Glow engine setup/tune

[Hoochykins]

Now the weather is just about improving I've been giving a few motors a run on my new test stand. I've never tuned glow engines before but have read up quite a bit and watched a fair amount of videos so I have the jist. 

 

My question is how should I be setting up the idle on the stand? Should I set the motor up to fully close the carb with no throttle to stop the motor or should it tick over with the throttle fully closed?

 

I presume I would have it so I can fully close the carb when installed into an aircraft then trim the throttle so it doesn't starve the motor or air unless I want to stop it?

[John Wagg]

From a safety point you always need to be able to stop the motor at any time. In the test stand and on the plane.

On the plane I have mine so that the trim will set the tick-over with being able to cut the throttle at full bottom trim.

With my current transmitter I also have a throttle cut on a switch. This is so I can leave the trim in the idle setting without having to twiddle the next time.

[Jonathan M]

 

On the test-stand I have a simple hand-operated piece of wire, so the carb goes from wide open to fully closed.

 

Fully closed will starve the engine of fuel and air, tickover will be with the barrel mouth open slightly, typically say 1/16th in (1.5mm).

 

In the model I personally don't touch throttle-trim, just leave it at neutral.  Instead the throttle is set up on a simple straight-line 2-point curve on the radio.  One point is stick fully forward and carb wide open (but no more else the servo starts buzzing and gets stressed).  The other point is stick fully back and carb slightly open to give a reliable tickover, and it is this point's value that I can easily tweak in the radio menu.  A separate throttle kill switch closes the carb completely.  This system has the advantage of not messing up the reliable idle setting between flights, etc.

 

An example of this setup on one of my models is (max available servo travel = +/-100):

Stick forward:  curve point at +60 (found by trial and error, i.e. when barrel is fully open, but no more pull from servo)
Stick back:  curve point currently at -64 (last time I flew, -62 was too fast, -66 too slow)

Throttle kill switch (which overrides the curve):  -85 (carb fully closed to stop engine, any more would result in servo buzzing under load)

 

I hope this makes sense.  Your transmitter might have this facility (to put throttle on a curve and change its end-point values, also to set up a kill switch), but if not then just get used to using throttle down-trim to kill the motor.

 

[Dale Bradly]

2 hours ago, Hoochykins said:

My question is how should I be setting up the idle on the stand? Should I set the motor up to fully close the carb with no throttle to stop the motor

 

To answer to this, would need to know how you're operating the throttle on the stand. If it's a just a manually operated pushrod/scrap of wire etc, then you will stop it when you fully close it, and its a fine movement between idle and stopped. Until you're more experienced, operating that pushrod by a servo will be better (more precise), even if it's just a simple servo hot glued adjacent your test stand. 

 

What i do when servo operated (irrespective of on stand on in plane)

All but identical to what Jonathan M does: I leave throttle trim at midpoint, and use end point adjustments to set the permanent idle position.

Then when actually flying i can tweak using the trim lever to tweak as needed. If i find i need to permanently trim, this adjustment is then moved to the endpoint adjustment.

I have a separate throttle cut switch, which when operated, irrespective of throttle position, overrides the previous throttle position, fully, firmly and promptly closes the throttle, thus ensuring the engine stops.

 

2 hours ago, Hoochykins said:

should it tick over with the throttle fully closed?

No, it can't tick over with the throttle fully closed. This means no air into the carb, thus no fuel, and subsequently no running. Idle will have a sliver of opening in the carb barrel.

 

 

[Hoochykins]

Much appreciated guys, perfect answers as always. My plan was to stick the carb fully closed when in the model on a momentary switch and adjust tickover with the trim, basically the same as you guys have described. I'm on RadioMaster so have every option under the sun.

 

I'll keep this thread for any more questions I have as no doubt there will be a few, I've got a few engines to get running including some doorstops I'm sure 😁 

 

Let's see which is going to give me the most jip, I thought I'd go with OS first to make my life as easy as possible.

 

 

Glow
MDS 61 - no exhaust or carb needle
Thunder Tiger 46 pro - loose carb
GMS 2000 40
MDS 18
OS 40 FP Max
Saito FA-45 Special
SC 25A
Thunder Tiger GP 42
MDS 148
MFA 40
OS Surpass 91 FS (FW190)
Magnum XL 46
OS Max 40
NS Bluebird 25
MDS 48
Merco .61
Thunder Tiger 45
Thunder Tiger GP 42
OS Max 46LA
OS Max 25LA
Cox 049 Surestart
Irvine 40 Mk3
MDS 17 Pro

 

Diesel

OS PET 099
PAW 19 Mk2

 

Petrol
CRRC Pro 26cc

 

 

 

 

 

 

[Jason Channing]

7 hours ago, Dale Bradly said:

 

To answer to this, would need to know how you're operating the throttle on the stand. If it's a just a manually operated pushrod/scrap of wire etc, then you will stop it when you fully close it, and its a fine movement between idle and stopped. Until you're more experienced, operating that pushrod by a servo will be better (more precise), even if it's just a simple servo hot glued adjacent your test stand. 

 

What i do when servo operated (irrespective of on stand on in plane)

All but identical to what Jonathan M does: I leave throttle trim at midpoint, and use end point adjustments to set the permanent idle position.

Then when actually flying i can tweak using the trim lever to tweak as needed. If i find i need to permanently trim, this adjustment is then moved to the endpoint adjustment.

I have a separate throttle cut switch, which when operated, irrespective of throttle position, overrides the previous throttle position, fully, firmly and promptly closes the throttle, thus ensuring the engine stops.

 

No, it can't tick over with the throttle fully closed. This means no air into the carb, thus no fuel, and subsequently no running. Idle will have a sliver of opening in the carb barrel.

 

 

They can run perfectly with the throttle closed if the front bearing leaks or is not air tight even on new engines,  My West 36T1 was notorious for it, annoyingly it was a very slow tickover even with a finger over the carb etc it would not stop and would run for 10 minutes at idle

[GrumpyGnome]

If I had an engine test stand, I'd want a servo to control the throttle so I wouldn't have to constantly hold a piece of wire 🙂

 

On my Radiomaster (for all my models), I use the throttle trim and have different trim settings for takeoff, flying, and landing modes. I like to have the trim available so I can adjust for wind strength if necessary, easily. The momentary switch top right kills the engine by completely closing the throttle/killing the ignition. The two position switch at top left is throttle hold.... sets the engine to fast idle and disables the throttle stick so I won't knock it if I have to carry the model. (I sometimes use a curve on the throttle to get a more linear response to throttle than some engines seem to have with no curve).

 

As with all things, many ways to skin this cat!

 

Yes, I'd start with an OS, but probably not the largest one.... Probably the 46.

[PDB]

49 minutes ago, GrumpyGnome said:

The two position switch at top left is throttle hold.... sets the engine to fast idle and disables the throttle stick so I won't knock it if I have to carry the model.

That's a great idea, often fly on my own, going to use that👍

[Paul De Tourtoulon]

You have some nice and not so nice engines there,

 

Saito .45s, my favourite of all time, I have 3 of them,

 all the OS ( except max .40 never had one) are all good.

 T Tiger .45 and .46 great motors, also the .42 plain bearing,

Magnum .46 xl some good as OS others not so good.

CrrC .26 one in the club, it runs well all the time.

 

 I have had some experience with some of the other motors most negative I will leave to people who have actually had them and used them.

 

 What fuel do you use ?, I will leave the fuel for the experts,

 

And also the self-named 'expert', 🤢don't quote me ***

 

 

[David Davis]

I agree with Paul's analysis of your motors Hooch but I would add that I have had excellent service from Irvine and SC engines. As for the venerable Merco 61 they were fine engines with a good carburetter but not so powerful as the Scneurle ported engines introduced by OS and Super Tigre.

[Jonathan M]

1 hour ago, GrumpyGnome said:

If I had an engine test stand, I'd want a servo to control the throttle so I wouldn't have to constantly hold a piece of wire 🙂

 

On my Radiomaster (for all my models), I use the throttle trim and have different trim settings for takeoff, flying, and landing modes. I like to have the trim available so I can adjust for wind strength if necessary, easily. The momentary switch top right kills the engine by completely closing the throttle/killing the ignition. The two position switch at top left is throttle hold.... sets the engine to fast idle and disables the throttle stick so I won't knock it if I have to carry the model. (I sometimes use a curve on the throttle to get a more linear response to throttle than some engines seem to have with no curve).

 

As with all things, many ways to skin this cat!

 

I've thought about a servo mounted on the test stand (via either a RX or a servo-tester plus battery) but the time taken to set it up for each different engine would be an unnecessary bother, plus it'd all get covered in exhaust residue.  My wire is held with a thick rubber band to the side of the fuel tank, which provides just enough friction to hold it at setting... KISS

 

My kill switch is always the one directly above the throttle stick, down is dead, up is live... makes sense to me and I've got used to it.

 

When carrying a running IC model from the pits to the runway, I move the stick to one click above idle to prevent an inopportune cutout, then hold the TX by the carry-handle in my mouth, controls facing forward so unknockable.

 

I know some people have a fast idle on a switch (e.g. for spins or safer landing approaches) but my brain can't handle more than one thought process every two minutes, so again I keep it all simple via the throttle stick.  Same with using trims as a control... I get confused! 🤣

[Jon H]

2 hours ago, GrumpyGnome said:

If I had an engine test stand, I'd want a servo to control the throttle so I wouldn't have to constantly hold a piece of wire

 

That ruins the fun!

[John Wagg]

 

11 hours ago, Hoochykins said:

Much appreciated guys, perfect answers as always. My plan was to stick the carb fully closed when in the model on a momentary switch and adjust tickover with the trim, basically the same as you guys have described. I'm on RadioMaster so have every option under the sun.

On my Radiomaster there is a Throttle trim setting which alters the way the trim functions.

Basically it allows the trimming of the throttle but doesn't alter the fully open end point.

 

Go into model set up (MDL button)

1st screen - scroll down and press "Throttle" box.

Source =  'Thr'.

Trim idle only = On

Trim switch = 'Thr'

Now when operating the trim there is no "Trim Centre" voice. You will still get the max' and min' voice.

 

I also think I had a similar function on my Taranis and is probably on other makes as well

[GrumpyGnome]

2 hours ago, John Wagg said:

 

On my Radiomaster there is a Throttle trim setting which alters the way the trim functions.

Basically it allows the trimming of the throttle but doesn't alter the fully open end point.

 

Go into model set up (MDL button)

1st screen - scroll down and press "Throttle" box.

Source =  'Thr'.

Trim idle only = On

Trim switch = 'Thr'

Now when operating the trim there is no "Trim Centre" voice. You will still get the max' and min' voice.

 

I also think I had a similar function on my Taranis and is probably on other makes as well

It's anEdgeTX/OpenTX function, so dependant on the version of OTX/ETX you had, then yes, you'd have had it on your Taranis

[Nigel R]

14 hours ago, Hoochykins said:

OS 40 FP Max

OS Max 46LA
OS Max 25LA

 

Simplest engines of the lot.

Well made.

Run nicely.

Start easily.

 

These three have one main needle to adjust... simple.

 

The idle is an air bleed screw, which, give or take, should be set to half way block the hole. It's unlikely to need much adjustment... simple.

 

Couldn't be a better starting point.

 

40FP would be my suggestion... strong contender for "best glow engine ever".

[Geoff S]

4 hours ago, Jon H said:

 

That ruins the fun!

 

The unpleasant 'fun' is how chilly your throttle-hand gets on a cold day in the full air blast from the prop 🙂   

[Jon H]

11 minutes ago, Geoff S said:

 

The unpleasant 'fun' is how chilly your throttle-hand gets on a cold day in the full air blast from the prop 🙂   

 

i do not have many fond memories of winter engine testing at laser i can assure you. Even with gloves it was awful

[Hoochykins]

Just bagged myself a Webra Speed 20 motor for my FlyBoy. Anyone know much about them as I can't find a while lot online?

 

 

[Merry Mark]

If you have not seen it, this might help:

 

https://sceptreflight.com/Model Engine Tests/Webra Speed 20.html

 

Links to the main index are at the bottom of the page. 👍

[Christopher Wolfe]

3 hours ago, Merry Mark said:

If you have not seen it, this might help:

 

https://sceptreflight.com/Model Engine Tests/Webra Speed 20.html

 

Links to the main index are at the bottom of the page. 👍

 

For anybody with a passion for I.C. engines the sceptreflight https://sceptreflight.com/Model Engine Tests/Index.html site is well worth adding to your bookmarks.

 

Great info posted by a passionate aeromodeller (with no pesky ads either) - a labour of love from down-under.

 

* Chris  *  🙃

[Cuban8]

With throttle control and engine test stands, rather than messing about with servos and having the risk of dropping your tranny and/or getting it covered in oil residue while you tweak the engine, on the rare occasions when I have run an engine outside of a model I've set up a kind of throttle friction arrangement.

Use your own ingenuity, but essentially, arrange the throttle pushrod wire to be clamped between a couple of bits of hardish foam that are attached somewhere convenient to the test stand. Hot glue works well.

Clothes pegs, small bulldog clips or mini clamps can be arranged to set a suitable friction on the foam and wire 'sandwich' so the throttle can be moved easily but will stay put anywhere else mid range or at idle.

[J D 8 - Moderator]

 Here's mine testing a Cox 09 with exhaust restrictor throttle, just a wire through a saddle clamp on a block behind the largest of 3 tanks fitted. On the other side a snake is fitted for more conventional throttles. Block can swivel side to side to get a good line to engine throttle arm.

 

[Jim Hearnden 1]

On 06/02/2025 at 19:41, John Wagg said:

From a safety point you always need to be able to stop the motor at any time. In the test stand and on the plane.

On the plane I have mine so that the trim will set the tick-over with being able to cut the throttle at full bottom trim.

With my current transmitter I also have a throttle cut on a switch. This is so I can leave the trim in the idle setting without having to twiddle the next time.

This is the way I have always done it. The servo sets the slow running, not the carb itself. Full slow trim & throttle stick stops the engine. High slow trim & low throttle stick is idle.

[GrumpyGnome]

All my ic models are set up so a momentary switch kills the engine instantly, without having to adjust trims, or wait while the trim clicks down. On petrol it kills ignition, on glow it drives the throttle completely closed.

 

I also find it easy to locate without taking a hand off the sticks