Charley

My Feedback: (2)

Sadly it's about par for the needles' QC. I met Duke Fox at the Lawrenceville Nats, years ago. I was trying to use the Fox Quikee 40 in Q-500 pylon racing and like lots of others, having trouble getting a consistent needle. After hearing me ***** Duke allowed that he thought he had a good product. My reply was that it was good but with a little better QC on the needles it would be a great product.

You could put a piece of fuel line on each needle so that when you screw them in the hose is forced over the spray bar ends. That'll stabilize the needles and prevent air/fuel leakage past the threads.

CR

Sport_Pilot

I have no bad needles on my Fox's. Though they do leak. The fuel tube does not prevent air from leaking in but fuel out. They do help some by centering the needle and not vibrating. I bought a used engine that had fuel tubing on it and it ran better without the tube, and the needle was easier to adjust.

Charley

My Feedback: (2)

I'm tired of you beating this dead horse. I disagree with you and there's an end to it.

CR

Sport_Pilot

I suggest you do some research. Several people told you the same thing and I don't think anyone agreed with you.

carddfann

Hey guys,

I found a 60 size tilt up quiet muffler. It appears the cylinder section is press fit into the cast front piece and/or with adhesive. There are no screws. I got it factory new still in the bag so nobody has messed with it. I have an extra, tilt down standard 60 size muffler. Has anyone ever converted a muffler from tilt up to tilt down (or vice versa) and can suggest the best way to separate the cylinder section from the cast front? Thanks, Gary

carlgrover

Fox 50 twin needle carb won't transition anymore

This engine is getting old but still makes plenty of power. Runs great on the top end and will idle well. However; It won't transition when it's under load. When I set the needles on the ground, everything is fine. I go up for a flight, come in for a touch and go, and it dies when I hit the throttle. The best it gets is that it will nearly die momentarily, then catch and go to full power. I'm also noticing that when I come in for a landing, the idle is really high. I had previously set it to idle slow on the ground. No amount of fiddling with the low speed needle helps and I've tried adjusting it one click at a time.

Here's what I've done to correct the situation. I figured it was sucking air from somewhere so I pulled off the carb and backplate and resealed them with high temp silicone. I replaced the backplate screws with socket heads and sealed the muffler at the engine and it's two joints. I put locktite on the low speed needle to help seal the threads. The head screws are tight. Fuel inlet has been sealed too. Glow plug is nearly new. All this and no change at all except that the high speed needle now has a wider range which is nice.

After flying when I got it home I noticed fuel leaking from the front bearing and the carb barrel. Engine is mounted at 45 degrees. I'm wondering if it's sucking air at the barrel or front bearing. Not sure what I can do about the barrel and also not sure if the bearing is even in need of replacement. Is there anything I'm missing? Tank has been pulled recently and checked. I don't think that is the problem.


Carl

Sport_Pilot

Fuel leaking from the front bearing is normal, especially on an old engine, but I am not sure about the carb. You said carb barrel, off to the side? That may be fuel leaking past the needle which is normal.

I suspect your idle mixture is a bit on the rich side. It will be even richer just after landing on a touch and go.

1QwkSport2.5r

If the idle hangs after running at speed and dropping back to idle, your idle mixture is likely lean. Any cutting out when throttling up from idle usually indicates the idle mixture is lean.

Sport_Pilot

You may be right, he said that it sometimes catch's so I thought it was dying slowly. But he said it also idles fast, so a lean idle on the ground may richen up a bit when tank pressure builds, then die off as pressure drops.

1QwkSport2.5r

After I thought about it, I should rephrase somewhat. Cutting out on throttle-up means it's lean on the idle. Hanging idle/high idle after coming down from WOT or high throttle can mean the high speed is a tad lean, but it could be that both needles are set a little lean in this most recent case.

Sport_Pilot

At any rate it sounds like tuning is needed. If off a lot there could be dirt in the needles.

1QwkSport2.5r

Agreed.

carlgrover

High speed needle is not too lean. I always have a smoke trail. No amount of tuning has fixed this problem. Needles aren't dirty. I recently cleaned the entire carb. I've been tuning Fox engines for 25 years and pretty well know the procedure. I've tried setting the idle rich so it spits raw fuel out of the exhaust and still have this same problem.


carl

1QwkSport2.5r

Smoke trail means nothing in regard to tuning AFAIC. Something changed if it ran fine before and now it doesn't. Change fuel, change glow plugs, etc. Process of elimination will find the cause.

Sport_Pilot

I agree a thick smoke trail often means your plug is too hot.

carlgrover

The fuel leak i'm seeing from the carb appears to be coming from around the O.D. of the barrel itself, not the needle.


carl

Sport_Pilot

Then it may be leaking air between the barrel and the housing when at or near idle.

carlgrover

That's what I thought. I also don't think there's much I can do about it except cuss it. All that vibrating when the engine is running and the plane is in the air must make it worse. I guess I need a new carb or a tighter fitting barrel.


Carl

Charley

My Feedback: (2)

Is there a spring between the barrel and the housing of the carb? All my MK X carbs have one to keep the barrel from oscillating back and forth around the screw that fits into the spiral groove that moves the barrel in and out. A few thousandths movement there can alter the mixture at idle.

Also, I hope you have fuel tubing over the needles. (wink)

CR

carlgrover

I don't remember seeing that spring. I'll look into it tonight and see what I can find. Luckily, I've got another twin needle 50 I can tear apart and check as well. Fuel tubing over the needles? ha ha ha. Oh yes. On every one of them.



Carl

Sport_Pilot

My Fox .50 works better without fuel tubing over the needles, a bit sloppy but easier to adjust. just need a good retaining clip.

carlgrover

I got to wondering about the spring so I did some searching around and found out the only spring my carb has is the one on the idle stop screw. However: I also found this jewel right here in this thread:

http://www.fayettevillercclub.com/id57.html

It's all about the MK-X carb and details a problem with it very similar to mine (towards the bottom of the article). The fix is a small spring that jams the barrel against one side of the cam screw. I'll give this a try and see if it works.


carl

Lou Crane

Carl,
Thanks for the link to the Fayetteville Club notes on Fox Carbs. Great info - pity the Fox factory is no longer the go-to for support parts...

Just looked into this topic - it's been going a while. I don't fly RC; tried it a few decades back and it did not give me the satisfaction CL does. Personal thing, not a knock on anyone. We fly what we like because we like it... 'Nuff rant...

One thing I note is missing through these posts is the metallurgy of the engines involved. Important because lapped iron-in-steel piston/cylinder sets DO need a bit more castor in the fuel. The way to be fairly sure there's enough going through the engine is a visible 'smoke' (actually vapor) trail. Similar, but not as critical need for ringed iron-in-steel setups. Doesn't need to look like skywriter smoke, just enough to be visible.

I've flown lapped and ringed Fox engines of smallish to mid-size displacement for several decades. Not as much experience with ABC Fox engines... Iron Foxes can serve consistently long and well with correct lube, and I'd expect ABC Fox engines would do the same with appropriate oil and %s. The modern synthetic oils should serve even plain bearing engines nicely. Appropriate fuel for the sleeve/piston wear characteristics of each setup is what would determine length of consistent usefulness. (IMHO)

If anything, I'd expect ABC Fox engines to be all that the iron engines have been, with less vibration due to lower reciprocating weight, and great dependable durability with appropriate oil-fraction fuels

Carbs: Fox carbs have never set as easily as Perry or basic level air bleed compensated carbs, but once set were dependably consistent. Most of what I used them for was fun or Carrier event type flying; dead low idle in flight was not of much use. Response, consistent mid-range, and full power at WOT were more important. The old Fox carbs - subject to QC variations - once set, were very good. The more recent Fox carbs I've used - granted, not that many and no need for low idle in fight, still seem quite usable to me.

Charley

My Feedback: (2)

That's the spring I mentioned a few posts back. It's easy to get at; just take out the cam screw and the barrel will pull out. While you're at it you can check out the wear on the cam screw and the barrel.

CR

carlgrover

According to the article on the website I posted, that spring is not there straight from the factory. It's a mod you have to do on your own with a spring from an ink pen. I've got a spring to use. I'll stick it in and see how it works maybe this weekend.

There is an additional article on the website that mentions an issue with the head button design of the Fox 50 and how it relates to throttle transition. The fix isn't as easy unless you know a machinist or have your own lathe.


carl