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  1. #1
    Tom Gottlieb's Avatar
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    91 FS tuning problem

    Bax
    My well used .91 FS II will not maintain idle. I have 3 other OS 4-strokes that run great and I am familiar with tuning. I have set the valve clearances, new plug, and based on reviewing your other advice, went to 13 X 8 from 14 X 6. Starts easily and set high speed to just rich of peak around 9000 and idle set to "stupid rich" and then leaned out. But I cannot maintain any idle under 3000 or so without engine cutting out after 30 seconds. I removed and squirted fuel through the carb and replaced. Engine has good compression and otherwise transition is good. I am suspicious of carb or needle but this is beyond my skill. Should I send in for repair? As always, any help appreciated.
    Tom


  2. #2
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    RE: 91 FS tuning problem

    The key is "well used". The first thing to start to go as an engine wears out is the idle. It's likely that the compression fit of the piston, ring, and liner is wearing out, or the valves are not sealing well. We can certainly look at the engine to see if that's the case, or if it's merely needing proper adjustment of the valves and carburetor. There's nothing wrong with your setting procedure.
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  3. #3
    Tom Gottlieb's Avatar
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    RE: 91 FS tuning problem

    Bax
    Thanks for your reply. I have decided to buy a new 91. I figure with the cost of shipping back and forth to Canada and assessment and repair, I am at least half way towards the price of a new engine. Meanwhile, is there any way to service, lubricate or replace the valves you might suggest I try at home? I like tinklering and don't like to give up on things. If not, thanks anyway.

    Also wondered if you would recommend the FS-91II Surpass 4-Stroke Engine or the FS-95V. Seems the 95 is more engine for less money and same size and weight. I also was wondwering if you could explain how the FS-91II Surpass works without a return fuel line to the tank.
    Thanks again
    Tom

  4. #4
    Tom Gottlieb's Avatar
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    RE: 91 FS tuning problem

    Bax
    I am hoping you are monitoring earlier threads like this. I decided not to give up on my 92 Surpass and took it apart for cleaning and inspection. Then I discovered a broken exhaust valve spring that would certainly account for the idling problems I reported to you. I ordered a new spring and was able to replace it. However, after I got it all back together I decided to start over and close the low speed idle screw and back it off 3 turns for a new rich starting position. Now my problem is that the low speed screw went in about 6 turns and didn't stop and now it won't come out when I turn it counter clockwise. It's like I ran out of threads before the screw stopped. ??? What did I do wrong? Can I fix this? Needless to say I was not able to start it. Pretty sure I got everything else back together OK. Lined up the dot on the cam to the push rods at top center, reset the valve clearances, etc. and I didn't have any parts left over after reassembly! Help!
    Tom

  5. #5
    Tom Gottlieb's Avatar
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    RE: 91 FS tuning problem

    ORIGINAL: Tom Gottlieb

    Bax
    I am hoping you are monitoring earlier threads like this. I decided not to give up on my 92 Surpass and took it apart for cleaning and inspection. Then I discovered a broken exhaust valve spring that would certainly account for the idling problems I reported to you. I ordered a new spring and was able to replace it. However, after I got it all back together I decided to start over and close the low speed idle screw and back it off 3 turns for a new rich starting position. Now my problem is that the low speed screw went in about 6 turns and didn't stop and now it won't come out when I turn it counter clockwise. It's like I ran out of threads before the screw stopped. ??? What did I do wrong? Can I fix this? Needless to say I was not able to start it. Pretty sure I got everything else back together OK. Lined up the dot on the cam to the push rods at top center, reset the valve clearances, etc. and I didn't have any parts left over after reassembly! Help!
    Tom
    One more thing.... when I flip the engine with a starter, there is fuel oozing out of the low speed needle cavity!!!
    Tom

  6. #6
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    RE: 91 FS tuning problem

    If you turned the idle adjustment in too far, you'll have to disassemble the carb to get it back in. It goes into the throttle barrel from the inside. With that carb, you do not turn the idle adjustment in until it stops...that's because it won't stop.

    You just start out with it set to "stupid rich", and then lean it from there. Start the engine at a medium throttle setting, open it to full and get the high end set. Then, you retard the throttle a bit at a time, and adjust the idle mixture as needed.
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  7. #7
    Tom Gottlieb's Avatar
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    RE: 91 FS tuning problem

    Bax
    Thanks for this info. I will give it a try next weekend.
    Tom

  8. #8
    Tom Gottlieb's Avatar
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    RE: 91 FS tuning problem

    Bill
    Just thought I would report that I ran a test of my .91 today and it is now running great! I was able to get a reliable idle to 2400 rpm and max 10,500 high end with 14 x 6 prop (more than I really need). Thanks for all the help. Great learning experience. Once I took the carb apart and pushed the low speed needle back to engage the threads again, it all worked perfectly!
    Best regards… Tom

  9. #9
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    RE: 91 FS tuning problem

    Glad we could help!
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com


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