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Author Topic: carb sputter...at a loss here.  (Read 5879 times)

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Offline Sapper

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carb sputter...at a loss here.
« on: June 03, 2012, 03:24:17 PM »
Since we bought 03 KX125 2 years ago. I've been fighting a bad sputter on the bottom. If it's on the pipe it runs hard and doesn't miss a beat. It has a hanging idle sometimes and it's is not an air leak. I've narrowed this down to the cable itself going into the top of the carb. If I move it, the idle drops back down. This bike has been rebuilt at least 4 times with new seals everytime si I'm sure it's not an air leak. I even did the carb cleaner spray down multiple times with no change.

Last year I had it fixed by moving the clip to the top position. Now, We just put it back together with a new topend and it's worse than ever. I changed all jets every which way...up, down & every in between. 

The kicker is, when I pull the choke back up, it doesn't kill the motor or even bog it. The idle will get higher. But it runs just the same as it is off. I've been through this carb twice, cleaning blowing it out, etc and gonna do it again tonight. The choke doesn't stick up anymore. It's wornout but does seat completly.

Any ideas from anyone??
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline eprovenzano

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carb sputter...at a loss here.
« Reply #1 on: June 03, 2012, 05:25:53 PM »
My 1st thought is jetting.  What needle and clip position are you running?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Eric Provenzano
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Sold 1974 Honda Elsinore CR125

Offline Sapper

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carb sputter...at a loss here.
« Reply #2 on: June 03, 2012, 05:55:28 PM »
I need to look at needle but it's stock. Top position. If I go lower, it gets worse.

Right now for jetting, I have 35 pilot, 400 main.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline GlennC

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carb sputter...at a loss here.
« Reply #3 on: June 03, 2012, 06:35:33 PM »
Here are the FMF specs. May be a good place to stert depending on your altitude....

Jetting Results
Main Jet
410
Pilot Jet
37.5
Needle
STOCK
Needle Position
2ND
Power Jet
STOCK
Air Screw
1.5
Fuel Screw
N/A
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« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline eprovenzano

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carb sputter...at a loss here.
« Reply #4 on: June 03, 2012, 08:18:07 PM »
Have you tried to adjust the air screw? I know with my katoom, as the weather changes, I need to adjust the air screw to get it to idle properly, and remove any bogging. 
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Eric Provenzano
2019 KTM 300 XCW TPI
2000 KTM 300 EXC (Son's)
2001 KTM 380 EXC
Sold 1991 KDX 200... fun play bike
Sold 1999 KX250
Sold 1999 YZ125 (son's)
Sold 2001 Yamaha TTL 125 (son's 1st bike)
Sold but never forgotten 1974 Honda Elsinore CR250M
Sold 1974 Honda Elsinore CR125

Offline Sapper

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carb sputter...at a loss here.
« Reply #5 on: June 03, 2012, 09:59:12 PM »
Air screw changes very little and runs best at about 1-7/8 out.

Glenn, I started with that jetting when we first put on the FMF pipe. I had to lean it out a little. It was running a little rich and spooging a little. Once I got it cleaned up and fought the sputter and moved the clip up, it ran great and zero sputter. Like I said above, it's worse than ever and moving the clip and and down makes a little difference and it's all the way up. If I do get another needle, Which one, there's 8 optional needles from OEM. I need to check the manual for which one is stock then research which way is leaner.

Why can't they use a Holley?!!! It'd be a whole easier.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline GlennC

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carb sputter...at a loss here.
« Reply #6 on: June 03, 2012, 10:33:54 PM »
I hear ya, but a tired top end requires leaner jetting, when you put in a new piston and rings you probably need to richen it back up.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Sapper

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carb sputter...at a loss here.
« Reply #7 on: June 04, 2012, 12:39:22 PM »
If I drop the clip or raise the Pilot size, it gets worse. The main is fine at 400.  It's gotta be in that choke circuit or something. I wish I had another carb to swap out and try.
I'd like to do a Keihen swap but that's more $$$ than it's worth for a stock setup.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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If you want cheap & fast, it won't be good.
If you want cheap & good, it won't be fast.
If you want good & fast, it won't be CHEAP

Offline VintageBlueSmoke

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carb sputter...at a loss here.
« Reply #8 on: June 04, 2012, 02:50:12 PM »
I hate to say it but it seems like you are chasing ghosts. Sometimes all your changes add up to the same sum but a different answer.

I would personally start over with the FMF setting - and forget about what you know about your area and bike. Then make small changes until you get it dialed in.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline SachsGS

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carb sputter...at a loss here.
« Reply #9 on: June 04, 2012, 03:22:42 PM »
Check your float level and needle and seat assembly for wear.Makes sure your choke is bottoming properly and that the rubber seal at the base of the choke plunger is not worn or damaged.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Sapper

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carb sputter...at a loss here.
« Reply #10 on: June 04, 2012, 03:37:20 PM »
Some things I double checked last night with it still being on the bike. (Was working on another home project too). Choke bottoms out all the way because as I thread the plunger back down in, the knob/shaft comes up. Did another spray test, No air leaks. Choke still will not shut down engine.

I need to check float level but I don't have the right tool to do it with. That little measuring deal that threads in the bowl. Is there another way? I may try bending up the tab a little to see what happens.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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If you want cheap & fast, it won't be good.
If you want cheap & good, it won't be fast.
If you want good & fast, it won't be CHEAP

Offline SachsGS

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carb sputter...at a loss here.
« Reply #11 on: June 04, 2012, 03:42:35 PM »
Flip the carb upside down.The tab that supports the floats should be parallel to the float bowl base.Make sure that the spring loaded pin in the float needle is free and not stuck.

The fact that the position of the choke has no effect on the engine running would have me check that circuit very carefully.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Sapper

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carb sputter...at a loss here.
« Reply #12 on: June 04, 2012, 03:49:15 PM »
Yep, gonna pull it off tonight after I paint the bathroom  ><img src=" title="Angry" class="smiley">

But I found this. http://forums.mxtrax.co.uk/showthread.php?282219-kx-125-slightly-boggy

I have a manual too.   :-[   
Just didn't look at it that well. Being an 03 and having alot of time on it, I'm probably gonna need a new needle seat. This sucks cause I just put an order into Motosport about an hour ago for some parts.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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If you want cheap & good, it won't be fast.
If you want good & fast, it won't be CHEAP

Offline SachsGS

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carb sputter...at a loss here.
« Reply #13 on: June 04, 2012, 03:58:11 PM »
Sometimes if I'm chasing a phantom carb problem I'll lean the affected circuits right out and then slowly enrichen them step by step.This way you will often stumble across a seemingly unrelated problem that turns out to be the root cause.I've pinpointed defective carb bodies this way.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline Sapper

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carb sputter...at a loss here.
« Reply #14 on: June 05, 2012, 12:42:01 PM »
OK, here's what I figured out last night. The float level according to the manuals setting was 10mm too deep. So I adjusted it according to the book. It didn't even allow fuel in. I was kicking for a min or 2, pulled sediment plug and it was dry. Went back, double checked measurement.

So then, I noticed that when the carb is upside down, the weight of the floats will compress the little pin in the needleseat. Not sure if that's supposed to happen. Weak spring in there??

So I easily tilted carb to the side, just enough for pressure to relieve off of little pin. set that to 9.5mm. Hooked up fuel line with carb level and got some fuel to feed bowl (I kept sediment plug out to see if fuel came out).

My dilemma here is, if I have float level too lean, I stand a good chance of leaning it out and melting my new topend. Too rich I just get the bog again. At least it's well lubricated.

The only other option I have is to try and track down, buy....whatever... the actual gauge used to set them.
This is Killing me. I want a Holley, DAMMIT!.

Update:
I found out after extensive interenet research, the small pin on the needel seat cannot be depressed. You actually have to  hold carb at an angle to where the floats are slightly released from pin but tang is still touching. So this means I'm about 2mm off. So, I'll be back at tonite after we get get back from a practice on the 250.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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If you want cheap & fast, it won't be good.
If you want cheap & good, it won't be fast.
If you want good & fast, it won't be CHEAP
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