hsukaria

Thanks earlwb. I had been using the Fox Gold #8, which is a cold plug. I think that was causing me some problems.

1QwkSport2.5r

Hot heat range plugs are the bees knees with low nitro, almost regardless of engine brand.

Here is my Fox 1.20 twin cylinder engine I acquired recently. It has the high nitro heads (for 25% nitro) and the old butterfly carbs. It needs a pair of mufflers and its ready for the test stand. I'm gonna have to find some heads for lower nitro or find someone to make a pair of heads. I don't want to use that much nitro.

earlwb

I would just try running the 1.20 twin engine with 5% nitro glow fuel. I doubt you'll need new head inserts.

1QwkSport2.5r

I understand the engine won't make make as much power on low nitro and the current head buttons. Since 5% fuel is what I want to and do use, I want to optimize the engine to better take advantage of the fuel. No different than adding head shims to an ST to run on 15% right (it's a waste to do IMO). Maybe that's not the best analogy but I hope you catch my drift.

hsukaria

It wont hurt to try it on the bench. Do the heads have shims under them, or are they a specific head button? You could get a pair of new head buttons from Fox. Even though they work ok with more nitro, they still work with low nitro. At least that's my experience on the 74.

As for running cold plugs, it may be that was causing me to tune the 74 leaner when running the cold plugs with low nitro. Consequently, their seals would crack due to lean runs? I am just speculating.

1QwkSport2.5r, I still have a pair of Fox mufflers that you can borrow if you want. (tilt up and tilt down).

hsukaria

That's a lot of metal there!!

1QwkSport2.5r

The head buttons on my 1.20 look like funnels. They're huge cones. There are no shims installed factory and there weren't any in the box. The current Eagle IV .60 heads are designed around 10-15% nitro so they'd be an improvement (on low 5% fuel) over the buttons I have on the 1.20. However there are modifications that can be made to the Eagle IV heads to better yet take advantage of the lower nitro fuel.
I attached a photo of the crater sized head button and a drawing by Konrad of the "ideal" head button for the Fox 1.20 twin cylinder engine.

earlwb

I always run the engines using FAI or low nitro 5% glow fuel at first, just to see how the engine runs and works. I have only encountered a few engines that tended to run poorly on the fuel. All the other engines didn't mind the low nitro fuel.

Yeah a cold heat range plug is more for high RPMs competition, higher nitro percentage fuel and for using tuned pipes. The standard Fox glow plugs work fine for most purposes.

1QwkSport2.5r

I will run it on my normal fuel and see how it does. At 2oz/min, this thing will suck the tank dry in no time especially with a bunch of nitro in the fuel.

I was was going to run it a bit differently than most; I'm going to run two tanks one to each carb and use pressure from their respective mufflers.

Hsukaria: I'll take you up on borrowing your mufflers. Not in a hurry though, it's darn cold out right now.

hsukaria

The cold and snow has delayed my engine testing I wanted to do on my Fox 74 with correct plugs and on other 2 engines. But now they sit in Ziploc baggies full of oil until a warm spell.
It would make more sense to run low/no nitro fuel on that Twin if it guzzles that much fuel.

1QwkSport2.5r

The notes from Duke say the engine takes 2oz per minute; I don't know if that's using the high nitro Missile Mist or the regular fuel. As it Dukes fuel? Either way, I will likely need to raise the compression ratio with a head button change so it will run better with less nitro. Likely it will run okay as it is with 5% fuel, but with the tendency of this engine to drop a cylinder on throttle transitions has me thinking some modifications will need to be made.

One cylinder's exhaust port will be on the bottom and one on the top I think. This is the best orientation as outlined by a mutual Fox officianado we know. There are design flaws with this engine that create some 'quirks' that need attention so the engine is reliable.

The Aluminum engine mount makes it easy to mount up to run it.

Oh, and yes it's a big hunk of metal. It's heavy at 2lbs or a little over. About as heavy as my Enya R120-4C 4-stroke.

earlwb

It is basically two .60 engines paired together, each .60 can consume about 1 ounce a minute. So 2 ounces a minute for it is what it consumes. But that is at full throttle. But if you fly around at less than full throttle the engine isn't all that bad on fuel consumption. It depends on the plane of course. I have been running a 30cc glow engine using a 16 ounce fuel tank and I can get 8 minute flights with it and still have some fuel left over. But I do not need to fly the plane full throttle all the time either.

1QwkSport2.5r

I thought the adage was 1oz per minute at WOT per 1.0 cubic inch. Either way, it's a big engine and it will eat fuel. My R120 Enya sucks down a bit over an ounce a minute at WOT on 10% nitro. 8oz on that engine lasts about 6-7 minutes on an airboat. So it lends to a 2-stroke sucking twice as much fuel as a 4-stroke.

Ill probably need to get some neoprene tubing to attach to the carbs as they have those goofy tapered non-barbed fuel fittings.

Hsukaria - there are no shims installed under the heads of my 1.20. The deck height is over .040"! If I could drop that down to .012"-.015" I'd be right on par for running 5% fuel and getting good power from it. It came with Fox idle bar plugs, one has a gold stem and the other has a silver colored stem. Not sure if they're the same heat range or not.

hsukaria

I can see where the uneven flow can occur because of the scavenging that the con-rod does on one cylinder while the other does not have the benefit of scavenging, as the Fox Aficionado explained to me. The idea of flipping the cylinder that does not get the scavenging to point the exhaust up would help, except installing it on a plane will cause muffler installation challenges. Maybe you could rotate both cylinders to the rear to make them equal? You would lose some power, but then both cylinders will be more equal. Just a crazy thought.

earlwb

I think you may be over analyzing the whole thing. Two of my Fox 1.20 twin engines have the large size combustion chambers in them and the engines ran just fine for me, using 5% nitro glow fuel. When you start going for high compression, then you start getting into other issues, such as detonation and overheating, etc. Heck I even used idle bar glow plugs too, Fox RC Longs as a matter of fact.

av8tor1977

My Feedback: (6)

Personally I would try it on 15% nitro and would be surprised if it didn't run well. That's a pretty common sport fuel anyway, and what I run in everything. I "massage" my various Fox engines until they are happy with it. I have an old, original, never been apart Fox .78 engine that just thrives on the 15% nitro in a Twist 40. (Yeah, it's a really fun combo.) I know the older Foxes were more nitro tolerant, hence the good performance of my .78, but I would bet that your twin 1.20 would run well on commonly used 15%. I made the recommended head for my Fox .74 for 10% nitro, and then used two shims. Runs pretty good here at sea level and with 15% nitro.

Sorry but I just don't have the time and energy to make heads for other people though.

AV8TOR

1QwkSport2.5r

I'm just basing my thoughts on what the expert had to say. Now don't take that as me thinking you guys don't know what you're talking about. Right now it's mere speculation on my part since I've no experience with the engine yet. Bear in mind, the engine will run fine as-is I'm sure. The modifications discussed elsewhere (ie: head button change, cylinder flipping, etc) are intended to get the engine to run more optimally. The conrod/crankpin induced swirl really has a strong effect on the charging of the cylinders. These modifications are aimed at reducing the effect the swirl problem has on the engine. I must confess I don't have much of an intention of using on-board glow to keep both jugs lit. My thought was to make it run as well as I could so it didn't need glow support. On the flip side, I've not had the intention to run high nitro in it. I have 3 engines that will run on 15% and the rest are all Italian ST's, Enyas, and old K&B's that don't need or run well on much nitro. On a whim I may try some of my 10% 4-stroke brew or 15% Jett brew just to see what it does, but 5% is what I intend to use in it regardless of cylinder orientation, head button model, etc.

Having the exhausts being opposed as I suggested may complicate things a bit, but the idea I have in my head is a big draggy biplane. It just sounds like it should go together even if the exhaust looks funny. The looks I'll get at the flying field will be priceless. But hell, what do I know? I'm a car and boat guy primarily.

Av8tor - I am really surprised to see a reply from you in the glow forum. Thank you for your input, as well as the rest of you guys. Earl, I may be overthinking all of this a bit, but I have good reason (at least I think so anyway). Reliability without losing a bunch of power by filling the gaskets to block the boost ports. Earl - I also noticed you have better carbs on your 1.20 as well. I have one of the older ones with the (what I call) goofy throttle valves. I know it's said it runs fine on the old carbs, but if I have too much difficulty with them I will switch them with MkX carbs or even the newest Fox carbs since they're supposed to work really well too.

av8tor1977

My Feedback: (6)

Oh yeah. I love gasoline airplanes, but I will always keep at least a couple of glow planes around too. Love the smell of methanol and nitro, and even the high speed buzz and lightning response of a good running glow engine. I pretty much love all kinds of engines really, though I've never gotten much into either full size nor model diesels primarily for the (to me) offensive smell....

AV8TOR

earlwb

Well, I always run a engine as is at first. If I have problems, then I need to put on the thinking cap to see about solving the problems.

The old butterfly valve carbs do not normally have problems. But they do tend to run a little bit on the lean side through the mid range, and with the 1.20 engine that may be a plus for it to not cause the left cylinder to run too rich then. Yes do use a short length of black neoprene tubing on the fuel inlet fitting on the carbs as the silicon tubing will just slip on off, but the neoprene tubing will stick really well. Make any carb adjustments one at a time, and do a tweak and wait to see what it does for a while before you try tweaking it some more. My very first Fox twin 1.20 had those butterfly carbs on it and I do not remember having any problems with them. But it has been quite a few years now though.

1QwkSport2.5r

I have a tach and was advised in the 1.20 thread to use it when setting the carbs and I will use the engine as-is first. I'm a good tuner I think so I'm sure I can tackle it. I can get an ST carb dialed in perfect so the Fox shouldn't be hard to figure out. Whenever I have an engine on the test stand I have a tach nearby.

As to the butterfly carbs running lean; this can be a plus for the rich cylinder but not for the lean cylinder. Perhaps adjusting the carb on the lean cylinder a tad richer to compensate. That is if I have much problem with one cylinder dropping out. I am gonna flip the cylinder and piston on the one side to better compensate for the charging problem (cylinder leaning out or being over rich case depending). If need be, I'll rotate the cylinder and piston back the other way if the plane I put it in needs it that way. What I want to accomplish is set the engine up the way it runs the best and when the plane is ready, make changes as necessary. I am fascinated with having this engine in a biplane. It just seems like a good idea. Any thoughts on that? This is one engine I want to be very familiar with before I send it into the air. When I get time, I was going to outline the changes I'm going to make and post a few pictures in case any of the other members have any curiosity to see what these engines are all about. If I run two fuel tanks one for each carb, do I still need to use large fuel tubing? I assume that's only if I run a single tank that I'd need large tubing...

Im in ready expecting to have to hand start this beast, my starter has no chance of turning it over. (Hobbico Torqmaster 90). As for props, common consensus is a 13x6. Sound about right?

on a side note: a glow engine left outside to get as cold as -5F locks up solid. Crank froze. (Not the 1.20)

earlwb

Yes a 13x6 would be a good choice to start with. The 1.20 engine likes to rev up more than the other single cylinder engines do. So you need to let it run free.
It likes to run around the 12,000 or so RPM range.

I can agree a glow engine tends to lock up solid when it is really cold outside. Years ago, I remember having to heat the engines up some before I could get them to start too.

1QwkSport2.5r

Yeah, my R120 was locked up solid. I normally don't leave models in my truck but we've had family needs that had to come before putting the model back up.

An elaboration from my last post; I meant it to say 'I'll change the setup of the engine (cylinder flip) if the airplane needs it to be changed'. My edit button isn't working for some reason. I'll edit the post when it will work for me again.

hsukaria

"on a side note: a glow engine left outside to get as cold as -5F locks up solid. Crank froze. (Not the 1.20)"

At -5F, you need another hobby... ice fishing, skiing, staying indoors and drinking a beer (or a few), etc...

1QwkSport2.5r

I had left one of my airboats in the back of the truck from a day it was +25F. I wanted to run in the snow, but I ended the run very quickly as the boat was much too fast for the area I was running. 5-7mph at 3,000rpm idle is too fast when you don't have brakes. If it was built out of oak I'd have not cared and bashed it up. Balsa and 1/32" birch ply do not stand up well to gravel, pavement, or ice even when fiberglassed.

TBH, I am an avid ice fisherman. I go ice fishing at least every other weekend. But my wife and I had a baby in March of this year which now takes up nearly all of my spare time. Actually, the spare time I have is when I am posting on the forums. To make things worse, I was in a bad auto accident Dec. 31st and a day later we find out my father in law has declined significantly since he has been undergoing treatment for asbestos related lung cancer and is now in his last days. I won't be fishing or modeling for awhile.

My 3hp Tecumseh ice auger really chews ice if I add a little glow fuel to the gas mix. The engine is of 1974 vintage, about 80cc or so. 3qt of 50:1 gas oil mix and a quart of 20/12 nitro/castor glow fuel make that baby really hum. Still using the factory original points and condenser. That makes the gas engine smell more like a glow and less like a chainsaw.

Back to the Fox 1.20 engine. Here is a thread on another forum that goes into great depth as to the operation of the Fox 1.20 twin cylinder engine and how to combat its quirks. It's worth a look if anyone has a 1.20 Fox or if anyone has any interest in owning one its important to have the information posted there. This is no engine for a novice the way I see it.
http://rctruth.com/index.php?topic=1761.0

hsukaria

Sorry about your troubles, Tim. I hope they all get resolved well and soon.

I admit, I don't think I want a Fox 1.20 twin for myself. But it is interesting to learn about it for academic purposes.