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Dec 06, 2019, 01:19 PM
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seriously considering converting an os-ft120-II to gas. looking for recommendations.


i plan to build a magnet ring and sensor bracket to convert an ft-120-ii i have to gasoline or at least sparked glow fuel if the gas conversion isn't advised. RCGF has a gasoline carb on the rcgf10 that seems just about the smallest gas carb i've found (its a different model from their 15 and 20cc engines). would this carb be suitable for the conversion if i build an adapter plate out of HDPE or is it going to be too big?

https://www.rcgfusa.com/product/rcgf...etor-complete/

can anyone recommend a safe fuelil mixture to use? anything else I should know before doing this? i was thinking it would go in a spacewalker, flybaby, or a clipped wing cub. any other airplanes that this would work well in? i prefer scale models and sport flying.
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Dec 06, 2019, 01:27 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by raleighcopter
i plan to build a magnet ring and sensor bracket to convert an ft-120-ii i have to gasoline or at least sparked glow fuel if the gas conversion isn't advised. RCGF has a gasoline carb on the rcgf10 that seems just about the smallest gas carb i've found (its a different model from their 15 and 20cc engines). would this carb be suitable for the conversion if i build an adapter plate out of HDPE or is it going to be too big?

https://www.rcgfusa.com/product/rcgf...etor-complete/

can anyone recommend a safe fuelil mixture to use? anything else I should know before doing this? i was thinking it would go in a spacewalker, flybaby, or a clipped wing cub. any other airplanes that this would work well in? i prefer scale models and sport flying.
If you can get methanol consistently why not just go with a CDI methanol burning engine. Gasoline is only if you are really tight in budget and in location like mine where I cannot get pre-mixed hobby fuel easily.

If you do use gasoline you need to run a bit more oil than the chain saw engines. At least 20 to 1 or maybe even 15 to 1. Be kind to your engine. Four stroke can tolerate a smaller carburetor. How about the NGH carburetor for their 9cc?
Dec 06, 2019, 02:55 PM
Whats that drip ?
ClubFlyer's Avatar
I run a FT-160 on CDI glow / fuel with 14% syn oil, and 5% nitro in the mix. Runs like a Swiss watch on CDI, tic over at idle can be adjusted ridiculously slow, but 1200 is a nice consistent idle.

CH sells a full on gas conversion, but easily done if you have the means. The only issue with the gas conversion is the walbro carb is quite bulky hanging under the engine, and it hangs considerably lower than the original glow carb.

Brutus1967, converted his ASP FT-160 to gas using the the original glow carb with a little modification. have a search here in the engines forum, you should run across his threads.

O S FT 160 Gemini CH Full Gass Conversion (3 min 11 sec)
Last edited by ClubFlyer; Dec 06, 2019 at 03:02 PM.
Dec 06, 2019, 02:59 PM
AMA 46133
SeismicCWave's Avatar
>>Brutus1967, converted his ASP FT-160 to gas using the the original glow carb with a little modification. have a search here in the engines forum, you should run across his threads.<<

Yes, seemed like Bert modified the carburetor groove to create a different carburetor barrel closing curve.

For an engine in the 120 size I think the CDI conversion is very nice with the engine running on methanol fuel. The fuel consumption goes down and reliability goes up.
Dec 06, 2019, 03:26 PM
Whats that drip ?
ClubFlyer's Avatar
Quote:
Originally Posted by SeismicCWave
>>Brutus1967, converted his ASP FT-160 to gas using the the original glow carb with a little modification. have a search here in the engines forum, you should run across his threads.<<

Yes, seemed like Bert modified the carburetor groove to create a different carburetor barrel closing curve.

For an engine in the 120 size I think the CDI conversion is very nice with the engine running on methanol fuel. The fuel consumption goes down and reliability goes up.
Yes, also the throttle response with glow fuel is quite a bit better than what you see in Adrian's video on gas, and that has a lot to do with the his setup, he hasn't refined in it in that particular video, he was still in R&D with it. But it can be made to respond a bit better than that on Gas. Burtus's was quite impressive using the modified glow carb, his had better throttle response than in Adrians video.

If you look closely in Adrian's video, you can see the carb dripping gas, something not seating properly in the carb, flappers or metering needle. As a result the engine was running rich / thats why it had the laggy throttle response.

Running on meth / glow fuel, I added the 5% nitro, get bit more out of the engine turning a 18-6. The only attention it needs is run it out of fuel at the end of the day, and use plenty of ARO throughout the engine, plenty inside the crankcase. I've got 2 seasons on mine, and the bearings are as smooth/clean as the day they were put in. But if you leave unburned nitro / glow fuel residue in the crankcase, you will be surprised how fast corrosion sets in. Its really not that much added effort to do the after run engine care.
Dec 06, 2019, 03:49 PM
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Thread OP
I'll probably just do CDI/methanol for now and see how it goes. The ngh 9cc carb is fairly expensive and this is a diversion for me until I figure out what airframe to put it on. I've got tools to build the conversion parts and frankly, the challenge seems interesting to me. I don't want to modify the old carb for gas in case I want to convert back to stock at a later date.

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Dec 06, 2019, 04:11 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by raleighcopter
I'll probably just do CDI/methanol for now and see how it goes. The ngh 9cc carb is fairly expensive and this is a diversion for me until I figure out what airframe to put it on. I've got tools to build the conversion parts and frankly, the challenge seems interesting to me. I don't want to modify the old carb for gas in case I want to convert back to stock at a later date.

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Exactly. It is fun and easy to do a conversion to CDI. Carburetor conversion is a different story. You can always use the glow carb for gasoline but you run the risk of vapor lock if the carb gets too hot.

Maybe if you just make an insulator for the carb and you can run gasoline with the glow carb for testing.
Dec 06, 2019, 04:38 PM
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Thread OP
My gaui t10 is about the same size cylinder. I wonder how that carb would do on this engine?

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Dec 06, 2019, 04:49 PM
Whats that drip ?
ClubFlyer's Avatar
Try it, that gaui T10 has a 10mm carb, basically looks like a modded glow carb. With an adapter to fit the ft-120, add a thermal insulator between the carb and adapter, it should work. Do the CDI / Glow conversion first, then adapt the T10 carb and see how it runs on gas, that way you have a comparison to base a decision on which way you want to go with it.
Dec 06, 2019, 05:30 PM
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Thread OP
Looks like I've found my winter project.

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Dec 07, 2019, 06:30 AM
Registered User
Quote:
Originally Posted by raleighcopter
i plan to build a magnet ring and sensor bracket to convert an ft-120-ii i have to gasoline or at least sparked glow fuel if the gas conversion isn't advised. RCGF has a gasoline carb on the rcgf10 that seems just about the smallest gas carb i've found (its a different model from their 15 and 20cc engines). would this carb be suitable for the conversion if i build an adapter plate out of HDPE or is it going to be too big?

https://www.rcgfusa.com/product/rcgf...etor-complete/

can anyone recommend a safe fuelil mixture to use? anything else I should know before doing this? i was thinking it would go in a spacewalker, flybaby, or a clipped wing cub. any other airplanes that this would work well in? i prefer scale models and sport flying.
I have a few of these, nice carbs, ZAMA clones, around 9mm-9.5mm venturi. Practically the same carb as used on RCGF 15 and RCGF 21 twin.
This carb would be good for your conversion, you can get smaller venturis (8mm) but I wouldn't bother.
Still a while away but I recently got a few twins that will be also converted, ASP ft160 and Saito FA 182, that would be one of my favourite carbs to use. The carb appears to have an accelerator pump, it is nice and responsive.
Dec 07, 2019, 06:40 AM
Closed Account
This engine will run very nice on glow ignition and FAI fuel.

OS FT-120 II Pure Sweetness (9 min 49 sec)
Dec 07, 2019, 09:20 AM
Registered User
AA5BY's Avatar
Among the several gas four stroke conversions I've done, all use the stock carbs. Just turn the needles in to suit the smaller fuel consumption. Sometimes a throttle servo speed slow down is needed to prevent spool up stumble but our modern radios do that without problem.

The prime consideration is not the ability of the engine to handle the different fuel, but rather whether the fuel change power trade off is within the thrust parameters needed of the engine. A gas conversion will forfeit 10-20% of its power.

If that trade off is acceptable, the benefits are worthwhile. Easier starting, more reliable running, 1/10th the fuel cost and easy accessibility to fuel, easy clean up, and better longevity of the aircraft covering.

Another plus is sound as gas fuel has a wider torque band allowing a little more loading for less rpms.

I've been running Stihl high performance @ 20:1 ratio. The first of my conversions was a Saito 125a and it now has 135 flights on it. Other engines I've converted are a Saito 182T, Saito 90TS, Saito 180, and ASP 1.20 FS. Again, all use the stock carbs and run fine.

Fuel tanks should be sized 1/2 of what would be used for glow fuel. Use a felt clunk and muffler pressure. The vent line to the muffler tap either needs to be Viton or if using Tygon, a small section of glow fuel line on the end to attach to the muffler tap as Tygon won't handle the heat of the muffler.

A note on Bert's carb modification. On carbs with a barrel that moves in and out, he ground the slotted angle guide to decrease the barrel travel in and out. I've not found it necessary to do so but don't argue that doing so had benefits, and perhaps wasn't necessary on smaller conversions. On the engines that I converted, several but not all required a throttle servo speed slow down of between .3 & .7 seconds.

The slow down really doesn't affect the spool up time much, it just preserves the air/fuel ratio during the spool up.

Of the two conversions I've done that have been flown a lot, (the Saito 125a & the Saito 182T) a notable difference between the two is the consistency of the needle settings. I've not moved the HS needle on the 125 since first dialing it in. It has been rock steady, with no dead sticks and no needle changes. The 182T on the other hand has needed a click change now and again to suit the weather conditions. This might be because it has two carbs and essentially two .91 engines and the smaller size engines compared to the 125 has a smaller fuel requirement and thus is a bit more sensitive.

I've noted on the Saito 180 conversion that I've not flown yet, that the needle setting is less sensitive, and have concluded that the larger the conversion, the less sensitive the needle setting is.

BTW, I just recalled leaving out an important advantage to a gas conversion, especially on the four strokes. I've a fairly large fleet of planes and was suffering valve sticking problems between flying sessions with some planes while on glow. On gas, those won't happen and bearing and internal rust associated with glow fuel will become a non problem.
Dec 07, 2019, 09:42 AM
Registered User
Thread OP
Thanks aa5by. Those are all reasons I wanted to do the conversion if I can find an airframe that will match up nicely. One thing is that I also would like to minimize the types of fuel I need to carry. I currently have a dle30 and rcgf21t on 30:1 that I may change to 20:1.

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Dec 07, 2019, 09:52 AM
Still gassin' it.
Quote:
Originally Posted by ClubFlyer
Brutus1967, converted his ASP FT-160 to gas using the the original glow carb with a little modification. have a search here in the engines forum, you should run across his threads.

https://www.youtube.com/watch?v=Z4ehMA7ctdo
Quote:
Originally Posted by SeismicCWave
Yes, seemed like Bert modified the carburetor groove to create a different carburetor barrel closing curve.
OK.... now that my name has been mentioned twice in consecutive posts, I can just als well go all "beetlejuice" and return...

I did modify glow carbs by grinding a different shape to the slanted groove in the throttle barrel. It works well, and for single cylinders is not very critical. It is not perfect, but in general results in perfectly flyable engines.
For the twin, there are some side effects to that. The lateral movement of the barrel as occurs with the ASP FT 160 carb, results in asymetrical distribution of fuel and oil at any throttle position below say, half opening. Remarkable is that the asymetry is different for the fuel, than for the oil.
Fuel and oil start separating immediately upon leaving the spraybar (fuel evaporates, oil does not), and once separated they behave differently in the long, unheated intake headers.

Never mind that, for me it resulted in an extremely userfriendly, extremely reliable and very fuel efficient engine.

Things are different for the OS FT120 and 160, because they either have airbleed carbs, OR they have twin needle carbs that are of a different design thant the "slanted groove" fuel metering principle.
My guess is, that OS did this in order to minimize the asymetrical fuel and oil distribution.
Airbleed carburettors are unsuitable for gasoline, period. You can get the engine to run, but you can't get usefull adjustments out of it.
The OS twin needle carb for the FT, also is not suitable for modification to gasoline, unless you have the metalworking equipment similar to the OS R&D department, and you are gifted with their design skills, but it can't be done with just a Dremel for example.

So.... All is lost.... Or is it?

Far from it. With minor machining skills (or access to a friendly machinist) it is fairly easy to fit any suitable "slanted groove" twin needle carb (the OS carbs for the .60 till .90 single fourstrokes, any of them would be suitable) and modify that carb.
It requires to compromise a bit on the running properties, but it WILL work, as long as you give installation of the fuel tank, fuel plumbing and muffler pressure line (it needs a dirt trap) a bit of attention.

Your end result would be something like this:
The boxer in its new office.... (5 min 47 sec)

Not perfect, but very flyable and I have flown this configuration for about 1,5 year pretty intensive, without a single deadstick.

For the airbleed carb, OR the original twin needle carb (without the laterally moving throttle barrel) I have developed a solution as well.
I am nowadays connecting a small, electronically controlled solenoid valve in the fuel line, that partly " overrides" the mechanical needles in the carb.
It is a very simple system, fairly cost-effective, but it requires a transmitter with good programmability WRT curves and mixers.
It allows you to continuously adjust fuel/air mixture, over the entire throttle range, and with an accuracy that is way, WAY better (by a factor 50 approximately, no joke) than what the needles would allow you to achieve.
It basically takes out the entire "compromise between idle, midrange and full", it simply can be set "spot on" for each and every conceivable throttle position.

That would be a bit like this:
ES and Boxer, 1st try (1 min 56 sec)

Short explanation of what you see here: prior to starting the video, the engine has been at idle for about 10 minutes at least. This caused it to collect some oil in the intake manifold. That is something that is unavoidable. So when I slam open the throttle initially there is a short puff of blue smoke coming from one cylinder.
Notice that during the rest of the video, there is not a single hint of smoke visible, the engine runs without missing a beat throughout the whole throttle range, and responds extremely well to small throttle shifts.
When I took it to the air, I had to make minor changes to get the same behaviour in the air (which logically made ground behaviour a bit richer).

This mod noticably reduced fuel consumption even further, improved spark plug cleanliness considerably, and reduced both the amount of oil residue on the plane, as well as its "blackness".

I have three of these valves in operation now in a large range of engines (a .30 fourstroke, a 1.60 fourstroke Boxer and a 4.00 fourstroke radial) so it is very versatile.
A flying buddy of mine runs one single valve on his Saito 130T odd firing twin (with dual carbs) and even there it functions exceptionally well.
So it is actually quite versatile.
I have not yet tested it in 2-strokes, but I will next Februari, I do not expect any issues there either

For anybody interested, I can share any information needed to make one of these "electronic needles" if one wishes to do so, and if really needed, I can supply them at cost (zero profit for me) but the latter option will be around 75 US$ plus shipping, and I won't get aroud making a few before mid February.

I am not on my home computer right now, so right now I cannot post the drawing for the solenoid-housing, which is the "critical, hard to get" component.
The solenoid valve is a Stihl M-tronic spare part that is commonly availlable, and the electronics can either be home made for those that know their way around small electronics, otherwise it can be had from another RCGroups member here by the name of "hmeijdam" (it is where I get them as well).
Last edited by 1967Brutus; Dec 26, 2019 at 06:31 AM. Reason: Corrected a few crooked sentences


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