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Old 06-04-2007, 10:48 PM   #1
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Default Pinch Test

How accurate is the pinch test?
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Old 06-05-2007, 02:40 PM   #2
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pretty good, it lets you know if you are too lean or too rich on the low speed needle.
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Old 06-05-2007, 09:14 PM   #3
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How does it work? What happens, or what's supposed to happen when you pinch the tube?
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Old 06-06-2007, 11:26 AM   #4
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Step 1. Start your engine and warm it up for about 30 seconds by revving the engine from idle to mid-throttle while holding the wheels off the ground.

Step 2. Allow the engine to idle for 10 seconds. If the low speed needle tuning is so far off that it won't idle, simply bump the idle position higher until the engine will reliably run at a higher idle.

Step 3. With the engine at idle, pinch and hold the fuel line near the carburetor, cutting off the fuel flow and carefully listen to the engine rpm.

If the low speed needle is set correctly, the engine should increase rpm only slightly and then die.

If the engine increases several hundred rpm before dying, then the low speed needle is too rich and needs to be turned in.

If the rpm doesn't increase at all and the engine simply dies, the low speed needle is set too lean and should be richened or turned out.

After doing this a few times you'll get the hang of it, and tuning the low speed needle will become easy. The only way to get that last 5% performance on the low speed tune is through careful track testing. By evaluating the engine as it accelerates from a dead stop or out of slow corners during actual race conditions is the only way to get those last few percent of power from your engine. Variables like the clutch setting, gearing, traction, atmospheric conditions and even the car's weight will have an effect on this last 5% of tuning performance, and the optimum setting can only be reached by careful on-track tuning.
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Old 06-07-2007, 10:00 AM   #5
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Quote:
Originally Posted by Kemorc View Post
Step 1. Start your engine and warm it up for about 30 seconds by revving the engine from idle to mid-throttle while holding the wheels off the ground.

Step 2. Allow the engine to idle for 10 seconds. If the low speed needle tuning is so far off that it won't idle, simply bump the idle position higher until the engine will reliably run at a higher idle.

Step 3. With the engine at idle, pinch and hold the fuel line near the carburetor, cutting off the fuel flow and carefully listen to the engine rpm.

If the low speed needle is set correctly, the engine should increase rpm only slightly and then die.

If the engine increases several hundred rpm before dying, then the low speed needle is too rich and needs to be turned in.

If the rpm doesn't increase at all and the engine simply dies, the low speed needle is set too lean and should be richened or turned out.

After doing this a few times you'll get the hang of it, and tuning the low speed needle will become easy. The only way to get that last 5% performance on the low speed tune is through careful track testing. By evaluating the engine as it accelerates from a dead stop or out of slow corners during actual race conditions is the only way to get those last few percent of power from your engine. Variables like the clutch setting, gearing, traction, atmospheric conditions and even the car's weight will have an effect on this last 5% of tuning performance, and the optimum setting can only be reached by careful on-track tuning.

useful infomation

thanks for sharing
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Old 06-08-2007, 12:28 AM   #6
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The load up time is more accurate and also helps on adjusting the idle better.

Warm up the engine,make a full throttle run to clear the engine and bring it to idle.Let it sit there and hear the revs.They should drop slightly at around 10sec.Any sooner and it's too rich, later means it's lean.You can adjust according to the track you race up to 15sec load up.Not more.It will heat up the engine especially on a tight track.
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Old 06-19-2007, 11:49 PM   #7
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Quote:
Originally Posted by vti-chris View Post
The load up time is more accurate and also helps on adjusting the idle better.

Warm up the engine,make a full throttle run to clear the engine and bring it to idle.Let it sit there and hear the revs.They should drop slightly at around 10sec.Any sooner and it's too rich, later means it's lean.You can adjust according to the track you race up to 15sec load up.Not more.It will heat up the engine especially on a tight track.
Right. What about the top needle, how do you know the setting if it gives
the peak power of the engine? Is it by looking at the plug? Or do you have
other means to find it out? What carb restrictor to use for a .12 engine,
standard 5.4mm or 6.0mm oversize?
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Old 06-20-2007, 12:08 AM   #8
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Start from rich main needle and start leaning it out while doing WOT runs.
When the engine begins to make good power and rpm the changes on the needle won't make too much difference in the engines power.STOP.
For a noob i would go 1/8th of a turn richer from the above point to be safe.

Listen to other engines at the track...you will be able to tell the difference between a lean motor and a fine tuned one.
After i'm done with my tuning i take some temps from the engine...if they look good then i'm done for that day-time.
If it's hot i'll open the main needle a bit.
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