allanflowers

My Saito 72 sometimes just won't stop, even though the throttle seems to be fully closed. It continues to run weakly and I have to use my fingers on the spinner to make it stop. I have already set the Tx adjustments (end points, etc.) and the physical linkage as much as possible so that is not the answer. Maybe I should just be happy that it wants to run, no matter what, and will be reliable at really low idle in the air - but it bothers me.
Has anyone stopped an engine by hand but from the back side of the prop, where it won't bite so much? Is the idle adjustment screw just too rich?

TFF

dont use your hand. you might have an air leak at some joint, and if not I would pinch the fuel line. I have seen people grab big spinners and my dad use to throw a rag in the prop. I'm not doing it that way. sometimes a heavy prop with the flywheel effect will allow it to idle lower than normal.

abufletcher

I've also seen guys stop an engine by covering up the muffler opening. I've also seen the "rag into the prop" trick but that seems like a just plain aweful idea unless it was some kind of emergency. I'd also advise against stopping a slowly spinning blade by hand -- just on principle!

If you can't get the engine to stop with your radio, I think you need to adjust the mechanical travel on the throttle servo linkage. When you push the Throttle Cut button (assuming your Tx has one) the carb opening should close down completely -- and no engine can continue to run without air. If it is closing completely and still running, air has to be getting in somehow.

Dr1Driver

Allan, I can't tell you that you're an idiot because a Moderator would pull my post. What you are doing is extremely dangerous. There are three good ways of stopping a glow engine.

1. Set the throttle barrel so you can stop it with the transmitter.
2. Put your finger over the muffler opening.
3. Cover the carb throat with your finger.

Stopping an engine by grabbing the spinner or throwing a rag into the prop are no-brainers, IMO.

I once had a Webra Speed .40 that wouldn't stop running. Found an air leak under the carb body. Sounds like that might be your problem.

Dr.1

allanflowers

The finger over the carb and pinching the fuel tube won't work with this cowled engine. The finger over the muffler sounds like it would. I probably have an air leak and will look at that.
These WW-I planes are problems because you have to recess the firewall and, even with the cowl off, access is very limited because the engine is back in a pocket.
Thanks everyone.

abufletcher

Allen, I just re-read your (edited) initial post and it sounds like you've checked all the usual things. If the carb is completely closed and it still won't stop then there's definitely a problem. The idle set screw (the little one in the middle of the plastic throttle arm) wouldn't have any effect on this. Closed is closed.

Are you perhaps adjusting that other screw (with the spring on it) that sticks up next to the throttle arm? I had to ask what that did the other day at the field. Turns out it just tightens the grip on the carb barrel rotation (and if it's too loose the carb barrel will actually come loose during operation which is obviously a bad thing. So it may be that this screw is too loose and some air is getting into the system that way.

BTW, neither the Saito 82a or 56 engine have this screw. Just the 72. I wonder why.

abufletcher

Also, Allen, my Saito 72 has the choke cover. When I finally install it in my Snipe I plan to attach a small wire to this so that I can open and close it from the outside of the model.

camdyson

Finger over the muffler works fine, but I agree, if the barrel's closed then you have an air leak.

Cam

jashley1

It may be a matter of semantics, but that little screw with the spring on it fits in a slot in the throttle barrel. It does serve to keep the barrel from falling out but it does some other things as well. It works to set the amount the barrel stays open at idle and since the slot in the barrel is cut a certain way, it moves the barrel closer to the spray bar end to adjust the idle mixture. It really does not use tension per-se. I have had motors that lost the screw through vibration and replaced the original with a small nylon screw that was a tight fit.

abufletcher

Thanks for the clarification. You're right that tightening the screw also moves the barrel. I just wasn't sure what this accomplished and neither were any of the guys at the field since the other Saito they were familiar with don't have this screw.

So you're saying it DOES affect the idle setting? How would adjusting this screw compare with (or interact with) adjustments to the idle screw in the middle of the throttle arm?

And why don't the other Saito engines have this (or the choke)?

allanflowers

My Saito 72 doesn't have a choke. I don't think any of the US sold Saitos do anymore. One can prime the engine with a finger over the exhaust while turning the prop and it starts fine.

abufletcher

I get the feeling that the one I bought (was sold?) from an RC shop in Osaka may have been "old stock." It came with the longer, thinner turned aluminum muffler and more angular attachment tube (which was perfect for my Snipe setup) instead of the shorter, stockier (cast?) mufflers that came with my 82a (GK) or my 56's.**

Allan, does your 72 have the barrel adjustment screw? Note that the 82 and 56 don't have either the choke or the screw. Unless someone can explain the advantage of either, I'd say "good ridance."


**The muffler in the photo above is from the 82.

Wayne22

My Feedback: (2)

Don't put your finger over a muffler...you will get burned.......no need to ask how I found that out.

If the throttle barrel is physically closed, then there is an air leak some where..It may require removal of the engine to get at the carb and manifold pipe. Take them apart, relube the o-rings, and re assemble.

How do you fuel?? Do you have a third fuel line with a fuel dot, or can you reach your muffler pressure line? Removing either of those will reduce the pressure in the tank and reduce fuel flow to the engine which may be enough to do the trick. You can also hold the plane nose up, and the engine should lean out and die....

Failing that, DuBro make a super smoker valve which is a simple inexpensive plastic fitting that pinches off a smoke line. Install one of this one your fuel line with a wire out side the cowl. Just pull to pinch off the fuel line.....

abufletcher

BTW, Allan, just how low are you able to get your 72 to idle? After about maybe a little less that 2 hours total of run time and a lot of fiddling with the throttle/idel setting I can get it to to idle (and not die) at around 2800 (with some burps down to 2600 and up to 3200). But it's a bit rough and irregular at this. I'd loved to be able to get the idle down to 2400.

Dr1Driver

Allan,

I meant no offense and I'm glad you didn't take any. You're right, the big round cowls of rotary-powered WWI aircraft make it VERY difficult to get to the engine while the cowl is in place. Maybe try some RTV or high-temp silicone around the carb base where it contacts the crankcase. Good luck with it.

Dr.1

Edwin

My Feedback: (2)

I use wd40 to find air leaks. With the engine running, spray (with the tube on of course) all the suspect areas. Carb base, needle valve, back plate and such. If there is a leak, the engine will die. Normally I run the engine up to a fairly high rpm so it just sags when you find the leak. In your case, just leave it at idle and see what happens. Just be careful how you spray so you dont get inconclusive results.
Then again, maybe a tweek on the low speed needle might help it die when you want it to.
Edwin

Juice

I recently went through this problem with an RCV-90SP with an APC 18x12 on a H9 Corsair. Lucky me, my attempt to shut down the engine was caught on video, here:

[link=http://www.rcuvideos.com/item/TBX7NK690NXB4T84]H9CorsairFlight2.wmv[/link]

Two minutes into this video, after I taxi back to the flight line... you'll see me adjusting the TX to close the throttle barrel. Lowest trim setting, maximum low-end travel, and lowest sub-trim. Failing that, the next thing I thought of was to close the high end needle to shut off the fuel supply. Typically, most people have this needle readily accessible.

Later in the pit area, a quick adjustment to the throttle linkage fixed the problem for good. Luckily, I didn't have any air leaks in the fuel system, and everything else was bolted down tight.

abufletcher

I had a similar problem IN FLIGHT once. I couldn't get the model to slow down and couldn't kill the engine using either the trim or throttle cut button. So I just flew it around in circles until the fuel ran out (25 minutes later!). Once it was down the problem was obvious the one of the bolts that holds on the carb on this 2-stroke had fallen off and the other had vibrated loose, so even "closed down" air was still getting in.

That was the longest 25 minute flight I've ever had!

Prop Nut

My Feedback: (3)

I have an ASP 1.20 four stroke that has this issue, I have not tracked down the leak yet but it runs very good. I also block the exhast pipe to stop it. (NOTE: Do NOT use the sleeve of your nylon jacket to do this, your wife might be very angry at the several round holes left in it )

jashley1

Abu:

When I said that it affects the idle mixture, I should have said it does it in a roundabout way. The screw is just an alignment pin and the spring acts as a lock washer of sorts. Some OS motors had the screw and a jamb nut instead of a spring. On some and maybe most motors without air-bleed carburetors, as the barrel rotates toward closed, the groove cut into the barrel moves the barrel toward the high speed needle which restricts the amount of fuel coming in. So, not only are you closing the opening and restricting the amount of air, but the the spray bar is affected and leaning the mixture. If you look closely at the carburetor while moving the throttle arm you should see the barrel moving in and out a bit.

There are alot of people with more technical knowledge than me who could elaborate more. RC Report has a good engine column from some Aussie and I think Clarence Lee writes for Model Airplane News now.