CL450K with VM32 trouble

J

Jan84

New Member
Hello there,

bought the Mikuni VM32 carbs with the jetting for CB 450 K from DCC. Now I overhauled my engine, but it doesn't run well. When I turn off the choke, it idles very high to 4.000-5000 rpm. With choke on 2.000 rpm. Played a bit with the idle screw, but that didn't help. The spark is kind of black. Makes only throttle til 6.000 rpm than stuttering and doesn't turn higher. Looks like the jets are too big?
Here's the setup:
185 Main, 35 Pilot, 6DH7 Jet Needle (clip in the middle), 2.0 Air Jet, 159 P-5 Needle Jet, 2.5 Slide, Air Screw 1,5 turns

So what's wrong? Who can help?
 
Compression is a bit low, but you'll want to double-check timing with a strobe light. It sounds like you have more than one issue and it may not be carb-related.
 
you got something like a workaround for checking the timing? I got a stroble light, but never did it...i guess timing is okay, but you're right, better check twice...
 
The problem is that issues compression and timing can mask issues with fueling. It's better to rule out the compression and timing because they're a lot easier to check than messing about with carbs.

High idle is probably an air leak, and not related (at least directly) to the carbs.

Loss of power past a certain RPM is probably retarded timing.

Because the Mikuni VMs are slide carbs, issues with them usually manifest at certain throttle positions rather than specific RPM ranges.
 
Air leak? The intakes (mikuni universal + new gasket) and carbs are brandnew with new unifilters - i cannot image an air leak? How can i rule out the compression problem? - i mean the engine 45 years old with 23000miles on it, i think 10-10,5 bar on both cylinder are okay?
 
Jan84 said:
Air leak? The intakes (mikuni universal + new gasket) and carbs are brandnew with new unifilters - i cannot image an air leak? How can i rule out the compression problem? - i mean the engine 45 years old with 23000miles on it, i think 10-10,5 bar on both cylinder are okay?
Click to expand...

Air leaks rarely occur within the carbs themselves (unless you've removed some hardware?). More commonly, they occur at the manifolds, in between the carbs and the head.

10 bar is OK for compression if you checked it when cold, but 11.2 is the goal for a warm engine.

How did the ignition timing look? It may also be worth while to check the valve gaps (this probably won't matter, but it's always nice to rule out one more possibility).
 
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