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2 stroke bogs down

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So kid has a 2002 kx125 we have been running it for about 7-8 races with no issues. Only recent changes were returning to stock exhaust because the old one essentially disintegrated. We are running Amsoil the red I believe it’s the Dominator 32:1, 91 ethanol free petrol. Have run about 2 motos with this type oil and exhaust with no issues. Saturday at practice first lap kid came off track complaining of no power, I knew the clutch needed replacing anyway so did that no change. While at race quickly cleaned carb replaced spark plug, which didn’t look to bad. Bike ran ok but not great for about 2 laps then bogs down at low RPM’s. Tonight removed air filter (thought might be over oiled and restricting air flow) rode in grass same issue.  Essentially bike has no power until it hits the power band just bogs down and now fouling plugs quickly. I checked the reeds and they look tight.  My next step is jetting and power valves but not sure why this would have changed since was running well with same combo of fuel and exhaust. I am not terribly familiar with 2 strokes but learning anyone have any suggestions?? 

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My guess is carb issue.

Check with chokey he will know, or William 1.

Could be a PV issue but I'm not a kawi guy.

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Has the weather changes drastically in your area ? If so it may be jetting or just needing tuned in . It was in the 60s here last week and 85 today i'm in the same situation on my sons bike turned to total crap. 

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Thought that may be the issue turned out due screw about 1 full turn no real diff, went back to stick 1 1/4 out issue continues. temp has been about the same 50's and damp

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Thought that may be the issue turned out due screw about 1 full turn no real diff, went back to stick 1 1/4 out issue continues. temp has been about the same 50's and damp

I would do some plug checks before i went any farther . Put a new one in let him ride it normally as he would and pull the plug and take a look. 

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When was your KIPS last serviced?

 

My bet is your PV is dicked up and needs cleaning.

 

In that regard it would be good to have that cylinder off to make sure your Piston and rings are in decent shape and your reeds arent frayed.

 

My money is on the KIPS goo'ed up.

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Sounds like a jetting issue your having after changing out the exhaust. I don't think it's the power valve as it not functioning would be a flat high rpm power. But it could still be a factor.

How hard is your kid riding the bike? you could be due for a top end.

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Need to know what jets you have in it now. Changing pipes and not jetting is not good. Going from stock to an aftermarket, the bike will run but not to its full potential. Then going back after bike has been jetted for pipe the going back to stock pipe creates the issue all over again.

But for a quick check, raise clip on needle and see what that changes.

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Thanks for all the great advice, I ripped carb apart, cleaned real well, put in a new iridium plug, flipped the reeds (didn't loo t bad) the internal set have a small gap on the sides but seal very well on ends. He has been riding pretty hard since and says power is back and better than when we bought it. For jetting I am running a 45 pilot and a 34- main (stock 45/350) scrapped the Amsoil and switched to Klots R50 mixing a 32:1 temps been in mid 70's, altitude in 1300 feet. Knock on wood seems to be running pretty well. Not sure how to check the PV valves (haven't broken down for the service manual yet) I did take cover off but do I need to remove head to to access??

My next plan is t replace reeds, any suggestions on best type?? oil mix and ratio??

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Thanks for all the great advice, I ripped carb apart, cleaned real well, put in a new iridium plug, flipped the reeds (didn't loo t bad) the internal set have a small gap on the sides but seal very well on ends. He has been riding pretty hard since and says power is back and better than when we bought it. For jetting I am running a 45 pilot and a 34- main (stock 45/350) scrapped the Amsoil and switched to Klots R50 mixing a 32:1 temps been in mid 70's, altitude in 1300 feet. Knock on wood seems to be running pretty well. Not sure how to check the PV valves (haven't broken down for the service manual yet) I did take cover off but do I need to remove head to to access??

My next plan is t replace reeds, any suggestions on best type?? oil mix and ratio??

I run the klotzR-50 32.1 with Vforce 3 reeds , and you can pull power valves through the exhaust port on my model Honda but a lot of them you need to pull the cylinder . Always service your PVs when you do a top end rebuild . Book on my sons 125 says every 3 races to give you an idea of how much they need cleaned .

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With Amsoil you don't need to run 32:1. You can safely run 50:1 but most that use it run 44:1.

 

Since you went back to a stock pipe, I think in that year, the recommended PJ was 48.

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