Only idles cold

[Luni]

So, I got this blaster running. Im still trying to figure out the kinks in it. It had a bad stator when I got it so I changed that and got it to run.

My problem now is, no matter what, when the engine is warmed up, I cant get the damn thing to idle. I can start it up cold (ambient temp in my garage is around 45-50 degrees) and it runs great, but then Ill go ride it around for a few, heat the engine up, and it just wont idle right.

I think its probably running too rich, but I dont know.

It has a Keihin carb on it. I havent pulled it apart yet to determine what jets are in it, I suppose Im going to be told to do that first, make sure the jetting is right, and make sure there are no air leaks.

One more thing worth noting, it has a K&N filter attached directly to the carb, there is no airbox in this thing (need to do something about that too cause I ride through mountains and streams sometimes and it will die)

Anyway, Ill see what jet is in there and post back.

 

[brandoz28]

well, take the air screw out a little bit and see if that helps. if it does then you need to put in a smaller pilot

 

[Luni]

Actually, I should have posted, when its warmed up, I can completely remove the idle screw and it doesnt help. It still wont idle.

 

[Luni]

K. More info. I pulled my carb out. I measured both sides. The side the air filter connects to was like 54mm and the side that connects to the engine was like 36mm.

So I think I have a Keihin 36mm carb. Im bored 20 over with a Wiesco Piston. My main jet is a 132. I have a K&N hanging right off the carb, so no airbox.

Can someone please help me get my jetting down? Im at 4200 feet elevation. The jet I have in there is too rich.

Also how do I adjust the needle? And which one of thes is the idle screw? Theres 2 of them.

Theres the little tiny one on the bottom right, and theres the larger of the 2. Which one does what?

Any help would be appreciated guys.

 

[webmonstro]

K. More info. I pulled my carb out. I measured both sides. The side the air filter connects to was like 54mm and the side that connects to the engine was like 36mm.

So I think I have a Keihin 36mm carb. Im bored 20 over with a Wiesco Piston. My main jet is a 132. I have a K&N hanging right off the carb, so no airbox.

Can someone please help me get my jetting down? Im at 4200 feet elevation. The jet I have in there is too rich.

Also how do I adjust the needle? And which one of thes is the idle screw? Theres 2 of them.

Theres the little tiny one on the bottom right, and theres the larger of the 2. Which one does what?

Any help would be appreciated guys.

OK
So the to big one is you idle speed , the small one is the idle mix(air screw)
The big top one should hit the slide and stop it from dropping and that is what gives you you idle speed
It also looks to be all the way in
Check your slide, it should have a small bump in it that hits the idle screw
I used to have a keihin just like this in a kx 250 that had the slide broke where the idle screw should hit it so it was'nt working at all and had to adjust the idle with the cable

Bye
Nuno

 

[Luni]

Ok, I got it to idle. There was a nut threaded on the end of my idle screw. I took it off and threaded it in all the way, started at 1.5 turns out on the small screw by the air inlet, and ended up turning it about 4 full turns. It now will idle. Or it seems to. A helluva lot better than it did.

So now, I just have to figure out my jetting.

I wonder if I should start a new thread. I think I will, since I seem to have it idling.

 

[dlporkchop]

The best thing to do is go under engine in the forum. It has great articles on plug chop,carb tuning,etc...... I use some or all of this information from time to time. Give it a shot. I think will help!

 

[Luni]

Ive found quite a bit of info.

Ive determined I had too small a main in there. So i upped that. I also know I have too large a pilot in there, so Im gonna drop that down. I also figured out where my needle is sitting so I have a baseline to go with on that as well.

 

[Wildcard2]

Luni,
What size is your pilot jet? Sounds like you may still be quite rich on the bottom end. 2.5 turns out from bottomed is the limit on the air screw. You will likely have to drop down 2 sizes or more, shouldn't have to have the idle screw (if it's the correct one for your carb) turned in all of the way to get it to idle. You can give me a call at 435 623-0148 if you'd like I can walk you through some jetting. Leave a message if nobody answers.

-Brandon

 

[Luni]

Brandon, my pilot jet was indeed rich. I got it to idle with 2.5 turns of the pilot circuit. I probably could get it down to another size, but Im more comfortable with it where it is because I know it isnt running lean.

I think Im still a bit rich, but Ive got it dialed in much better now.

I have a thread open about jetting, I posted my results from the jetting tonight.

But as an overview, Im running a 132 main and a 42 pilot. I also have a 38 pilot I could go down to if I am still rich, but my powerband is much better than it was with the 55 in there. It pulls hard through the midrange and top end is still pretty good too.

Can you tell me if on a Keihin 36mm carb, do you think my jets are too small, too big? Im in Utah as well, so maybe youd know the best.

I know my carb is too big, but its all I have right now. And my bike runs pretty damn good at the moment (at least it FEELS like it runs good. I dont really have much baseline to compare to)

 

[yb200]

sounds like u got her figured out

 

[royalt67]

How is your throttle response now when you "blip" the throttle from idle? A PWK should have really good throttle response so if you aren't there you might want to try the smaller one.

I've decided recently that jetting a bigger carb is a bit counter-intuitive. It seems like with a bigger carb you would want a bigger jet to compensate for the extra air, but reality has proven the opposite. I just dropped from a 55 to a 48 in my 34PJ (almost idles now, runs MUCH better) and I'm going to drop it lower as soon as I pickup a 42.

BTW, I am also at 4000ft. It boggles me how much a difference the altitude makes sometimes. I lose about 20psi of compression between sea level and home.

 

[Luni]

My throttle response is pretty good actually. I blip the throttle it winds up quick, drops down quick, doesnt stumble and just resumes idling.

Im pretty sure I got my pilot worked out.

I guess ive read if I can get it to idle at 1.5 turns out thats close to "perfect" as Im 2 or 2.5 out, but it still runs better than it did with that 55 in there.

So, in Keihin world, is a 132 main jet big? Small? If I had a mikuni, whats the equivalent?

 

[royalt67]

Can't talk equivalencies, never messed with a mikuni. A 132 is def on the small side, stock on an aftermarket PWK28 is a 135, but it comes down to determining what the motor wants. I just dropped that 34PJ down to a 148 (from a 155) and it liked it (no top-end sputtering). I would think you'd want at least a 140.

Of course my bitchin' ported cylinder is hampered by a stock pipe right now....

 

[Luni]

Well, keep in mind Im at 4200 feet elevation, and I was told, youd think youd need to run more jet on a larger carb, but I was told jetting a larger carb can be counter intuitive and you sometimes need to run less jet than the carb came with or youll bog down.

I think in my case thats the problem, cause my engine cant use all the air that carb offers, so I can only burn so much fuel.