Help with cr125 carb

Ace Rossi · Posted: Wed Sep 19, 2012 11:15 am Post subject: Help with cr125 carb

Starts fine, Runs fine, but while idling it poors fuel out of the bottom of the float bowl at the brass fitting in this picture.
Why, and what can you tell me to correct the problem that JUST started?

Ray Lovestead · Posted: Wed Sep 19, 2012 11:40 am Post subject:

Are you running a pump around? (I assume not).

This can only mean that at idle you have too much fuel pumping into the bowl and not enough leaving the bowl (going into the engine). I would guess that your not getting enough fuel flow through your idle jet. Try pulling apart your carb and cleaning the jets.

BTW, cleaning the jets doesn't work with just some carb cleaner. You have to get in there with a tiny wire and brush back and forth through it. The gunk that gets in there takes some elbow grease.

Ray
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Ace Rossi · Posted: Wed Sep 19, 2012 11:48 am Post subject:

Ray you assume correctly! No pump around. When I first had it plumbed it didnt do this but than a fellow karter who frequents this board whom Ive never met other than on FB said to re-plumb my system as he described using NO T's and NO Y's and NO inline filter of any kind BUT to be sure to filter fuel before pouring into tank using a coffee filter or such!
I have one line coming from tank to IN on pump, one coming from pulse on engine to IN on pump, one coming OUT from pump to carb and one coming OUT on pump back to tank!
Thats it!
Could this be my problem because it only started spewing fuel after this plumbing change?

Benn Herr · Joined: 18 Jul 2001 Posts: 1580

Yes, the plumbing change caused your problem.

Unless your carb is equiped with a small inlet seat, a pump-around, a certain DelOrto fuel pump, or some other kind of bypass system, the fuel will just blow right out of there.

In no way will the stock Kehein needle and seat handle full pump pressure.

Put it back to the way you had it and go from there.
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Ace Rossi · Posted: Wed Sep 19, 2012 1:40 pm Post subject:

Thanks but does it matter if its a Mukuni carb?

Benn Herr · Joined: 18 Jul 2001 Posts: 1580

On some Mikuni carbs they may have a smaller inlet seat, I'll bet yours doesn't.
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Ace Rossi · Posted: Wed Sep 19, 2012 6:44 pm Post subject:

Okay I came home and started by installing a T in the line going TO the carb and a T in the line from the pump returning to the tank, then connected the two together. Dont blame me if its wrong. Heck Im at a guessing stage on this but the main thing is after starting and running, all fuel lines stay full and NO fuel is pissing out of the bottom bowl fitting!

Tom Barth · Posted: Sun Sep 23, 2012 4:04 pm Post subject:

With the plumbing you described: put a tee in line between pump and carb. Now run line from tee back to tank. Excess fuel will bypass back to tank.
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Ace Rossi · Posted: Sun Sep 23, 2012 4:16 pm Post subject:

Thats what I think I did except the pump had a line from it back to the tank and I just connected the two!

Noah Stark · Posted: Mon Sep 24, 2012 11:17 pm Post subject:

Keep the lines routed as I told you. They are right. Period. Your issue is in tank venting, not enough. When revving and driving, the carb is burning the fuel, and less is going back to the tank. When idling, most of the fuel is being returned, but without enough vent, it will push the inlet needle and overflow the bowl. Dont change the line routing, just increase the fuel tank vent opening or add another line. I guarantee your problem will go away.
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Tim Salvino · Joined: 20 Nov 2010 Posts: 258

Noah, how much venting is needed? What should be the inside ID of the vent hole on the tank?

I ran my lines the same way, and am having the same problem. I was pretty sure it was venting related...

Jim McMahon · Posted: Tue Sep 25, 2012 8:14 pm Post subject:

Pull the cap off the tank fuel while idling and see if the issue goes away. That will answer the venting question for you.
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Tom Barth · Posted: Wed Sep 26, 2012 4:18 pm Post subject:

Fuel does not return to tank at idle. The idle circuit is in control at closed throttle providing only enough fuel for idle. I've plumbed a few Keihins and using a tee is simple and effective. Or you can go with a Dellorto fuel pump which has an internal bypass circuit. I have customers who have purchased Dellorto pumps specifically for CR engines. But be sure to vent tank.
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Tim Salvino · Joined: 20 Nov 2010 Posts: 258

Tom, is this the fuel pump you are referring to?

http://sharkshifter.com/zc/index.php?main_page=product_info&cPath=20&products_id=1388

Steve Buckner · Joined: 22 Apr 2003 Posts: 839

Tim, thats all you need. I run one on my Mod Honda and have had no problems at all. I see a lot of guys now switching to this set up. Word is out.