Hi,

I have a saito 100 which can't manage to suck fuel right. I thought I had an air leak in my tank system but I changed all the tubes and the tank and the problem persists. When I push the thottle air bubbles appear in the tube that brings fuel to the carb. Sometimes the engine seems to work fine on the ground but it it stalls during the flight.

I recently adsuted the valves, so they're ok.

Can someone help me? I'm really sick of this engine, and I hope some saito expert on this great forum will convince me that this brand is not crap!


Cheers,

Ludo, France

You still have an air leak in your fuel line. It is not the engine.

I had an OS .25 that would only run for a minute on the ground and then air bubbles would kill it...[&o]..the fuel lines were backwards....try that, you've got nothing to loose...Rog

Do you have a lot of vibration? prop/spinner well balanced? tank padded with foam? sounds to me like your seeing fuel foaming not an air leak... generally an air leak will produce air bubbles even at idle... from the way I read your post you only see the bubbles once you power up.

The Brand is not crap... I run 5 Saito's on a regular basis... like any engine make you can get bad one out of the box... in this case I think you'll find something other than the engine is your problem.

Good luck

John

Thanks guys for the fast replies.

My tank is padded with foam and the prop is properly balanced. I'm sure it's the engine.

Back your Low Speed needle out even with the end of the throttle barrel, back the High Speed needle out about 4 turns, now start it up, set the High Speed needle to peak rpm then slow to the lowest idle that it does not quit, start lean ing the Low Speed a bout 1/8th turn at a time, checking the transition after every other change. At some point it will start to idle very smoothly, gradually reduce the throttle setting to about 2,000 to 2,200 rpm. Now richen the peak down by about 200 rpm amd check transition, it should accelerate and run smooth as silk.

Sure sounds like you have an air leak somewhere in your system. Clamp the carb line, remove the vent line at the muffler nipple and pressurize the fuel system with a 50cc syringe. Clamp the vent line and remove syringe. After 30 mins, release the carb line clamp, and see if there is any air that rush out of the line (you may need to place your ear near the line to listen). If there is, then your fuel system is OK.

Yesterday I had a Saito 100 doing this. I found that the brass tube for the clunk line was cracked under the rubber. The pressure test was OK but the engine would suck air.

Good point Jim. Any "closed loop" leak that does not have a direct path to the atmosphere will not show up in the leak test.

The Saito 100 is a bone-shaker when it comes to vibration. A very light 4-stroke engine with a large displacement creates huge torque-pulses that manifest themselves as vibration.

Vibration (despite the foam rubber) can easily produce fuel-foaming and that results in bubbles in the fuel-line.

The fact that your engine runs okay on the ground but stops in the air is further evidence to support the fuel-foaming theory. This is because when your plane is on the ground, much of the vibration is absorbed by the fact that the undercarriage is touching the ground -- absorbing much of the vibration. Once the plane takes to the air however, it's free to vibrate more wildly and that's when the foaming becomes *real* bad.

However, just to make sure it's not an air-leak, here's what you can do to check:

1. fill your tank.
2. connect your fuel pump to the clunk line (that normally goes to the engine).
3. reverse the pump so as to suck the fuel out of your tank and look for bubbles.

If there are no bubbles then you *don't* have an air leak and the problem must be foaming.

The "suck" created by a fuel pump is many times greater than the suck of the motor so if air is getting into the line it'll be far more apparent while the pump is connected and running.

I have two 100's and three 91's among other Saito's. It's not manually perceivable that my 100's vibrate anymore than my 91's

The 100's jumped up and down when new but after running in and getting the needles set, I cannot see them being any different than My Magnum 91FS or OS 91 Surpass or other Saitos I own.

Maybe some 100's vibrate more than others?

Xjet
bet you have a hard time finding a hat to fit that big ***** head of yours !!

Just my opinion...

XJet

balance your props and your engines will shake LESS in flight, not more ! Hell , you might even be able to get a few more mph out of your trainers. Just my opinion...

Don't worry, my props are balanced and my low-end is leaned out perfectly (1/8th turn richer than a failure to transition).

My SA100 is in a Mojo 60 profile 3D (which is light at 5.5lbs) so the torque pulses are *really* noticeable.

Strangely enough, my SA82 is in a *really* flimsy profile but it hardly vibrates at all.

Quite a few people I've spoken to say that their 100s also really shake -- but some others don't. Likewise, some folks have 82s that are bone-crushers -- but mine's not.

I suspect that some Saitos are just more inclined to vibrate more than others -- end of story.

However, one thing's for sure, the vibration level of a very light and powerful 4-stroke will always be higher than that of a 2-stroke of the same power (assuming all else -- like prop balance, etc is equal).

I'm about to try using wooden props to see if the reduced mass will also reduce the magnitude of the reaction-torque pulses and therefore the levels of vibration. Some guys have had great success with this approach.

I had a Saito 100 that started running badly as you describe and it turned out to be trash in the needle seat. I pulled the needle and then pumped fuel through to blow it out, then re-installed the needle. It ran great for a few weeks then the same problem. I blew it out again and then put a filter in the line. No more problems.

Yes Saitos vibrate more than 2-strokes and some other 4-strokes. But the ones that I have seen that really shake have the idle set way too rich. A Saito will have a reliable idle and good transition when set very rich, it but will really suck fuel and vibrate a bunch.

Walt

A very rich low end will actually have the opposite effect.

A rich Low Speed needle makes the transition smoky, stumbly and shaky.

Its fuel foaming. Putting foam around the tank does NOT mean that fuel will not foam. The fact that it gets worse in the air just seals the deal for the fuel foaming case.

Wrap the clunk in felt, and safety wire it... All my tanks foam like crazy, but the system will not suck air with felt wrapped around the clunk

JettPilot

I didn't say the engine would have the BEST idle and transition when set very rich, but unlike an OS 2-stroke a Saito won't stop running or sag badly when the throttle is advanced. So many people just run them way too rich and tolerate the vibration and fuel consumption. I've leaned a bunch of them at my field for folks that are new to Saitos and didn't know any better.

Walt

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I have eight, or more, Saito engines and I am quite frugal. These engines would not be in my ownership if they were not good engines.

What you are describing fits the "fuel foaming syndrome". If the fuel tank is rigidly mounted to the model, the engine's vibration shakes the fuel tank so hard that foam is formed and picked up by the pickup tube. The solution is to isolate the fuel tank from the model (or test stand, if that is the case) so that the fuel does not have an opportunity to foam in the first place. Some models being sold are designed in such a way that it is very difficult to accomplish the necessary isolation.

Packing the fuel tank in loose foam is the answer, if there is space to do so. If not, a few squirts of Armor All plastic finish restorer in a gallon of fuel will usually alleviate the problem enough to tune the engine and fly successfully. While the Armor All works the majority of the time, it is masking the problem. It is better to fix the cause of the problem in the first place.

As your Saito engine accumulates running time, it will smooth out and not shake/vibrate as much. Be patient and stick with it. You will overcome this problem, one way or another.

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Addendum:

JettPilot is on the right track suggesting the felt wrapped fuel pick up inside of the fuel tank. I haven't tried the felt in a glow engine, but I know it works from watching others using this "trick".

I use a Dubro sintered bronze fuel pick up, which works on the same principle as the felt.

OS sells a bubble removing clunk.. They work great.

I SOLVED THE PROBLEM !!

It turned out that the pressure fitting was blocked by residues of oil and tiny bits of metal due to the break-in period!

Thanks everybody for the help.

I hope this experience will benefit some of you guys!

How did blockage in the pressure line cause bubbles? You forgot to mention that the engine once ran OK, or did it? I hope the metal came from the muffler and not the engine; metal particles are not normal wear. This shows once again the KISS principle works in trouble shooting.

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Xjet, as an engineer you should know that there is not enough latitude in the production of these engines for some to be significantly more out of balance than others.

I'll bet those complaining of shaking are those trying to break-in their engines while flying. This is not meant as a shot. But I'll bet it is the truth.

If we were talking GMS or some other cheap Chinese engine I'd agree -- but the Saitos seem to be very well made and decidedly well made. When you consider the magnitude of the vibrations experienced by some, the kind of mis-machining or deviation from spec would be obvious to anyone with a dial-indicator or set of calipers and micrometers.

Both my "smooth" and my "jackhammer" Saitos show exceedingly good fits and tolerances. There's no perceptable runout on the crank, no perceptable radial or axial movement from bad bearings etc. The only thing I haven't checked is endplay on the conrod -- but they certainly feel about the same when rocked around TDC.

I'm using the same fuel, same prop brands, same glowplugs -- there are very few variables not accounted for.

In the next couple of days I'll be reinstalling my SA100 on a plane and running it up again. I might fit some accelerometers to the airframe and build a four-axis vibration map throughout the rev-range. That may give more clues as to what's causing the vibes.