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Old 07-13-2008, 07:46 PM   #1
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Default OS Speed 21 Low Speed Needle Problem

Had a strange tunign issue this weekend.

The low speed needle on my 21 Speed seems to have no effect.

I noticed that if I revved wide open, then backed off throttle then gave full throttle quickly after backing off the engine would choke. Very symptomatic of too lean low speed.

I richened low speed andnothing happened.

Turns out no matterhow far i screwed out the LSN the engine response was the same. Very snappy, no bogging like you would expect when richening the LSN so muh.

Anyone got any hintswhat could cuase the LSN to not have any impact on engine ?

I changed fuel lines, changed plug, check carby was seated. Checked engine backplate. Rinsed carby with fuel. Unscrewed all needles hit needles and carby with airgun and same issue.

Any ideas ?
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Old 07-13-2008, 07:49 PM   #2
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Sounds like the top end is a bit too lean. Usually that hesitation when you nail the gas is a lean top end. Richening the bottom can sometimes mask it but not always. Richen the top and try again.
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Old 07-13-2008, 08:47 PM   #3
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Also make sure your testing the engine on the ground and not in the air when you blip the throttle. That engine will spin-up very quickly with no load and make the mixture sound like its off if it does bog. The hot P3 plug makes the LSN needle seem like it doens't do much, but it does. I tune these by power, smoke from pipe and temp.
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