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2007 CR125 Tuning Help

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I have a stock 2007 CR125 with the Mikuni Carb with a 50 slow jet and a 430 main. It loads up at idle and blubbers until I clean it out. The bike runs fine off idle, but loads up when I let it sit and idle. I have tried different slow jets...it came stock with a 55 slow jet...I went down to a 45 and it still loads up on Idle. I have changed the needle one size down to a 6DGY28-69 from the stock 6DGY28-68...both were set at 3 down from the top.

What else could it be? Could it be the float level? I haven't checked that yet.

Any suggestions would be helpful.

Thanks, shortcircuit

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The 45 pilot is still way to big for that setup and those needles. You will need to go all the way down to a 35 or a 32.5 pilot to work with those needles and it still won't be that good. There are much better setups if you want to run a Mikuni carb. You may want to try one of these. The needle jet is the key to making that carb work on that bike.

needle- 6bfy42-74 #3 (from a late model yz125)

pilot- 32.5

main- 420

or

Needle- 6chj10-82 #3 ( from a late model kx125)

pilot- 37.5

main- 420

These are just suggestion. You may have to move the clip position up or down, but they should get you in ball park, and be much much closer than the any of Honda needles.

Edited by rtv

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Holy Crap...I have to go down that much on the pilot? Why the heck do they spec a 55 pilot stock? I'll order that parts and give it a try...thanks.

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Holy Crap...I have to go down that much on the pilot? Why the heck do they spec a 55 pilot stock? I'll order that parts and give it a try...thanks.

I have know idea why Honda would spec a pilot jet that fat, I have been there and felt your pain in trying to jet these bikes,but honestly you'll need atleast a 35 if not the 32.5 in order to make the bike run OK. I would really consider the other needles/setups though for the best results.

Edited by rtv

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Where is your air screw set at in all of this? It runs in conjunction with the pilot jet.

I was working the air screw between 1.5 and 2.5 turns out. I did have a somewhat better idle with the 45 pilot at 2.5 turns out...

I'll order the parts and give it a try.

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Holy Crap...I have to go down that much on the pilot? Why the heck do they spec a 55 pilot stock? I'll order that parts and give it a try...thanks.

Honda sold most of their 2 strokes fat off the floor as an insurance motive so that people wouldn't blow the bikes up after a week of riding them and then go and complain to the dealer that it exploded after a week. Also because some people do not take the time to break in their brand new bikes. The best results I have had on my 05' CR125 is with the JD jetting Kit. Using the 32.5 pilot, not sure on the main, with the red JD needle in the 2nd clip from top, with 1.75-2 turns out on the air screw depending on humidity, weather, temp. Bike rips. Only thing I have on it is stock pipe, R304 Shorty, V-Force Reeds, polished head, and Wiseco Piston. Loves to eat the 110 Sunoco mixed with Castor 927 @ 32:1!!!

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I just delt with this problem today. stock 2006 cr125

MX track only not sure if this will work for trailriding!

I had the recommended jetting in my 06 cr125 from MXA and it rain hard from mid to top but bogged on the bottom and would bog on landings when the weather got really warm.

I did alot of research on this site and found that answers were all over the place.

Then i found a post where HI-TECH HORSEPOWER a shop that builds and dynos bikes.

Work your way down slowly on leaning the main and pilot jet, you will proable end up with a *410 or 400 main a *40 or 35 pilot and lean the needle out *1st or 2cd clip (might have to go one needle leaner)

That bike is very very fat from the factory.

*(you will proable end up at those spec's.)

Are you running a 10 or 9 plug? I'd go with the 9.

Gene

So I ripped the carb apart check float height it was in spec, checked reeds, and changed the jetting to the following.

410 main

27-67 MXA recommended needle in the 2nd position.(needle is 1/2 clip leaner and slightly richer straight section guessing stock needle would work just as good though)

40 pilot

Air screw 1 1/2

Weather sunny/70f

Elevation 2200ft

Bike still loads up slightly when warming up but is a beast on the track.

This bike rips when jetted properly, I have rode YZ125's(05,06,08,2010) the last 6 years and the 06 cr125 engine is way faster and torquer than they were.

Long hills, tight corners,deep sand rips through it without a wimper this bike is so easy to stay on the pipe its silly.

Did plug test and the plug was perfect where as before it was a dry black carbonized.

This was not a case of just thinking bike ran awesome because jetting was crisper, I had just rode a 2013 ktm250sxf(amazing bike feels so light could use a bit more over rev though) and 2013 150sx (not that impressive bad jetting also, but fun)an hour earlier at a KTM demo ride and was worried I would think my cr125 would feel slow after riding them and i would want to buy one but that was not the case.

Like I said not sure how these setting would work for trail riding but on a MX track they are awesome.

This bike should have won the 125 shootout in 05-07

Edited by qwert321

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The best way to fix any of the mikuni carbed hondas jetting issues is to replace the carb with a keihin PWK airstriker carb.

I read you lose top end with pwk is this true?

I don't see the need to change for track riding, maybe trail riding.

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I read you lose top end with pwk is this true?

I don't see the need to change for track riding, maybe trail riding.

Not if the Mikuni that is on it is 36mm and the PWK you put on it is 38mm. You would gain a bunch of top end at the expense of low end. I have a feeling that the loss in top end is a myth though. If the mikuni is 38mm and the PWK is 38mm, there shouldn't be any loss in top end both carbs should flow about the same. Plus since the Keihin is easier to get jetted crisply, you are probably going to gain a bunch of HP all over the RPM range simply because your engine will be getting proper amounts of air/fuel mixture all of the time.

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Not if the Mikuni that is on it is 36mm and the PWK you put on it is 38mm. You would gain a bunch of top end at the expense of low end. I have a feeling that the loss in top end is a myth though. If the mikuni is 38mm and the PWK is 38mm, there shouldn't be any loss in top end both carbs should flow about the same. Plus since the Keihin is easier to get jetted crisply, you are probably going to gain a bunch of HP all over the RPM range simply because your engine will be getting proper amounts of air/fuel mixture all of the time.

The only reason i say that it will lose top is I have read that disconnecting the TPS will affect top end power.If not always good to have options.

As for jetting crisp my bike is crisp bottom/mid and top with the jetting I posted earlier. It loads up when idling on stnd to warm up but I think most 2 strokes do(my yz125 always did).

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The only reason i say that it will lose top is I have read that disconnecting the TPS will affect top end power.If not always good to have options.

As for jetting crisp my bike is crisp bottom/mid and top with the jetting I posted earlier. It loads up when idling on stnd to warm up but I think most 2 strokes do(my yz125 always did).

You can get YZ250 pwk carbs that allow you to connect the TPS. There are 2 opinions on whether it makes any difference or not to have the TPS plugged in. Some say they can't tell a difference others say that they have better off idle throttle response with it plugged in. There have been some, you included, who have been able to solve the mystery of jetting the mikuni carb I guess if you have it running crisp, it would not be worth it to buy a PWK.

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I have went through the same thing as everyone that owns an '05-'07 CR125, Here is what I am currently running in my '07:

420 main jet

35 pilot jet

6CHY6-81 needle

#3 position

I am going to try the 6bfy42-74 needle, I have one in my truck that I just haven't had a chance to try. I have a bunch of the honda needles that I bought trying to get it right with their -dgy series, what a waste - the yamaha needles are about 1/3 the price!! My setup still has a rich spot to it but it's mainly just there when warming up.

I find it funny that everyone wants to change out the carb - the YZ125 has used them for quite a while and no one seems to complain about the tmx-x carbs, KX & RM 125's used them as well and I don't think those guys are buying the keihins' up.

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I have went through the same thing as everyone that owns an '05-'07 CR125, Here is what I am currently running in my '07:

420 main jet

35 pilot jet

6CHY6-81 needle

#3 position

I am going to try the 6bfy42-74 needle, I have one in my truck that I just haven't had a chance to try. I have a bunch of the honda needles that I bought trying to get it right with their -dgy series, what a waste - the yamaha needles are about 1/3 the price!! My setup still has a rich spot to it but it's mainly just there when warming up.

I find it funny that everyone wants to change out the carb - the YZ125 has used them for quite a while and no one seems to complain about the tmx-x carbs, KX & RM 125's used them as well and I don't think those guys are buying the keihins' up.

I wasn't having any problems with my Keihin PJ carb on my 94 either. I thought I would try the PWK because I got a good deal on a used one on ebay. Made a huge difference. Of course it added top end because I went from a 36 to a 38mm carb but it was crisper through the entire RPM range, no more spooge, and it will idle forever without loading up. The keihin is simply a better carb. If you have your mikuni jetted good and it is working awesome for you then great but IMO the keihin PWK is a superior carb.

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