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Newbie tuning help-nitro-.21 motor

Old 09-07-2014, 06:04 AM
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Default Newbie tuning help-nitro-.21 motor

Ok so yes I searched threads before asking this but I really got information overload, so I figured it best to ask my specific situation.

all scenarios I describe below are when engine is warmed up, this much I know to do.

I have a nitro buggy, .21 motor, first car will start cold within three tries, and first time every time when warm.

I have the idle set good, smooth low rpm's and will idle without dying no problem.

when researching the LSN I found most advice says to tune by pinch test, my LSN is tuned so that when I pinch the fuel line RPM's rise as it leans out and dies within 3-5 seconds. This I have read is what you want to happen. when I slightly open the throttle it is punchy and blows a nice even line of white smoke.

so this tells me so far my idle screw and LSN are set right, is this correct?

now here is where the problem starts, when I grab full throttle sometimes the buggy takes off nice and punchy, accelerates great and gets to full RPM, other times when I grab full throttle it barely moves and stutters barely moving two feet real slow and the motor goes "burrrrrrr" and it is real deep and throaty. If it get off the throttle and give it partial throttle and then ease into full throttle it will accelerate properly and reach full RPM's. Other times when I ease into full throttle it stutters makes that "buuuuuuurrrrrrr" noise then takes off and accelerates good.

everything I have read says this means my HSN is set too rich, but leaning it out seems to make the problem worse. In fact when I first got the car it had no full throttle it would bog down but not die, I richened (turned counter clockwise) the HSN 1/8 of a turn 3 times and that is how I got it to run better as I described above.

the other thing that seems weird to me that richening the mixture is the answer is my motor won't get above 200*F.

So please help me, do I want to keep to keep richening my HSN?

oh also if this is important I am running O.S. #8 glow plug and I live in a humid environment, southwest Florida to be specific.

thank you in advance for your help.

Last edited by BigNickC; 09-07-2014 at 06:26 AM.
Old 09-09-2014, 02:10 PM
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Really??? Not one reply? Thanks
Old 09-10-2014, 06:07 AM
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Hi Nick,
Welcome to the forum.
I read your post and was also awaiting a (any) reply. Your symptoms mirror my own and your text explains it better than I might.
There has been plenty of view of your post so interest is not the issue. I'll do a little light searching to see if the issue is so well discussed in old posts that readers don't bother to post a response.
In the mean time, if any reader knows where these 'old posts' are, please drop in a link.
Old 09-10-2014, 08:39 AM
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Forget about the pinch my opinion it is pointless. Always tune the engine so that it performs and only use temperature as a warning that you are wayyy too lean or there is a problem..
Try this-
Adjust both needles so that they are rich and adjust the throttle gap to 1mm.

Start engine and warm for a few minutes....then adjust the HSN by driving with wide open throttle and high may have to be gentle opening the throttle if the LSN is very rich...this does not matter, all you are doing is adjusting the maximum amount of fuel allowable........lean the HSN until it is too lean then richen it back a little!
With experience you can tell when it is becoming too lean and at the start this can seem daunting...basically you should be listening to the engine but using a temp. gauge can be a useful safety net for beginners, also if you lean the HSN in 1/4 turns the lean point will be more apparent because the engine will just cut out from fuel starvation...

Now the LSN (+throttle gap)...bring the car to a standstill for 20 seconds or so and then apply full throttle....keep leaning the LSN until you get a clean take off. Everytime you lean the LSN then the idle rpm will rise...adjust the idle gap to keep the idle rpm low enough not to engage the clutch and that is prizes for getting an engine to sit at low rpm for an hour.

The engine should now perform well when warm at high/low rpm and varying throttle positions...providing everything else is ok.

Last edited by Anthoop; 09-10-2014 at 08:42 AM.

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