highside

Good morning to you all.

I've been wrestling with a Saito 82 for a few months now, struggling to get it to swing largish props (noise sensitive site etc.). By largish I mean 13x8, 14x7, 14x6, (all APC standard width) so not massive. I am running 5% nitro Southern ModelCraft fuel (great UK stuff!). It's had about 2 hours of running in total, and was run-in according to the book. Valve gaps are spot on.

I'd been through two tank set ups (both tried with and without Cline regulator) plus my usual test stand set-up, plus OS type F, Enya #3 and Firepower medium & warm plugs, plus with and without a velocity stack. Everything had been cleaned and flushed and cleaned and fettled etc till I was blue in the face. Despite all this, it really didn't want to swing a big prop. Taking the main needle progressively from rich through to a lean quit, there was no setting where the engine got "on song", instead it would constantly hunt around, changing by say +/- 300rpm all the time. A change to a 13x7 or 13x6 and off it would go, singing away.

Throughout all this, once the LS needle was set tickover was good and pickup reliable.

Then I found a thread on another site to do with back plate flex on the old design Saito 72. This is inspired me to disassemble the carb, clean and reassemble, sealing everything as I went with thread-lock or PTFE plumbers tape. Note that I didnt find anything amiss at all. I removed the plastic backplate and reinstalled sealing into the cranckcase with PTFE tape.

Now it runs just fine, giving me a static 8300rpm on a 14x6 APC (remember only 5% Nitro). Now I wish I'd done it a stage at a time so that I knew what the culprit was!

Has anyone else had a similar experience? Did you pin down what the problem was? There was no doubt that the backplate was leaky, but this shouldn't matter to a 4cyc, it's got a breather anyway. And I found nothing amiss in the carb, which I'd already stripped and cleaned at least once before.

Other comments I would make if you're thinking of buying one of these engines:
: It liked the OS type F plug best by a long shot
: If you want a soft mount, the Hyde YS63 mount (no nose ring) has exactly the correct beam spacing and the front hole pair are in the right place so you only need to plug and redrill for the rear holes.

:-)

daveopam

My Feedback: (9)

The problem with the back plate is not around the crankcase. The problem is the intake tube will leak air around the "O" ring at the back of the head.(at least in most cases). The early 72s were terrible in this area. The backplate would flex and slightly pull back on the tube. Then air would come in around the "O" ring. One of mine did it because the throttle linkage was to tight. It is possible in you carb repairs you fixed this area without realizing it. I got a tip a few years ago I use on both my 72s. That is to run a small zip tie around the base of the intake tube and cylinder. This will stop any flex in the back plate.


David

highside

Hey David,

That makes a lot of sense. It's funny, I'd contemplated smearing the manifold tube with a bit of 5min epoxy before assembling to give it a bit of mechanical support where it enters the head and the carb. Eventually I decided not to because it all looked well engineered and was a snug fit anyway. If the problem returns I'll try the tie wrap idea first.

Ta muchly!

w8ye

My Feedback: (16)

The back plates on the current production 72's and the 82"s are identical

Yet the 72's still tend to give trouble at the junction of the intake tube and the cylinder head.

If you look at the 72 intake tube and compare it with the 82 tube - The 82 has a better shoulder for the backing washer at the junction of the tube and the head. Maybe that is why the 82's are not as bad as the 72's about leaking air at this point.

DarZeelon

HighSide,


It could very possibly be the nitro...

Four-stroke engines are much more sensitive to the percentage of nitro in the fuel, than are two-stroke engines.


This Saito is designed to run better on 15% nitro, or more. The minimum recommended percentage is 10!

Using only 5% will, by all likelihood, make it run somewhat erratically.

highside

Yeah, I appreciate I'm out of the norm on Nitro percentage. I haven't got any 10% to hand, in fact its unusual for me to have 5%, I usually only use straight. I've got a pile of engines (2 and 4 cyc, OS, ASP, SC, MVVS, Saito, Laser and Enya all represented) and (sometimes with a bit of plug experimentation) they all run fine on straight once set-up properly. Usually its the low-end which is a bit sensitive rather than the top end. I think manufacturers often recommed 10% nitro because it makes the engines "easier" to operate and set-up leading to them getting fewer returns. (For sport engines of course; I'm sure higher performance stuff needs the nitro due to more agressive tuning, and maybe the Saitos are getting close to that category because the figures are certainly impressive.)

Having said that, just before I finally made some progress on this issue, I had made up my mind to go get some 10% just to rule it out. And I might still do that, 'cos now I'm interested in what it might do for me (other than corrode my bearings quicker :-) ) when swinging these big props.

DarZeelon

HS,


The OS (and clones), the Enya and, of course the Laser, will run well on 5% nitro.

The Saito (and for sure the YS) wouldn't.


If you're already at it, just get the 15% nitro fuel; not the 10%, which is on the very edge...
It wouldn't be that much more expensive; even in the UK.

ChrisAttebery

My Feedback: (15)

HS,

You will find that the Saito loves nitro. I'm currently running 30% in mine because I have a bunch of 60% and 70% left over from my boat racing days. After running 30% it's going to be hard to go back to 15%. The motor idles better and has alot more power. You can get roughly a 1:1 increase in HP by adding nitro. IE 10% will yield about 10% more power than 0% fuel.


Chris

daveopam

My Feedback: (9)

30% is highly addictive. It's all I will run in my 82. I swing a Zinger Pro 15x4 and it needs the big nitro My 72's both swing 13x4W APCs. They do just fine on 15%. I have run 14x4W on them with 30% but the planes they are currently on don't need the extra punch. I also have a 1.80 Saito. It's way to thisty for 30%.

David

Hobbsy

My Feedback: (102)

Dave, if the weather is slightly warmer tomorrow, I'll run my .82 on 5% WildCat with 16%/80/20 syn/castor lube. I'll use a 14x6 APC, I get 9,450 using 10%, I can't belive there is that much difference using 5%. I might be wrong though. I am referring to his 8,300 rpm on 5%.

highside

Hey,

Firstly thanks muchly for all the recommends. Good stuff.

I made it to the field yesterday afternoon and, after about 5mins of "OK but not mega" running, the uneveness really started to come back. I tried the tie-wrap trick and it made the problem worse which is actually a good result, since I'm now pretty sure it's related to the inlet manifold seals. Since I've had this problem since new I'll order a new manifold (in case it's deformed) and some new O-rings*.

I also found this thread http://www.rcuniverse.com/forum/m_33...mpage_2/tm.htm which says:

" The only ones prone to intake leakage are the mid block engines, the ones with the carb screwed to the back plate and a curved pipe for the intake. The pipe tends to vibrate, causing failure of the o-ring at the cylinder end. The FA-72 seems to be the worst of the lot for doing this. I've found a thin smear of RTV keeps the pipe from vibrating, usually prevents any further problem until the next tear down. Than another smear of RTV... " (Will Robison).

So it'll be going back together with a smear of instant gasket as well.

Hobbsy, I'll be very interested in your rpm on 14x6, I dream of >9k on a 14x6!!! For completeness, the 8300rpm was on 5% nitro with 15% synthetic and 2% castor.

HS

* Yes, I could just send the engine back. But where would the fun be in that?

buzzingb

My Feedback: (2)

It sound like it migh be starving for fuel as the rpms increase. Check the intake as some indicated and while you are at it clean out the high speed jet. There can be trash and restrictions there. Most likely if you mount it to the front of an airplane and run a few gallons through it the problem will go away.

Hobbsy

My Feedback: (102)

I ran about 10 oz of the WildCat 5%/16% lube today using the Saito .82 and the APC 14x6

RPM sustained more than 3 minutes 9,300, it didn't lose much changing to the 5%.
The plug was a GloDivil 4C Special, stock exhaust. Gotta go my wife wants to go out on a date.

highside

Hi Guys,

Fitted new seals and a new inlet manifold, all sealed up with instant gasket.

Now I get nice even running, easy to adjust, I'm happy!

RPM were APC 14x6 8900, 14x7 8500 (adjusted ready to fly rather than absolutely peaked out). So a bit less than Hobbsy, but close enough for fuel/plug/environment differences. I'm still happy!

Thanks for all your help and advice.

Cheers,

HS

Hobbsy

My Feedback: (102)

Good job all around.

Lynner532

Stay with your 5%. I know guys in America think other countries around the world you can waltz in LHS and buy 30% nitro and $50 a gallon isn't too much. And yet when our gas goes up 25 cents a gallon drive offs increase by 4 times over. Funny how a quarter a gallon makes some people into criminals. Funny we are now burning our food (corn,soybeans) for fuel and importing our food rather than petrolium. The glow fuel prices are going up this year....................

highside

Yep, currently gas is $9.50 a gallon here. I could almost run my car on straight glow fuel for no extra!

:-)

highside

I have one other remaining concern with my 82a engines. Am I the only one that thinks the carb barrel spring is ridiculously soft? I have one soft mounted, with a bellcrank on the mount so that the link "follows" the soft-mount movement. The link from the bell-crank to the throttle arm is short (40mm ish), light and ball jointed at both ends. But the midrange running is awful, the rpm "wows" over about a 1000rpm range at certain throttle settings. This is being caused by the carb barrel floating with engine vibration and consequently leaning the mixture. It cycles round speeding up, floating and going lean, slowing down, richening up and speeding up etc. I can actually see the barrel floating and causing the problem.

I'm currently on the hunt for a better spring, the only candidate I have is a cut down spring out of an ASP120FS carb which is about twice as firm as the Saito one (as standard its just slightly too long when compressed). I'd rather solve the problem with a firmer spring than by springing the linkage away from the carb; the spring in the carb acts coaxially on the barrel, whilst the linkage is offset by the length of the throttle arm.

Anyone know a source of a suitable spring?

HS