1989 CR125 Jetting help

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2/18/2020 6:41 PM

I recently restored the bike. Totally stock with the original bore. Only mod is Boyesen reeds.
Stock jets are 165 main and 60 pilot. Air screw 2.5 out. Needle - 3rd slot

I bought a service kit out of the UK with an OEM piston and rings and it came with a gang of jets.
Main - 170, 172, 178, 180
Pilot - 50, 55

Not even broke in it smokes like crazy and leaks out of the muffler. So I dropped a 172 main and 50 pilot.
Haven't started it yet as I am rebuilding the shock.

Any advice would be greatly appreciated. Its been years since I messed with jetting.

Thanks in advance!
-Robbie

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2/18/2020 6:53 PM

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2/20/2020 11:53 AM

Pro Circuit web site has jetting listed for these old2t”s. Search their site. I use it as base line for my old builds.

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2/20/2020 11:55 AM

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2/20/2020 1:04 PM
Edited Date/Time: 2/20/2020 1:04 PM

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

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2/21/2020 4:46 PM

mxrose3 wrote:

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

Salient point, no I did not.

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2/21/2020 4:57 PM

mxrose3 wrote:

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

bonseff wrote:

Salient point, no I did not.

Weird thing it starts fine, right side isn't sucking air making it hard to start, fired right up.

I went through though that deal with my daughter's 86 jr 50 and it wouldn't start because if that issue.

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2/22/2020 6:05 AM

I’ve seen, and had bikes start fine with bad right crank seals. They smoke like a train, and smell bad. If you replace the seal, replace the collar the seal slides over too.

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2/22/2020 6:06 AM

Do you still have the old piston? Shoot a photo of the underside and post it on here.

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2/22/2020 9:55 AM

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2/22/2020 3:54 PM
Edited Date/Time: 2/22/2020 4:09 PM

mxrose3 wrote:

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

Crap, I totally misread your statement. Yes I replaced that seal, I replaced every seal except the left side crank.
I have the seal, I should just buy a flywheel puller and replace it.

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2/23/2020 2:50 PM

mxrose3 wrote:

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

bonseff wrote:

Crap, I totally misread your statement. Yes I replaced that seal, I replaced every seal except the left side crank.
I have the seal, I should just buy a flywheel puller and replace it.

What kind of premix and ratio are you running, and what kind of riding? I ride woods and tight single track on my 88 CR125 which is essentially identical in the engine department, and have no issues. I’ve always run Maxima Castor 927 at 40:1. I don’t remember off the top of my head what my jetting is, but it’s pretty close to stock.

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2/23/2020 3:22 PM

Well good thing you replaced that seal because the old one was definitely sucking some transmission oil. I’d say try PC’s jetting and see what happens.

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2/23/2020 5:18 PM
Edited Date/Time: 2/23/2020 5:19 PM

Huge thanks to everyone who responded, it means a lot to be a part of this community. Your insights helped me greatly.
As anyone of you know, building a 30yr old bike with no records is like whack-a-mole.
You all rule.

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2/23/2020 5:56 PM

SLOWTIME wrote:

Well good thing you replaced that seal because the old one was definitely sucking some transmission oil. I’d say try PC’s jetting and see what happens.

For the record, that underside of the piston where the carbon was collected was the same side where the piston and ring showed blow by. Not sure I would blame it on a blown crank seal. If I am wrong, please clue me in.

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2/23/2020 6:07 PM

mxrose3 wrote:

the stock jets should work fine. You said it smokes like crazy - not to lead you down a wrong path (because two strokes normally smoke some) but did you replace the right side crank seal?

bonseff wrote:

Crap, I totally misread your statement. Yes I replaced that seal, I replaced every seal except the left side crank.
I have the seal, I should just buy a flywheel puller and replace it.

Jim in VA wrote:

What kind of premix and ratio are you running, and what kind of riding? I ride woods and tight single track on my 88 CR125 which is essentially identical in the engine department, and have no issues. I’ve always run Maxima Castor 927 at 40:1. I don’t remember off the top of my head what my jetting is, but it’s pretty close to stock.

It is not even broken in yet, running 927 32:1 like I have been forever. My plan on riding is just moto tracks on practice days.

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