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Engine tuning

Old 03-20-2017, 09:05 AM
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Talking Engine tuning

Hi all, Just wondering about tuning and if i am doing it correctly. I have a .21 novarossi 9 port with ceramic bearings in my mrx5 WC spec and i have idled it through around 6 tanks and drove it at the local car park. All is brand new. I am very pedantic about having it sounding right and making sure there are no lean fuel mixture sounds. When i punch the throttle, it operates perfectly and very punchy. However when i am at a speed and not wanting to slow down or speed up, i notice it sounds like it is leaning out and doesn't sound healthy at all.... Any suggestions as to what i can do to fix this??
I have tried making it richer on the high speed but it doesn't really help that and the idle screw a fraction. This worries me. I am wondering if because it is built for racing and i use it as a hobby that it either wants to go or stop instead of in between. Any advice for tuning would be great and would be appreciated.

Thanks
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Old 03-20-2017, 09:20 AM
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Originally Posted by Nitromad1020 View Post
Hi all, Just wondering about tuning and if i am doing it correctly. I have a .21 novarossi 9 port with ceramic bearings in my mrx5 WC spec and i have idled it through around 6 tanks and drove it at the local car park. All is brand new. I am very pedantic about having it sounding right and making sure there are no lean fuel mixture sounds. When i punch the throttle, it operates perfectly and very punchy. However when i am at a speed and not wanting to slow down or speed up, i notice it sounds like it is leaning out and doesn't sound healthy at all.... Any suggestions as to what i can do to fix this??
I have tried making it richer on the high speed but it doesn't really help that and the idle screw a fraction. This worries me. I am wondering if because it is built for racing and i use it as a hobby that it either wants to go or stop instead of in between. Any advice for tuning would be great and would be appreciated.

Thanks
Your description leads me to conclude that you are running at partial throttle opening - unfortunately the carbs are not very sophisticated and don't seem to like partial throttle settings (ran into the same problem while getting a new racer going last year myself and another experienced racer could drive the car and the motor sounded fine , but he'd drive it and the motor sounded horrible - we finally figured out that he was trying to part throttle the straight)
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Old 03-20-2017, 09:29 AM
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Cheers for replying.. What exactly is a part throttle ? It also doesn't like to idle for anymore than 10 sec and when idling for a bit and then punch the throttle it bogs down.. So lean it off and for some reason it gets to the point where it is leaned off to much and still happens. I think i may have to adjust the idle gap. When i i gas it and it stops it keeps a bit of rev and then drops down to low idle
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Old 03-21-2017, 06:53 AM
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Originally Posted by Nitromad1020 View Post
Cheers for replying.. What exactly is a part throttle ? It also doesn't like to idle for anymore than 10 sec and when idling for a bit and then punch the throttle it bogs down.. So lean it off and for some reason it gets to the point where it is leaned off to much and still happens. I think i may have to adjust the idle gap. When i i gas it and it stops it keeps a bit of rev and then drops down to low idle
Sounds to me that the top end is gine but the low speed needle is a little on the rich side. Always start with the top rich and work your way in to a usable tune over all. Then tune the low speed needle to clean up the off idle and low speed tune. Engines will tend to pick up ifle speed after a rev up if its a little rich on the bottom and to much ifle gap. This happens cause engine is burning off excess fuel in case from rich low speed setting and a big idle gap. You will notice that as you lean the bottom a little, the idle will increase and idle gap will have to be closed abit.
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Old 03-23-2017, 07:02 AM
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That does make sense. It is all factory set still except for the high speed needle and take off is sluggish, i tend to not like messing with the screws but will do what you suggested. Just to clarify, the low speed is the flat head screw that is just under or next to the high speed screw? Or is it the flat head screw that is on the end of the slide carb itself? Cheers for the help
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Old 03-23-2017, 07:53 AM
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Originally Posted by Nitromad1020 View Post
That does make sense. It is all factory set still except for the high speed needle and take off is sluggish, i tend to not like messing with the screws but will do what you suggested. Just to clarify, the low speed is the flat head screw that is just under or next to the high speed screw? Or is it the flat head screw that is on the end of the slide carb itself? Cheers for the help
The one on the end of the slide
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