I've been having trouble getting a used Magnum XL-52RFS to start. When I hit it with the starter it just spins, like it's not even trying, and I didn't notice it sucking any fuel. I've checked the glow plug and the tank, and the fuel is new, so I think I didn't set the needle valve right. I gave it three turns out. If it matters I'm turning a 12" prop and useing Sig four-stroke fuel. This is my first four-stroker and I would appreachate any advice I can get. Thanks

You mention that it's used. If it has been sitting for a while there is a good chance that the valves are stuck.

If that is the problem, how would I fix it?

Take the valve covers off and squirt some oil down the rods and try to free them up.

OK I removed the valve cover and rotated the prop a few times and the valves seem to be moving fine. I'll put some After run oil down there anyway, but I think (I could be wrong of course) the real problem was the needle setting. Could somone tell me what I should set it to. Thanks for the help guys

Sounds like it needs a prime, or choke. Take the glow plug clip off. Put your finger over the end of the muffler, or the top of the carb and turn the engine through by hand a few times. You should see fuel getting sucked up the line and into the carb. After going through about 2 compression strokes, re-attach the glow plug and give it a try. You may want to open the needle up a turn or so also, just to get it running, then adjust it right

Well I got fuel going into the carb now but it still won't fire. I tried starting with 4 and 5 turns out on the NV. Could the valves be misalined or somthing. I'm praying that the berings havn't worn out[:@].

Is your glow plug OK. The magnum 52 runs best on an O.S. type F plug. It should fire with any of them though as long as they light up OK.

Inital needle valve settings are 2 1/2 turn out after closing the high speed, Same for the idle. These will get the engine running so you can tune it.

Take both valves out. and then remove the line from the muffler and blow into it with fuel in the tank. You should get a good flow of fuel out the ends of the spray bar with not to much lung power. Also a quick check to make sure the lines are not reversed.

The magnum 52 four stroke doesn't have much compression. It is quite different than the O.S 52 fours stroke. You can feel the engine come up on compression, but it is no where as much as you feel with the O.S.

Has the engine been taken down?? could the valve timing be off? Pull the glow plug and using a small wood dowel find top dead center. Mark the front bearing housing and the prop thrust with a single line. Use a sharpie fine point and it will clean right off after. Remove the cover on the cam. There is a dot on the cam face and it should be facing straight down or straight up, depending if were at the top of the compression stroke or top of the exhaust stroke. Don't crank the engine with the cam cover off as you may skip a tooth without the end bearing support.

Fuel, the Magnum four strokes need 15% nitro. They just don't run right with less.

Once you get the engine running, and warmed up, adjust the needle valve for maximum RPM, you should get around 10,000. The ramp on the highspeed valve is stubby and one click makes a big difference. After each click wait 15 seconds or so befor changing again. Once you have the engine maxed out, then go rich to drop the high end by 500 rpm or so. Better more drop than less. Now idle down as slow as you can and keep the engine running. Screw in the idle for maximum speed at this throttle setting. A long thin screwdriver, 8" blade is best, for this. Now go back and readjust the top end again. back to the slowes idle and this time when you have it running as slow as you can without stalling, punch the throttle. If it stutters and fumbles, you are running to lean on the idle, back it out 1/8 Turn. If it slowly comes up to speed, you are running to rich and in this case 1/16 turn closed on the idle. This takes some hunting to get to the sweet point. After every couple adjustments on the low end, re-do the top end. What you should end up with is an idle around 2000, and top end at 9500, and when you punch it from idle, it barks to life and doesn't stall. If the engine is older, I would suggest gettting a replacement set of Orings for both the needle valves and the carb to manifold. The fit of these rings is very important to having an engine that runs well. I have two magnums now, the 52 and a 70. The 52 has been troublesom in the idle, even after 1 gal or so of fuel through it. The 70 is a sweetheart, right out of the box. I've two O.S. 52s, actually one as I lost my plane with one of them, and they are rock solid and quite eaiser to adjust.

Thanks for all the help. I'm thinking it must be the glow plug, I took it out to check it again and saw no visible glowing, though it did fisel when I put some fuel on it. I'll try changing the battery in the glow starter.

Generally the glow plug should glow an orange color - really hot!

OK, I got the glow plug glowing as bright as the sun and the engine is gettign fuel but the darn thing still won't fire. I guess the only thing left is the valve timeing. Campgens, I took the cam cover off like you said but I don't see any "dot", what do I do now? Again thanks for all the help.

Some cams have a dot and some have a line. It usually has a little sludge on it. You may have to wipe around in there with a Q-tip to find it.

Engine piston at top dead center and dot or line on cam aligned with the lifters or cam followers

Go to www.hobbypeople.net , click on engines, locate the Magnum 52 and you should be able to down load the basic instruction sheet. It will tell you how to adjust valves, do a break in, how to tune the carb, etc.

Also locate a old timer who has some experience with 4C engines. An instructor out at the field may help. Ask for help!

While the 52 may not have much compression, it should have some. If the valves are adjusted correctly, and are moving up and down (could have a broken valve spring for instance), try putting a little oil into the cylinder via the glow plug hole. If the ring is stuck that may free it up.

Also there is an O-ring between the carb and the intake manifold, make sure it is there otherwise you are sucking a lot air into the engine and without fuel it will not fire.

There are lots of things that can prevent the engine from firing. Hard for us to tell what is wrong at such a long distance of the internet. Could be a gummed up needle valve for all we know.

Get help locally.

Cheers,

Chip

When turning the prop on a four stroke, you need to have the thottle open.

With the throttle closed and you turn the prop, The second time around it will not have any compression.

You can open the throttle and it will have compression again.

Thanks for all the help. I'm loading the manual as I type this, I have been trying to start with the throtle at idle. I'll try it full open. If that doesn't work I'll check for the O rings and all the other things you guys menchioned. If none of that works I know a guy about forty miles from here that is a miricle worker with Glow engines, I can take it to. Thanks again for all the help.

For some unknown reason Hobby People do not have a manual for the OS 52 on their site. As an alternative, you can use the Magnum RFS61 manual. The engines are identical except for the cylinder bore.

http://media.hobbypeople.net/manual/210985.pdf

The OS 52 is almost identical to the SC/Magnum/ASP engines except for the low speed needle on the carburetor and the name on the side.

http://manuals.hobbico.com/osm/fs-52s-manual.pdf

Awesome, thanks so much guys. I tried starting it at full throttle and the thing fired up on the first revolution. Thanks for all the help.

Blue Skies and Tailwinds.

Most four strokes like to be started at about 1/3 throttle.

Agree,
Starting at WOT puts your fingers and anything else close by in real harms way. If the plane isn't held by someone or fully ingaged in a tail holder or secure on a test stand BE CAREFUL.


Pete

My 4-strokes like to be started at idle. It makes for much less load on the electric start and once they fire up I just leave them running for 30 seconds or so with the glow-lead on so they're nice and warm.

My Saitos and my ThunderTiger never miss a beat and start first touch of the starter when I use this method.

My 12V electric starter wont' even turn them over if they're set to more than about 1/4 throttle because they have too much compression.

I have an OS 52 four stroke that hasn't had more than a couple hours run time. It has always started and run really well. Today was no different but after I brought it back home and was cleaning up the plane, I noticed I could turn the prop over very easily with hardly any resistance on compression stroke. I have an OS 120 four stroke that has acted the same way but it also continues to run very well and strangly enough, once in a while, the compression stroke feels fine. Other times, it seems like there's a significant loss of compression. Does anyone out there have any idea of what's going on? Is it something I should be concerned about?

they both have piston rings, which don`t have to much compression till running. What your probably feeling at times is fuel in the cylinder , which will bring up the compression.

there is a quite noticable difference in compression resistance depending on the position of the throttle. Fully closed results in almost no resistance on compression, while fully open gives you the most. I had heard this before but never checked it until just now. It does work that way on my OS 52 4s

Don

You're absolutely right. I tried the same thing with mine. It sure made a BIG difference. Thanks a lot for the good info.