OS Max .25 carb adjust
03-19-2004, 07:21 PM
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OS Max .25 carb adjust
I need some help getting my carb adjusted. I know the screw on the right is a mix screw but what are the 2 on the left ? One is on the top of the carb the other is on the side. (Are they the high and low mix screws ? Idle screws ? )
Right now the motor runs rough at idle then it will stumble to a higher RPM when the carb is opened. After it cleans itself out it will run for awhile at 3/4 to full throttle then just stop like it ran out of gas! This is an older motor but it seems to have good compression and the cylinder looks good
Right now the motor runs rough at idle then it will stumble to a higher RPM when the carb is opened. After it cleans itself out it will run for awhile at 3/4 to full throttle then just stop like it ran out of gas! This is an older motor but it seems to have good compression and the cylinder looks good
03-19-2004, 11:39 PM
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RE: OS Max .25 carb adjust
Left and right... simple enough but!! from what perspective?
From behind the engine (a safe position) the high end adjustment is on your left; it can be tuned with your fingers. The Low end adjustment is on your right it must be adjusted with a long screw driver. The screw in the front is an idle bar lock - if you don't know what that is; DON'T touch it!
The two main adjustments are constantly changing in relation to each other as you tune the engine - if ypu have never tuned an engine before the best advice that I can offer is to find a local Engine guru and ask for help!!
The odds of you figureing it out alone - no bookie would ever take.
From behind the engine (a safe position) the high end adjustment is on your left; it can be tuned with your fingers. The Low end adjustment is on your right it must be adjusted with a long screw driver. The screw in the front is an idle bar lock - if you don't know what that is; DON'T touch it!
The two main adjustments are constantly changing in relation to each other as you tune the engine - if ypu have never tuned an engine before the best advice that I can offer is to find a local Engine guru and ask for help!!
The odds of you figureing it out alone - no bookie would ever take.
03-20-2004, 01:44 AM
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RE: OS Max .25 carb adjust
Does it have a tiny hole cast in the front of the carb body? Then it's an air bleed carb. The top screw is the idle stop. It sets the point to which the barrel will close at idle. Adjust until the carb barrel just closes completely when it hits the stop. That way you have an idle cut-off.
Now adjust the other (horizontal) screw until the air bleed hole is half open. The end of the screw extends half way across the hole. Now start it up and set the hi speed (big) needle valve to a good setting. Turn the needle in (leaner mixture) until the RPMs start to drop a little. Back the needle out 4-8 clicks until you have a nice smooth run, slightly rich. Never take off with the mixture set to maximum lean. It will lean out more in the air and overheat the engine.
Now set the idle. Let the engine idle. Set how much the carb barrel is open with the transmitter idle stick trim. Just a crack should do it. Then when you pull the trim all the way back, it should die. Back to the idle mixture:If it slows and dies, it is too rich. Open the air bleed screw (let in more air) about 1/8 turn and try again. If it speeds up and dies, it's too lean. Close the screw about 1/8th turn and etc. If it stumbles when you open the throttle, you may be able to lean the idle mixture a little more. (Just a tiny bit at a time!) Shouldn't take many tries to get it right. Just take it a little at a time. Old OSs idle really nice once set. Takes longer to tell than to do. Usually guys see the air bleed screw and turn it all over and then wonder why it doesn't run well. The idle mix is all off, that's all.
If it still acts up, don't hesitate to change the glo plug. Even plugs that light up may not be working well. And confirm that the fuel passages in the carb aren't gunked up.
That ought to get you going.
Now adjust the other (horizontal) screw until the air bleed hole is half open. The end of the screw extends half way across the hole. Now start it up and set the hi speed (big) needle valve to a good setting. Turn the needle in (leaner mixture) until the RPMs start to drop a little. Back the needle out 4-8 clicks until you have a nice smooth run, slightly rich. Never take off with the mixture set to maximum lean. It will lean out more in the air and overheat the engine.
Now set the idle. Let the engine idle. Set how much the carb barrel is open with the transmitter idle stick trim. Just a crack should do it. Then when you pull the trim all the way back, it should die. Back to the idle mixture:If it slows and dies, it is too rich. Open the air bleed screw (let in more air) about 1/8 turn and try again. If it speeds up and dies, it's too lean. Close the screw about 1/8th turn and etc. If it stumbles when you open the throttle, you may be able to lean the idle mixture a little more. (Just a tiny bit at a time!) Shouldn't take many tries to get it right. Just take it a little at a time. Old OSs idle really nice once set. Takes longer to tell than to do. Usually guys see the air bleed screw and turn it all over and then wonder why it doesn't run well. The idle mix is all off, that's all.
If it still acts up, don't hesitate to change the glo plug. Even plugs that light up may not be working well. And confirm that the fuel passages in the carb aren't gunked up.
That ought to get you going.
