Author Topic: Magnum gp 25 runs good for two minutes or so. Then slows down and stops (Read 1617 times)

Allen Eshleman · « **on:** June 21, 2020, 08:18:54 PM »

I have a Magnum Gp 25 which I bought off of Ebay, I think. I have it on a Shark 402, inboard mounted with a 3 1/2 or 4 oz uniflow tank. Yesterday, it ran a perfect run for 9 minutes. Today, I went out to fly. I couldn't get a sustained run. It ran 2 cycle for 2 or 3 minutes. Then it began to slow down and stopped. It is an RC engine converted with a Super Tiger nva setup.

Any ideas what is going on.

I must say that I don't think it is new but I actually don't know.

Dane Martin · « **Reply #1 on:** June 21, 2020, 08:56:08 PM »

Could be a few things I suppose, but with my own magnum 25's and 28... they hate the wrong muffler. On my 28, I couldn't actually get it to start by hand flipping it, until I figured out it was the wrong muffler. I flew my twister with that 28 in many a contest, and it performed excellent. So, get it figured out, you'll like that engine

Craig Beswick · « **Reply #2 on:** June 21, 2020, 09:53:48 PM »

Hey Allen how are you?
I hate to admit this but somehow I got a Randy Smith LA46, second hand, from I don't remember where. It did exactly what you are saying. First run perfect, never missed a beat. Then, after that it would run okay for 2 minutes or so, slow down, not lean out it would just slow down then stop!!!

I sent it to a mechanic, here in Australia, who told me the head bolts were loose! I felt very stupid! I had taken the head off to check the wear and hadn't tightened them properly. So dumb.

Works like a watch now.....

Probably not what is going on with yours but sounds so similar.
All the best

Craig

Allen Eshleman · « **Reply #3 on:** June 22, 2020, 03:48:32 PM »

Thanks all. Hi Motorman. I did just put a new tank mounted on the outside of the profile fuse - a new Hayes Tank. I was somewhat suspicious of the bends needed to get through the fuselage. I will give that a try. I love how this motor runs, when it runs well. I will report again soon.

Brett Buck · « **Reply #4 on:** June 22, 2020, 09:42:41 PM »

Quote from: Allen Eshleman on June 22, 2020, 03:48:32 PM

Thanks all. Hi Motorman. I did just put a new tank mounted on the outside of the profile fuse - a new Hayes Tank. I was somewhat suspicious of the bends needed to get through the fuselage. I will give that a try. I love how this motor runs, when it runs well. I will report again soon.

Remove the needle and clean that out, too, and if you have a filter, look for that being clogged.

Brett

Dan McEntee · « **Reply #5 on:** June 22, 2020, 09:46:52 PM »

Quote from: Allen Eshleman on June 22, 2020, 03:48:32 PM

Thanks all. Hi Motorman. I did just put a new tank mounted on the outside of the profile fuse - a new Hayes Tank. I was somewhat suspicious of the bends needed to get through the fuselage. I will give that a try. I love how this motor runs, when it runs well. I will report again soon.

You have an inboard mounted engine on a profile and the tank is mounted on the outboard side? I know it is done the other way around, ( tank inboard and engine outboard when there is little room for the tank) but this set up will have the fuel fighting centrifugal force every bit of the way to the spray bar. I don't think I have ever seen anyone operate a profile in this manor. If this is the way you had it before, this may be the problem???
Type at you later,
Dan McEntee

Ken Culbertson · « **Reply #6 on:** June 23, 2020, 12:53:08 PM »

Let me preface this with something that all of the folks I fly with know and that is that I don't know squat about IC. That is why Electric has changed my life. HOWEVER, I do have some experience and this exact thing has happened to me on two very different engines. Both had a lot of runs and, in spite of them being one flip starts and easy to set the NV, they both were reaching the end of their lives. One was a McCoy 35 with about 50 flights on it and the other an OS35s with about 2,000. In both cases they were overheating. The McCoy made a sickening sound that reminds you of a horny cat with laryngitis before it sputtered and died. The OS just sputtered and died. I have been told that these engines needed to have the right fuel and should 4 cycle in level flight which is how I ran them until they wore out. Do you know how old yours is?

Just a thought, probably a brain fart - ken

Allen Eshleman · « **Reply #7 on:** June 23, 2020, 02:40:46 PM »

I don't know how old it is. I actually think that it was only lightly used. I have read in other threads here on Stunt Hanger that these are a clone of OS FP's, which, I understand are to be run in 2 cycle or very fast 4 cycle. One person on this Forum said that they may even be a tad better than FP's. I haven't tried it with the new tank yet. I did find a bit of dirt in the fuel filter. However, I am also going to take out the Needle and flush that out too.

As to inboard tank mounts for engines outboard mounted, I have been led to believe that it's a good setup and that there are others who do it. I have run several plane/engine combinations this way and they ran great. Especially a fox 35 on a Flite Streak ARF. However, I used pressure on that one and almost cooked it. It had a great 4/2 break.

Allen Eshleman · « **Reply #8 on:** June 23, 2020, 02:42:27 PM »

Muffler for a Magnum gp. The back extension of the muffler broke off on a hard landing. Anyone know where I can get one or whether I can use it the way it is.

Dane Martin · « **Reply #9 on:** June 23, 2020, 04:41:50 PM »

Quote from: Allen Eshleman on June 23, 2020, 02:40:46 PM

As to inboard tank mounts for engines outboard mounted, I have been led to believe that it's a good setup and that there are others who do it. I have run several plane/engine combinations this way and they ran great. Especially a fox 35 on a Flite Streak ARF. However, I used pressure on that one and almost cooked it. It had a great 4/2 break.

Inboard tanks are cool. Most of my profiles have been set up inboard tank. Especially my 4 stroke models

bill bischoff · « **Reply #10 on:** June 27, 2020, 12:36:43 PM »

Initially he said inboard engine, outboard tank. Like Dan said, that's very bad physics. Outboard engine, inboard tank is vastly better, but still less than ideal IMO.

Allen Eshleman · « **Reply #11 on:** July 15, 2020, 06:18:40 AM »

I changed tanks and moved the tank outboard. It ran over five minutes on 2 oz. of fuel on the ground. I think the plumbing of getting the fuel through the fuselage from inboard to the engine may have been at fault. Next test will be in the air when the wind is low and it suits me. I now have a new 4oz Hayes tank on it.

Allen Eshleman · « **Reply #12 on:** July 15, 2020, 06:28:08 AM »

I have another question. It's very hard to remove APC propellers. I have to use pliers and it's messing up the piece that it connects to - what is the name of that? Should they be drilled out just a bit so they can come off easier? If so, what sized bit should I use?

Tim Wescott · « **Reply #13 on:** July 15, 2020, 09:17:42 AM »

Quote from: Allen Eshleman on July 15, 2020, 06:28:08 AM

I have another question. It's very hard to remove APC propellers. I have to use pliers and it's messing up the piece that it connects to - what is the name of that? Should they be drilled out just a bit so they can come off easier? If so, what sized bit should I use?

If you're talking about the threaded bit -- that's the end of the crankshaft. For me the APC props are usually a tight fit but I can spin them on and off against compression. If you're using pliers, something is definitely wrong. If you've bunged up the end of your crankshat with pliers, just send the motor out to someone who can run a thread-cleaning die down it to clean up the threads.

Get a prop reamer, and see if you can clean up the prop a bit. If you trust yourself, use a fine rat-tail file that's just a bit smaller than the hole and then carefully, lightly and evenly stroke the inside of the hole to smooth it -- all around.

Ken Culbertson · « **Reply #14 on:** July 15, 2020, 10:24:55 AM »

Quote from: Tim Wescott on July 15, 2020, 09:17:42 AM

If you trust yourself, use a fine rat-tail file that's just a bit smaller than the hole and then carefully, lightly and evenly stroke the inside of the hole to smooth it -- all around.

I tape a piece of medium grit emery cloth to a smaller dowel then wrap it till it just fits in the hole. Twist the dowel to slowly ream out the hole - OR - get a prop reamer. You can usually find one in the grass near the pit area after a contest.

Ken

Allen Eshleman · « **Reply #15 on:** July 15, 2020, 09:19:28 PM »

The prop could be melting into the drive washer. I don't know for sure. I am ordering bigger wheels so that hopefully, props don't get their ends worn off. Also, I might try the 9.625x3.75N mentioned by Al Ferraro in a thread about an LA 25 and an ARF Nobler.

I haven't worked again yet at getting the old prop off.

john e. holliday · « **Reply #16 on:** July 15, 2020, 10:35:22 PM »

Years ago I was told about what is called a plumbers reamer. It is my go to tool for tight props. Have two of them, one in the tool box and the other in the shop. Tried the commercial reamers like Fox used to make.

Allen Eshleman · « **Reply #17 on:** July 16, 2020, 09:12:59 PM »

Thanks to all of you. Doc, you jogged my memory - that - yes, I do have a prop reamer. Problem solved. Props now go on and off with ease. I don't think they were melted to the drive washer. I need to make one more modification before flight. I want to make a kind of stooge hook that doesn't rear up the back of the plane - thus clipping the tips of props. I have one made. I just have to install it. I am getting closer to another trial flight.

Brett Buck · « **Reply #18 on:** July 17, 2020, 04:05:53 PM »

Quote from: Allen Eshleman on July 16, 2020, 09:12:59 PM

Thanks to all of you. Doc, you jogged my memory - that - yes, I do have a prop reamer. Problem solved. Props now go on and off with ease. I don't think they were melted to the drive washer. I need to make one more modification before flight. I want to make a kind of stooge hook that doesn't rear up the back of the plane - thus clipping the tips of props. I have one made. I just have to install it. I am getting closer to another trial flight.

The Tower Hobbies/hobbico reamer is excellent and a great step up from the Fox reamer. It's also *much* harder and will last a reasonable amount of time reaming out carbon fiber props. A Fox, you sometimes have to use three of them to get one hole reamed, literally a few turns and it's about like using a fingernail, it gets so dull.

Brett

Allen Eshleman · « **Reply #19 on:** July 17, 2020, 07:08:22 PM »

Mine is in a plastic red box. I had to use the second dimension to make the hole big enought.

Bootlegger · « **Reply #20 on:** July 20, 2020, 12:08:46 PM »

Might add a small amount of oil, see what that will do for you, could be a might shy..

Allen Eshleman · « **Reply #21 on:** July 20, 2020, 06:45:00 PM »

I am hoping to fly this plane soon. It's been very windy most of the time and I am still busy, even though I am temporarily retired (hopefully temporarily). This plane, engine and prop is ready to go.

BillP · « **Reply #22 on:** July 21, 2020, 08:34:59 AM »

Quote from: Brett Buck on July 17, 2020, 04:05:53 PM

The Tower Hobbies/hobbico reamer is excellent and a great step up from the Fox reamer. It's also *much* harder and will last a reasonable amount of time reaming out carbon fiber props. A Fox, you sometimes have to use three of them to get one hole reamed, literally a few turns and it's about like using a fingernail, it gets so dull.

Brett

Thanks for the info. I don't fly carbon but the Fox reamer I have stayed sharp using it on wood and nylon props. APCs being the most used on. Looks like the hobbico reamer is in my future if I try carbon.

Allen Eshleman · « **Reply #23 on:** July 21, 2020, 09:45:51 AM »

Well, today I finally got to run the Magnum engine on its Shark 402 test bed. I ran one flight of 5 minutes or so with 10% nitro. The second flight, it did not run the whole tank full through and quit about 3 minutes into flight.
I think it over heated.

Then I started using 5% nitro and it ran the tank dry. It needs another pitch propeller, I think. I am going to bump it up to 9x5 or an 8x6 three blade.

Does it make any sense that it might run better on 5% nitro or that it wouldn't get as hot with 5%.

Allen Eshleman · « **Reply #24 on:** July 21, 2020, 09:47:41 AM »

From the beginning of this thread, the major change I made was to move the tank inboard. That must have been the cure for the 2 or 3 minute run.

Allen Eshleman · « **Reply #25 on:** July 21, 2020, 09:48:57 AM »

The true account is: I moved the tank outboard.

Allen Eshleman · « **Reply #26 on:** August 01, 2020, 02:21:12 PM »

Since I moved the tank outboard I am getting long runs and decent flight. However, getting enough fuel in to get it started is difficult. I put the starter on the nose and spin it with my thumb over the venturi.

I ran it today with a three bladed prop 8/6 by Master Airscrew. It was a nice run. However, I did not get to try the 9/5. I need just a bit more pull from this plane/engine combination.

I recall reading in a thread here that the gp engine does not have much compression. Today, after flying the Shark 402 with the Magnum gp, I put up another 402 with an FP 25. It has the tank mounted inboard but does not have any trouble pulling in the fuel. It is a powerful screamer. I might have to look for a 9/3 prop, if such a thing is made.