Hello I am new to 4-strokes and am having a bit of an issue with a Saito 100. I am using a Kelco custom exhaust on a Hangar 9 Spitfire with a blade 13x8 prop. I am having issues trying to get the engine tunned. The issue that I am having is the high speed needle valve doesn't seem to have an effect on rpm. It peeks out around 10,300 rpm. When I turn out the needle valve it richens up but the rpms dont seem to change. 1 full turn will cause a 100 rpm drop. As it is richened the exhaust gets smokey and sloppy so it seems it is running rich but the rpms don't seem to change. When I shut it down there is oil and resuide covering the plane as you would expect from a rich engine.I have tried different fuels 15% synthetic and castrol blend and 30% all synthetic. I verified no issues with fuel lines and the Carb has no obstructions. As all of my previous experience is with 2 strokes I don't know if I am doing something wrong. I just dont know how to tune it if propperly if the rpms dont change. Thanks Adam

Open up the low speed needle a little and try the high speed again

It sounds like your low speed needle valve is too rich.

Is it possible that with that custom exhaust that you are not getting enough pressure to the tank somehow? I've had that happen and richening the HS needle didn't have much effect. Keep us posted, thanks,

Ernie Misner

Adam i'd set your low speed needle back to factory settings and peak the hsn, i think w8ye is saying you are to lean on the LSN.The prop figures at peak sound really too.

Well, that's embarrassing for sure. I meant too lean. Good grief.

<p class="MsoNormal"><span style="font-size: 10pt; font-family: Verdana; background-color: rgb(251, 252, 255); background-position: initial initial; background-repeat: initial initial; ">I took a look at the low speed needle and it was turned in substantially. I think more than 4 full turn out to get it back to factory settings. I had my flying clubs "Saito expert" help me set it up originally and that is where he set it. I think that the low speed needle combined with the custom exhaust could be the problem. It does have a pressure tap but the scale exhaust system has 6 outlets so I am sure that it gives less pressure to the tank then the stock muffler. I also think a contributing factor was the fuel lines used to have a siphoning effect. When I was breaking in the engine, I had to clamp off the fuel lines to keep the carb from filling with fuel when the engine wasn&rsquo;t running. The siphoning mysteriously stopped and that was around the time I started having issues with the needle. I suppose the siphon effect was pushing more fuel in. Why the siphon stopped, I do not know. Adam<span class="apple-converted-space"></span></span></p>

The further the carb is closed or the LS needle leaned, the less siphoning will occur.

Hi ernie if the fuel tank is high in relation to the carb with a saito single inverted then you need to completely have the throttle barrel shut or it will continue to dribble fuel..the tank not me i hope

Never sweat on a cheerfull post,i've got a good idea about embarrassing thowhat about a you tube vid(shoulder cam of course)of our mate hairy knuckle dave riding a fatboy down his favourite stretch of straight road stark naked and a guitar strapped to his back.What movie theme music would be playing while all that went on guys

Keep in mind that the factory setting for the low speed needle is sloppy rich. This is intended for the initial break in run on the engine.

If you have it that rich, you can watch all the smoke as you advance the throttle. If your high speed is set nearly right you can see the smoke begin to disappear near 80% throttle. This shows where the low speed stops having effect.

Right on Old Fart. If you have a switch on your tx set up for engine kill / carb fully closed position, you can shut the power off on the plane while it is in that position and you shouldn't get any siphoning.

While your at it change the prop as a 13x8 is way too small for a Saito 100. I agree with some of the other posters that your low end is probably too lean so after you change the prop richen up the low end and try again.
fred

I had assumed that he was running A 3 blade 13 x 8?

Yeh i assumed that too.Anything over ten on that size prop sounds good to me,don't know whether it's a wide blade or not,adam ain't far off the mark.

Yeah it is a 13x8 3 blade. I also tried a 14x9 3 blade. Seemed to struggle in flight with the 14.

My Saito 100's are happy with a 15x6.

My low speed needle wound up flush with the throttle lever face, nothing protruding past the lever. Results may vary.

Good luck,
Dave Olson

I have a Saito 100 coming for a 3D profile plane. Will it pull a 16x4 APC Wide prop? That's the same prop my Saito 125 pulls though ... ?

I think you'll find a 15X4W a better fit, after you get the engine broke in.
Just my opinion.

Dave Olson

Yeah, that makes more sense. The wide series props can be quite a load. Thanks.

It looks like it is a lack of muffler pressure is causing the problem. I switched back to the stock muffler for trouble shooting purposes. It cleared up all the issues I was having. I left the needle at the positon I had set it with the scale exhaust. With proper exhaust pressure it wouldn't even run without continuous glow heat. I leaned it out to the pointI had it running at 6000 rpms wot pulled off the muffler pressure and it surged to over 10,000. I guess I will have to switch to a perry pump of something to provide fuel pressure at the needle since the scale system doesn't provide enough pressure. Thank You Everyone for your help. Adam