Crf150f won't run with choke on

[ferrari96]

Hi all, I have stock jetting 95 main 38 pilot. The bike won't run with the choke on. It jus keeps cranking over will not run at all. On a cold start. Only way the bike will run on a cold start is with choke off. And WOT. When I took apart the carb the previous owner had a 42 pilot and a 110 main. So I thought putting it back to stock would do the trick. But nope. Same thing. Any help would be appreciated. Thanks so much

[socalxr]

It's not supposed to run with the choke on.  Depending on how it's set up, some bikes will use a choke to start for and warm up (for a minute), but that's it.  

[ferrari96]

It's not supposed to run with the choke on.  Depending on how it's set up, some bikes will use a choke to start for and warm up (for a minute), but that's it.  

I'm talking about a cold start. Normally you start a cold motor with the choke on. Then when it warms up. Turn it off. When the motor is cold, the bike won't even start with the choke on.. at all. It'll only start with the choke off with WOT. I can't get it to start with the choke on. Was thinking it's too lean on start up I see a lot of guys running a 140 main jet on those bikes. Was wondering if anyone else had the same problem and how they fixed it. But thanks for the reply

[wchefd]

An over oiled or clogged up air filter could cause this. Sounds like a rich condition as that's what the choke does and if the air is lacking then the choke is aggravating an already rich condition caused by lack of air. Could be that the throttle wide open is opening up the throat of the carb enough to let air in to get it started.

[ferrari96]

An over oiled or clogged up air filter could cause this. Sounds like a rich condition as that's what the choke does and if the air is lacking then the choke is aggravating an already rich condition caused by lack of air. Could be that the throttle wide open is opening up the throat of the carb enough to let air in to get it started.

Hey man I appreciate the time you took to reply, I just cleaned and re oil the filter. I tried starting it with the filter completely off the bike and still nothing. The plug is brown colour, so what are you thinking then bike is running too rich on start up ? Even if I try to start the bike without the throttle being wide open. Giving it 1/4 throttle still nothing with the choke on when the motor is cold. Can't find any info on it. Nothing is dirty inside the carb I took it all apart and cleaned with carb clean when I put the stock jets back in. So you think it's getting too much fuel and not enough air on start up? Cause one the bike is running its runs really good

[wchefd]

I assuming you have checked your pilot jet and circuit for clogs and have properly adjusted your fuel screw somewhere around 1.5 to 2 turns out.

[ferrari96]

I assuming you have checked your pilot jet and circuit for clogs and have properly adjusted your fuel screw somewhere around 1.5 to 2 turns out.

Yeah man carb is clean and fuel screw is 2 turns out

[socalxr]

Idk, I guess it's the way you set up your fuel screw and pilot.  All my bikes with Keihin PD style carbs, I never touch the choke for starting.  I only use it for jetting, so I get an idea what it's doing without air.  But once it's set up, it's first or second kick.  And make sure you can see right through the pilot when holding it up to the light.  Most starting issues is a plugged pilot.  Use compressed air.

Edited August 9, 2017 by socalxr

[wchefd]

Spring, washer, and Rubber o ring in place on the fuel screw?

[ferrari96]

Idk, I guess it's the way you set up your fuel screw and pilot.  All my bikes with Keihin PD style carbs, I never touch the choke for starting.  I only use it for jetting, so I get an idea what it's doing without air.  But once it's set up, it's first or second kick.

Hey man, this bike is electric start and doesn't have a back up kick start unfortunately, I'm trying to figure out why it wont start with the choke. It's been bugging me. And when I haven't started the bike in like a week it takes like 4 cranks to get it started (without choke)

Spring, washer, and Rubber o ring in place on the fuel screw?

Yeah that's right man. No air leaks there.

[socalxr]

Oh ok, I used to have a kick start one.

[wchefd]

Yea so when a bike is cold it requires a richer mixture. Generally when you start a cold bike with the choke on it will run on for a minute and then start to gurgle as it warms up. Hence you would shut off the choke, leaning the mixture and off you go. When you talk about starting it cold, is it that it just has not started in a while, or is the air temp actually cold? Bikes will often come from the factory a little lean, so as you go up on the pilot size the choke becomes less effective/relevant, unless your dealing with very cold air temps. The main jet has no bearing on this as the pilot, idle screw, and fuel screw are the only circuits dictating your idle to 1/4 throttle.

[Old School Al]

Has checking float level been mentioned...............?

Old School Al

[ferrari96]

Has checking float level been mentioned...............?
Old School Al

Can't find any info on that. Looking to find out the measurement from the top of the float bowl to the bottom of the float. (While the carb is upside down) so I can use my micrometer.

[Old School Al]

 

4 hours ago, ferrari96 said:

 

 

Can't find any info on that. Looking to find out the measurement from the top of the float bowl to the bottom of the float. (While the carb is upside down) so I can use my micrometer.

 

First, you don't measure upside down as you'll collapse the spring in the needle and get a inaccurate measurement ................ and calipers will be better suited to measure with. 

What year CRF150F do you have..................?

Old School Al

Edited August 9, 2017 by Old School Al

[ferrari96]

Firs





First, you don't measure upside down as you'll collapse the spring in the needle and get a inaccurate measurement ................ and calipers will be better suited to measure with. 



What year CRF150F do you have..................?



Old School Al

Hey, the opposite side of my micrometer is a caliper.. it's a 2009. Help would be greatly appreciated. Thanks man

[ferrari96]

Yea so when a bike is cold it requires a richer mixture. Generally when you start a cold bike with the choke on it will run on for a minute and then start to gurgle as it warms up. Hence you would shut off the choke, leaning the mixture and off you go. When you talk about starting it cold, is it that it just has not started in a while, or is the air temp actually cold? Bikes will often come from the factory a little lean, so as you go up on the pilot size the choke becomes less effective/relevant, unless your dealing with very cold air temps. The main jet has no bearing on this as the pilot, idle screw, and fuel screw are the only circuits dictating your idle to 1/4 throttle.

I'm talking about motor cold aka hasn't started in a couple days. So the previous owner put a 40 pilot jet in I put it back to stock which is a 38 pilot. So should I go to an even smaller pilot to make the choke effective. ?

[wchefd]

Try this- start the bike and warm up completely. As the bike is idling at normal operating temp, close the fuel screw all the way. If the bike continues to run, your rich enough on the pilot to go down a size. There is no guarantee that you won't end up with a lean bog at idle to 1/4 throttle. As a side note, when you switched the pilot out from the 42 to 40, you would have wanted to adjust the fuel screw accordingly as the setting would change with the pilot. If you dial in the fuel screw properly and you are at or under 2.5 turns with no bogs when fully warmed up your done. You may just have to wait for colder temps to see your choke become relevant.

[ferrari96]

Try this- start the bike and warm up completely. As the bike is idling at normal operating temp, close the fuel screw all the way. If the bike continues to run, your rich enough on the pilot to go down a size. There is no guarantee that you won't end up with a lean bog at idle to 1/4 throttle. As a side note, when you switched the pilot out from the 42 to 40, you would have wanted to adjust the fuel screw accordingly as the setting would change with the pilot. If you dial in the fuel screw properly and you are at or under 2.5 turns with no bogs when fully warmed up your done. You may just have to wait for colder temps to see your choke become relevant.

Hey man thanks for the great reply!! I would love to try that but I don't have the adjustable fuel screw it's the one thats hidden. Would you recommend me getting that ? Im guess I'm gonna have to in order to trouble shoot. I'm going to try and see if I can get a socket with a flat head to turn it but I don't think so. I'll go ahead and get the adjustable screw and then give that a shot. Thanks a lot for the reply really appreciate the info

[socalxr]

If there's a brass cover where the fuel screw is, you can drill a little hole in it and use a pick to get it out.  I just did that on a TTR.