Hello, Ash.
You have a most interesting setup there.
I've been using four cycle engines for around 25 year but I've never heard of swapping a carburettor like that!
First off, are you sure that's an OS carb?
I have a SAITO 62 and the carb is nearly identical (?)
In any case, the SAITO 72 is a great engine. I've had a few and they are very powerful and reliable.
For your setup, I would suggest that you try it as is. If you plan on doing C/L and don't need the throttle, just wire it wide open and see how it performs. I have done that many times with flawless performance.
I did make a number of plain venturies for the 72 which worked quite well. I used a single taper with the vena contracta at .30 inside diameter. I used stock OS Max and Super Tiger NVAs, both yielding very good results.
Keep in mind that the four-cycle engines are very sensitive to air leaks - make sure everything is well sealed.
Also, check your valve tappet clearance - should be around .002.
In general, the four cycle engines run best with a 20/20 nitro/synthetic fuel and an OS 4-S plug.
The 72 will easily turn a 13-6 or 13-7 prop.

Use it on the biggest plane you have - it will easily handle things like the Patternmaster.
Remember, one test is worth a thousand expert opinions!

Bob Z.

Thanks for the tips, Bob.

I'll give it a test run as is before deciding how to go. In fact I'll probably test fly it with the throttle fixed until I know what it wants in the prop and RPM department.

It'll be going into a rebuild of my old Zone 2 designed by Brad Walker for the Saito 72.

Well, I've given it some test runs on the bench and it seems to go OK. Starts easily when choked properly, and runs about 9200 on a fat 23x6. I expected a bit more than that, but maybe the OS carb bore is smaller...

One thing I've noticed is that there is quite a lot of axial play in the crankshaft, both cold and hot. About 0.3mm (.012"). That would not be unusual on some engines set up for peak perfect at maximum running temperature, but I wasn't expecting it on this one. I don't think my Saito 62 exhibits any such play.

The bearings sound and feel clean and smooth. Could they be due for replacement?

Any thoughts on what is normal for crankshaft/bearing axial play on a Saito?

Mr Ash: First off, you may have a carb for a smaller Surpass engine, like a 52.
Second, I hope you meant a 13-6 and not a 23-6!
Lastly, I checked a number of my engines and they ALL exhibited no crankshaft endplay that I could feel or see. Possibly a very very slight preload(?)
I would suggest not running your SAITO until you have identified/eliminated the axial play.
I will try and send a photo.
The spacer and cam drive gear determine the axial location of the bearings on the crankshaft.
If it is wrong or has been modified, the crank can move axially. NOT GOOD.

Bob Z.

Well, I've given it some test runs on the bench and it seems to go OK. Starts easily when choked properly, and runs about 9200 on a fat 23x6. I expected a bit more than that, but maybe the OS carb bore is smaller...

One thing I've noticed is that there is quite a lot of axial play in the crankshaft, both cold and hot. About 0.3mm (.012"). That would not be unusual on some engines set up for peak perfect at maximum running temperature, but I wasn't expecting it on this one. I don't think my Saito 62 exhibits any such play.

The bearings sound and feel clean and smooth. Could they be due for replacement?

Any thoughts on what is normal for crankshaft/bearing axial play on a Saito?

Was in a Stunt News , Hoffman & his Firecracker Build .

Made the fuselage a touch wider , and considered tank should be as far inboard as you could get it .

Tecnically , side mounted , with the outer face of the tank level or inboard of the N V A ,

in level flight , all the fuel has a positive head .

dead overhead it is a negative head .

seems to work , if you set so not lean in the o. h. eights . or your doomed . the other aspect is in WIND the fuel head keeps it rich , so limits speed up . Drops the power as you go low .
2 strokes and 4 strokes . Just like the inboard tank on profiles , as a extreme example .

" I’m  using  the  same propeller/tank/fuel   setup   as   in   the original model and am happy to find that  the  aeroplane  is  behaving verysimilar to its stablemate – as it should. "

HOLD YOUR SEATS . !   https://pampacl.org/wp-content/uploads/2020/02/SN_Magazine_-NOV_DEC_2007.pdf ( computer was in feminist mode earlier . Uncopperative . It had to ' find itself ' . 

THERE is a DIAGRAMME of the FUEL TANK , there . ( Now were off to find his Numero uno fryercracker builld issue , with the r elefant statement .

Boer Elephant !  https://pampacl.org/wp-content/uploads/2020/02/SN_Magazine_NOV_DEC_2006.pdf  ( just kidding ? )

Direct from




"" The Tank. For some time now with 4  strokes  I’ve  been  using  a  ‘Uniflow’ type  home  made  clunk  tank.  The approximate dimensions are (in metric) 92mm long, 30mm deep, 30mm wide at the front and 50mm at the rear. The feed and vent pipes are central to the depth with the vent pipe being about 20mm from  the  back  of  the  tank  and  flush with the outboard side. The inboard of the  tank  should  be  mounted  inboard as far as possible – this seems to aid in the prevention of ‘wind-up’ in windy weather, as when the model tends to speed  up  in  consecutive  manoeuvres the centrifugal force increases ‘pushing’ the  fuel  into  the  engine  (4  stroke –  normally  aspirated)  and  tending  to ‘richen’ it up – consequently the motor tends  to  slow  a  little  and  the  model doesn’t ‘wind up’ as much. I’ve found that tanks of this design have supplied very consistent engine runs right to the last drop of fuel.  ""

invented on THIS . The NVA is out on the plug in venturie , so therefore ALL the FUEL is inboard flying level , and below the intake , overhead . Thi'd fly in a gale despte the weeny FSR 25 clone . on .018s , Mate .


I think it was Ash , actually ? at Onehunga around 2002 with a white ( and blue ) profile OS FS .40  side mount clunk tank , with outboard edge aligned fore & aft with needle . I pointed out the run .
' No its Not , we're off to Mc donalds "
Right then .
There huge H T lines there . Like the cell phones - Currents discernable at the handle at the far edge of the field , on Dew Point days .


In a valley with a huge power station , in winter . I said to someone ' everyone seems to opperate at about 80 Hz here ' . the Reply was " Everyone knows that " like living in slow motion & various other ' benefits ' .

perceptual , logical , etc . a bunch of flavour enhancing substances apparently was considdered sufficent remidy to get them home . 
Having been brought up on the outskirts , the city mugs are made for observation . Most irregular , mostly .



this place was 1.000 megawatt . ( Onehunga is Aucklands main In Line . buzz hum wirr . )
only day tthe people appeared sane was when there was a big bang one evening , and everthing went OFF . after a half hour the troglodites started appearing from their curtained tevevision indoctrination
and were bewildered by the sky ( blue ) and clean cool evening air . They adjusted . ( some anyway ) and stopped looking like they wernt about to die a dawn . Most irregular . The car would loose a cylinder driving past it . ( loose / Un tight clip on H T Lead ) Theyed say you could hold a flourescent tube up , in there . It would light up , it didnt need to be plugged in . " NO , IT DOSNT AFFECT US "  ~^too , stands on end
if you get out to check it .

Cognition .