OS FS 92II P carb tuning
07-22-2013, 08:12 PM
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OS FS 92II P carb tuning
have a used OS FS 91II P and I am having problems tuning. Seems to run strong and finally getting near tuned and does not seem to need glow driver to run inverted. However, although seeming strong it will not take wide open on carb barrel. At about 60% of the max opening it drops rpm and sounds bad? The mix needle that would be idle seems to chase the barrel, ie, it cannot be backed out all the way as though it must be loaded in the carb body while the barrel is out??
Anyone have experience with these motors??
Thank you
Charles Rye
Memphis TN
Anyone have experience with these motors??
Thank you
Charles Rye
Memphis TN
07-23-2013, 10:42 PM
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RE: OS FS 92II P carb tuning
Charles, is your engine the pumped engine? If so, the tuning is different than the standard. Let me know and I'll have a go at helping.
Don
Don
07-25-2013, 09:03 AM
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RE: OS FS 92II P carb tuning
Don,
Yes this engine has the pump on it. I actually ground the end of the brads off and dissembled the pump for check out reassembled it and it works. I don't really understand the pressure regulator. Internally it looks more like it blocks min pressure instead of capping max pressure?
Any input would be appreciated.
Finally realized sound engine makes reminds me of valve float on full scale gas engines. Will check prop recommendations and rpm on next run.
Charles
Yes this engine has the pump on it. I actually ground the end of the brads off and dissembled the pump for check out reassembled it and it works. I don't really understand the pressure regulator. Internally it looks more like it blocks min pressure instead of capping max pressure?
Any input would be appreciated.
Finally realized sound engine makes reminds me of valve float on full scale gas engines. Will check prop recommendations and rpm on next run.
Charles
07-25-2013, 03:41 PM
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RE: OS FS 92II P carb tuning
Those pumps are not very complex, unlike the two earlier versions. Those were mechanical driven gear pumps.
The pumper engines tune different than the regular carbs. At full throttle, lean out the top end until the RPM just drop. Just as you hit the peak RPM is where you want the needle set. Now you can adjust the idle on the carb. Yes, some of the carbs have the idle mix screwing in from the inside vs outside. I don't have the manual for that engine but it should be available on Global Hobbies web sit. It tells you to set the screw slot at some measurement from the outer edge of the throttle arm. If you try screwing it in to the stop, you are screwed as far as trying to initially set it, and may disengage the threads.
The regulator you have has some issues with the cap warping. That was a replacement part. It might still be available.
The good news is that once you get them tuned, they are pretty much bullet proof, very seldom requiring any adjustment to the carb. Bax on the O.S direct support made the comet not to long ago that the diaphragms would tend to stiffen up if the engine hasn't been run for a few months but after running a half tank or so through they would regain their flexibility. This maybe some of what your are running into. It might also be a good idea to check the valve lash. 0.002" go and 0.004" no go.
Don
The pumper engines tune different than the regular carbs. At full throttle, lean out the top end until the RPM just drop. Just as you hit the peak RPM is where you want the needle set. Now you can adjust the idle on the carb. Yes, some of the carbs have the idle mix screwing in from the inside vs outside. I don't have the manual for that engine but it should be available on Global Hobbies web sit. It tells you to set the screw slot at some measurement from the outer edge of the throttle arm. If you try screwing it in to the stop, you are screwed as far as trying to initially set it, and may disengage the threads.
The regulator you have has some issues with the cap warping. That was a replacement part. It might still be available.
The good news is that once you get them tuned, they are pretty much bullet proof, very seldom requiring any adjustment to the carb. Bax on the O.S direct support made the comet not to long ago that the diaphragms would tend to stiffen up if the engine hasn't been run for a few months but after running a half tank or so through they would regain their flexibility. This maybe some of what your are running into. It might also be a good idea to check the valve lash. 0.002" go and 0.004" no go.
Don
07-25-2013, 06:59 PM
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RE: OS FS 92II P carb tuning
Don,
Thanks for the info. When I noticed the idle screw was chasing the throttle barrel setting when I would attempt to screw all then way in and then back out x turns like other carbs is when I realized I don't know this carb at all. I will try the open throttle mix setting and follow up with idle. If the idle needle ever got off the threads it is back on now.
I only checked to make sure there was valve clearance, a little free rocker movement, on the heel of the cam. I will get feeler gauges and check dimension before next tuning session.
Will post progress
Charles
Thanks for the info. When I noticed the idle screw was chasing the throttle barrel setting when I would attempt to screw all then way in and then back out x turns like other carbs is when I realized I don't know this carb at all. I will try the open throttle mix setting and follow up with idle. If the idle needle ever got off the threads it is back on now.
I only checked to make sure there was valve clearance, a little free rocker movement, on the heel of the cam. I will get feeler gauges and check dimension before next tuning session.
Will post progress
Charles
