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4 strokes

Old 06-07-2008, 04:46 PM
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J2LANDIS
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Default 4 strokes

I'm looking for a new 4 stroke and can't make up my mind. Is the magnum 4 stroke any good? I'm looking at the magnum 90/120 4 stroke or maybe go Super Tigre 2300 2 stroke. What do yall think. Thanks for any advise.
Old 06-07-2008, 06:00 PM
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waterloged
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Default RE: 4 strokes

I have 2 Magnum 91s, and a 70 4 stroke The 90 have been fantastic. I have over 30 gallons of fuel through tthe one and all i have done to it is adjust the valves and the carb. last year the oldest one just started losing power and needs rebuilt but it does have over 30 gallons of fuel through it. the new'st 91 has been real good also but the 70 really has been junk. i can'nt keep it running or keep the carb adjusted. It just doesn't seem to be any good. The 91's broke in quick and good. the 70 who knows. The ST 2 stroke will be quicker too. I'm sticking with Saito on my big ones.
Good luck
Old 06-07-2008, 08:37 PM
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Gringo Flyer
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Default RE: 4 strokes


ORIGINAL: J2LANDIS

I'm looking for a new 4 stroke and can't make up my mind. Is the magnum 4 stroke any good? I'm looking at the magnum 90/120 4 stroke or maybe go Super Tigre 2300 2 stroke. What do yall think. Thanks for any advise.
What type plane are you looking to put this in? A magnum 90 4 stroke and a ST 2300 are 2 different animals completely.

I like my magnum 4 strokes. They are great sport engines and run super on low nitro. Easy to tune and reliable runners.

They arent the most powerful engines on the market but for general sport flying they are hard to beat.
Old 06-07-2008, 09:43 PM
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Deadeye
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Default RE: 4 strokes

Magnums are reliable. So reliable I put a 91 in my scaled out Cessna 182 with over 300 hours of work in her. I also have a 120 Magnum in my Skybolt, and it tears the crap out of the sky. My next scale project, the Piper Arrow II is getting the Magnum 91 treatment as well.
Old 06-07-2008, 10:49 PM
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Don41
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Default RE: 4 strokes


ORIGINAL: waterloged

I have 2 Magnum 91s, and a 70 4 stroke The 90 have been fantastic. I have over 30 gallons of fuel through tthe one and all i have done to it is adjust the valves and the carb. last year the oldest one just started losing power and needs rebuilt but it does have over 30 gallons of fuel through it. the new'st 91 has been real good also but the 70 really has been junk. i can'nt keep it running or keep the carb adjusted. It just doesn't seem to be any good. The 91's broke in quick and good. the 70 who knows. The ST 2 stroke will be quicker too. I'm sticking with Saito on my big ones.
Good luck
This seems to be a trend (as least the way I see it). Magnums are either great and will run forever or they are full of bugs right from the factory. I have some Saito and OS four strokes and they have always been quality from day one.

Of course,, if I had run across a bad one I'd be singing a different tune (:-).

My brother bought a 50 size four stroke Magnum and he has had a lot of problems with it. The first one arrived with no compression. You literally could not tell the difference with or without the glow plug installed. The factory sent a replacement but we have yet to get it to run consistently smooth. It seems to have its good days and bad days. The low speed adjustment screw has no resistance to moving so it looks as though it could easily change settings from vibration. Possibly it was assembled at the factory incorrectly?

In my opinion you should stick with the Saito or OS
Old 06-07-2008, 10:53 PM
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Jester241
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Default RE: 4 strokes

I've only heard mixed reviews of the magnums,but the one thing I noticed about them is that they now cost more then they used to. There not really much cheaper now then a Saito or an O.S. I think they're trying to cut into the sales and price range of Saito's and O.S.'s,but I just dont think they have quite the reputation to be charging that much money for them yet. I know it is about $50.00 difference,and that may seem like alot to some people,but 50 bucks isnt alot to me considering with a Saito or O.S. your almost garanteed to have your engine work great as opposed to HOPING your engine is gonna work. Anyway.......I'd rather pay the xtra $50 for the confidence of knowing I have the best and it will not let me down.

If I could only ever have one brand of engine it would be SAITO.


Old 06-07-2008, 11:17 PM
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traxxboy
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Default RE: 4 strokes

I have a magnum .52 rfs in my four star 40....starts and runs great. I have a about 3 flying gallons through it. Take the time and break it in properly and you have a great running engine.
Old 06-08-2008, 02:31 AM
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Default RE: 4 strokes


ORIGINAL: Jester241

I've only heard mixed reviews of the magnums,but the one thing I noticed about them is that they now cost more then they used to. There not really much cheaper now then a Saito or an O.S. I think they're trying to cut into the sales and price range of Saito's and O.S.'s,but I just dont think they have quite the reputation to be charging that much money for them yet. I know it is about $50.00 difference,and that may seem like alot to some people,but 50 bucks isnt alot to me considering with a Saito or O.S. your almost garanteed to have your engine work great as opposed to HOPING your engine is gonna work. Anyway.......I'd rather pay the xtra $50 for the confidence of knowing I have the best and it will not let me down.

If I could only ever have one brand of engine it would be SAITO.



I couldn't agree more. For the difference in price, you gain reliability and peace of mind. An initial cost savings can kill you in the long run.

If price is an obstacle, buy a used Saito or an OS.
Old 06-08-2008, 09:40 AM
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carrellh
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Default RE: 4 strokes

When Global dropped the price last year so you could buy the Magnum 91 for $150 (even less with various promo codes), it was easy to justify buying it versus spending $250 for the OS or $265 for the Saito.

At 190 vs 250, I'd choose OS.

If I actually needed an engine today the choice would probably be Saito because the OS is currently on backorder.
Old 06-08-2008, 06:20 PM
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Default RE: 4 strokes

I am a Saito kink of guy, have had several from 50 on up to a .80 and all run great. My friend bought a new Mag. 70 and we broke it in, it runs great, but I think my Saito .56 can preform the same as the Mag. .70 Both are new and been broke in with the same fuel and setup.
Old 06-09-2008, 11:01 AM
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alfredbmor
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Default RE: 4 strokes

Magnums are great engines but way underpowered, I have a 4 stroke 1.20 which swings a 15 x 6 prop at the same revs as my Saito 1.00 does, I believe smaller magnum engines performs better but always underpowered when comparing with Saitos or OS engines. My magnum will haul a Dynaflite SE5a next year (great idle and acceptable power for this application), I highly recommend this engine for any other scale application, if you are looking for a sport, pattern or 3D application then you should look for a lighter and more powerful engine.
Old 06-09-2008, 09:06 PM
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chashint
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Default RE: 4 strokes

I have not found the Magnum 91 or 70 to be underpowered compared to the same size OS engines. Between my brother and I we have several of each, we use 14x6 on the 91s and 13x6 on the 70s and with the same fuel they are all about the same. Less than 500 rpm from the strongest to the weakest and the line-up is mixed so it not like the Magnums are all bunched at the bottom.
The Magnums run every bit as reliably as the OS and we are very satisified with them.
Now after having sang the praises of the Magnums, I will also echo the sentiment that if the price difference is only 50 or 60 dollars I would buy the OS or the Saito. While I have no personal experience with the Saito engines I would say that the OS engines are just a little more refined than the Magnum engines. All of my Magnum engines have large RPM changes with one click of the HS needle, this has not really presented any issues but in three clicks you go from to rich to right on to to lean .... the engines hold the needle setting very well and you don't have to fiddle with it, but the OS needle lets you dial in the RPM you want and it holds the needle setting too.
So that is why I say the OS is more refined.
If there is not a sale on the Magnums and I was choosing between OS and Saito that choice would be greatly influenced by the plane the engine was going in. If it is known to need nose weight then the engine would be an OS Surpass, if the plane is known to need tail weight then it would be the Saito.
I don't have any large displacement engines but the 70 and 91 size OS and Magnum engines have very little vibration, I cannot comment on the Saito engines since i do not personally own one.
Old 06-09-2008, 09:23 PM
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J2LANDIS
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Default RE: 4 strokes

Thanks for all your help guys. you helped me alot.
Old 06-13-2008, 08:33 AM
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circuitelec
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Default RE: 4 strokes

I have a Os Fl70 and I dismantled it for servicing, including the carburettor screws. What I didn't know was I also unscrewed the air bleed screw as well. Now I have trouble figuring out how many turns the actual factory settings of the air bleed screw. Can anyone help?? Thanks
Old 06-13-2008, 08:34 AM
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circuitelec
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Default RE: 4 strokes

I have a Os Fl70 and I dismantled it for servicing, including the carburettor screws. What I didn't know was I also unscrewed the air bleed screw as well. Now I have trouble figuring out how many turns the actual factory settings of the air bleed screw. Can anyone help?? Thanks
Old 07-07-2008, 03:17 PM
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Default RE: 4 strokes

Hello All,
I am very new at 4 strokes and would appreciate some help !!!

I've bought my first 4 stroke engine last week ... It's a Magnum 70 RFS. Did the break-in as recomended by manufactor and I'm still running it a little ritch. I'll try to give as much information as possible so you can have a better idea of what is going on...

Prop: 13x6 (master)
Break in fuel: Wild Cat > 2 cicle fuel - 10% nitro 18% castor oil
Current Fuel: Wild Cat > 4 cicle fuel - 15% nitro 18% oil
Engine Mount: Inverted
Tank position: ABOVE CARB position (I know that this is a problem ... not sure HOW much of a problem)
Tank size: 12 OZ
# of tanks ran after break-in: 4
Glow plug: OS type F
Airplane: Extra 300S 46 (Phoenix Models)

After the break in and with new fuel I've started to adjust the idle .... It idles pretty good for a few seconds and it will start to slow down. If I give some throttle it will get back to normal but will get back to the same situation in a bit. The problem I have is ... I can't get the engine to idle on a speed that the plane with sit still... I noticed that if I leave the glow in for a couple of seconds and let the engine warm it will give better idle for a while.

Does 4 stroke engines work like this ?? I wont be able to get it to idle unless a give some throttle now and then ??

something else I've tried : If I leave the glow starter plugged In I can idle as slow as I want !!! and the engine wont stop... Once I remove the glow starter it will slow down and die... Already changed a glow PLUg and it didn't help at all.

What about the tank position.... could that be the problem ??? maybe that + the inverted position ? Maybe 4 tanks after break-in is still not enough to set it properly.... ?

I am trying to read all I can about 4 stroke engines.... but any help would be appreciated.

Thanks a lot,

Renato.
Old 07-07-2008, 03:36 PM
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Jburry
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Default RE: 4 strokes

You're describing a very typical rich idle condition. The engine is "loading up" at idle, excess fuel puddles in the inlet passages, and then finally slugs into the engine, putting out the fire. Continue to lean the idle mixture needle (or open the airbleed a bit further if its' an airbleed type).

It can help to use a tach when setting up a 4 stroke. Really, tho, it's the same as a 2 stroke, except you'll have to check the valve clearances from time to time. To set the idle using a tach, slowly close the idle screw until the RPM's peak (at idle). Go VERY slowly. Once you've found the idle peak, rich it just a hair until it will accelerate cleanly after idling 30 seconds or more. Test by running WOT for a few seconds, idle for 30 or more, then back to WOT.

A 4 stroke can idle as nicely as a 2 stroke, but they speak with a different accent. Once you've burned a couple gallons of fuel and got those needles tweaked, your idle will come down more. The Magnums can take quite a while to break in enough to idle really well, but they'll get there!

J
Old 07-07-2008, 03:45 PM
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Bananaboat
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Default RE: 4 strokes

Thx a lot J !!! I'll try that out WED and get back to you with the results...

Hope it works out cause I am loving to fly with that engine !!! The sound is awesome and the power is nothing like 2 stroke ...

What about the tank position ?? will that do any harm besides flood the carb occasionally ?? I am trying to find out the best way to fix that... maybe a valve, also read about oscilating pumps...


Regards,

Renato
Old 07-07-2008, 07:23 PM
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ernbar
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Default RE: 4 strokes

Some guys like their Magnums, others like me will never buy another one! See my thread: http://www.rcuniverse.com/forum/m_7690537/tm.htm

Their either junk or are ok. I'm getting an OS to replace this Chinese junk!
Old 07-08-2008, 11:36 AM
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Jburry
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Default RE: 4 strokes

Your high tank position could cause flooding when the engine isn't running (use hemostats to pinch the fuel line until you're ready), but if it's not REAL high, most engines will tolerate it. Work thru the tuning dance, and if it can't be tuned successfully, then address the tank.

The flooding potential can be eliminated by using a uniflow tank setup, where both the supply and vent lines are set up with clunks. A separate "filling vent" is used to vent the tank when it's being filled, and is plugged when running.

J
Old 07-08-2008, 10:01 PM
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chashint
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Default RE: 4 strokes

I agree with trying to adjust the low speed needle and I also strongly recommend putting in a new OS f glow plug if the engine does not respond favorably to the low speed needle adjustments.
I figure the glow plug installed in the engine now was probably new only a few tanks of fuel ago, but it has been my experience that new engines (especially four strokes) tend to eat the first couple of glow plugs pretty quickly.
I would not hesitate to install a new glow plug, you have nothing to lose as long as you don't throw anything away.
Old 07-09-2008, 07:36 AM
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Gringo Flyer
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Default RE: 4 strokes

Also, you might be happier with 5% on that engine. It will run ok on 10% and even 15% but I dont think you are going to get that big a boost from it.
Old 07-10-2008, 07:24 AM
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Default RE: 4 strokes

Ajusting the low speed neddle did the trick !!! Thx a lot for all the help !!! I am teaching some new students to fly so I could not flight mine plane more than 3 times.... but the engine was doing GREAT !! :-) now that I am confortable with it I'll try to change the propeller and see if I can get a little more torque than the 13x6 is giving right now...

I also wanna try that uniflow system and see how it works on the plane...

Now I am trying to help a friend with another Magnun 90... we couldn't get it to iddle properly and I did the same thing I did on mine.... but looks like the low needle is way too loose !! so after a couple of minutes we decided to leave it for the time... my friend will remove the cowl and take a look at the o-ring and change it so we can give it another try over the weekend ... Something that I thought was weird was that the engine would only start with more than 6 to 8 turns open (LOW SPEED NEEDLE) !?!?!??! is that a normal setup for this engine ??? I am used to 1-2 range....

Regards,

Renato
Old 07-10-2008, 10:40 AM
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khelsea
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Default RE: 4 strokes

I had the same thing happen to my 52 Magnum, changed the o ring and no more starting and idle problems. The only I don't know is what oring it was as it was just in my stach. Anybody know? Khelsea
Old 07-11-2008, 06:50 AM
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ranger351w
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Default RE: 4 strokes

I have a OSfl70 . Is this good for a .46 powered plane as in will it replace the 46 and get the job done?

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