125-200cc 2007 Wr125 Jetting Issue

Hello,

I apologize, I coundn't find a good anwser in the jetting database nor with the search function.

I'm running a 35 pilot, 400 MJ, 6dj8-60 2nd clip. I'm at sealevel with temps of about 40-45 F*.
going by the charts its already leaner than needed and yet at WOT it still doesn't want to clear out and has quite exessive smoke. Especialy when revvign up on the stand. seems to be still very rich.
The engine is a fresh rebuild with +2mm overbore. It has the oldes square slide TMX.

I'm not hoping for someone to use psycic powers to correct my jetting of anything, but I'd like to know if it is normal for these bikes to be jetted leaner than the factory charts.
As I'm quite new to dirt bikes in general, I'd like some confrimation that i'm not missing some underlying issue and confusing it with a jetting problem.

Best regards,
Inar

I hate to tell you this but you need to ditch the mikuni and go with a Keihin airstriker ... I had an 04 and no mater what I did it would not jet correctly... it's a lost cause .. I spent too much time and money on jet kits etc.... I couldn't give it away... I put the Keihin on and my problems were solved..

https://www.amazon.com/Keihin-016-167-38mm-Striker-Carburetor/dp/B00C178JY4/ref=sr_1_1?crid=2SEELTNBGXJ&dchild=1&keywords=keihin air striker 38mm&qid=1609058979&sprefix=keihin air,aps,228&sr=8-1

I did the airstriker and a JD kit and I was done.. You can also get a Carb from JD jetting which in hindsight I would recommend.. disregard the previous link to Amazon ...


https://jdjetting.com/

On the 125s Crank seal might be worn which would explain excessive smoke you could be burning gearbox oil too they are a common issue on them bikes I have a box of them I change mine regular might be worth a try before you spend out on a carb

the mikuni can be jetted fine. has been done properly for decades.
As suggested in previous post, you must make certain all parts of the system are working correctly.
= crank seals, float needle seat and float height adjustment., it is something simple.
my little '06wr125 rips w t mukuni

look at the plug too

Hey again,

So it turns out it isn't a jetting issue. Took the engine off the bike and removed the cylinder and found a a puddle of coolant and fuel in the crankcase.

I had used 2 base gaskets to set the squish so figured it might have leaked from there. made a new gasket, applied a thin coat of Permatex no.3 just for insurance, reassembled and tried again. At first seemed to be OK, but within a minute it was just as it was before... But I'm now quite sure the leak doesn't come from the base gasket. feels like it really starts leaking once the components start to heat up. head maybe? There are some defects in the head. cracked/previously overheated? There is some detonation marks from before I owned the bike.

The sad part about it during this hour of runtime the cylinderwall has gotten some damage...
Can't really feel it with the finger that much, only on the very top part near the deck. teflon deposit?
Found 2 places of pitting, marked with red.
Compresion was good.
The piston is fine, just the teflon coating is a little worn in places.

What are your thought? head done for? Cylinder still usable?
I could really use a second opinion here...


What a bummer tho. I haven't really even gotten to ride it yet..


Best regards,
Inar

It’s hard to say for sure Without seeing it in person, what are the bottom of the barrel and the casing surface like?
I would say your head might be the issue it maybe warped, the cracks will possibly open up when it’s warm, I wouldn’t run two base gaskets either, I would get OEM or pattern replacement they come in various thicknesses, you shouldn’t have any issues with the pitting on the bore there not big enough, I have a couple, a factory one and a factory tuned one with some small pitting it’s never affected running or HP it’s good to change the o ring head seals every time you have the head off too they can go hard although I ve never had any issues. But before you go spending out on a new or 2nd hand head I would maybe consider splitting the cases and replace that gasket too where the coolant passage hole is in the cases sometimes that gasket can fail and leak into the crank if you don’t know how old it is

What thickness base gasket do you need and what squish you running?

Forgot to mention that it's a freshly rebuilt engine. Did both bottom and top end on it. The cylinder was overbored +2mm, too.
Totally my ignorance for not thinking much of those defects on the head when i reassembled.

I can't say for sure that it didn't leak before. I only have ridden it for a few hours in total and it didn't run all that well even then. Until the magneto side seal destroyed itself, literally. Amazed me that it sarted just fine basically without a left side seal. no power and not rideable, but it ran. I'll add a picture.(Yeah, seems like it was leaking way before I even got the bike... I'll write it up a school money)
Decided to do a full rebuild after it.

The dual basegasket bulls**t I did because I didn't have a think enough one on hand. a 0,8mm gasket is on the way. Aiming for 1mm of squish

I'd hope that the crankcase gasket is good. I used an OEM gasket with a thin layer on permatex no.3 as insurance. Never had one leak before. But just in case I reassembled the top end today, filled the cooling jacket with coolant half-way and pressurised it. If it leaks, there'll be a puddle in the crankcase tomorrow. hopefully not, tho.

Had a more careful look at the barrel too. the lines only seem to be where the ring touches the wall. But it seems that scrubbing with a fingernail seems to smooth the roughness out and fresh crosshatching appear underneath. I think i'll clean it up the best I can and use it as it is.
Really needed that input about the pitting, made me feel a lot more at ease. Thanks Sonnie!

So if there is no coolant in the crankcase by tomorrow evening, I think I'll start looking for a new head.

Best regards,
Inar

That crank seals not helping matters at all dude that is likely your issue I would try again once that seal is replaced you might not need a cylinder head after all
I ve got a box of them seals OEM, I could send you one if you struggle to get one

that picture is taken prior to the rebuild. a new OEM seal is in place now along with evertything else.

So... I have now replaced the head and the basegasket now. Doesn't seem to be burning coolant anymore. But it still doesn't run right. Bogs badly at medium to high load. Not a lean bog tho. So investigating futher i discovered that the spark is very weak. The wierd thing is that when I first start it when i has sat overnight, it runs a lot better for the first 5-10 secounds and then progressivly gets worst. so today after letting it sit, i took the spark plug off and kicked it over. at first the spark is really strong like i'm used to seeing on other machines. but when you kick it over enough times it becomes drastically weaker. I'm guessing this is why it doesn't run at load...

Didn't really think to check it before as it has been starting really well.

So i turned to the manual to see how to test the coil and stator. unfortunately I couldn't find any good information there other than how to test the lighting coil. but the lighting coil has no bearing on the ignitions operation, right?

Pehaps someone could point me in the right direction

1st of all If you take the coil off the Bike check your coil mountings are touching bare metal make sure the coil is earthing to the frame properly
Then take the coil and put onto a bench and get a multi meter
Set the multi meter to ohms 1st test across the primary side of the coil so positive on the input prong and negative on the mounting that bolts to the frame it should read approximately 0.6 ohms
Then put the negative into the spark plug cap and positive into the input prong again it should read approximately 10.95 resistance if you don’t get close to those figures it’s could be faulty or if you get the letters OL its means you have an open line or break in the wire so the coil could be faulty
Hope that helps

Also The 2nd measure 10.94 ohms could be higher around 12 ish but if it’s lower you could have an issue

Image attached

I tested a brand new one haven’t been on a bike yet

Thanks, Sonnie!

Checked the grounds, all were fine. measured the coil as well and couldn't get any measurement from the input prong to neither ground or to the cap.
Regardless, managed to source an universal coil for testing and couldn't get any spark with it. I think the original coil has a CDI element in it.

Anyhow, as these bikes ar rather rare in these parts of the woods, I decided to test out a HPI ignition system. Will let you know how it turns out.

Really thankful for all the input

No worries