125 carb

[ecojbr]

I know we all bore our carbs to 36mm. But has anyone thought about the earlier kx 125 carbs? I know they are 36mm, but don't know if they would be any better than the stocker.

[fuzzy]

They are the larger carb body (same as 36-41mm), and makes fitment very difficult for no benefit. 35mm is 28-35mm body size. KDX Carb master RB tried this, and abandoned the project.

[Julien D]

Unless your name is MotoPsycho.

[fuzzy]

[Terrence Sprocket]

Really? I also considered the kx125 36mm carb for my KDX200. I have one from a 94 KX. I have the reed boot aswell. Do u think it's a waste of time?

[rbates9]

Give it a try and let us know how it worked out.

[Terrence Sprocket]

Lol will do. The only prob I can see is getting the airbox boot to work cause of the difference in diameter. Like I said tho, I have the intake boot which bolts right up to the KDX cylinder. I got the parts for free, so I guess it's worth a try. I'll play around with the jetting. I'm in southern NB Canada, my elevation is from anywhere around 0-400 feet. I wonder how the KX needle will perform?

Seriously? No body tried this b4? I suppose, with RB doing a super job with the 35mm, who would really bother. I figure I'll try it tho where I got the parts for free. If anyone has done b4, please, by all means, speak up. Thanx!

[factoryX]

If you have, do it. It might work better, who knows . Kind of interesting how the 125 boot bolts on.

[Julien D]

Good luck. The 35mm carb works perfectly. With the RB mods it should be even more perfect. Going larger with the carb, by nature, will give you more top end speed at the expense of low end throttle response. If you do go with a larger carb, I would retard the timing a bit to give the motor a bit more over-rev. Might help take advantage of the extra CFM.

[Terrence Sprocket]

Yea, the boot definitely bolts on the same as the KDX boot, I just went out and double checked. I wasnt sure when my buddy gave me the parts. The 94 kx has incase reeds, so its definitely hard to believe that it bolts the same.I also have the reed block and reeds from the KX ( 94 125). Think I should give those parts a try, or just stick with the KDX reeds? And what's that divider plate RB installs on the 35mm carbs called? U know, the plate that helps it react better at low rpms? Maybe I should install one of those in the 36mm.

Oh Juliend, which way should I rotate the stator plate to retard the timing? Clockwise, or counter clockwise? I always get confused with which way to retard, and which way to advance. Lol. Thanx. Seems like u always have the best educated answers on the site. I always look forward to seeing your replies.

[Julien D]

I believe it's clockwise to advance, counter-clockwise to retard. You will notice 3 marks on the stator plate that relate to a pointer mark on the case. The center mark would be standard. I would not advise going past the outer marks. If you don't mind pulling the flywheel off a couple times, it would be worth trying all three settings before settling on one. You can always stop between two of the marks as well. A tiny bit does make a difference!

[Terrence Sprocket]

Yea, I think in between the standard mark and the next mark would prob be enough to do it. I'm starting to get pumped about the build. I should have my cylinder back at the first of next week with fresh plating. Ordering new rings tomorrow. It's a B cylinder and the piston looks like it was never used, looks like it's been chamfered properly. I wonder if the new plating will match the B size piston? I hope so. I'ld hate to see that mint B size piston to go to waste.

[Julien D]

If you had sent the piston with the cylinder, they could have matched it up perfectly for you. Hindsight is 20/20, as usual. Just check your clearance when you get it back. The difference between an A and B piston is only .01 mm. I think you will not have a problem.

[Terrence Sprocket]

Well, I hope so. But they might fit it to wisco's STD KDX 66mm. In that case, it would prob require a D size or larger.

Thanx

[Terrence Sprocket]

Hey guys. I pulled the 36mm carb apart to see what was in there. A 158 main jet, which is pretty normal. My 35mm has a 160 main, needle clip in the middle. The pilot in the 36 mm was a wopping 55. Wow! ! That's pretty big. My 35mm has a 42 pj.
So, I know jetting is trial and error, but do u guys think I should leave the 55 pj in, or put my 42 pj in the 36mm for a good starting point? 55pj seems awfully rich, but maybe it needs it to make up for the low speed circuit in the 36mm? I'ld really like to try this carb out. For all u guys with the RB modded carbs, what does he put in for a PJ after he bores it to a 36mm?

I hope no body is getting sick of my questions yet, I think I have alot yet to learn about this stuff.....

Thanx.

[rbates9]

When I got mine back it had a 40 PJ in it and he sent a 38 and 42.

[Terrence Sprocket]

Yikes! Sounds like my 55 pj is Ganna be horribly rich then. Maybe I'll stick my 42 in and go from there. I'm pretty handy to sea level. Where abouts is your elevation? I'll be going to the dealer tomorrow to do some jet shopping.

[rbates9]

They are different carbs. You are better off going too rich than too lean. It wouldn't be a bad idea to start rich and work your way down.

[Julien D]

Exactly. I'd start exactly where it is and go from there. First thing to do is warm it up good and play with the airscrew to determine if the pilot is close or not.

[KarlP]

I'd leave the big pj in there to start. It should run but be rich.
The big pilot made sense for a 125. Fewer CC's, less air going through the carb so less suction, you'd need a bigger pilot to send enough fuel.
Your motor will want a smaller pilot.

I think if you search for posts by RBD you'll find some mention of work he did years ago with the KX125 carb