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LSM fighting with HSM

Old 01-29-2007, 09:12 PM
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mwilkie
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Default LSM fighting with HSM

Currently, if I tune my LSM (low speed mixture) correctly, I lose my ability to richen my HSM adjustment. In other words, with my LSM set, I can screw out the HSM with zero effect. When my LSM is set correctly, whatever I do to the LSM affects HSM as well...that is, to a point. Once my LSM is rich enough, then I have control over my HSM again. But at that point, my LSM is way too rich.

Anybody else hit this? What can I do to continue to have HSM adjustment (I need it richer) when my LSM is set correctly?

By the way, I've sealed the engine and it's currently airtight.

Thanks in advance,

Mark
Old 01-29-2007, 10:34 PM
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nayslayer
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Default RE: LSM fighting with HSM

by any means am i an expert with tuning engines, but from what i read and try to do is: Set both back to factory, make 1 hour adjustments with hsn till no perfomance gain, then back it off about an hour, then do the same with lsn. Never adjust lsn first
Old 01-30-2007, 10:02 AM
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jombo
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Default RE: LSM fighting with HSM


ORIGINAL: mwilkie

Currently, if I tune my LSM (low speed mixture) correctly, I lose my ability to richen my HSM adjustment. In other words, with my LSM set, I can screw out the HSM with zero effect. When my LSM is set correctly, whatever I do to the LSM affects HSM as well...that is, to a point. Once my LSM is rich enough, then I have control over my HSM again. But at that point, my LSM is way too rich.

Anybody else hit this? What can I do to continue to have HSM adjustment (I need it richer) when my LSM is set correctly?

By the way, I've sealed the engine and it's currently airtight.

Thanks in advance,

Mark
yes you are correct, if the lsn (low speed needle) is too lean it will affect the hsn(high speed needle). you need to set the lsn this way, start the car pinch the fuel line it should stall after 5 to 6 seconds, and its done. then set your hsn by putting it up on blocks and open her up, if it stalls its either 2 things its either too rich or too lean on the hsn. if it stalls as soon as you give it throttle then its too rich, if it stalls when its wide open and it hits peak rpms its to lean. i would start there and fine tune if needed. good luck
Old 01-30-2007, 02:05 PM
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mwilkie
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Default RE: LSM fighting with HSM

Thanks for your responses.

More specifically, after tuning HSM to optimal, I move to adjusting LSM. After adjusting LSM to optimal, not only is my HSM too lean, but I've lost my ability to richen HSM. Any idea what could be causing this problem?

Thanks,

Mark
Old 01-31-2007, 11:24 PM
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mwilkie
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Default RE: LSM fighting with HSM

Not understanding exactly how the Cen rotary carb worked on my NT-16, I took a closer look at mine. What I learned is that as you rotate to open the throttle, it acts as a screw and pulls out the LSM needle from the main spray bar. That is to say, when the throttle is at the idle position, the LSM needle is "jammed" way into the main spray bar, essentially "clogging" it according to how much you adjust using the LSM screw. Then, as the throttle is opened up, the LSM needle is pulled out of the main spray bar more and more, although interesting enough, never all the way out.

So, it seems to me that depending on how far the LSM needle is pushed into the main spray bar, opening the throttle has the potential of not pulling out the LSM needle enough, ("unclog" the main spray bar) which would render it impossible to richen the HSM to the proper mixture. Said another way, based on this design, the farther you screw in your LSM needle, the less fuel is available to the whole system, even at WOT. This means that after some adjustment of LSM, you've lost the ability to get enough fuel to the system for a good HSM setting.

Anybody out there run into similar situations? I'm perplexed, and I'm sure I must be missing something pretty obvious. Or, at least I hope I am.

Thanks!

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