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Author Topic: Saito FA-40 MK 3 rpm cycling  (Read 7548 times)

Offline Terry Caron

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Saito FA-40 MK 3 rpm cycling
« on: May 01, 2016, 12:27:59 PM »
This is a used late '80s ABC ringed version, my first and only 4-S'er, and I've been running various props on the bench.
I know Bob's carb mod,  OS F plug and Powermaster YS 20/20 fuel are the popular recommendations but going with what I have:
It has the stock carb, an unknown plug, muffler pressure and I'm burning Morgan 15/15 (50/50 oil) 4-S fuel (what the LHS carries).
The engine has a solid 200 rpm hi-lo cycle with all props - is this a 4-S thing or something as peculiar as it seems?
Other questions to follow.  ;D

Terry
« Last Edit: May 01, 2016, 10:43:46 PM by Terry Caron »
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Offline Bob Reeves

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #1 on: May 02, 2016, 10:24:22 AM »
Not exactly sure what you are saying but if the rpm is changing without moving the throttle then no that isn't normal. Never had one do that and can't be much help figuring out what's going on. Something is changing probably in the fuel system.
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #2 on: May 02, 2016, 11:02:34 AM »
What you are describing is surging, and like Bob, I am not familiar with
Saito's doing that,(they tend to be pretty steady). I would go after the plug first to see if that settles it down. I break in Saito's on the stock plug, and switch to the F to fly,(they are expensive).

In all honesty, I am not aware of anyone that uses anything other then an F plug on Saito's. Also, I use a lot more oil then are are using,and that tends to make my Saito's rock steady.
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Offline Brett Buck

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #3 on: May 02, 2016, 11:02:56 AM »
Quote from: Bob Reeves on May 02, 2016, 10:24:22 AM
Not exactly sure what you are saying but if the rpm is changing without moving the throttle then no that isn't normal. Never had one do that and can't be much help figuring out what's going on. Something is changing probably in the fuel system.

   Everybody I know that had this issue fixed it by replacing the carb with a venturi or Berringer-style carburetor. Its something about leaks in the barrel but no one ever managed to figure out what exactly it was. This is going back to 1985.

    For whatever reason (more critical mixture requirements?), the same happens on a 2-stroke but it is much less obvious.

     Brett
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #4 on: May 02, 2016, 12:25:13 PM »
The barrel is locked open, Bob, and I didn't time it, but I think it's maybe a 3-sec cycle.
Just about has to be something in fuel delivery.
Milt - I've run it on the same fuel with added castor to 20%, same cycling. I'll spring for an "F", see if that cures it.
Brett - I commonly see slight variations in 2-strokes too, but never with this regularity.

For anyone who's had one apart, for just a ring replacement is a teardown necessary or can the (1-peice) jug simply be lifted off?
Of course, pushrods and tubes will come loose.

Terry
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #5 on: May 02, 2016, 12:52:54 PM »
Terry, it just so happens that I am going to put this guy on the test stand today. Maybe I can find something of use to you.
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Milton "Proparc" Graham

Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #6 on: May 02, 2016, 01:01:40 PM »
Someone else's experience is always welcome, Milt, but for your sake I hope you don't have the problem.  ;D

BTW - a beauty!

Terry
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #7 on: May 02, 2016, 01:43:06 PM »
Quote from: Terry Caron on May 02, 2016, 01:01:40 PM
Someone else's experience is always welcome, Milt, but for your sake I hope you don't have the problem.  ;D

BTW - a beauty!

Terry

Well, I just cranked it up and, I wish I could tell you something. Same Oh, same Oh. Heck, I flooded it by accident and it still cranked up. That said, what I can say so far is that, it seems to be about dead-on for top performance with a about a sixty ounce ship. Seems about right. The 40 is tops with a 50oz ship, the 72 is tops right around 70oz.

40A - 50oz.
56 - 60oz.
72 - 70oz.
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #8 on: May 02, 2016, 01:53:53 PM »
Congrats on another good one then, Milt.
As I said, I got mine used so no idea of it's history, 'though that may have nothing to do with how it's running for me.
I will say mine seems low on power, but a new ring may help that.

BTW, mine's ABC, I think current FA-40As are AAC - any Big Deal difference ?

Terry
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #9 on: May 02, 2016, 02:03:18 PM »
Quote from: Terry Caron on May 02, 2016, 01:53:53 PM
Congrats on another good one then, Milt.
As I said, I got mine used so no idea of it's history, 'though that may have nothing to do with how it's running for me.
I will say mine seems low on power, but a new ring may help that.

BTW, mine's ABC, I think current FA-40As are AAC - any Big Deal difference ?

Terry

No, no difference.

Well I did have a problem-the rain is starting!! And, I can hear thunder so, I don't think I can sneak in a third run. Tip, don't try to run a Saito in a Texas storm.
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #10 on: May 02, 2016, 02:08:04 PM »
Ha! Rain here too, so I can't play with any of mine.  :'(

Terry
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #11 on: May 02, 2016, 02:30:11 PM »
Quote from: Terry Caron on May 02, 2016, 02:08:04 PM
Ha! Rain here too, so I can't play with any of mine.  :'(

Terry

Got in another run. The motor is running as we speak. It surged a lot on first start-ups but, it is smoothing, out nicely even now. Man oh man, these small Saito's sure are economical on gas-incredible. I've got video of it running but, I can't post it because of size restrictions.

So far, it's a nice motor,(hey it's a Saito) but it's no sweetheart like the 40A.
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #12 on: May 02, 2016, 02:43:47 PM »
I was also pleasantly surprised by the economy.
I noticed mine drops ~200 rpm after running a minute or so, I suppose from heat expansion.
Another thing I don't see on the 2-strokes.

Terry
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Offline proparc

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #13 on: May 02, 2016, 02:52:08 PM »
Terry,
What I should have said prior is, "no practical difference". The "technical difference" between the ABC and the AAC is that, the AAC is slight lighter, and supposedly has marginally better heat transfer. In practical terms-no difference.
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #14 on: May 02, 2016, 02:59:09 PM »
Good enough then, Milt - thanks.

Terry
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Offline Terry Caron

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Re: Saito FA-40 MK 3 rpm cycling
« Reply #15 on: May 07, 2016, 03:53:17 PM »
Well, FWIW, I put in an OS "F" and it didn't make any difference in the rpm cycling.
Not saying they're as good, but the Fox 4-S plug runs the same on the bench in this engine.

Terry
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