I'm new to 4 stroke engines. What does one need to know to properly maintain this engine? It may be easier to tell me your list of "DO Not's". Where can I get a manual for a Magnum XL 91 RFS?

maby in towerhobbies or in hobbypeople?

don't run lean
use after run oil if not using full sinthetic fuel
don't run on too much nitro more then 20%. it may predetonate when hot(or add gasket between head and case)
periodically check valves (after every 5-10 hours)

jawsmon, I think I have an extra manual for the Mag 91RFS. PM me your address and I'll put it in the mail for you.

Just download your own copy here.... http://media.hobbypeople.net/manual/210970.pdf

Enjoy,

Jim

Guys I need some help, I have a 4 stroke .70 and it fell into water over the holidays. It was all rusted and wouldn't start  so I decided to take it apart. When I finished cleaning it and I have assembled it, there is no more compression. The engine won't start and whenever we plug the ignition in and try to start it, it make a strange bubbling sound. I think there is too much fuel in the piston or carburetor. I got so frustrated that I just went to go buy a new engine.

Well I would take the carb off the back of the engine.  Remove the back plate and check the main bearing for rust.  I would then put oil into the cavity and make sure it moves all around inside the cavity.  I would invert the engine so that the intake manifold with the carb off is facing upwards.  I would shoot some oil down that manifold, turning over the engine will introduce the oil to the top of the enginel (piston area),  I would take the valve cover off the top, check the tappet clearances and oil that area up too.  I would dribble a little oil down both push rods so that some oil gets to the top of the cam area, it will seep around the cam followers and get into the cam shaft area.

Then I would reinstall the back plate and carb and with no glow plug installed turn the engine over 15 or 20 times.  That will get the lub every where.

Then I would attempt to start the engine with a new glow plug installed. That should get it running The actual running will expel all the extra oil.

BTW, if the carb is not open with testing for compression you may get low compression.  So make sure the carb is open when testing for compression.

Otherwise, get someone who knows the engine to disassemble it, clean it up and install new bearings.

Rust after cleaning may have caused you to lose the tolerances between piston and sleeve.

Use after run oil especially if you've only ran with synthetic in the mix.

Hi!
No compression after a dissasembly is not uncommon! Just run the engine and it will just be as new again.