OS speed refuse to tune,HELP!

Old 04-07-2011, 11:31 AM
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Default OS speed refuse to tune,HELP!

I have a OS Speed .21-B V-Spec2 who refuses to tune. I started experiencing a flat spot when pulling off or coming out of a slow corner. (Why?) The local track experts started "tuning" to solve the problem. Unfortunately one of them also tampered with the Mixture controll valve. No its impossable to get any decent tune.

Basically as a starting point, can anyone please tell me what the standard positions are for all 3 tuning screws- the Needle valve (top end), Metering needle (bottom end), and the Mixture contoll valve (the one I wasnt suppose to tamper with). Once I have the standard settings, I can start to tune again.

The Mixture controll valve was about 2.5 turns out when I got the engine.

HELP, advice on how to sort it will be appreciated.
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Old 04-07-2011, 11:40 AM
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Before you even start make sure the bellows on the carb does not have any holes in. I had this once and it made the engine a right night mare to tune. Next make sure that with the engine in your hand horizontal and then pus and pull the crankshaft up and down 90 degrees to the angle of the crankshaft and if you can feel it move then change the bearings. Check the compression of the piston and liner and see what it does with a very small amount of fuel in the main chamber. If you see foaming through the exhaust port then there is alot of wear and the piston and liner maybe too worn. The carb needles should be set as per factory settings:-

(top end) Needle Valve: 2.5 turns open from fully closed position
(bottom end) Metering Needle - Rotate until slotted head is extruded by 0.5mm into ball link body
(mid end) Mixture Control Valve - Rotate until slotted head is flush with ball link body

Make sure that the plug is good and then fire up the engine and tune from this point using hour adjustments to the main and low end needles.

Hope that helps
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Old 04-07-2011, 11:48 AM
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Originally Posted by Dave1GP View Post
I have a OS Speed .21-B V-Spec2 who refuses to tune. I started experiencing a flat spot when pulling off or coming out of a slow corner. (Why?) The local track experts started "tuning" to solve the problem. Unfortunately one of them also tampered with the Mixture controll valve. No its impossable to get any decent tune.

Basically as a starting point, can anyone please tell me what the standard positions are for all 3 tuning screws- the Needle valve (top end), Metering needle (bottom end), and the Mixture contoll valve (the one I wasnt suppose to tamper with). Once I have the standard settings, I can start to tune again.

The Mixture controll valve was about 2.5 turns out when I got the engine.

HELP, advice on how to sort it will be appreciated.
hi speed needle out 3 1/4 to 3 1/2 from closed
low speed needle flush
fuel mixture shoud be flush and then turned in about 3 hours,
thats the way mine is set running 20% byrons fuel

here is factory settings.....
NEEDLE SETTINGS: These are pre-set from the factory and require little or no adjustment
Needle Valve: 2.5 turns open from fully closed position
Metering Needle - Rotate until slotted head is extruded by 0.5mm into ball link body
Mixture Control Valve - Rotate until slotted head is flush with ball link body
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Old 04-07-2011, 12:07 PM
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Thanx guys, its a good starting point. I'll test, tune and report back here tomorrow.
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Old 04-07-2011, 12:38 PM
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Just to clarify you want the MRN(The one you weren't supposed to touch) to be flush with the carb body between 11 O' clock and 2 O' clock.

LSN should be about 3 1/2 turns from fully closed and HSN should be about 2 1/2. Idle gap should be .5-.7mm(roughly 1 1/4 turns in from just closed) That should get you close.
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Old 04-07-2011, 12:59 PM
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Originally Posted by JAMMINKRAZY View Post
Just to clarify you want the MRN(The one you weren't supposed to touch) to be flush with the carb body between 11 O' clock and 2 O' clock.

LSN should be about 3 1/2 turns from fully closed and HSN should be about 2 1/2. Idle gap should be .5-.7mm(roughly 1 1/4 turns in from just closed) That should get you close.
+1

to be more exact the MRN is 3 1/4 from closed. and anytime you bottom out the LSN or MRN you have to hold the slide wide open throttle to avoid the LSN from jamming into the MRN. if you jam them together you have to replace both needles.
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Old 04-07-2011, 01:02 PM
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Originally Posted by jpalessi View Post
+1

to be more exact the MRN is 3 1/4 from closed. and anytime you bottom out the LSN or MRN you have to hold the slide wide open throttle to avoid the LSN from jamming into the MRN. if you jam them together you have to replace both needles.
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Old 04-08-2011, 02:52 AM
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Originally Posted by JAMMINKRAZY View Post
Just to clarify you want the MRN(The one you weren't supposed to touch) to be flush with the carb body between 11 O' clock and 2 O' clock.

LSN should be about 3 1/2 turns from fully closed and HSN should be about 2 1/2. Idle gap should be .5-.7mm(roughly 1 1/4 turns in from just closed) That should get you close.
Just ran it at these settings, it was almost perfect, I had to lean it out the HSN only 2 minutes. No more flatspot. I also gave it a 20 second stationary idle, and it pulled off like a mad banchie. Its running at 250'F.

Thanx for all the advice guys.
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Old 04-08-2011, 04:46 AM
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thats a bit hot for a speed, around here they like to keep them around 210 so they last a bit longer. if it idles that long with a clean takeoff the low end may be too lean, it should only be a clean takeoff at about 5-7 seconds, anything longer than that should be gurgly and smokey. it will not lack in performance at all there.
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Old 04-08-2011, 12:51 PM
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Originally Posted by j_blaze14 View Post
thats a bit hot for a speed, around here they like to keep them around 210 so they last a bit longer. if it idles that long with a clean takeoff the low end may be too lean, it should only be a clean takeoff at about 5-7 seconds, anything longer than that should be gurgly and smokey. it will not lack in performance at all there.
Agreed, at the track today I richened the hsn 1-2 minutes, and it was still good. That small adjustment brought the temp down to 230.
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Old 04-08-2011, 12:54 PM
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Glad to hear it is running well.

230, 240, 250 whatever. As long as you've got good smoke and you're not lean 250 is not too hot. 230 to 240 is ideal on a slightly conservative tune.
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