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Vet Rider Vet Rider
10/22/2017 2:57 PM

So we got a 2018 CRF50 this year for my son. Runs ok. Has never idled correctly. Dealer says its normal and not supposed to idle for more than a minute. I think thats bullshit.

Anyway forget the dealer. I see several online where people show them idling for a long time with no issues. Furthermore we decided to ditch the stock filter assembly after he dumped it a few times and the filter enclosure was filled with oil.

So now its rocking a UNI pod filter and its running as bad as ever. I assume with the extra air its running super lean. Now it wont let you go WOT without bogging bad. It will start to run better as it gets to full temp, but unless I take it out and run it to WOT in 3rd, my sons riding style never lets it really get to full temp.

So I have been reading articles about changing the a/f it with some imaginary A/F screw that our 50 doesnt have. It has what looks like a brass cap. HOW THE HELL DO I ADJUST THIS THING?? WIll I need to rejet? What the hell is the needle jet and so on.

I pulled the carb and blew out every hole I could find with carb cleaner. The bike will start first kick even dead cold. Just wont barely idle. One of us has to keep it going while he gears up, and when he stops to talk to me it dies and I have to pull him off and kick it over again. Huge pain in the ass. And now its doing this bog thing. Keep in mind this is a 2018 with maybe 5 hours on it. Oil has been changed twice and only shell 93 has been used. Its literally a brand new bike. So "clean the carb" not only has been done, but is obviously not the problem. See the pic for the brass fitting. Any ideas other than buy an older carb with the adjusters??

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Vet Rider Vet Rider
10/22/2017 3:06 PM

Here is a screen cap of the carb. The #15 thing is the cap. Its called 16312-KYK-91 CAP, ADJUSTING SCREW. Can I get that off somehow? Do I want to? Should I just rejet?

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FGR01 FGR01
10/22/2017 4:28 PM

1) yes, absolutely a clogged pilot jet can be the problem on even a brand new bike. As I explained in your other thread, shit pump gas can varnish in as little as a week and clog the tiny pilot jet on these.

2)You should not have to adjust your air screw from the factory setting. But, if you feel the need, you have to remove that brass cap to get at it. As explained in your other thread it has to be drilled/pulled off as it is pushed in there with a light press fit.

3) I would ditch the aftermarket filter setup and go back to stock. You are correct that it is making the bike much leaner and is likely the root of all your probs. The reason the stock airbox filled with oil was probably because either the bike was laid over at some point or the engine oil was overfilled. The parts circled in red are the engine breather that vent the crankcase to the airbox. Oil will come up this and get in the airbox if the bike is laid on its side. The part circled in blue is the airbox drain. The part circled in green is a plug that must be removed from time to time to allow any collected oil or moisture to drain. Clean all the stock stuff well, put it back on, don't lay the bike over or overfill the oil, and drain that tube every few rides. Your life will be much easier.
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Powerband in every gear !

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Vet Rider Vet Rider
10/23/2017 5:28 AM
FGR01 wrote:

1) yes, absolutely a ...more

I do appreciate your help. But I took your advice from the last thread and ran through the carb with lots of carb cleaner and a very small gauge wire. There is nothing in the pilot jet. The bike seems to need to be tuned. So thats where Im at. Ive cleaned it twice.

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bf884 bf884
10/23/2017 5:55 AM

Go back to the stock air box. Its going to run worse with more air from UNI with no where to go.

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Vet Rider Vet Rider
10/23/2017 5:57 AM
bf884 wrote:

Go back to the stock air ...more

The stock airbox is gone. There is an a/f screw and I should be able to tune for changes to both intake and exhaust. There is no need to just go back to stock. What do people do when they install big bore kits and full exhaust? You have to be able to tune them...

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RCF RCF
10/23/2017 6:23 AM

Just buy a Chinese one off eBay they're only $12 you will spend more than that on just buying new Jets

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FGR01 FGR01
10/23/2017 7:21 AM

The uni filter is matched for big bores with bigger carbs. It is too much air for that carb and that engine. Even if you get at the air screw I doubt it has enough tuning range to compensate for that filter. These bikes are cold-blooded and run on the lean side even with the stock airbox. I have to keep mine about 1/4-1/2 choked to run right. Even if you put on an aftermarket carb that has the tuning range for that filter the end result will be too much gas and too much air for that engine, especially if you still have the stock exhaust plugged up with the spark arrestor and all. You're chasing your tail by keeping that filter on there.

Powerband in every gear !

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Tracktor Tracktor
10/23/2017 12:28 PM

Buy a bigger pilot jet? Have you checked the valves?......

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bf884 bf884
10/23/2017 6:14 PM
bf884 wrote:

Go back to the stock air ...more

Vet Rider wrote:

The stock airbox is gone. ...more

Exactly what you said. Big bore, pipe and all the goodies. Your stock engine is not meant to accomadate that amount of air flow. Id bet it runs better on choke huh? That air screw is for fine tuning and its not going to fix your problem.

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mark911 mark911
10/24/2017 5:04 PM

Buy a few sizes larger pilot jets and remove the air screw cap so you can adjust it. Those little bikes are jetted so lean for emissions it's ridiculous. Add a really good inline fuel filter as well, the smallest piece of debris can clog those tiny jets.

After the bike is warmed up, turn the air screw out until it starts to misfire and then slowly turn it back in until the idle is the fastest and smoothest. You should end up about 1 to 2 turns out from seated. You might need to turn down the idle speed and repeat if the idle is too high.

Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

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lumpy790 lumpy790
10/24/2017 6:52 PM

I have found bigger draft needs smaller jets

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Falcon Falcon
10/25/2017 3:33 PM

Also, make sure you are using fresh gasoline. The cleanest pilot jet in the world won't help if the gas is bad.
My kid's PW50 is extremely sensitive to this issue. I always run fuel stabilizer in the gas and it definitely helps.

Braaapin' aint easy.

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