ. Anything under between 1/4 to 1/3 throttle and it just acts up as I described. It runs like a raped ape once it hesitates it's way up past 1/4 throttle or so.

The throttle slide doesn't seem to be too worn and everything in the carb seems to be stock (slide, jets, etc.). Like I said-- I've tried different fuel mixtures and pilot jets to richen and lean things out and have adjusted the hell out of the mixture screw and just can't seem to shake this problem, or even get it closer to running right with the adjustments I've made. I know it's nearly impossible to tell me what needs to be done when you can hear it or ride it yourself, but I'm having trouble determining that it's running too rich or too lean and could really use some more suggestions. Should I maybe just try a different carb all-together???

Thanks,
Andrew

[matt bristol]

Have you checked for air leaks in the air filter box? Or a blocked air filter? 2 strokes - especially race engines don't like to tick over and do nothing below 2000rpm. They are also very succepitble to temperature - make sure its warmed up properly before you tinker with carb settings!

[matt bristol]

Having re-read your post, Iwould dis-count the blocked air filter idea, however it could be too much air getting in the air box/inlet before the carb.
you did get the power valve back on properly I assume? I ahd a suzuki 250 that the power valve jammed open and it made it terrible at low revs

[Burke_78]

Some people are right... this is very typical of a 2t machine.
]
My banshee is a turd until about 5500 rpm and then you had better be holding on with every muscle in your body. 2 Strokes really only make power in about a 1000 - 2500 rpm range and it is usually very close to or at the rev limiter depending on porting and other mods. Lots of shifting and clutch feathering involved with them (especially smaller displacement).

[06yzrider]

That's pretty similar to any 125 2 stroke. If you're expecting to give it a little throttle (1/3 to 1/4) in first gear, it will start going (BRRRRMMMMMM 'Click') and it will die. The whole idea with 2 strokes is to keep it "riding on the pipe." What i mean, is that once you hit a certain level of RPMs your power valves open up to create almost a "turbo" feel. Whenever you want to climb a hill always hit the pipe and get lots of momentum. If you don't, go by a 4-stroke.

[jaradx7]

Originally Posted by matt bristol

Having re-read your post, Iwould dis-count the blocked air filter idea, however it could be too much air getting in the air box/inlet before the carb.
you did get the power valve back on properly I assume? I ahd a suzuki 250 that the power valve jammed open and it made it terrible at low revs

Fully support what you have said, I also think so. Come on.



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