Hello,
  A friend of mine has a Saito 56 which is the genuine Saito control line version. He is having lots of problems with getting a consistent run. He has just about changed everything, plugs props and fuel. No matter what he does, the runs lack any consistency and seems to be down on power. The engine has been thoroughly checked for valve clearances, timing, spray bar blockages, you name it and it has been checked! It has been run in as per book.
  Is there a known problem with the Saito 56 control line setup? Any suggestions would be gratefully received, the poor man is tearing his hair out and wants to invent a Saito Hurl competition!

Regards,

Andrew.

In my opinion Saito missed the boat when they designed the CL intake and the results you are seeing are pretty typical. The first thing that needs to be done is to disassemble the spray bar and drill the feed hole out to .046 (#56 drill bit), this will allow it to draw more fuel. The second thing is to provide some means to adjust the intake choke area. Once these two items are in place you can go on to finding the best available prop etc. I have posted so many threads on how I set up my Saitos a search should find most of what I have discovered.

The best fix is to make another barrel and use a spigot needle assembly from an OS RC carb with a 10-32 nylon screw into the opposite side. I am sure I have posted on doing this with photos, maybe on the 40 but same principal.

Hope this helps..

Not really that much to learn, just don't try to apply 2 stroke thinking to a 4 stroke and it will work out. From my observations a Saito 4 stroke is the least expensive way to get runs that can compete head to head with pipes and electrics.

Andrew,
Tell your friend to follow Bob's (wise) advice and that Saito will be running as it should. Do the carb modification shown here http://www.tulsacl.com/SaitoCarb.html (don't mess arround with any other system).
This just WORKS!
I run a Saito .72 myself and I can't be more happy with it.

And remember that a Saito .56 won the 2006 World CL Champs in Valladolid!

Good luck,
  Claudio.

It's been a while since this was discussed and I'll try to explain some of my theory on why it works.

Four strokes only suck fuel for a very short time during the intake stroke, anything we can do to help it get as much fuel as possible will result in a bigger bang when it fires. One item that effects it's ability to draw is the viscosity of the fuel. All synthetic flows easier than a Castor mix and as long as you use an after-run oil to protect the bearings Castor isn't needed nor desirable.

Choking down the intake also helps it draw bigger gulps of fuel. Nitromethane (CH3NO2) comes with its own oxygen atoms to help it burn, the result is a bigger bang with less outside air.

Quoted from a hot rod site..

The big advantage of nitromethane is that you can get a lot more power from each explosion inside the engine. Pound for pound, nitromethane is less energetic than gasoline, but you can burn a lot more nitromethane in a cylinder. The net result is more power per stroke. You typically need about 15 pounds of air to burn 1 pound of gasoline, whereas you need only 1.7 pounds of air to burn 1 pound of nitromethane. This means that, compared to gasoline, you can pump about 8 times more nitromethane into a cylinder of a given volume and still get complete combustion.

A conventional vent clunk tank on muffler pressure feeds easier than a uniflow tank. Again we are doing everything we can to help the engine take as large a gulp of fuel as possible.

Also, we want the engine loaded and running in an RPM range that takes advantage of it's torque curve for speed regulation. This is down around 81-8500 hence large high pitch props, 11-7 on a 40 and 13-7 on a 56.

Last but not least is the reasons for side mounting. First it oils better as the oil blown by the ring gets forced back out to the cam, pushrods and rockers. The position of the tank is below the engine when it's overhead, think about that for a bit..... And because the engine mass is on the outside of the circle you need less tip weight.

That about covers everything I think I know about 4 strokes....

Thanks Claudio,
  The mod that Bob has done is on the R/C carb. This Saito is a control line version, so the mods will need to be modified! I have not had a good look at the C/L carb, so I don't know if Bob's solution will be applicable.
  There are a couple of points that I can't yet figure out. It would appear that the lack of power is primarily a restriction in the NVA and drilling out the spray bar should fix that problem? Reducing the venturi area is a bit puzzling to a non 4 stoke man. I always assumed that having too large a choke area affected fuel draw and precious little else, except to increase power. So why would one need to reduce the choke area, after all fuel draw on this engine seems to fine. I am obviously missing something here?
  The second point is that the UK importers add a leaflet, which basically says that one should use a 20% castor 80% methanol fuel. They add that the addition of nitro is a waste, because the engine is plenty powerful enough without it. All this seems to be the exact opposite of what the Saito instructions say. I assume that this is because people without 4 stoke experience run the engines too lean and the castor is recommended so that the importers don't get claims on wrecked engines?

Regards,

Andrew.

You're welcome Andrew.
My Saito .72 is a CL version too and the mods to the CL carb can be done with no problems (the carb body is the same in both carbs, the RC version and the CL version) In fact, it's even easier because I used the same spray bar and the same aluminum barrel supplied with the CL carb. All I had to do (actually a machinist did it for me) is enlarge the spray bar intake hole per Bob's specs (#56 drill bit), cut the spray bar end as Bob shows in his tutorial and then drill and tap the barrel to receive the nylon bolt. That is it.
Unfortunately I don't have any pics to show you, but you can't miss it following Bob's tutorial and my brief explanation.

Cheers,
Claudio.

Thanks guys,
   Looks like Bob's mod can be easily done on the C/L version, so that is good news! On this carb, there is an insert to reduce the carb intake diameter and the Saito blurb says that this can be removed for more power. I assume that it is better to remove this insert, before doing the carb mods. Any increase in area can then be reduced and more with the nylon screw.
  I am looking forward to seeing this engine sorted out. My friend will be even more grateful after all the frustrations so far. It will be interesting to see how the Saito will perform and compare it to my MVVS big diesel. I may even be surprised at the outcome.
  Many thanks to everyone who has offered such good advice.

Regards,

Andrew.

Have posted these before but worth repeating, intakes off a Saito 40 and a 62 showing where the choke screws are set as I run them. The 40 flys my Shoestring (really a Brodak P-40) and the 62 was flying a 68 ounce Score. I think it's pretty amazing the power these engines are producing from such small intake areas but think my above post explains how it all works.

Hello Matt,
I am having some trouble in working out what point you are trying to make. Any chance you put it another way?

Thanks,

Andrew.

I've gotten to the point where I dont try to understand his post. 
I just read them for the entertainment value.

<snip>

Hypothetical , But a straight ( as possible) intake runner should lead to a few things , with
tuned for r.p.m. s length to jet and mouth . potentially better power / control and vacuum.
but could narrow the powerband .

Norton 750 with runners 14 in. to jets was allegedly worth power , but lost a cylinder below
2.000 r.p.m. s , the worlds worst Idle .      

Both Saito, OS and others put that "kink" in the intake tract for a reason and it's not just compact packaging, it's to slow reversion of the intake charge as the piston comes up on compression and the intake valve is still open (closing).
Long runners promote torque when tuned to length but give up high RPM HP. If you notice the few four strokes built for R/C cars they have the carb. bolted near the head - straight shot for max. RPM/ HP.
Aircraft engines req. TORQUE. What Bob R. has done is found the sweet spot of a Saito and maximized the fuel atomization by placing the venturi screw next to the nozzle. High velocity charge + excellent atomization = Torque.

ps- [Spell Check] is your friend.

Hello Chris,
Thanks for illuminating Matts's reply. I am still a little puzzled with the mention of runers (did a lot of 4 stroke car engine tuning in my younger days, but never heard the term).
  That there is twice the time between intake pulses on a 4 stroke (compared to a two stroke) is a given, but what is the significance of that? Larger venturi maybe? I am still puzzled.
  Fuel injection seems to be a total no on this sized 4 stroke, unless I am very much mistaken?
  No intention of trying to be awkward, just trying to understan things.

Regards,

Andrew.

Guess I'm one that might owe Mat an apology, hope he understands he needs to speak in terms us common folk can understand or we don't have a clue what the heck it is he is trying to say.

The problem with fuel injection on engines this small is the overhead needed to make it work. It would add a fuel pump, some means to time the squirts plus injectors. It could be done but don't think it's worth the added complexity.

OS made a FS .91 II EFI. Not sure if it's still avail. Here's the manual to give you an idea what's involved in Miniature Fuel Injection;

http://manuals.hobbico.com/osm/fs91-ii-fi-manual.pdf

I stand corrected Mike, fuel injection IS practical!

But the supplied PDF shows the YS powerhouse's weight as 17.7oz with muffler and the OS as 24oz!

Interesting reading though, thanks.

I just saw the mass listing on the pdf article. The Central hobby site lists the motor mass at 455g or 15.1 oz and the muff at 33g or 1.1 oz.
Yamada listing here
http://www.yspower.co.jp/en/engine/plane/fz70s.html
Apparently, they still make the 63. Hmmm.
Oh well, the Saito 62 is ~ 14.7 oz less muff, so mass-wise they are close. Cost-wise the YS is $80 to $100 bucks more. Simplicity-wise the saito is much simpler.
In general a 4 stroke will be slightly heavier, but the fuel load is reduced so T/O weight is lower.
Even with the YS at $100 bucks more than a Saito, it is tempting (some day).

Hi Bob,
I am sure that given time that they can get it sorted but its going to be one very powerful and heavy model before its finished.

I believe that the YS loves to rev out a bit more than the Saito's - time to go back to a lower pitched prop again?