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Pinch Test and tuning question

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Old 07-27-2012, 08:55 AM
  #1
biomanz
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Default Pinch Test and tuning question

Just began breaking in a new LST XXL with the 454 engine, and I read the engine should rev up slightly then die after 3-4 sec. Mine started very rich and would stop at 8-10 sec, so I leaned the LSN until it stops at 3-4 sec. But it seems like the rpm goes even higher and much louder than when it stopped at 8 sec. It pretty much screams but doesn't really engage the clutch yet (maybe a little as I was holding it down). It actually sounds ok and rises just a little when it stopped at 8-10 sec. I pinch the tube about 4 inches from the carb since the filter is in the way, but not sure if that'll affect it? I wasn't able to run the truck at all yet since the pull start's spring broke right after :/ The temp was around 180 F.

Also, how much does the HSN affect the LSN? Heard it leans/richens the low end as well, but is there a general rule like for every full turn of the HSN it'll be like a quarter turn to the LSN?

Thx!
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Old 07-27-2012, 09:05 AM
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Default RE: Pinch Test and tuning question

I think the pinch test as I understand it is to pinch just a short period of time and if the engine rews up it's OK if it dies it's too lean.
(I could be wrong )
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Old 07-27-2012, 09:48 AM
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biomanz
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Default RE: Pinch Test and tuning question

It's pinching until the engine stops. Just confusing that it would rev higher then stop after I leaned it.
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Old 07-27-2012, 10:28 AM
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Default RE: Pinch Test and tuning question


Quote:
ORIGINAL: biomanz

It's pinching until the engine stops. Just confusing that it would rev higher then stop after I leaned it.
Pinch test is a "get in the ballpark" test. If an engine is not fully broken in ornot up fully to temp, results can be dicey.

If the engine revs up more than about 500 RPM, idle gap is too large. If it takes more than 3 - 4 secs to die, LSN is too rich.
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Old 07-28-2012, 03:15 AM
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biomanz
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Default RE: Pinch Test and tuning question

I'll try lessening the idle in a few days when my pull start replacements arrive.
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