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91 KX 250 won't ide...


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I have a 1991 KX 250 that will not idle in neutral or in gear. The idle screw (now bottomed out) does nothing other than slow the rpm decent to stall when turned inward. The farther you turn it in, the longer it takes to fully stall, but it will not hold idle.

Carb settings are all completely stock as are component part numbers and values. Needle clip is in middle position and air screw is 1.5 turns out. Carb is clean (really), jets are clear and no buildup.

I had to replace the throttle cable this past weekend and discovered that the needle clip was in the top setting (needle sitting low) and that the air screw was 2 turns out so I set them back to stock (middle pos and 1.5 turns out) thinking maybe it was too lean to idle with the needle low.

Unfortunately this seems to have taken me in the wrong direction. It didn't idle well before, but it took longer to stall before than it does now.

I'm not sure what compression is, but the bike runs well otherwise and starts easy enough. It just won't hold idle. The bike is otherwise completely stock except for a turbine core SA/silencer and UNI air filter.

I would appreciate any advice (other than get a new bike 🙂). Thanks in advance!

-Wes

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I'll pull the reeds when I get a chance and see what they look like. I'll also check on the price of a smaller pilot jet.

Isn't there a way to use the air screw to determine if the pilot jet is large or small? turn it in or out until it'll idle and then if it is too far in it is one condition, if it's too far out it's the other (rich/lean)?

not sure, just wondering if anyone knows. My budget is very limited so I can't afford to throw parts at this unless I know for sure it is the culprit. Thanks again 🙂 jets usually are cheap, but sometimes no :banana:

-Wes

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I turned the idle screw all the way in, backed the air screw out about 3 turns and it finally idled. Not perfectly, I would still have to blip it here and there, but it did idle.

Backing the air screw out more didn't seem to improve things though.

I think I am going to try a smaller pilot jet to see what the effect is. Hopefully it will allow me to set the idle screw and air screw in more normal positions and be able to maintain an idle.

how much smaller should I go?

it was just a good feeling to have it idle. wohoo!

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I am a little over 1100ft in elevation and temps are 70's and 80's. I will double check tonight on the 58 number for the pilot. I really can't afford to buy too many of these at $12 a piece. I won't be going too far with a 50 or 52 will I? Thanks again for the advice.

Also, there is no local kawi dealer and I'm not exactly sure how to go about getting one from a non kawi dealer (other than online). I know my carb is a pwk model. I would have to check the service manual for sure for the specific bore and any other details, but would any dealer carry jets for that carb? or are they brand specific?

Thanks again guys.

-Wes

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I am a little over 1100ft in elevation and temps are 70's and 80's. I will double check tonight on the 58 number for the pilot. I really can't afford to buy too many of these at $12 a piece. I won't be going too far with a 50 or 52 will I? Thanks again for the advice.

Also, there is no local kawi dealer and I'm not exactly sure how to go about getting one from a non kawi dealer (other than online). I know my carb is a pwk model. I would have to check the service manual for sure for the specific bore and any other details, but would any dealer carry jets for that carb? or are they brand specific?

Thanks again guys.

-Wes

Like Ed said, go to your local bike shop. They should have one for like $5 or free if you put on a sob story. A dealership will most likely charge you MSRP. I'd mail you one but the only 50 I have is in my bike. lol

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I checked the manual last night and it is a 58. I confirmed it was the same as the book spec when I had it apart, but couldn't remember for sure.

I know with mains you usually go in increments of 5 or so (160 to 155 to 150) and that seems to work. I would think on a pilot you wouldn't want to jump so far. That is why I was questioning the 52 and 50 from the 58.

I think I'm going to look for a 52 just because I am out of the range of adjustment for the idle screw as is and it seems like I need to move a bit. I like to run things on the rich side to be safe and as a result, I usually just stick with stock settings (they have always worked well in the past).

I'm honestly a bit surprised it isn't possible to make this 58 work with the adjustability that is there in the idle screw and air screw. I have never had to change jets away from stock to make a machine run properly. Granted I know that there is always room for improvement and that stock is sometimes far from ideal, but it has always worked with decent running characteristics... except in this case.

Hopefully this will get me back into the range where my idle and air screws are where they should be.

Thanks again guys for the input!

-Wes

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I installed the 52 on saturday thinking it would put me back in the ranges of the air and idle screws. I did get the bike to idle, but the idle screw is still bottomed out and the air screw is out almost 3 turns.

I checked the float height and it matches spec. I also pulled the choke assembly to make sure it was fully seating and it is...

am I missing something?

Not sure what else to check.

It seems that I am going in the right direction, but I don't think I want to go much leaner on the pilot. I'm guessing I figured right that is was a rich condition as going leaner allowed it to idle, but it still doesn't seem quite right.

Not sure what else to check. reeds? I still haven't checked them, maybe that's the next logical step? any other input would be great.

Thanks again.

-Wes

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