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Discussion Starter #1
Okay so after I rebuilt the carb, checked the valve lash, rebuilt the carb again I can't figure it out.

The bike is harddddd to start, to keep it running I have to keep the choke out just a bit. Telling me its running lean. I've some propane and I'm going to check for leaks tomorrow.

Problem two is the bike is really slow to idle down. Just a small, and I mean small, blip on the throttle, the bike revs like its a race car. No rpm gauge so I don't know how fast the motor is spinning over. Once it revs up it takes a good few seconds to come back down to idle.

Problem three; while sitting at idle the bike will rev itself rather high, stay a moment, start to come down slowly bottom out and seem to want to stall, balance out and idle smooth for a few moments and then repeat the process. It's not rhythmic, rather spontaneous.

Last thing, occasionally it will "burp" through the air box. Not really a back fire, just a burp. After the burp happens the idle drops and the bike will almost stall.

That's it, just not sure what to do from here.
 

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Okay so after I rebuilt the carb, checked the valve lash, rebuilt the carb again I can't figure it out.

The bike is harddddd to start, to keep it running I have to keep the choke out just a bit. Telling me its running lean. I've some propane and I'm going to check for leaks tomorrow.

Problem two is the bike is really slow to idle down. Just a small, and I mean small, blip on the throttle, the bike revs like its a race car. No rpm gauge so I don't know how fast the motor is spinning over. Once it revs up it takes a good few seconds to come back down to idle.

Problem three; while sitting at idle the bike will rev itself rather high, stay a moment, start to come down slowly bottom out and seem to want to stall, balance out and idle smooth for a few moments and then repeat the process. It's not rhythmic, rather spontaneous.

Last thing, occasionally it will "burp" through the air box. Not really a back fire, just a burp. After the burp happens the idle drops and the bike will almost stall.

That's it, just not sure what to do from here.

I assume you've already checked it's not the throttle grip or cable that's holding the throttle plate open?
Sounds like a vacuum leak or lean pilot circuit.
Try turning the mixture screw out a half-turn more.
Starter fluid into the intake and see if it gets better or worse.
Starter fluid sprayed around the intake manifold will identify any leaks if the engine note changes.
Is the float height correct?
 

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Discussion Starter #3
I assume you've already checked it's not the throttle grip or cable that's holding the throttle plate open?
Sounds like a vacuum leak or lean pilot circuit.
Try turning the mixture screw out a half-turn more.
Starter fluid into the intake and see if it gets better or worse.
Starter fluid sprayed around the intake manifold will identify any leaks if the engine note changes.
Is the float height correct?
didn't get a chance to check for leaks this morning. i got to sleep in instead :).

first thing i looked for was a mixture screw, this particular model carbuerator does not have one. hell i even pulled some of the freeze plugs out of another junk one i have to see if maybe it was covered up..alas no. the only adjustment screw on this model (kehien) is an atomospheric adjustment screw(?) located below the float bowl, but not connected to the float bowl. adjusting this makes no differance in the idle on the bike.

as for the floats...again this model comes with a non adjustable float design. normaly you can move the tab over the needle valve to adust it. this is an all plastic design. i'm afraid that if i bend the plastic too far that over time it will creep back into the postition it's in now.

i'm thinking that it's an intake leak, at the intake gaskets. they use a rubber type gasket that pressed into the intake. but that's all i can think of. i see no vacuum ports on the carbuerator anywhere so the only vacuum is from the airbox to the carb to the intake to the combustion chambers

i've rebuilt and diagnosed holley's, edlebrocks, rochesters, mopar, FoMoCo..you name it. i've been messing with car and truck carbuerators most of my life....this little thing on the other hand...i have no freaking clue :)
 

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didn't get a chance to check for leaks this morning. i got to sleep in instead :).

first thing i looked for was a mixture screw, this particular model carbuerator does not have one. hell i even pulled some of the freeze plugs out of another junk one i have to see if maybe it was covered up..alas no. the only adjustment screw on this model (kehien) is an atomospheric adjustment screw(?) located below the float bowl, but not connected to the float bowl. adjusting this makes no differance in the idle on the bike.

as for the floats...again this model comes with a non adjustable float design. normaly you can move the tab over the needle valve to adust it. this is an all plastic design. i'm afraid that if i bend the plastic too far that over time it will creep back into the postition it's in now.

i'm thinking that it's an intake leak, at the intake gaskets. they use a rubber type gasket that pressed into the intake. but that's all i can think of. i see no vacuum ports on the carbuerator anywhere so the only vacuum is from the airbox to the carb to the intake to the combustion chambers

i've rebuilt and diagnosed holley's, edlebrocks, rochesters, mopar, FoMoCo..you name it. i've been messing with car and truck carbuerators most of my life....this little thing on the other hand...i have no freaking clue :)

Is this the carburetor you have?
Ronayers.com Microfiche Honda>Motorcycle>1982>CM250C>CARBURETOR 82
 

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Discussion Starter #5
that it is, it's no longer available here in the states. so i have to go to salvage yards and ebay to search for usable bodies.

i'm cheap and would rather fix it then anything else...but i do know that i can use the intake and carburetor from a newer model cmx250

i'd just rather keep this original
 

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that it is, it's no longer available here in the states. so i have to go to salvage yards and ebay to search for usable bodies.

i'm cheap and would rather fix it then anything else...but i do know that i can use the intake and carburetor from a newer model cmx250

i'd just rather keep this original

In that case the mixture screw is part #5. It has the tamper-proof cap on it that you'll need to pull off.
 

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Discussion Starter #7
that particular screw makes no diffrence in anything when adjusted...turn slightly, wait, wait, listen, wait...nothing adjust and repeat.

it's a bang my head to the wall kinda of thing :)

and why are you awake...is it not dark where you are right now?
 

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that particular screw makes no diffrence in anything when adjusted...turn slightly, wait, wait, listen, wait...nothing adjust and repeat.

it's a bang my head to the wall kinda of thing :)

and why are you awake...is it not dark where you are right now?

But you did remove it to clean out the pilot circuits when you "rebuilt" the carb twice?

Yep, 0500 here :)
I slept early yesterday, rolled into the sack at 1630 so I had to get up for a feed :)
 

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Discussion Starter #9
But you did remove it to clean out the pilot circuits when you "rebuilt" the carb twice?

Yep, 0500 here :)
I slept early yesterday, rolled into the sack at 1630 so I had to get up for a feed :)

i did, and then i did again...second time running some air through it for good measure ;)

drink coffee and good morning
 

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i did, and then i did again...second time running some air through it for good measure ;)

drink coffee and good morning


If adjusting it makes no difference then the pilot jet is probably far from correct - or blocked or damaged.

I don't drink coffee or tea but I'll have an orange juice on you, and good night ;-)
 

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Discussion Starter #11
i'm going to dig around and see if i can find my jewlers loop...i have one for work...checking for burrs on needles.

i'll pull it when i get home and see if the tip has been damaged.

and it's far from bed time...i've still 4 hours of work before i get to go home
 
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