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Hello! I removed the auto-choke from my Keihin KT carb. Is this what it normally looks like? The needle and cylinder are protruding from the barrel by 20 mm. When I plugged it into 12V, the cylinder extend so that the needle protrudes by about 24mm after 5 min.

I am debugging a problem where my 2006 LX150 will start and run for about 30 seconds, slowly losing RPMs, and then stall. It will stall immediately if I give it any throttle. It won't start again. After several hours, I've tried to start it again and it does the same thing. It is seemingly the identical issue to this thread: Help - LX 150 Carb Clean (Keihin CVK). Anyway, i could imagine such a problem being caused by a choke that is always engaged, meaning it always creates an over-rich fuel mixture. That would help it start, but would eventually make the mixture too rich to combust, perhaps flooding the engine, and making it hard to start until the mixture leaked out. Thus, it makes me wonder if my autochoke somehow always engaged. Haynes unhelpfully gives a spec of "10mm," whereas other carbs have an Initial and Final spec.

I understand that when the needle is retracted, it runs rich. When extended, it blocks an auxiliary fuel passage and results in a leaner mixture.
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it works, so I wouldn't be terribly concerned about it.

what else has been done to the carb?

was it running fine and suddenly this problem came on? need a little more info to go on.
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greasy125 wrote:
it works, so I wouldn't be terribly concerned about it.

what else has been done to the carb?

was it running fine and suddenly this problem came on? need a little more info to go on.
I bought it a month ago in non-running condition. It hadn't been run for four years. So this problem has persisted as long as I've had it. It seems like a fuel starvation issue. I assume some passage in the carb is blocked with crud. I was asking about how a functional auto-choke looks because that could be a possible (though unlikely) source of the problem.

I've confirmed fuel flow to the carb, and the ignition is sparking. I put starter fluid down the throat of the intake manifold, and it ran strongly for a second.
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Are you trying to run it on fuel that's been left in the tank for four years? or have you drained it off and replaced with fresh fuel.
Also have you cleaned the air intake/filter system with it being stood so long?.
⚠️ Last edited by BUGGSY on UTC; edited 1 time
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BUGGSY wrote:
Are you trying to run it on fuel that's been left in the tank for four years? or have you drained it off and replaced with fresh fuel.
It's fresh fuel.
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Air filter/Intake system clean?
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BUGGSY wrote:
Air filter/Intake system clean?
In fact, I have the air filter removed right now. I have seen it mentioned that the carb expects the air resistance of the filter to be present, and lack thereof can be a problem. I'm doubtful that could result in the engine dying and subsequent inability to start, but I wish I had re-installed the air filter before taking the carb out, just to rule that out.
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1- you absolutely need the airbox assembly in place to run*, it may idle but cracking the throttle will stall it.

2- have you cleaned the carb yet? and when I say cleaned, I don't mean just hosed it down with carb cleaner. I mean cleaned in terms of a full strip and dip, blow out every jet and orifice with compressed air and checked operation of the systems. if not, start there. a bike will idle with gummed up works and then stall out promptly when the throttle is touched or what little fuel that is getting to the proper channel gets used up.

3- forget the choke. it can't run rich enough to stall out in 30 seconds. I mean, it can but if it is, then you've got bigger problems.

clean the carb, check the vacuum lines, check the intake manifold for cracks and replace as necessary. attach the airbox and intake, knock in a new air filter.

*the CV carb operates on a tuned intake tract. there needs to be resistance present in order to create velocity and draw vacuum and raise the slide (this is an overly simplified explanation in the cause for brevity). you can, in a pinch, use your hand to partially cover the mouth of the carb and "fake it" for testing purposes.
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Okay, while the carbs out and you say you have fuel to the carb is it a good flow being delivered by the pump, have you checked or replaced the fuel filter and checked the vacuum valve is operating okay, this is a process of elimination.
I guess with you having the carb out you have cleaned it out.

Last one, Spark Plug, Have you replaced?, don't quote me but I think the gap is 0.06mm.... no point in wrong place and .1 out 0.7mm (as corrected by Greasy) not intentional misinformation given, and is it a good continuous spark and is it wet.
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BUGGSY wrote:
Last one, Spark Plug, Have you replaced?, don't quote me but I think the gap is 0.06mm is it a good continuous spark and is it wet.
I will quote you for giving out poor information. nothing I've ever heard of takes a .06mm gap.

correct gap is 0.7~0.8 (or .028~.031" if you prefer)
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Greasy's got a point Cracked air intake manifold, remember if cleaning air filter sponge or replacing to use air filter oil on the sponge but not to soak it, just a nice liberal spray.
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Sorry greasy, that was off the top of my head and rushing, got my point in the wrong place and 0.1mm out just thinking back to when I had LX, poor information unintentional, good job your on the ball Clap emoticon and a good job I wasn't aiming for the moon Id miss it by miles ROFL emoticon
greasy125 wrote:
I will quote you for giving out poor information. nothing I've ever heard of takes a .06mm gap.

correct gap is 0.7~0.8 (or .028~.031" if you prefer)
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I've been continuing to wrestle with "this problem" (hard start, won't idle, throttle needs to be more open than it should to keep running, exactly symptoms described in ET/GT/LX: Hard Starting, Rough Idle, or Stalling in my 2006 LX150 for the last six weeks. In my case, what cured it is removing the auto-choke and covering the hole with my finger. With this, it starts well and idles smoothly.

Obviously, that's not how it is supposed to be. It seems likely that there is some other thing wrong, and removing the choke compensates for it. I believe with the choke removed, that will make the mixture richer (since the choke's needle extends to block a fuel path). That might imply that the mixture is way too lean to start with. Am I thinking about that correctly?

I removed the needle from the choke assembly, and I can just plug the assembly back in and so far everything seems fine. That seems a bit too good to be true, and now I feel I'm really close to resolving this for real.
With choke removed - won't start, doesn't run.
With choke removed - won't start, doesn't run.
Covering choke assembly socket - it starts and runs well. If I remove my finger, it stalls immediately.
Covering choke assembly socket - it starts and runs well. If I remove my finger, it stalls immediately.
Choke assembly. There was black crud on the brass cylinder. I cleaned that later, and it ran better, but still needed throttle blips to avoid stalling every few seconds.
Choke assembly. There was black crud on the brass cylinder. I cleaned that later, and it ran better, but still needed throttle blips to avoid stalling every few seconds.
Needle removed from choke assembly. When the choke is installed without this, it starts and runs well. It's just like having my finger covering the hole.
Needle removed from choke assembly. When the choke is installed without this, it starts and runs well. It's just like having my finger covering the hole.
⚠️ Last edited by TobyFoster on UTC; edited 1 time
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Seems that either

1) you have a big intake leak and need a lot of extra fuel
Or
2) your low speed circuit in the carb is blocked

Have you disassembled the carb and given it a good clean? Sometimes you need to soak the carb body and jets in cleaning fluid for a few days if it's really gummed up.
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Grumpy, thanks. I did clean the carb, soaking it in a vat of Chem-Dip carb cleaner for the recommended 30 min, then blew out channels with compressed air. Nothing really seemed clogged up or visibly gunky, but hard to tell.

Which is the low speed circuit? I'm guessing it is the one flush in its socket, second brass insert from the left.
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The red arrow points to your slow speed circuit jet.
The blue arrow points to your idle mixture screw. The EPA doesn't like us to adjust these so they put a plug over it. You can drill out the plug and access the idle mixture screw. Don't just remove it. First gently screw it in (clockwise) until it touches the seat. Don't crank it tight against the seat be gentle. As you are doing this, count how many turns it goes before it touches the seat. Then when you reinstall it, you can set it back to exactly the same position. Remove the idle mixture screw and give that area a good clean with spray carb cleaner. You might get better performance by setting the screw back to where it was from the factory and the opening it (anti-clockwise) a bit. Small adjustments. Maybe 1/4 turn, then see how it idles, repeat until it idles well. Don't go more that a turn or so or you'll be idling too rich.
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Grumpy, thanks! The process your are describing for adjusting the idle mixture screw sounds the same as the process for adjusting the "minimum flow adjustment screw" (per photo from workshop manual) Are those two separate adjustments?

I'm quite leery of drilling out that plug - as I thought it was there to block a fuel passage rather than block access. Additionally, adjusting it is a huge PITA since you need to remove the carb each time you make an adjustment. It doesn't seem like Keihin would make their carb in such a way that was so hard to adjust. So I'm not sure I'm understanding your suggestion correctly!
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TobyFoster wrote:
Grumpy, thanks! The process your are describing for adjusting the idle mixture screw sounds the same as the process for adjusting the "minimum flow adjustment screw" (per photo from workshop manual) Are those two separate adjustments?

I'm quite leery of drilling out that plug - as I thought it was there to block a fuel passage rather than block access. Additionally, adjusting it is a huge PITA since you need to remove the carb each time you make an adjustment. It doesn't seem like Keihin would make their carb in such a way that was so hard to adjust. So I'm not sure I'm understanding your suggestion correctly!
Yes, don't drill out that plug! Sorry to miss lead you. All the Keihin carbs I've worked on had this plug covering the idle mixture. But on your carb the idle mixture comes in from the side.
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TobyFoster wrote:
Grumpy, thanks! The process your are describing for adjusting the idle mixture screw sounds the same as the process for adjusting the "minimum flow adjustment screw" (per photo from workshop manual) Are those two separate adjustments?

I'm quite leery of drilling out that plug - as I thought it was there to block a fuel passage rather than block access. Additionally, adjusting it is a huge PITA since you need to remove the carb each time you make an adjustment. It doesn't seem like Keihin would make their carb in such a way that was so hard to adjust. So I'm not sure I'm understanding your suggestion correctly!
there is no separate adjustment, they are one in the same. on this particular carb it is adjusted via that screw in the photo. please don't drill out anything on the carb, there is no need to.

speaking of the idle/air fuel/minimum adjustment screw, when you cleaned the carb did you remove that and the tiny washer/o-ring to ensure that the passageway was clear?

with that removed and the idle jet out you can blow brake/carb clean and compressed air thru to verify it is clean and clear. while it's apart I'd up the idle to a #38 if you haven't already.

the choke plunger looks awful, but it should clean up fine. check that the bore of the choke pull off assembly is not gummed up or scored preventing the movement of the plunger. clean it with a q-tip if need be.

did you have the choke pull off off of the carb or just the choke itself?

everything here points to dirty carb/jets/passageway, something reassembled incorrectly or missing, or a massive air leak.
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