98 YZ125 carb question

[NJGregsCR]

Just bought my son a 1998 YZ125, it's at a buddies and I haven't gotten a good look at the carb mounting. Based on the way he will be riding (slow tight woods then WOT combos), I'm sure I'll be jetting it, since the first go around last weekend he fouled the plug twice (replaced with new plug both times and started right up).

My question is, can I just take out the slide cable cap and then loosen up the carb barrel clamps and twist/tilt the carb sideways to fiddle with the jets? Or, will I need to take the carb off to play with it?

I was gonna go up to my buddies to play with the carb, change the gas, etc., but if it needs to come off the bike I'll just plan to bring it home to my shop.

thanks!

 

[rmc_olderthandirt]

Once you have the cap off and the boots loose all it takes is a little tug and the carb is off. Getting it back between the boots with the clamps in the right spot can be a little tricky but once you get the hang of it its not difficult.

If you are going to play with the jetting it is best to do it where you can ride the bike. Make an adjustment, take it for a ride, make another adjustment, take it for a ride. You just don't want to be pulling the carb off if there is dust blowing around.

The first thing you will want to do is adjust the needle position. You can probably do that without pulling the carb off at all, just remove the cap/slide. If it is running rich you will want to move the clip on the needle "UP" (which lowers the needle). If you end up with the clip in the top position and it still isn't right then you will need to buy new jets.

Rod

 

[NJGregsCR]

OK, went up and played with the bike this afternoon and I don't think it's the jets. I'm leaning more towards a right side crank seal leaking. (Or could it also be a waterpump seal leaking antifreeze?).

Bike starts right up with a NEW plug. Then after 1/2 hour of riding hard it will stall out or he will stop for a break and can't restart. Clean or replace the plug and it starts right up.

I'm gonna put in some fresh 40:1 tomorrow, and I'm gonna repack the silencer, but the white/grey smoke and going thru 3 plug changes in 5 1/2 hour sessions has me worried.

If it is the rt side crank seal, do I have to split the cases? If not, what is the method of getting that seal out, The 2 screw method?

Bike is a 98 YZ125, thanks for any input.

 

[jb_dallas]

On my 82 RM 125, there is no need to split the cases to get to the right crank seal. You pull off the clutch and a few more bolts. I too, had myself convinced that my crank seal was bad....it wasnt. I was putting in a new clutch anyway, so it wasnt that much more work. Make sure you are right before you go tearing out the clutch. My problem turned out to be jetting. It appears as if the genius that owned the bike before me drilled out the jet...because more fuel is more power...right? I replaced the jet with a visibly smaller one and the difference was huge. Make sure your jetting is right.

 

[NJGregsCR]

thanks for the ideas guys,

I think we have it fixed up, I ended up just bringing it back to my shop to play with it and also teach my son how to do some maintaince jobs. We changed the oil and I measured the old oil, which was dead nuts on 700 ml so I don't think it was sucking thru the seal.

The silencer packing was the worst I've ever seen, and I bet that was a major contributor to the fouling. We drained all the old premix they had used and also the carb bowl. Used some fresh 40/1. The air filter was dirty too, so we cleaned and reoiled that.

Put on an 11oz flywheel weight, and after getting it started played with the pilot screw alittle to dial it in. The pilot screw is now about 1 3/4 turns out, so I'm guessing that the jet is about right.

Bike runs good and the more he rode it yesterday the better it got. Thanks for the ideas, and I gotta say that this Forum rocks- just doing some searches gives you loads of info to work with.

 

[NJGregsCR]

Another update.
Although it was running 100% better, it was still loading up if he let it idle too long or lugged it thru the woods.

We took the carb off and did a full cleaning, I raised the clip on the needle up to the 3rd slot to lean it a bit, and we put in new Boyesen Power Reeds.

Bike seems to run real clean now. He rode it thru the woods at an idle and lugging it then slowly rolled the throttle on and it was clean and had a linear pull. So I'm hoping this will be more reliable.