I am installing a Magnum XL .71 4 stroke engine on my Thunder Tiger J 3 Cub. I haven't had any experience with 4 strokes so looking at this engine has got me confused. The question is that on this engine there three nipples, one just below the needle valve, which is for the incoming fuel, the second nipple/pressure fitting is located just above the first nipple on the intake manifold, and the third is located in the front of the engine just below the push rods which I guess would be the crankcase. Now I have three lines coming from my fuel tank, one for filling and siphoning, one for the fuel line itself which I will attach to the nipple just under the needle valve. Now the third line I normally would attach to a pressure fitting on the muffler on a two stroke but which fitting shall I attach the line too on the 4 stroke the one on the intake manifold or the one down on the crankcase? Or do I need to just ignore one of them and pick the one that has easiest access? Again thanks to all that have answered my questions in the past they were greatly appriecated and your suggestions have worked out great!!!

Steve

The one on the bottom of the crank case is a crank case vent, leave it open. Hook up the muffler pressure as normal, to the muffler. If it doesn't have a fitting on the muffler, or a muffler, leave it open.
I have a magnum FS, and I'm not sure of the "second nipple" you are talking about. There is one on the carb (fuel in) one on the bottom of the case (vent for crank case) and one on the muffler, (pressure). What is the other one you're talking about? Pictures?

The second nipple, on the in take manifold, can be connected to the crankcase vent with a length of fuel tubing to send the oil residue out the exhaust.

If you don't do that, you will have to seal the nipple.

The nipple on the intake mainfold is the one you use to pressurize your fuel tank. Do you have a nipple on your muffler? If not you use the one on the intake. My magnum has one on the muffler and not one on the intake but I have see this question on here before.

Rick

ui_fearmaite, Here is a manual for a Magnum XL 1.20 four stroke. It also has a nipple on the intake manifod. It has the information you are looking for: http://media.hobbypeople.net/manual/210975.pdf

Look at the pictures in the lower left corners of page 1, and 2, of the document. You will see the "Crankcase breather return tube" hooked up to the intake manifold nipple.

jettstarblue is correct on the crankcase breather(bottom nipple)..
Just leave it unhooked, Or if you have a cowl, you can hook-up a
tubing to outside of the plane.. At least thats how it reads on my
manual for my Mag 91 4s I just leave my open..
But if I read your post correct, You have a thrid or forth nipple
counting the muffler?? My mag has only three nipples 1: intake
by needle valve. 2: crankcase breather on the bottom of engine
and the pressure on the muffler.. So if you do have the extra nipple
I guess it could be as Jim said... But... If it does not plug if just
left open.. Why would you want to return "junk" to the engine..
Thta's just my thoughts though..

Guys.... he has a nipple on the intake manifold. I'm no expert, but I don't beleive this is terribly uncommon. You can see the same setup in the Magnum 120 manual. Look and see. I have an old OS Surpass 120 that is setup similarly, and it has a breather return tube that connects the case vent to the intake manifold.

If the crankcase breather is vented to the atmosphere, then the nipple on the intake will have to be sealed. For example, by sticking a plugged length of fuel tubing over it.

They return the junk to the engine so that the mess gets routed out via the exhaust. I have no idea whether that is good, bad, or of no difference.... but that's why it is AFAIK!

An intake tap is used on a few engines and the purpose is the same as it is in automobiles as case vent recirculation system. Cleaner more complete burning of the fuel with an added bonus of the lost oil recovery for at least one more cycle. It is not a huge issue and does not have to be used however if not, it should be capped with a vacumn cap. If left open it can cause eratic leaning of the mixture. Never run an intake tap to the tank vent. This is a vacumn line not a prssure line such as we have from the muffler and will hamper fuel delivery from the tank.

John

To all that have posted thier answers to this post. Thank you for all your input and advice. I appriecate it. The download of the manual was very informative since I bought the engine at a sale with no paperwork. All your advice was insightful and valuable as I try to make sense to all this new technology. Thank you!!!!!


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