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Old 01-12-2008, 02:31 PM   #1
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Default I need advise on pinch test/tunning...

Hey guys.


With all your help I got everything working well.. now Im down to the tuning part...

I have a m26 motor (same as the 427 losi motors). I have the LSN and HSN set to the factory settings with a adjustable OPS pipe on the motor.

The motor will idle fine. Motor temps are gettign into the 240-260 (too hot), There is lots of smoke coming out the pipe. Power is good.
Ot will stumble a bit after a extended idle.

Question:

When I pinch the fuel line the motor dies right away.. Does that mean its lean?

My thoughts were that if the motor was lean it would have a small opening for the fuel to get through there for run for a while before using up the fuel..

Please fill in the blanks.

When the motor dies right away it too ___________.

When the motor runs for 10 or more seconds its_____________.


I have read the statment below, but it does not say how to adjust the settings if.....

do the pinch test about 2-3 inches from the carb fuel intake , should take about 3 seconds for the engine to idle up if the low needle is set properly . adjust the idle as low as it will allow you to and still stay running after reving out the engine and it comes back down to idle . after you get the perfect tune richen up the lsn 2 hours and idle up about 1/4 turn to stop engine from flaming when race conditions are applied . when adjusting the high speed , start off very rich but runnable , lean out to desired temp and feel , watch for good smoking for at least 6 feet and pay attention to the engine , if it starts to lose power on the bottom , you either have the wrong clutch/pipe combo or if there is no smoke it is a lean bog (dangerous) stop running it on the track , bring it in and richen the low speed at least 6 hours and the high needle at least 3 hours and start over .REMEMBER WHEN TUNING : FUEL MAKES POWER , NOT AIR !!!!!!
happy tuning bro ,
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Old 01-12-2008, 02:53 PM   #2
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When the motor dies right away it is to lean.

When the motor runs for 10 or more seconds its to rich.
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Old 01-12-2008, 06:23 PM   #3
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Originally Posted by kmorast View Post
When the motor dies right away it is to lean.

When the motor runs for 10 or more seconds its to rich.

Does that mean you keep opening the LSN untill the motor will idle for 3-4 seconds.....

Wont that effect the HSN, im guessing that after you retune the LSN you need to go back and make an adjustment to the HSN.

What should the idle tempature be on a motor.
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Old 01-12-2008, 06:37 PM   #4
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Quote:
Originally Posted by Mpowerz View Post
Does that mean you keep opening the LSN untill the motor will idle for 3-4 seconds.....

Wont that effect the HSN, im guessing that after you retune the LSN you need to go back and make an adjustment to the HSN.

What should the idle tempature be on a motor.
The high speed needle changes the low speed needle. The high speed needle actually feeds the low speed needle. So you first tune the high speed needle and when that is how you want you then tune the low speed needle.

The high speed needle is the one pointing up in the air and where the fuel line connects to, the low speed needle is the one in the front of the carb where the throttle linkage connects to. I know that's basic info right there but sounds like you may have them backwards in your mind. If not, sorry and don't take offense.

Idle temp is unnecessary to know since you need to tune the high speed properly before tuning the low. If your high end is out of whack it makes no difference if your low end is correct because as soon as you change your high setting the low will change also even though you did not touch the needle.
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Old 01-12-2008, 07:13 PM   #5
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Originally Posted by Mpowerz View Post
Does that mean you keep opening the LSN untill the motor will idle for 3-4 seconds.....

Wont that effect the HSN, im guessing that after you retune the LSN you need to go back and make an adjustment to the HSN.

What should the idle tempature be on a motor.

I understand how the needle work , thats no problem.. Im use to tunning 2 stroke seadoo`s where the LSN is part of the total fuel system.

They work off both the hight and the low speed needles..

Now back to Nitro.....

So the HSN is more or less a tap that controls the total flow of the fuel... The LSN is more for adjustments in the low end..

What roll does the LSN play at 50% throttle due to the needle still being in the slevee. Looking at the CARB the LSN is all the way out at around 2^3 throttle.

So from my earlier post. Would richening the mixture of the LSN richen the whole fuel curve untill about 2^3 where the needle would be fully out of the slevee.
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Old 01-12-2008, 08:02 PM   #6
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Sounds like you have a good grasp of the whole engine tuning thing then. I think you will benefit much more by just going out and trying different things than from what you will read here.

I suppose your last question is probably true. That yes it will effect it until it's fully out of the sleeve. But it gets out so quickly it's really not noticeable other than take-off and idle speed.
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Old 01-12-2008, 08:09 PM   #7
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Originally Posted by jbrow1 View Post
Sounds like you have a good grasp of the whole engine tuning thing then. I think you will benefit much more by just going out and trying different things than from what you will read here.

I suppose your last question is probably true. That yes it will effect it until it's fully out of the sleeve. But it gets out so quickly it's really not noticeable other than take-off and idle speed.

So from my earlier question.. So wonce you get the motor setup on the HSN do you open the LSN untill you can pinch the fuel line for 3-4 seconds..

Please let me know.. Im going to be back at it in the morning..
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Old 01-12-2008, 08:34 PM   #8
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Originally Posted by Mpowerz View Post
So from my earlier question.. So wonce you get the motor setup on the HSN do you open the LSN untill you can pinch the fuel line for 3-4 seconds..

Please let me know.. Im going to be back at it in the morning..
You would then tune the low speed needle to get the takeoff and idle setting you desire. Say if the engine is all warmed up and then you let it sit in one spot for ten seconds or so and then nail it. You want a nice crisp out of the hole start and smooth transition into the full throttle range. No stumbling or gurgling at the initial throttle input, and again none as it goes from the low id to full throttle revs.

The pinch test is mainly used when somebody has an engine that won't tune. They do the pinch test as a quick reference to see if their low speed is way out of whack.

But you're always better off being a bit rich than a bit lean. Engines last much much longer when run a little fat.
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Old 01-12-2008, 09:30 PM   #9
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Originally Posted by jbrow1 View Post
You would then tune the low speed needle to get the takeoff and idle setting you desire. Say if the engine is all warmed up and then you let it sit in one spot for ten seconds or so and then nail it. You want a nice crisp out of the hole start and smooth transition into the full throttle range. No stumbling or gurgling at the initial throttle input, and again none as it goes from the low id to full throttle revs.

The pinch test is mainly used when somebody has an engine that won't tune. They do the pinch test as a quick reference to see if their low speed is way out of whack.

But you're always better off being a bit rich than a bit lean. Engines last much much longer when run a little fat.
jbrow1, Thank you for all your help...

If the motor is tuned right, the idle is good throttle response is good as well as top end, does the 3-4 second pinch still apply?

Also if the motor is running HOT 240-260 do you still open the HSN up more?

I think my motor was running good. I pinch it it dies...
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Old 01-12-2008, 10:19 PM   #10
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Depending on what you're doing 240-260 isn't so bad. If I were racing and it was getting to 260 I would run it there if it felt good. If you're not racing you would be better off to keep it below that, say 220-240. Also the amount of time you are running it will affect the temp. If it's that hot after five minutes then you have a problem. If it's that hot after 20 or 30 minutes than it's not so bad.

If it was 240-260 I wouldn't lean it out any more on the high end. Would think about richening it up, not sure if that's what you meant by opening it up. Richening is actually opening the needle to let more fuel thru.

If it idles nice and you think the tune is good but it dies right away when you pinch it.. sounds lean on the low end. That's when you need to pull the air filter off and verify the correct idle gap when the power is on and sitting at neutral. If the idle screw is set so the carb is open to far at neutral you may compesate that rich setting by having the low speed to lean.

If you're to lean on the low speed needle the engine will continue to get slowly hotter and hotter the longer you run it. Just a steady climb in temp that you can't stop even by richening the high speed needle.

And once you get your good tune all set and say you are going to run a main that's 30 minutes long.. it never hurts to give the high speed needle 2 hours worth of a turn more rich to compesate for the longer runtime.
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Old 01-12-2008, 10:34 PM   #11
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So by added more fuel on the HSN I will be able to control the motor temp.

What should the idle gap be set too?

Also will a sticking clutch kill the motor when you squeeze the fuel line? The motor will idle fine with out creaping forward.
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Old 01-13-2008, 09:16 AM   #12
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I always set my idle gap about the width of a fat paper clip, tune, then maybe slightly adjust it from there.

When your tune is good, the high speed will be the one you adjust to cool things down.

If the engine idles and doesn't stall when you hold the brakes then your clutch and bearings are fine. You'll know to check your clutch/bearings when the car stalls everytime you hit the brakes.

What engine and vehicle are you running?
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Old 01-13-2008, 12:57 PM   #13
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Quote:
Originally Posted by jbrow1 View Post
I always set my idle gap about the width of a fat paper clip, tune, then maybe slightly adjust it from there.

When your tune is good, the high speed will be the one you adjust to cool things down.

If the engine idles and doesn't stall when you hold the brakes then your clutch and bearings are fine. You'll know to check your clutch/bearings when the car stalls everytime you hit the brakes.

What engine and vehicle are you running?
Thanks for all the help guys... I was outside tuning today with all your advise... Motor runs great...

A last few questions...

The motor would idle up slightly around 4-5 seconds before wanting to cut out.. Should the LSN be leaned out a 1-2 hours?

I have a Raytek temp gun.. (High end) I and getting a Block temp of 160 and a head temp of 210.... What number should I be working with ?

Its about 40 deg outside today.

Thanks again..
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Old 01-13-2008, 01:02 PM   #14
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Take the temp at the Glow plug.
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Old 01-13-2008, 01:32 PM   #15
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Originally Posted by Woof View Post
Take the temp at the Glow plug.
Thank you...

Will the temps rise rear the end of the tank when it becomes empty?
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