Author Topic: Pressure on a Fox? (Read 2309 times)

Joe Messinger · « **on:** July 29, 2010, 09:22:02 PM »

I imagine this subject has been discussed before. I couldn't find anything specific in the search. Perhaps I didn't look in the right place?

Anyhow, does muffler pressure on a tank work (or not) for an older Fox engine? Specifically, a Fox .25 c/l engine, factory muffler.

I've found that some engines perform well on pressure, some do not. I don't have much experience with Fox engines and thought I might give muffler pressure a try. Some advice from someone with experience with this might save me some headaches and or make things easier .

Thanks for any opinions/advice.

Joe

Joe Messinger · « **Reply #1 on:** August 02, 2010, 06:02:52 AM »

Opinions, advise? Well, I guess not. Looks like "trial & error" is gonna' have to do.

Joe

FLOYD CARTER · « **Reply #2 on:** August 02, 2010, 10:19:53 AM »

Joe. I think people do not reply is because there is no real answer. There are too many variables involved. The safest method is to use a tank plumbed for uni-flow. The uni-flow tube can be either left out in the open, or connected to a muffler tap for pressure-feed. Try both and keep the one that gives the best run.

Tanks plumbed for "over and under" venting can also be used with muffler pressure. One of the vents (either one) is capped off and the other connected to the muffler tap.

Floyd

Jim Thomerson · « **Reply #3 on:** August 02, 2010, 01:51:12 PM »

Muffler pressure is the way to go on Fox stunt 35's. Uniflow is the way I plumb my tanks. Here is the world's smallest and least effective muffler for Fox stunt 35.

dennis lipsett · « **Reply #4 on:** August 02, 2010, 02:03:20 PM »

Jim, any type of muffler on a Fox 35 is better then no muffler. Sunday there were several people flying unmuffled Fox 35's and to tell you the truth they wern't appreciated very much. I hate to say it but even with hearing loss the sound of an unmuffled engine is just bad manners.
When you have people holding their hands over their ears and complaining about the noise you know that an era has passed and it is time to enter the present time. In other words stiffle it Edith.

Dennis

Joe Messinger · « **Reply #5 on:** August 02, 2010, 06:59:06 PM »

Floyd & Jim,

I appreciate your responses. I've tried both standard and uni-uniflow tanks on the .25 Fox with less than desireable results. Today I added muffler pressure (to the standard vent tank) and that didn't work any better. I'm beginning to think a better NVA might be the answer if I can find one the right size. I have some Super Tigre and OS NVA's but they're too long for the Fox .25 venturi. If I can't find the right size NVA (other than the Fox) I'll try making some modifications (spacer) to the ST and see if that helps. If that doesn't work, an OS .25 should do it. . .

Dennis,

I agree! Un-muffled engines are not much fun to be around when they're running. Foxes seem to be especially annoying.

Joe

Jim Thomerson · « **Reply #6 on:** August 02, 2010, 07:45:18 PM »

You can get spacer washers at your local hardware store. There are spacer washers on the ST NVA in the Fox 35 in the pictures. As far as noise problems go, first fly an Arden 19 or TD 09, and no one will complain about Fox noise.

kenneth cook · « **Reply #7 on:** August 02, 2010, 07:55:47 PM »

Joe, is the .25 your talking about the one with the 4 bolt backplate and straight up venturi stack? There was the older .25 that looked just like the stunt.35 as well then you have the newer .25 with the cylinder that you could rotate. I own the .25 with the staight up stack and I found it not real user friendly. I tried at first and also not knowing about this engine to get it to run like a traditional Fox .35. This engine doesn't like that and likes to be run a lot faster more like a solid two stroke. I was also using a 9x6 and found a 9x4 to work better for me. I was able to find the correct muffler for the engine which cost more than the engine itself. This muffler didn't work well until I took it apart and opened the holes and removed the baffle inside. The engine wouldn't overheat and sag now. I'm using a standard vent tank but when I installed the muffler I used the pressure nipple to hold innards in the muffler as its a two piece muffler. I then went to muffler pressure. I only did this due to the plane choking a bit in the overhead maneuvers. Remember that muffler pressure is going to richen the run but its still going to speed up as the flight progresses . As others state, uni flow will prevent this and give you a steadier run throughout the tank. This is all theoretical and could change due to many factors such as vibration. In the event the nose is vibrating, your going to have problems no matter what option you choose. A squirt of Armor All in the fuel can somewhat remedy this problem as I've found out. One or two pumps in a gallon will do you fine. Not a cure all but can help. Keeping the prop balanced is also a must. I use muffler pressure on just about all of my engines except for a few which I use uni flow. The neat thing about uni flow tanks is that you have the option of using them open with the uni flow pipe to the atmosphere or just running the tank with muffler pressure. When all options I try fail, this usually results in opening and replumbing the tank. I've had more tanks with split pickups internally. Ken

Kim Mortimore · « **Reply #8 on:** August 02, 2010, 11:37:44 PM »

Joe,
What are the "less than desirable results" you're getting? As Floyd mentioned, there are many variables, and knowing what the specific problem is might help us pin it down for you.

Bill Little · « **Reply #9 on:** August 03, 2010, 01:56:04 PM »

Quote from: Joe Messinger on August 02, 2010, 06:59:06 PM

Floyd & Jim,

I appreciate your responses. I've tried both standard and uni-uniflow tanks on the .25 Fox with less than desireable results. Today I added muffler pressure (to the standard vent tank) and that didn't work any better. I'm beginning to think a better NVA might be the answer if I can find one the right size. I have some Super Tigre and OS NVA's but they're too long for the Fox .25 venturi. If I can't find the right size NVA (other than the Fox) I'll try making some modifications (spacer) to the ST and see if that helps. If that doesn't work, an OS .25 should do it. . .

Dennis,

I agree! Un-muffled engines are not much fun to be around when they're running. Foxes seem to be especially annoying.

Joe

H iJoe,

The Fox 25 with the bolt on venturi and 4 back plate screws is not a friendly stunt engine. Bob Hunt used one in his Frisky Pete, but I understand Tom H,. breathed on it.

It will probably run good in a high rpm, low pitch set up like a FP. I would try an APC 9X4 and set it just back from peak.

If it is the 1955-1957 Fox .25 (built in the OLD Fox 19 case), then I can't tell ya.

That one is one of the best running factory 4-2 engines out there, and will easily fly the smaller .35 size Classic planes..

Mongo

Joe Messinger · « **Reply #10 on:** August 04, 2010, 12:25:45 AM »

Hello,

My thanks to all who have offered help regarding my troubles with the Fox .25 engine(s) on my Ringmaster.

I'll try and describe what the problems are and what I've done attempting to correct them.

I have two Fox .25 engines. They're both 4 bolt back plate, 6 bolt head engines. One has a factory muffler and one does not. They both have straight up, bolt on venturis. Flat base venturis bolt onto the engine block.

Neither engine will run at peak rpms. They lack power enough for maneuvers. Both stop running when the tank still is about 1/4 full. Fuel draw appears to be the cause of the poor performance. I have tried new uniflow and standard vent tanks. Have tried adding muffler pressure to both tanks on the engine with a muffler. I've checked the tanks for leaks and used all new fuel lines and filters and checked them for leaks. I made new back plate and venturi gaskets. I tried a ST nva and made sure it was sealed tightly at the venturi. I'm using Fox 5%/29% fuel and have tried 9/4, 9/5 and 9/6 props on the engines. I don't know what else to do to correct the running problems.

Several have mentioned that these 4 bolt back plate engines were not so good for stunt flying and I'll have to agree with that.

I think I'll order an LA .25 for my Ringmaster and put the Fox engines back in their boxes. Several years ago, I had a Ringmaster with an LA .25 and it flew quite well with no problems. I sold it to a friend who needed a Ringmaster for an event he wanted to compete in and didn't have time to build a new plane. I kinda' miss the Ring as (with many who flew c/l in the 50's & 60's) that was the first plane I ever flew. So, I built this one and since I had the Fox .25 engines, thought I would give them a try. It ain't' workin'!!

Thanks again for your interest and advice.

Joe

dave siegler · « **Reply #11 on:** August 04, 2010, 07:42:42 AM »

While not my favorite engine, I have serveral and run a ton of fuel through them. Some notes

1) They are not world beaters, they like to run a slightly rich 2 stroke. They don't like to be overproped.
2) Use fuel with castor, 20-25% oil 10% nitro.
3) Make sure the little #2 screws that hold the venturi are snug, use locktite and don't over torque. 3) 8-6 or a 9-4 prop. A 10-4 will work but might be too much load.
4) Fuel draw has nver been a problem. Poor fuel draw may be a air leak.

OS is a lot better engine, but these will run.

Kim Mortimore · « **Reply #12 on:** August 04, 2010, 12:46:28 PM »

Depending on the weight of your Ringmaster, an older, mild .25 might be marginal on power even if it is running well (especially if it was built from an old Sterling kit). The newer aluminum-piston engines like the LA are both more powerful and more user-friendly. And the investment will keep paying off for many years to come. My 2 cents. And this time tell your friends that it's not for sale!

Author Topic: Pressure on a Fox? (Read 2309 times)

Joe Messinger

Pressure on a Fox?

Joe Messinger

Re: Pressure on a Fox?

FLOYD CARTER

Re: Pressure on a Fox?

Jim Thomerson

Re: Pressure on a Fox?

dennis lipsett

Re: Pressure on a Fox?

Joe Messinger

Re: Pressure on a Fox?

Jim Thomerson

Re: Pressure on a Fox?

kenneth cook

Re: Pressure on a Fox?

Kim Mortimore

Re: Pressure on a Fox?

Bill Little

Re: Pressure on a Fox?

Joe Messinger

Re: Pressure on a Fox?

dave siegler

Re: Pressure on a Fox?

Kim Mortimore

Re: Pressure on a Fox?