The Saito 56 in the ebay link below seems to have a conversion on it for CL use. How well do these conversions work?
http://www.ebay.com.au/itm/331198257536?ssPageName=STRK:MEBIDX:IT&_trksid=p3984.m1431.l2649

That's the UHP intake, if you get it, ask Doug Moon or his brother about getting the different size insert set. You will need them to tune it to the prop and airplane and didn't see where they came with the engine in the listing.

The difference is with a fixed intake you have to find the exact prop that works with that choke area and airplane. Most fall into the trap of if it's flying too fast drop down in pitch, that doesn't work very well on a 4 stroke.

Mike,
Just try running a C/L Saito in, following the Saito instructions. It simply doesn't work! You either need to block off part of the venture with the thumb or use an R/C carb for the break in.
If your stock Saito C/L engine is running well, then fine, that is what it is all about! Using the stock system, you need to know exactly what you are doing to get good results or just maybe you get lucky and it works first time!
The beauty of Bob's conversion is that it makes setting "up a plane prop rev equation" and solving it relative child's play. Just follow his instructions and you are there.
I have tried both setups (plus the R/C carb option). There is no doubt that Bob's conversion is by far the easiest to deal with. Nothing is wrong with the stock C/L Saito as such, provided it is set up correctly, but getting a stock system set up is nowhere as easy as the Bob Reeves conversion.  Simple as that.

Andrew.

[snip]
If your stock Saito C/L engine is running well, then fine, that is what it is all about! Using the stock system, you need to know exactly what you are doing to get good results or just maybe you get lucky and it works first time!
[snip]
Andrew.

Andrew (and others reading this), (1) luck should have nothing to do with achieving success, and (2) technically speaking, YES, one SHOULD always know what they are doing - whether it applies to 4-strokes, 2-strokes, electrics, boats, helicopters, their 401(k) investment allocation, or that new propane grill on the back patio.  Such knowledge is gained by first studying the principles of operation of whatever system is being worked on, then applying that knowledge in practice (along with MEASUREMENTS or at least observations), recording and analyzing those measurements or observations, making corrections, discussing findings with others, etc. etc.  That's what this forum is for.

Let me share the basics of Control Line 4-strokes as I understand them, and why some people have been able to achieve good performance with those.
The 4-strokes have a completely different gas (fuel+air mixture) dynamics from 2-stroke engines, and therefore cannot be tuned the same way traditional stunt 2-strokes operate (2-4 break through port timing and mixture control, etc).  Stunt 4-strokes are set about 200-300 RPM on the rich side of peak (ground) RPM.  The key to steady stunt run and to preventing run-away is operating 4-strokes at the peak of a NARROW, "steep" torque curve.  The 4-stroke torque curve changes depending on the air intake (venturi) opening. The larger the intake, the more peak power can be obtained - but at the price of broader, shallower torque curve, which accommodates a wide range of RPM and will therefore allow your engine to "unwind" when prop is unloaded (like during consecutive loops downwind).  And conversely, the smaller the venturi, the smaller the peak power - but with a narrower "happy" RPM range.
Saito torque curves have been published, both by Saito / Horizon Hobby and by individuals (simply Google: Saito 56 torque curve). All Saito's in the .56-.72 range peak in the 8000-8500 RPM range...  which is where most people recommend running them.
Here's where people get into an argument (where there is nothing to argue about): how to get the Saito's to run at that RPM.  The Bob Reeves' approach says: pick a 6"-7"-pitch prop and keep closing the intake until you get to the desired RPMs, then set the mixture and fly.  My approach (similar to that originally described by Brad Walker in his 4-stroke article) is to leave the stock CL carb (venturi?) intact (I always leave the supplied insert in) and simply LOAD the engine with the appropriate SIZE prop until the desired RPM range is achieved, then fine tune airplane lap speed with prop pitch variations and fuel nitro content.  Just as an example, I had to use a 15"x6" prop (yes, 15 inch diameter) on my new Saito 72 to get it to run at 8500 RPM - but guess what, it pulls like a freight train, and hauls a 70 oz. Strega ARF on full 70' lines at 5.0" lap on 10% nitro fuel with power to spare!
If you re-read the above, you will understand that there is really nothing radically different in these two approaches.  No one advocates running the Saito's in the high-RPM (10,000+) low-pitch (4") regime; no one has succeeded with the use of the R/C carburetors.  Bob's approach is actually more convenient, because there is no need to have a wide range of props.  I was lucky enough to find stock props that do the job (for the benefit of others: Saito 56 = APC 13x6, Saito 62 = Master Airscrew 12x6 3-blade, Saito 72 = APC 15x6). I simply don't have either the equipment or the skills to machine custom parts.
The only point where we (Bob Reeves/Steve Moon/Brad Walker and I) differ is whether to feed the Saito's from a conventional suction tank or a uniflow....  But I will not be kicking this horse again, as it is already dead. 

The only thing I ask is please, PLEASE do not make the 4-strokes seem more complicated than they are.  After struggling for over 20 years with various 2-strokes, I can confidently say that the Saito range of control-line 4-strokes (especially the .56 and .62) is one of the best, most reliable combustion power trains for CL stunt available to the public.

Hello Mike,
I am sorry you took offence at some of my statements. Unfortunately people DO get lucky and hit on a set up that works well. It actually doesn't do them any good as they assume setting up a 4 stroke is child's play. I knew nothing about 4 strokes when I purchased my first C/L Saito 56. I DID however take the time to thoroughly read Bob's take on 4 strokes . They made total sense, so I went on from there and things worked very well.
  I cannot see for the life of me why anyone should buy a fistful of different props to find one that will load the engine to the correct revs. Bob's system is far easier, faster and cheaper to accomplish the desired loading. I would not consider anything else.

Regards,

Andrew.