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Backfiring/Won't Idle

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My son has a 2018 CRF150RB.  We went for a ride today, about an hour and a half long.  Everything seemed fine.  Towards the end of the ride, I topped off his tank with some gas a friend of his had brought.  He went and rode another fifteen minutes after that with no issues.  We finished our ride and put the bikes on the trailer.  When we got home, my son and his friend went for a quick ride at a neighbors mini track.  It was at this point that the bike started to backfire and sputter.  If he wasn't on the gas, the bike would just die.  If I put the choke on, the bike seems to run fine.  But as soon as I take the choke off, it starts sputtering and backfiring.  I drained the gas that was in the tank and put in gas I purchased yesterday.  Ran it up and down the road five or so times, but it's still doing the same thing.  Could it be a bad spark plug?  Clogged carburetor?  The air filter was brand new at the beginning of the ride and looks only slightly dirty.  Any suggestions would be greatly appreciated.  I'm hoping it's not something major.  The bike is like brand new!!

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When I bought my sons 2018 it wouldn’t even start with the 38.put in a 45 and 2 turns out on fuel screw and bam fired right up

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Take the pilot jet out and see if it has anything in it.should be able to see through it.

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14 hours ago, CarlandNicki Johnsen said:

The bike still starts right up.  It idles when the choke is on, but as soon as the choke is off it starts sputtering, backfiring and simply dies.

That's classic plugged pilot symptoms, can't get enough fuel through the pilot to idle and the choke adds enough to let it run.  Pull the 38 and stick a 42 or 45 in there, my bike likes a 42 tried a 45 and it was too fat but others do well with a 45.

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4 hours ago, Danceswithtrees said:

That's classic plugged pilot symptoms, can't get enough fuel through the pilot to idle and the choke adds enough to let it run.  Pull the 38 and stick a 42 or 45 in there, my bike likes a 42 tried a 45 and it was too fat but others do well with a 45.

This ^^^^^ x2

Dave

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I have a 08 150r and they never happens to me but your problem isn’t the Jetting it’s the valves . 150s have a terrible valve problem

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On ‎10‎/‎23‎/‎2018 at 9:21 PM, andrewespo318 said:

I have a 08 150r and they never happens to me but your problem isn’t the Jetting it’s the valves . 150s have a terrible valve problem

Seriously?  It's a 2018 bike and he stated so much as it had been topped off with unknown fuel then it began with the problems described.  It's not the valves.

Dave

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I agree with Dave. It's not a valve issue. I just checked them 4 hours ago and both intake and exhaust were spot on. I'm going to take the carb off and clean it. Wondering if a piece of dirt got in there. Seems like it's a fuel problem. Thanks for the help. 

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On 10/20/2018 at 7:33 PM, CarlandNicki Johnsen said:

My son has a 2018 CRF150RB.  We went for a ride today, about an hour and a half long.  Everything seemed fine.  Towards the end of the ride, I topped off his tank with some gas a friend of his had brought.  He went and rode another fifteen minutes after that with no issues.  We finished our ride and put the bikes on the trailer.  When we got home, my son and his friend went for a quick ride at a neighbors mini track.  It was at this point that the bike started to backfire and sputter.  If he wasn't on the gas, the bike would just die.  If I put the choke on, the bike seems to run fine.  But as soon as I take the choke off, it starts sputtering and backfiring.  I drained the gas that was in the tank and put in gas I purchased yesterday.  Ran it up and down the road five or so times, but it's still doing the same thing.  Could it be a bad spark plug?  Clogged carburetor?  The air filter was brand new at the beginning of the ride and looks only slightly dirty.  Any suggestions would be greatly appreciated.  I'm hoping it's not something major.  The bike is like brand new!!

Would go through the carb, pull the jets and clean them. If it was a valve problem, it would be very difficult to start. 

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