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Author Topic: Magnum GP 25 Tips  (Read 4937 times)

Offline Allen Eshleman

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Magnum GP 25 Tips
« on: July 14, 2018, 10:41:06 AM »
I just a used Magnum GP 25 RC for a total of around $43.00.  I have no idea if this is good. I'm looking for a few tips.

Props that work well.

Fuel recommendation -  I'm hoping 11 1/2 x 11 1/2      I have 5% and 10% batches.  I usually mix for 7.5

Possible parts for C/L setup

I will probably use it first with the throttle wide open as I am a sport flier.

I've read some things here especially in comparison to other 25's. 

I'm interested in your experiences with this puppy.

Thanks ahead of time. 
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Online Dan McEntee

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Re: Magnum GP 25 Tips
« Reply #1 on: July 14, 2018, 02:36:24 PM »
  Any thing you can read on any other ball bearing .25 will probably apply. If you do a search and nothing comes up ion the Magnum .25, than most likely no one is using it a lot. For a prop, start with a 10-4. If using the throttle, close it down just a bit before locking it. I have found that locking carbs wide open tend to leak a lot of air and cause trouble or use more fuel that you want, so closing the throttle a bit and then needling it to the speed you want will simulate using a smaller venturi. Find out what size venturis are used in the LA.25 and use that as a starting point. This engine may pack more punch than you think so be ready for it.
   Type at you later,
   Dan McEntee
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Offline Air Ministry .

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Re: Magnum GP 25 Tips
« Reply #2 on: July 14, 2018, 09:05:44 PM »
To all thingos theyre a FP 25 Clone .



Theres a Bill Bischoff  N.C.L.R.A.  ASP 15 Intake that fits , as Here .
But 1/4 in. bore .

The FP 25 rant is Here : https://stunthanger.com/smf/engine-set-up-tips/os-25-fp-performance-against-os-25-la/

The ST 35 C stunt intake fits and works well .
The MVVS D7  (.15 Diesel ( & G-7 ? ) ) intakes good.
Theres a Magnum 25 & 40 intake , plus the Thunder Tiger intake . But theyre Hens teeth.

These'r all the periferal multi jet type , with the spraybar through FORWARD . As thats where the Hole Is .

A 9 x 4 wont overprop it . a narrow blade 10 x 4 would be good .

The Muffler Bolt Patterns the same as the FP 35 / 40 and T T 36 . NOT the FP 25 ? maybe . :-\ have to check the FP 25 There .
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Online Chris Brainard

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Re: Magnum GP 25 Tips
« Reply #3 on: July 14, 2018, 09:23:58 PM »
My Magnum .25 is a plain bearing engine and is a clone of the FP 25. I believe, that later, it became the Thunder Tiger 25. From my experience, I prefer them to the FP 25. Use same props as on FP. I drilled my case for a FP needle valve assembly and Venturi.
Chris
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Offline Dane Martin

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Re: Magnum GP 25 Tips
« Reply #4 on: July 14, 2018, 11:26:13 PM »
I'm not an expert, but in my magnum 28, I'm running a 0.155 venturi. This set up came from expert help at VSC.
I bought a .145 venturi from Jim Lee and drilled it out to .155.
Standard super tigre NVA
APC 9x4 prop.
20% fuel. I run lower oil than you might need to however. The 28 is a bearing engine.
This is in my now infamous 38oz twister flown on 57' lines.

I think in the 25, I'd buy the .145 venturi from Jim Lee and try it first.
 Chris's recommendation above is obviously a good idea also, effectively making your engine an os 25 fp. But if you're not comfortable drilling your case, Jim has the sprinkler type venturis for a couple bucks.
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Offline GERALD WIMMER

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Re: Magnum GP 25 Tips
« Reply #5 on: July 15, 2018, 10:00:07 PM »
Hello We have a Magnum Pro 25 and it looks just like the GP 25 but is ball-raced. Nearly ready to bolt it onto a stunt hack model for my youngest son . My older son has a Thunder Tiger 25 of the same era that seems to put out more power then many old 35's (and my nice old Enya 45 model 6001) Normally use a 10x4 and muffler pressure , venturi (6mm)
Regards Gerald
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Offline Allen Eshleman

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Re: Magnum GP 25 Tips
« Reply #6 on: July 16, 2018, 06:11:12 AM »
Thanks guys,

Sound like I basically have an FP.  Also, it looks like there are several options for converting to C/L.  I might get to play with it this week.  I'll let you know what I find.  I find the idea of setting the throttle a bit off of wide open interesting and will probably try it that way. It will be hitched to my twice resurrected Shark 402 for now.  I expect to receive it today and tomorrow at the latest.
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Offline Geoff Goodworth

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Re: Magnum GP 25 Tips
« Reply #7 on: July 17, 2018, 01:50:05 AM »
I have one that I'm running at present with a Scott Riese [sp] 0.136" ID sprinkler venturi and 4mm (0.158") dia ST-style NVA in the pinch bolt hole. It's quite happy on a Bolly Clubman 9.5 x 5.
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Offline RandySmith

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Re: Magnum GP 25 Tips
« Reply #8 on: July 17, 2018, 10:41:13 PM »
The  GP means  plain bearing, and is  an  OS  FP Clone,  the  Pro  is the  dual ball bearing engines,  and  there is  a very large difference  between the  2.
Both can be made to work pretty well, the difference  is  a  25 Pro  will fly a Nobler, the  25 GP will not  do a good job of that.

Randy
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Offline Air Ministry .

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Re: Magnum GP 25 Tips
« Reply #9 on: July 17, 2018, 10:50:45 PM »



=================================================
And . ( As the widdle pitcher at Bottom Right  has the ' Pro ' Box & Injun pic . )

THATS A 40 or 45 in the TOP PICTURE Below .  . YES , the Printed Pages are on the PRO / FSR Clone . The Top PHOTO is the Grand Prix  :-X .



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Offline Air Ministry .

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Re: Magnum GP 25 Tips
« Reply #10 on: July 17, 2018, 10:57:23 PM »
And the Chunder tiger Plain Bearing and Dual Ball Race , OS Clones . Look like the series II FPs .





Fairly Obvious is the big lump or not , where the big ball race is , or isnt . Front of Cylinder .
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Offline Allen Eshleman

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Re: Magnum GP 25 Tips
« Reply #11 on: July 24, 2018, 06:30:18 PM »
I just got to run this for the first time on the test stand. It seems as though it has low compression but it ran well after I got the needle adjusted.  I really flooded it first.   

Does anyone know the recommended need opening.  I do not have the manual.

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Offline Allen Eshleman

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Re: Magnum GP 25 Tips
« Reply #12 on: August 20, 2018, 06:19:27 PM »
I have finally gotten time to run this engine more on the stand.  It wasn't running right.  Then I found three things:

1.   A leak in the fuel line
2.   The arm of the throttle was loose.  It would stay at high rpm and would always drop back.  I could see the throttle closing a bit.  All I needed to do was to tighten the screw on the arm (idk the name for it).  Now it holds steady speed and good rpm.
3.  Changed glow plug.  It would sag when I took the batter off.

It still doesn't have a lot of compression but seems to run well.  I checked all the screws in the head and the back plate.  No fuel leakage.  Any advice on that?

Doesn't start well except with an electric finger.

Regardless = next it will be installed on a twice wrecked and reconstructed Shark 402. 
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Offline Dane Martin

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Re: Magnum GP 25 Tips
« Reply #13 on: August 20, 2018, 07:26:34 PM »
Piston and liner sets are still easy to come by. Might be worth it, but....

Now, that being said, my magnums don't feel like a lot of compression. I installed a new piston / liner in my 28 and I think it felt the same. However, it did start easier. Also, it wouldn't start to save my life with the muffler on. Took it off and it fired on the first flip. Until I got everything else dialed in, I had to leave the muffler off. Maybe try that until it's sorted out. I found later that had nothing to do with the problem, but it made it easier to troubleshoot.

Also, they start pretty wet. At VSC I would do 6 choke flips and clear it 6 times. Fired right up. My magnums never feel like they have a "bump". Sounds dumb, but they run and start great. But I rely on a routine rather than a bump feel to start by hand.
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Offline Steve_Pollock

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Re: Magnum GP 25 Tips
« Reply #14 on: August 25, 2018, 04:49:10 PM »
Allen, here's the TT GP Manual.
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Offline Air Ministry .

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Re: Magnum GP 25 Tips
« Reply #15 on: August 25, 2018, 08:23:27 PM »
Anyone tried bunging the bypass / boost port , on these or FPs , to match the ' No Boost Port ' LA 25 .

Seems like it might be ' the Trick ' .
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Offline Dane Martin

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Re: Magnum GP 25 Tips
« Reply #16 on: August 25, 2018, 09:47:45 PM »
Quote from: Matt Spencer on August 25, 2018, 08:23:27 PM
Anyone tried bunging the bypass / boost port , on these or FPs , to match the ' No Boost Port ' LA 25 .

Seems like it might be ' the Trick ' .

I was actually tempted to pull one of my FP's apart and see what that may entail.
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