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Saito 72 running backwards repeatedly

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Old 05-15-2010, 01:00 AM
  #1
kargo
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Default Saito 72 running backwards repeatedly

Hey Gang, trying to get my Saito 72 going strong for the season and running into a little trouble.

I can get it to start, but can't get much above idle without it quiting. It'll run for a bit, usually 30 to 60 seconds, once a couple minutes, seem to idle too low and die just to come back to life running backwards. It must of done this 5 times or more. It started VERY easily. I use an electric starter and it hardly took anything to make it go. What gives? I've heard of a 4stroke running backwards but thought it wasn't very common.

Its two years old, I followed Saito's break in instructions for 45 minutes plus and 40+ ounces of glow fuel. I flew it twice last summer, 20 minute flights each time. We really had to work hard to get the idle down so my portly sig senior would land. Guess thats what happens when your ailerons add an extra 2 1/2 inches to the trailing edge

Thanks in advance for any advice. Right now the plan is to go back to the manual and find the break in settings.
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Old 05-15-2010, 01:25 AM
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Default RE: Saito 72 running backwards repeatedly

You may have the low end needle set too rich.

And the low end has an effect up to 75% of the throttle (that is what the people say around here)....so you basically have to retune your engine....

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Old 05-15-2010, 01:49 AM
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Default RE: Saito 72 running backwards repeatedly

I was wondering about that... that guy is not something I usually mess around with, but I've had to on a few of my other engines so I guess I better quite my whining and do it.
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Old 05-15-2010, 03:47 AM
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Default RE: Saito 72 running backwards repeatedly

I spend a whole season once flying with a new Saito 72 that I could not get below 4000 rpm to idle. All experts went to work, we adjusted all you could imagine. No success. I did learn to make hot landings succesfully though :-) .

In the end somebody mentioned that a too high oil percentage gives trouble as well. I was absolutely sure that could not be the case. However I did go out and bought some new fuel (at the beginning of the season I had bought 6 gallons so that never ran out until end of season) at 18% oil and it was perfect. It seems the hobby shop I bought my fuel from made a mistake. My 2-strokes had no problem so maybe it was only 25% oil. Since then I converted all my fuel to 18% oil and also ran my 2strokes on it without a problem.

Please take care with your engine. If it first runs forward and then after idle goes to backward running it might dislodge your propnut in the process. Make sure it is still tight or your prop might come off, very dangerous.

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Old 05-15-2010, 03:49 AM
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Default RE: Saito 72 running backwards repeatedly

Remark #2: in my experience the Saito idle needle comes from the factory way too high. After your first runs you really have to turn it down significantly. Try that first.

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Old 05-15-2010, 04:04 AM
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Default RE: Saito 72 running backwards repeatedly

Kargo,


A four-stroke engine can run backwards, if it can induct fuel through, or from its muffler...

Change your fueling and starting procedure...
Never refuel with the muffler pressure line, connected to the fuel-tank breather, since it causes excess fuel to collect in the muffler...

Make sure the tank breather is above fuel level in the tank.
It takes several seconds of full-throttle running, to expel all traces of raw fuel that did manage to accumulate in the muffler. In fact, you can clearly smell it...


Essentially, a four-stroke engine; although it does generally have a larger intake valve and slightly different exhaust and intake timing, will run almost equally well, but the other way; if you mount the carburettor on the exhaust tube and the muffler on the intake tube.

Having volatile fuel accumulated in the muffler, 'transforms' it into a makeshift 'carburettor'.
The carburettor becomes the exhaust...


EDIT: Enhancement.
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Old 05-15-2010, 04:10 AM
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Default RE: Saito 72 running backwards repeatedly


Quote:
ORIGINAL: DarZeelon

Kargo,


A four-stroke engine can run backwards, if it can induct fuel through, or from its muffler...


Yes, what Dar says about fuel in the muffler will cause a 4 cycle to run in reverse, I have had it happen before. Maybe you are not removing the pressure line from the muffler when you fill your tank?
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Old 05-15-2010, 11:49 AM
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Default RE: Saito 72 running backwards repeatedly

Thanks for all the advice gang, it does shed some light, both about the backwards running and the high 72 idle. I'm currently out of glow, so maybe its time to find a different oil content... Anything that would get the idle lower for that big senior wing area.

As for fueling, I do remove both lines (intake and muffler). I set the system up with a header and main tank so I could fit close to 44oz of fuel in it. Its worked reliably except this year. When I did the initial break in on a test stand I put the main tank at least 10inches below the header and it ran without even a burp. The only thing I can think of screwing it up now is if the lines got pinched somewhere when I repacked the guts this year. It does appear to be getting fuel without large bubbles. There was however still fuel in the muffler line. Maybe I'll bring a good clamp and clamp it off half way down. The only other ellement to this is a third line to fill the maintank through a fuel dot. I've never gotten this to work right, I don't know why. It seems like it'd be a simple matter of pumping the fuel in...

Something else interesting. It does kill, but while its idling it does so very well. Its not popping, hiccuping, burping or anything. Its the sweetest idle I've ever heard on a motor.

I'm going to reset the highspeed to 2 and half turns as per the manual. I'm also going to try a 18% oil content fuel. And I'll very gently touch that lowspeed needle after I've got the high speed one reset with a tach.

Any other input is much appreciated. I LOVE my Saito, even with my troubles now, to hear that thing idle so low and so sweet is awesome.
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Old 05-15-2010, 03:04 PM
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Default RE: Saito 72 running backwards repeatedly

The other day a guy at the field was starting his 72 Saito on a profile plane and it kept starting backwards with an electric starter. I offered to help because he was on a stand it almost got away fom him. He started it again,running backwards,couldn't kill it with the tx so I stuck my finger over the carb-BIG MISTAKE- it was hot enough to burn a ring on my finger.
As with most situations there is a simple explanation .Keep the good information flowing,
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Old 05-15-2010, 05:16 PM
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Default RE: Saito 72 running backwards repeatedly

Trying to set any needle valve at a certain setting, such as 2 1/2 turns won't work. You have to tune the engine. Your .72 may be a whole turn, or more, off of what mine is set to. You can't go by that except to get back to a starting place to tune the engine.

A high idle setting is usually a sign of the low speed being too rich.
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Old 05-15-2010, 05:40 PM
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Default RE: Saito 72 running backwards repeatedly

A lot of good thoughts on this here. Especially the 'go back to the beginning' idea. Make sure not to overlook the obvious. By that I mean is the prop in the right size range, is the glowplug strong and is your fuel reasonably 'fresh'. Is the tank height right?

Assuming all that is ok, go back to the original settings (I think they are mentioned in the manual), adjust the high end needle then the low end. Then re-adjust the high end as there definitely is a relationship between the 2.

Best of luck!
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Old 05-16-2010, 12:49 AM
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Default RE: Saito 72 running backwards repeatedly

Here is a simple thought.

Do have the fuel lines on Backwards? You say you take both off when you fuel. A simple mistake? if it run good before and now it does not what you are saying well this might be the problem.

(Hmmm ask me how I know that one.)

If you do it will blow the fuel into the muffler. That is why you are seeing fuel in the muffler line. That is why it will run good for a few seconds. Then it runs out of fuel to the carb.

Worth a second look?
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Old 05-16-2010, 12:54 AM
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Default RE: Saito 72 running backwards repeatedly

My two four strokes just do that...

It is quite easy to overprime a four stroke when they are inverted, both of mine are inverted.... sometimes they just start with a back flip, and sometimes I just use the starter because they don't want to start easily or kick back .... In my case I can't take the pressure line out because of the cowling...is just impossible to take it out... but since the engines are installed inverted, fuel just go out.

Running backwards is in most cases caused by more than enough fuel!
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Old 05-16-2010, 02:21 AM
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Default RE: Saito 72 running backwards repeatedly


Quote:
ORIGINAL: estradajae

Running backwards is in most cases caused by more than enough fuel!
Jorge,


This is incorrect...
In a four-stroke engine, over-priming will not do that (cause the engine to start backwards)... This 'trait' is two-stroke specific.

Four-stroke engines only run backwards, if they can use their muffler as a 'fuel source'...


If your starting 'technique' does cause the muffler to fill with some fuel; well, there you have it!
But it is not the kind of over-priming that would normally cause a two-stroke, engine to flip-start backwards...
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Old 05-16-2010, 03:57 AM
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Default RE: Saito 72 running backwards repeatedly

Once filled,(without glow power) try tipping plane towards exhaust and rotating prop in opposite direction a few times to remove the excess fuel through the exhaust.
Then apply starter,low throttle (WITHOUT GLOW POWER), Spinning the the prop in normal direction, again to remove excess fuel out of exhaust.

Connect glow power,starter and go fly.

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Old 05-16-2010, 08:30 AM
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Default RE: Saito 72 running backwards repeatedly

Dar

There is no way that in both engines the muffler acts as a tank, since they are both pointing down. And the engines can run backwards quite for a while sometimes.....Maybe they are sucking some fuel from the pressure line too.

And Dar, Over priming in the four stroke makes them kick back hard, that makes them backfire and start backwards. Now I prime them and start them backwards to make them start in the right direction.

The Thunder Tiger can be started with a back flip on the spinner...the ASP 91 not....because it doesn't have spinner , but starts normally with a back flip....sometimes starts backwards too that way.
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Old 05-16-2010, 09:36 AM
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Default RE: Saito 72 running backwards repeatedly


Quote:
ORIGINAL: estradajae

There is no way that in both engines the muffler acts as a tank, since they are both pointing down. And the engines can run backwards quite for a while sometimes.....Maybe they are sucking some fuel from the pressure line too.
Jorge,


It is not that the muffler actually acts as a makeshift tank...

But after fuel drips back through, the amount of fuel present in the muffler, on its internal walls and cavities and in formed carbon residues (a four-stroke exhaust is much hotter than that of a two-stroke), is enough for more than just a few seconds of running.

And then your suggestion of more fuel being siphoned through the tank breather... In short, the conditions in the muffler can be such that a four-stroke engine can run backwards, for much longer than you would care to know... It surely does not run backwards, on fuel taken through its carburettor.

Quote:

...Over priming in the four stroke makes them kick back hard, that makes them backfire and start backwards. Now I prime them and start them backwards to make them start in the right direction.

The Thunder Tiger can be started with a back flip on the spinner...the ASP 91 not....because it doesn't have spinner , but starts normally with a back flip....sometimes starts backwards too that way.
Both true; especially the kick-back part...

I cannot be sure about the traits of the ASP, but I always try and usually succeed to start my Saito that way.

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Old 05-16-2010, 11:04 PM
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Default RE: Saito 72 running backwards repeatedly

Thanks Gang, lots of good info coming up in this thread. My Saito did all its reverse thrusting after backfiring. Runs sweet at a low idle, acts like its being fuel starved for half a second, backfires and comes to life turning the wrong direction.

I did rethink the fuel system, I have a header and maintank. I didn't pull anything out (read pain in butt in the Senior, impossible without a saw for the header), but blew in both tubes. Blow into the carb line in and get bubbles in the main tank, the muffler line and you push fuel out the carb line. Seems like it should be working unless someone knows something I don't which is COMPLETELY possible. The height on the 4 oz header is about as good as it'll get too, and as I remember was within what I've read.

The tipping the airplane to see if any fuel runs out is a good idea, I'll try that.

The information about the low needle usually being too rich if the idle is high is good too.

We ran it at the field again. It went backwards a few times and we messed with the high until we just threw up our hands and tried to reset the low speed needle. It was set VERY rich (I must of messed with it trying to make the throttle linkage work inside that balsa cowl...). We closed it all the way and opened it 2 turns. Much fiddling and much more opening of the low speed later it ran much better, never backwards (this stopped after resetting the low speed), for longer periods, at a fairly high idle, and with the highspeed set towards 3 turns. It would eventually kill. Its not ready yet, but its much improved. If anyone has anything else, I'd really like to hear it. Thanks again for everyones help.
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Old 05-17-2010, 02:28 AM
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Default RE: Saito 72 running backwards repeatedly

The low speed needle setting is roughly judged by its position relative to the surface of the throttle arm. No one ever references the low speed on a Saito glow engine from the closed position.

They are usually recessed about 1/16th inch below the face of a plastic throttle arm or flush with a metal throttle arm.

The actual position is as lean as possible and the engine still able to transition from low idle to full throttle without quitting

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Old 05-17-2010, 11:40 PM
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Default RE: Saito 72 running backwards repeatedly

Thanks for the guideline and low speed setting. The low speed setting sheds some light on the backfiring, I had the needle set outside the throttle arm. When I closed it the backfiring stopped. I've got the highspeed set pretty rich now too. I know the low speed is set inside the throttle arm, next time I run it I'll see how close to 1/16 below it is and try it there if its not. Maybe I'll find a better setting for the high once the low is set correctly.

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Old 05-18-2010, 01:31 AM
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Default RE: Saito 72 running backwards repeatedly

I'm surprised that Hobbsy hasn't jumped in here wwith the proper way to set the needles?

Start out with the low speed needle flush with the surface of the plastic throttle arm.

With the correct prop, run the engine at full throttle and peak the high speed needle.

Return to lowest posssible engine speed and begin to lean out the low speed needle

You will notice that to push in on the throttle arm will lean out the mixture? Make sure the throttle rod doesn't push in on the throttle arm.

Lean the low speed needle a little and check your acceleration. The final stting of the low speed needle will be in little 1/8th turn increments or you will be chasing your tail.

After you get the low speed as lean as posssible and still able to accelerate to high speed, - return to the highest speed and peak your high speed needle and then richen (turn the needle out a couple clicks) the high speed needle 200 to 400 rpm. Now your needles are set for today.

On a different day, you may need to readjust the high speed needle?
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Old 05-18-2010, 04:51 AM
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Default RE: Saito 72 running backwards repeatedly

Keep in mind that if you get the low speed "IN" too far, you cannot get the high speed needle rich even if you screw it out all the way.

This is the reason for setting the high speed at PEAK first before you ever try to set the low speed.
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Old 05-18-2010, 11:17 AM
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Default RE: Saito 72 running backwards repeatedly

Thanks again. I knew the basic stuff of setting to peak on the highspeed and then backing it off a little, and setting the idle with the low speed (I usually didn't touch the low speed anyway) but the steps you listed are a big improvement on that. I'll be sure to check if the linkage is pushing in on the carb any. Maybe with a little tinkering I'll get more comfortable at this, I know I am after getting it to run a little better with my buddies help and the folks here at RCU. Another thing I've discovered in this process. They say you can run your motor in on the airplane, but if you want stuff ready to go in the spring you better get your motor ready on the test stand while you're building your kit. Otherwise its WAY too much messing around at the field. Especially after you've been spoiled by ABL/non-ringed motors...

W8YE, is that initial low speed setting applicable to other 4 strokes?
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Old 05-18-2010, 11:55 AM
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Default RE: Saito 72 running backwards repeatedly

I learned a lot just running engines on a test stand on a windy day or maybe it was too rainy or cold to fly, I would be in the door way of the garage running engines.
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Old 05-18-2010, 12:02 PM
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Default RE: Saito 72 running backwards repeatedly


Quote:
ORIGINAL: kargo

...I knew the basic stuff of setting to peak on the high-speed and then backing it off a little, and setting the idle with the low-speed (I usually didn't touch the low-speed anyway) but the steps you listed are a big improvement on that.

Otherwise its WAY too much messing around at the field. Especially after you've been spoiled by ABL/non-ringed motors...
Kargo,


This may have been a part of the problem, that brought you to seek assistance here...

The low-speed needle (at least you don't call it 'the idle needle') is the engine's MAIN fuel control; not its secondary control...
This is in contrary to what many RCers think; and apparently (judging by what you wrote in the bold part of the quote), also to what you thought.

Why 'main', you ask?, because it controls and tailors the fuel-curve, over the entire idle-to-80% throttle range.

The high-speed needle is just the 'secondary' control, because it only affectls the very top of the engine's operating range.
If forms nothing of the sort of 'a curve'; and just sets the maximum amount of fuel the engine can suck in...

I do believe many of the newer modelers have become 'spoiled brats'; expecting things to just work 'out of the box', without bothering to actually need to learn how to perform the chore of operating them...
Some of the moderators don't really like it when I use this term, but I am just portraying reality... Add higher nitro fuel that does not require the user to know, how to set the top-end perfectly either and add that to your ABN/non-ring remark...


I believe this thread has pretty much run its course. I am getting off at this point.
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