Hello,

Thanks for looking at this post.

I hope someone could help me or have a few suggestions. I have a Saito .91 that I bought used. The person I bought it from said he only ran about 5 tanks through it at the most. This is my first 4-stroke. I tried it out a couple of weeks ago for the first time in my Venture 60 swinging an APC 14-6 prop. It started right up and ran great. Vertical performance was fantastic. Tach showed 8800 rpms. Was using Sig 4 stroke fuel. I ran about 6 to 8 flights that weekend.

The following weekend I started it up as usual, and noticed my vertical performance was nowhere near what I had the weekend before (barely any). So I checked and adjusted the valves but it made no difference at all. Lots of smoke coming from the exhaust. I tried Byron 16% 4-stroke fuel and even changed the O.S. type F glow plug with a new one and it didn’t make a bit of difference. It was a lot more hot and humid than the weekend before and thought this might be the problem so I adjusted the rpms up to 9800 thinking this might help. All it did was make the engine very hot. My guess is it’s too lean. Backed it down some to about 9200. Now you could hear the engine fluctuation in rpms at full throttle. By the way, it seems to idle just fine at about 2300. The engine just sputters in the air with hardly any power but if I lean it out a bit, the engine gets very hot.

I noticed that the engine would rev when I touched the h.s. needle. Just by pushing down on it slightly would increase the rpm by 1000. I took the engine off last night and looked at the needle valve. It wiggles slightly. Is this my problem?

I checked all fuel lines and tank for leaks. I also checked for loose screws. Everything seemed fine. My H.S. needle valve is out 5 turns and my idle screw is out 4 turns.

I am at a loss any suggestions would be greatly appreciated.

By the way, how do you figure the peak rpms? I had it up to 10,200 and it still seemed like it could go more but I was afraid that was too much.

Thanks,
Dave in Missouri

It sounds like there is a mechanical problem with the high-speed needle assembly. Maybe some damage from the previous owner ??

Yep, sounds like your highspeed needle may have an air leak. Try some silicone around it (temporary fix) to seal any leaks and fly it. Could also take some fuel tubing and place it around the needle valve and reinstall.

Or, more likely, your engine is hotter because you are running it leaner! You said you originally flew at 8800 rpm, and it was fine. Then it was HOTTER outside and you LEANED it out. On a hot day you should richen up the needle, and know that you will have less power than on a cooler day...Its just the laws of physics

Quote: "I tried Byron 16% 4-stroke fuel ... " If this is 16% oil, be carefull if you lean it out too much. Saito recommends 18 to 20% oil. Dont want you to burn it up before you enjoy it. Keep the rpms in the mid 9000. Heed the above advise and try to get the needle right.

5 turns on the high speed needle valve sounds like alot to me. Try taking the needle valve out and clean it. Blow throught the assembly to make sure there is no crud in there. It was running good originally so I don't think it is a mechanical problems with the valve.

Blackdog

First off I would like to point out that Satio recomends against using fourstroke fuel in their engines due to the lower oil content. They instead recommend using two stroke glowfuel of at least 18% oil. I have owned a Satio 91 for quite some time now and it is a great engine. I usually run either Powermaster 20/20 or Morgan's 30% Heli fuel in mine with excellent results and power. You usually richen the engine off peak about 200 to 300 rpm for flying. I usually tach around 10000 rpm rich with a 14x6 but I prefer the Apc 15x6 prop instead. With 30% fuel I can run this prop about 9200 rpm with excellent results.

I too believe the high speed needle is your problem. There should not be any play in the needle valve. Check the O ring and you might have to use the previously mention idea about using fuel tubing to help seal the needle valve. Good luck with the engine.

I agree that five turns out on the main needle is a lot, is your idle needle set very nearly even with the end of the throttle barrel. If you remove both needles to blow through the carb, replace the idle needle dead even with the end of the barrel and it will be within 1/8 of a turn either way of where best idle is. Start with the main at four. I believe five turns is causing your engine to be way rich and not very powerful in the midrange. Don't be afraid to let it approach 10,000 rpm you're not going to fly it much at that rpm anyway.

I have a Saito 91 that has about 100 hours on it. 5 turns out on the high needle is what I did to break in my engine. I won't tell you where my needle is now, because all engines set up a bit different, and I don't want you to run your Saito lean. But I will say that your needle is quite a bit to rich.
Get a good quality 15% fuel, 2stroke. Start the engine up and let it run for about 2 or 3 minutes at idle or just above. You will need a tachometer for the next step. Set the prop speed on a 14X6 prop at about 9800 rpm. When you fly you should see a bit of white smoke, but not a lot. Run your Saito's just a tad rich. Never lean. But too rich will cause dead stick.

Thank you all that have replied to this message.

My problem was the h.s. needle being loose. I used the piece of fuel tube as was suggested and it cured it. It's great to have a reliable engine again!! After the fix, I did have to turn it in at least a whole turn from the 5 turns it was before.

Thanks again for your suggestion and the comments regarding the fuel too.

I was running 4cycle fuel in my 4cycle (go figure ), but should I switch to 2 cycle fuel? Is it ok to do so now that I have about 30 tanks through it using 4cycle fuel? I have the Saito91SGN too.

I also have a Satio 91 with almost 50 hours on it. No real problems. I use 15% omega 2 stoke fuel, and add 2 to 3 OZ of caster oil to it. Brings oil content up to about %20. I don't notice much power loss with the higher oil content. LEAN RUNS ARE VERY BAD FOR 4 STROKES

Senior citizen here,, but I use the Cool Power 15% and peak rpm, then drop 300 rpm to fly. Never had a problem w/my saito's, all are still flying.. Jim (prop them for about 9200-9500 rich)

thx for the info.
I planted my 91 1.5 feet in the ground this weekend.
Hope she's ok. Haven't cleaned 'er up yet. Was just about done my 4Cycle fuel jug, and had just bought a new Omega pink 15% 2 stroke jug to try. Will have to wait for a new plane now.

crossing fingers she's ok.