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  1. #1

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    ASP FS61 midrange problems

    Hello, it's me trying to get my "problem engine" to run again I apologize for the long post.

    Background:
    A few years ago I bought an ASP FS61 for my Flyin' King. No matter how I tuned it, the midrange was way too rich, even with the top and bottom leaned out as much as possible. I got a new carb from the shop, and the problems were still there. After a couple of gallons I finally gave up and decided not to use the engine. Earlier this week I decided to try again. Top and bottom are great, but if I leave it at half throttle, rpms gradually decrease, and it smokes and vibrates a lot.

    What I have tried so far:
    - A new carb (same type)
    - Several glow plugs (all OS F)
    - Different types of fuel (Byron 4T 15%, Rapicon 15% HLS, JeRo 5%)
    - Different APC props (12x6, 12x8, 13x6, 13x4W)
    - Checking the valves
    - Moving the camshaft one tooth either way
    - Using RTV on the intake to prevent leaks
    - Fuel tubing on the needle valve
    - I even tried the carb from my FS30. The mounting pattern is the same. With this carb the midrange is clean, but the engine won't idle, and the top end RPM is lower (for obvious reasons).
    - If I turn the needle valve appr. half a turn in, the midrange is clean, but I can't go past 2/3 throttle without running too lean. This leads me to thinking that the carb is the problem.

    Next on my list is:
    What if I bought a 40N (OS FS-52S) or a 40NA (OS FS-56a) carb? Correct me if I'm wrong, but I have understood that they are interchangeable. I have only had good experience with OS carbs myself, and my OS FS-52S (sold) was smooth regardless of rpm.

    What do you think? Should I buy an OS carb and give it a go? It is less than half the price of a new ASP engine.

  2. #2
    Moderator w8ye's Avatar
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    RE: ASP FS61 midrange problems

    I don't know about the OS 56 carb but the OS 52 carb is a direct bolt on swap with the ASP/Magnum FS52 and ASP/Magnum FS61 carbs. These carbs will also directly bolt onto the OS 48 four stroke.

    I have a OS 56 venturi on one of my OS 52 engines so it is highly likely this carb will interchange also?

    At one time I had a Magnum and a ASP FS61. They were identical except for the name on the side. Magnum only sold the 61 for about 6 mos back in 2001.
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  3. #3

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    RE: ASP FS61 midrange problems

    Is it possible that something other than the carb is causing the rich midrange?

  4. #4
    Moderator w8ye's Avatar
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    RE: ASP FS61 midrange problems

    I would first try re-adjust the carb.

    Open up the low speed screw about one full turn

    Now run the engine with the throttle full speed and adjust the high speed needle to peak RPM

    Then lean the low speed needle just to the point where the engine doesn't want to accelerate from idle. At this time open the idle needle up just enough to where you can accelerate to full throttle after the engine has idled for 10 sec.

    At this point, you are ready to go back to full speed and find the peank rpm and then richen the needle out three or four clicks.

    The engine should now run fine.
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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    Original AMA #31261

  5. #5

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    RE: ASP FS61 midrange problems

    strange, it sound like you have tried everything. I have two of these engines myself and both run just great.

  6. #6

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    RE: ASP FS61 midrange problems

    w8ye, I'm no engine expert, but I think I have tuned the engine like you describe. And I really appreciate your help. When I tried to find the correct setting for the low speed needle, I leaned it until it wouldn't accelerate when I hit the throttle, and then I richened it by a few degrees. Just enough to make it respond to the throttle stick. Even with both needles at their leanest possible setting, the midrange is very rich (rpm decreasing, vibration and lots of smoke). If I advance the throttle slowly from idle to full, it sounds clean at idle, then gradually rougher, then at about 2/3 throttle it jumps up to a much higher rpm and sounds clean again. I have several other engines and tune them the same way, and they all work well (except this one).

    The strange thing is that the engine behaves the same with two different carbs. At first I thought the original carb was faulty and got a new one from the hobby shop. Then I started the engine with the new carb and saw the exact same problem. What is the chance of getting two faulty carbs in a row? It sounds strange to me...

  7. #7
    Moderator w8ye's Avatar
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    RE: ASP FS61 midrange problems

    I had two of these for four years and they did not have this problem. I ran APC 12 X 6 props

    I have experienced your problem with a Saito 72 once. I had been using a 13 X 6 and never noticed a problem but changed to a APC 11 X 9 that was in a drawer at home and the engine had a very rich mid range at the flying field. I ran the engine at home on the bench and it was the same way. I changed back to a APC 13 X 6 and the problem went away.

    But you have already been there and tried different props.

    I have seen some fuels make an engine more rich in the mid range but you have tried that too
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  8. #8
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    RE: ASP FS61 midrange problems

    Try a plug other than the OS F. I would try 15% or more nitro and a cooler plug such as the K&B 4C. But try Fox Miracle plug, Hobby People's Thunderbolt, Enya #3 and #4, and others. Also if you are running it on the bench try differant tank heights, you may have it set too high.

    Oh and when you use higher nitro fuels there is a flat spot where there is little change in RPM, set to the lean side of that flat spot and then it may run well at the rich side of the flat spot when in mid range.
    Glow Head Brotherhood #15

  9. #9

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    RE: ASP FS61 midrange problems

    Maybe I'll just buy a new engine to replace it, and pretend this one never existed. It might be risky to buy a new carb, in case the carb isn't the problem...

  10. #10

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    RE: ASP FS61 midrange problems

    Sport_Pilot, thank you for the tips! I will try some other plugs and see if that changes anything. I don't fully understand the theory behind hot/cold plugs, but I guess it has something to do with the hot plug igniting the fuel too early, and that this is compensated by turning the needle valve out. With a slightly colder plug, I would be able to run slightly leaner?

  11. #11

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    RE: ASP FS61 midrange problems

    One thing I did not see mentioned and can often have an affect is the location of the fuel tank. Since all else has been tried I suggest you check on that. If tank is too high (above center of needle valve) this may be your problem. This often occurs when engines are cowled inverted.

  12. #12

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    RE: ASP FS61 midrange problems

    ...I only had two stroke plugs. Tried an OS 8 and an OS A3 just for fun. The A3 wasn't too bad, but I couldn't get steady rpms at full throttle. My LHS sells Enya #3 and #4, are those worth a try? Other recommendations?

    One thing that I noticed is that there is about a quarter of a turn on the HSN where there is practically no change in rpm. I have always tuned my engines towards the rich end of this "flat area", but if I go towards the lean end the midrange is better. It sags slightly when I point the nose up and shake the plane. Until now I have thought of this as the "warning area" that is slightly too lean. Comments?

  13. #13
    Moderator w8ye's Avatar
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    RE: ASP FS61 midrange problems

    Some people run the Enya A3 in their four strokes. it is a hot series plug and is the one that comes in the Enya four strokes

    You are correct, the flat area of tuning for the HSN is getting into the danger area. You are supposed to be on the rich side of this flat spot.

    The Sag when vertical is a indication that you are too lean
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  14. #14

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    RE: ASP FS61 midrange problems

    Cold. Snowing. Indoor activities. I took the FS61 apart to look for damage on the inside. The cylinder liner has a few vertical lines. One of them looks serious. When I slide my fingernail over it, I can feel that there is "something" on the cylinder wall. If I put some oil on the piston, block the crankcase vent and move the piston down, I can see air coming up between the piston and liner. How did this happen, and could this be the reason for the problems?

  15. #15

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    RE: ASP FS61 midrange problems

    MY ASP FS .61 has the rich mid-range problem as well. It occurs between 1/4 - 1/2 throttle. It's in a Thunder Tiger Ready MK3...

    I'm running PowerMaster 15% nitro w/ 18% oil. I'm sure I have the engine tuned properly. Have tried the Fox Miracle plug...didn't help mid-range. It idles better with the OS F plug which is what I am running. In the review section someone else mentioned this problem.

    Looking for a solution myself.

  16. #16
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    RE: ASP FS61 midrange problems

    I have had problems with Chinese engines in the past. Years ago they couldn't make a decent carb at all. But lately they seemed to do better. Still seems it is hit and miss though, so hard to say if they got it down pat yet.

    About a year ago I did a little writeup and review of a couple of ASP 61 four strokes I saved from a fellow modeller's junk bin. The engines ran OK using 15% or 20% nitromethane content fuel, they did not like my regular 5% fuel at all.
    Anyway, you can read about my experiences at the time with the carbs on them here in this thread. I had to mess with the carbs to get them to work.
    it starts at post number 10 in this thread here
    http://www.rcgroups.com/forums/showthread.php?t=1116753

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    RE: ASP FS61 midrange problems

    Thanks Earlwb, that was helpful.

  18. #18

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    RE: ASP FS61 midrange problems

    I have 2 ASP61s One runs a mac's pipe on a Tiapan purple plug and the other is stock, had all sort of tuning problems. Fitted the new OS 7 plug and no more probelms.
    Right after a spectacular crash, the pilot yelled out \'\'Channel 35 clear!

  19. #19

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    RE: ASP FS61 midrange problems

    I have two of these engines and none of mine has any issues at all. I use OS F in all of my fourstrokes and usually run a normal 15/15 fuel

  20. #20
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    RE: ASP FS61 midrange problems

    Before you buy another carburetor try lapping the end of the needle on a piece of glass using some wet/dry fine sand paper. Make it a little shorter....
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  21. #21

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    RE: ASP FS61 midrange problems


    ORIGINAL: Broken Wings

    Before you buy another carburetor try lapping the end of the needle on a piece of glass using some wet/dry fine sand paper. Make it a little shorter....
    Do you mean making the end round or tapered, or just make it shorter with a squared end like it is now?

  22. #22
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    RE: ASP FS61 midrange problems

    Yes, just the end. If you have a caliper measure the overall length. Lap the end of the needle flat on the end just a very small amount. (squared end, just like it is now) Two or three strokes and measure it again.

    A lot of times the needles are not machined properly, magnified you can see it. Try and clean up the flat on the end and try running the engine. If the mid range starts to get better you're on the right track.

    A little goes a long way.
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  23. #23

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    RE: ASP FS61 midrange problems

    .
    \"Practice makes prefect\"

    Saito Club Member #52

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    RE: ASP FS61 midrange problems

    What prop are you using are you loading your engine enough, I have seen this before.

  25. #25

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    RE: ASP FS61 midrange problems

    Broken Wings; thank you for the tip! I'll give it a try.

    kerwin50; APC 11x7 to 13x6. I even tried an APC 15x4W, but I won't use that prop for flying. APC 13x4W gives better midrange than the other prop sizes I have tried, but still not acceptable.


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