Hello,
I have a Magnum .91 that I have put about 10 flights on. I put it in storage for the winter and have brought it back out for the summer flying season. I got it mounted and fired it up. It runs but the difference between idle and full throttle is only a few hundred RPM. The idle is too fast as I have to hold the plane back. When I open the throttle the engine increases by a few hundred RPM and goes really rich-puffing out the typical "rich" smoke, and sounds like it bogs down. I have the high and low end needle settings to the factory settings and I have adjusted the valves. The engine ran well before I put it in storage.
The gasket on the intake is worn off. Does anyone think this is what's causing it? Anyone else have any ideas?
Thanks!
Darin

yea!!! you need to make me a good deal on it. I am looking for one. Are you sure you have the valves adjusted right. Sounds a little snug. should be I think from .06 to .10

Um, it's not for sale, I have a problem with it.

Rest assured, darinself, that there is plenty of expert advice to be found in the glow engines forum:

http://www.rcuniverse.com/forum/forumid_114/tt.htm

You can search through other threads there on the Magnum XL .91 RFS, or perhaps even ask a moderator to move this thread to that forum for you.

There are a couple possibilities. First, if you're running it as recommended with a castor oil fuel, you may have some varnish around the carb. Does the throttle barrel turn freely over the entire range or is it binding?

Can you turn the engine freely when not in compression? You could have a rusty or gummed up bearing.

You say the full throttle is only a few hundred rpm above idle, and the idle is too high. How fast is it actually turning?

Did you adjust the needle valve settings after you took it out of storage? You say they are at the factory settings. Does this mean you never adjusted them before?

The gasket on the intake could be causing an air leak. I would definitely replace it if it looks worn.

Brad

you get what you pay for.... y yes

I have 3 of the Magnum 4 strokes, and they are some excellent running engines. I have one mounted in my hangar queen, my kit built Cessna 182. The engine is cowled, and I haven't touched the needle valve since the maiden flight. These engines are way less picky on the needle than my Saitos. And while I can't help out the original poster, I can't see what a comment like yours is supposed to accomplish, other than start an engine war.

I will jump in on this response also.
Magnum makes a fine 4 stroke engine and when I need a new engine I look at magnum first.And yes I have OS and Saito 4 stroke engines as well and my Magnums are on par with any of them.

wow....thanks for all the help

Darin, like a previous suggestion, there may be a bit of gum in the fuel lines/carb. I would firs make sure the throttle travel is OK. If it was OK when you put the plane away, it still should be, but it would be the first place to look. Then I pull the line off the carb and also off the muffler and then blow into the muffler/vent line and make sure you have a clean fuel pickup. Just a slight blow into the vent line should result in a flow from the supply line, assuming fuel in the tank. OK there, then pull both the high speed and low speed needles and plug the line back on the carb. Blow in the vent line again and you should see fuel exiting both the high speed needle opening and the ilde opening. OK there, then replace the screws. Set the High speed a 1 1/2 turn out from closed and the idle to two turns out. This is the starting point and both settings should result in at rich setting. Go throuth the tune up, first high speed for max RPM then back off 400 RPM or so to the rich side. set the throttle as slow as it will go and keep running. At this throttle setting, lean the idle for max rpm. The go back and do the high speed again and then the low end again. You should now be able to get that engine to idle down to around 2200, and 2000 if evey thing is OK. The high end will depend on prop, but with a 14-4W APC, I get right at 10,000 RPM tops and fly at 9500RPM.

Like a couple guys said, there is nothing wrong with the Magnum engines. I also have OS, Saito, and Thunder Tiger four strokes and the biggest difference between them in like size engines is price and bragging rights.

When you say the gasket on the intake is worn off, what do you mean?? Are you talking about the manifold to head gasket? And by "worn off", I'm not following you. Please expand that explanation.

On the valves. if you use the standard US feelers, they should be loose at 0.002" and tight at 0.004" with the enging on TDC on the stroke where both valves are closed and when the engine if room temp.

Without seeing the engine first hand, my guess would be some gum in the carb, or in the tank, and a little running should clear either up.

Give us some more info and we'll get it going for you.

Don

I found a hairline crack in the crank case breather tube. I also made a new gasket. I'm thinking the breather tube was the problem. Thanks for all the help fellas!!

Good work !
Is it running correctly now ?

I will fire it up this weekend. It should run, it was a great runner when I put it away.

Hey if it is still giving you problems come back on and give a real detailed description of what it is doing.

The breather tube was the problem. Runs like a top. Man, these engines can scream.

WHERE CAN I FIND A MUFFLER FLEX EXTENSION FOR MY MAGNUM 91 AND MY MAGNUM 120 FOUR STROKES. WHAT IS THE THREAD SIZE ON THE MUFFLERS.

The OS 91 has the same thread as the Magnum 91, so these will work for sure.
Thread size M11 x .75mm
http://www3.towerhobbies.com/cgi-bin...&I=LXXE97&P=SM
http://www3.towerhobbies.com/cgi-bin...&I=LXXE98&P=SM

I am not sure if the OS 120 and the Magnum 120 have the same thread, if they do ...
http://www3.towerhobbies.com/cgi-bin...&I=LXCB20&P=SM
http://www3.towerhobbies.com/cgi-bin...&I=LXCB21&P=SM