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86 CMX450
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Discussion Starter · #1 ·
I’ve got a problem on my 86 450, I’ve put new pipes with baffles, foam air filters, and larger jets. When I’m riding in 5th the engine begins to die. If I shift down it just sputters and struggles it will continue to do this in all gears after, when I try to restart it in neutral it revs like it’s got a mind of its own, and when I give it throttle it shuts down.
This started my last few rides I’ve had the bike about 2 years and it’s got 47000 km on it 2000 of which are mine. What might be causing this? I’ve got a licence exam in a month or so and need my bike!
 

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85,86,87 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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What did you recently work on on the bike. Out of curiosity anything to do with the carburetor other than what you discussed, or the tank?
It almost sounds like too much vacuum in the fuel tank to me. Replace the gas cap?
 

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86 CMX450
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Discussion Starter · #4 ·
What did you recently work on on the bike. Out of curiosity anything to do with the carburetor other than what you discussed, or the tank?
It almost sounds like too much vacuum in the fuel tank to me. Replace the gas cap?
I checked the valve clearance, Pilot jets, main jets, and had it in a ultra sonic cleaner. I had a mechanic at the shop set the fuel air mixture screw for me.
edit: I cleaned the tank after the second time it did this, there was some residue inside the tank.
 

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Mixture too rich.
Definitely sounds like a carb issue, or maybe air filter? Something to do with fuel delivery-
My bet is on the air/fuel mixture being too rich.
 

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1987 CMX250C AC
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if it's been a few hundred miles since adding larger jets one may have fallen out..
If you just added larger jets go back to smaller ones.
stuck float could be a problem
 

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1987 CMX250C AC
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lean mixture by turning screw in
Adjusting pilot screw on each carb is how they are balanced while engine running, of course the butterfly valves position have to be matched first.
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I wouldn't change the settings at first. double check the enricher/choke valves are closing on each carb..
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It’s at 2 1/4 turns out, to lean the mix do I turn out or in?
I did not mean "that" screw. I meant either your jets are too large or air flow is restricted. If you remember what you did just before you had the problem, people here can give you a better advice, better than I can.

What does your exhaust smell like? Does it smell of unburnt fuel? What is the colour of your exhaust?
 

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85,86,87 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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I’ve got a problem on my 86 450, I’ve put new pipes with baffles, foam air filters, and larger jets. When I’m riding in 5th the engine begins to die. If I shift down it just sputters and struggles it will continue to do this in all gears after, when I try to restart it in neutral it revs like it’s got a mind of its own, and when I give it throttle it shuts down.
This started my last few rides I’ve had the bike about 2 years and it’s got 47000 km on it 2000 of which are mine. What might be causing this? I’ve got a licence exam in a month or so and need my bike!
If you want a parts bike, & are willing to go to Columbia S. Carolina, FB marketplace has a running titled 450 Rebel for $900. Just a thought. I'm sure that it won't last long at that price.
 

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85,86,87 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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There's also a 450 parts Rebel in Monroe, N Carolina on FB for $150. He said he'd take $100.
 

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If your engine revs up as you say like it has a mind of its own is an indicator of a lean mixture. That type of behavior would not be caused by jets wrongly adjusted, most likely an unwanted vacuum leak at the carb or manifold. When it is running spray some water around the intake system if the engine sputters would indicate a vacuum leak.
 

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85,86,87 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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Good thought & Good test! But personally I prefer to use starter fluid, the opposite occurs. The engine speeds up.👍
 

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Yes, I have used ether and propane as well, but I don't like to offer volatile products unless you are aware if their inherent risks. With water it evaporates immediately with no additional risks and it is readily available everywhere.
 
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