eric gorr 99 kx125 big bore jetting

Check with Bedell99, I think he had a big bore KX125, and he's really good about keeping good jetting specs.

John,

That bike was so tough to jet correctly. I can give good baseline jetting spec but it was so tempermental. I had the bike at sea level in New York so this is a good baseline. I highly recommend puting a 13 tooth sprocket and take away the 12. The bike just had so much low end it was hard to ride. Also make sure you check the crank condition. I went thru 2 of them.
Here where my jetting settings.

Pilot #42(Stock 45) You must constanly play with ait screw. Start at 1 1/2 out.
Needle N7P? It is the leanest needle they offer at the 2nd and 3rd positon. ( I could never get the middle right. Sometimes it felt good and sometimes it felt lean, but going back to a richer needle always seemed to screw up throttle response)
Main jet- For high speed circuits a 155 was fine, a 152 during the winter
I also went to a hotter plug A BR8evx. That helped.
"Never" go to a 40:1 ratio on the bike use 32:1 oil, it always had a little seizure at the exhaust port brigde and seemed to eat up rings there also, be real careful. the bike was hell for maintence. All I have to say after owning that bike, thank god I own a honda now. The bike can't hold up to race conditions week in and week out. You must take care of it,if you plan to race it. Plus the clutch was horrible also.

Erik

The bike was done by EG and ported for MO-better. I f i could go back in time I would slapped myself in the face and bought a YZ125. I put so much money in that bike and it still wasn't as good as a yamaha (between the suspension and motor). The biggest improvement was the 144cc kit by eric, but it wasn't woth the maintence. My bike had a procircuit pipe and sliencer and boyesen rad valve. I like 125's that scream, that bike had way too much low end for a 125. I t would of been a great trail or play bike, but it was really hard to race. I had the stock power jet in there and never bothered to touch it. I wonder if that would of made a difference.

Erik

BEDELL

I am thinking about the 144 kit for my 02 cr125. I am plan on racing it in probably vet g.p.'s. What waas the problem with racing that made you not like your bike- too much low end and not enough over rev.

troy

I think it was more the bike and how I ride than the 144cc kit in general. That is the bike I started racing on and as I got better, the bike didn't hold up to its end of the bargain. My friend got his done at the same time as me and had the same problems. He actually went back to the stock bore.The bike is a high maintence bike if you ride 3 days a week and try to race competitvly. It was great in the beginner & novice class, when I was learning because of the lowend but its over rev capacity was very limited. The bike fell off the pipe hard at high rev's. This was my first "real" dirtbike and I wasn't a very experienced mechanic at the time. I learned a lot with that bike in a mechnical sense.. Plus this a general rule of thumb with big bore's. They are hard to jet. Maybe not as hard as a modern Honda CR250, but close. They will never be perfect. As for the Honda CR125. I rode a 2001 with the 134 or 139. I can't remember the exact displacement, but it was an LA sleeve engine and I came away very impressed. The bike was really good and as far as know he hasn't had any problems at all. Also my best friend rides a 2001 Rm125 with a 134cc kit and he granaded his bike last fall and had to get the cylinder resleeved by LAsleeve. It all depends on how you ride the bike and how competitve you are. If I was going to get a kit done I would probably opt for the high rpm kit with race gas. Eric gorr does superb work and I was very impressed, plus the price is unbelievable compared to other hop up guys. Just be prepared for the maintence side of the big bore. In order to be competitive at a national level in mod class it like you almost have to get it done. The bike will definetly be faster. John I wish I still had the jets for the bike cause I would of sent them to ya. i ended up giving them to guy I sold the bike to also. Remember When you do get the big bore the resale of the bike goes way down. I took a huge loss on my bike and the bike was completely tricked out. Probably had at least a couple of grand in it and got 2200 for it and that was last year. :(

Erik

Yeah Im with Rich on that jetting thing . And How come whenever somebody gets a cyl bored out they always think that they need to richen it up .Must be something burned into their think circuits that says to.Usually when Ive been doing these 144s were running close to stock or stock jets and sometimes a bit leaner . I must add though that I only did Two Late KXs < but lots of CR RM & YZs . Some of the motors werent on dirt bikes though .

am i correct in thinking that if we run a bigger cc's in the same engine, then the velocity of the air through the carb is higher and thus it sucks too much fuel (gasoline) for the same amount of air and the bike runs rich?

its really difficult for my head to understand that a bigger engine doesnt need bigger jets, LOL!;)

John, The 13 tooth sprocket will help. I actually ended up putting the stock sprocket back on the bike. So I ended up running a 13/48. It had enough power to pull that gearing. That is a testament to low end power on that thing.
Dean, I found that most of my settings for my kx was leaner. I remember asking eric gorr specifically where I can start with the jetting issue and his response was generally. The pilot circuit needs to be richened, while the main circuit needs to be leaner.
Rich, At that time I wasn't much of mechanic, but I don't think that effects on how I change jets. Learning how to jet is not rocket science and I believe that anyone who wants and is willing to learn to jet there bike can. That bike was a difficult bike to jet even in stock form. The stock bike was very tempermental to humidity and temperature changes. And I found that the big bore was even more picky.

Erik