Hi all,

I just recieved a Magnum .91 RFS 4 stroke motor, and after securing the break in prop and such, pulled it out and fired it up tonight.

Well, it started right up, sounds like a Harley, break in is easier than the MDS .40 and OS .65 LA I have, but do have one question.

On the intake manifold, there is a nipple, just like the crankcase breather, the one on the silencer, and on the carb. There is no mention of it in the paperwork, and I am wondering what it is? I have never seen one before, but then this is my first 4 stroke.

Thanks.
Drew

Drew are you saying you have a nipple on the intake pipe between the carb and cylinder head? My about one month old 91rfs only has 3 nipples... crankcase breather, carb and muffler pressure, mine does not have a nipple attached to the intake pipe. If it's newer than mine it must be some design change...I have no idea what that nipple could be for... try going here and ask Mike G

http://globalservices.globalhobby.co...orum/index.php


John

It MIGHT be.... a connection yuo can lop the crankcase breather to as in an automotive PCV system.

Can you post a pic? Does the nipple on the intake have a tiny ball in it? (like a "zerk" grease fitting) If it does... I'd almost bet its a PCV valve.

I looked it up on the Magnum distributer website. The doc is a PDF.... so I can not copy it.

It IS fo the crankcase breather. route a piece of fuel line from that nipple near the front engine bearings to the npple on the intake manifold. You may have trouble getting a stable idle if you don't.

jsn- That is exactly where the nipple is, thanks for the link, I will check it out...

FHHuber- it is not a zerk fitting, I probed it to see if it was blind, it is not.
It seems to idle fine right now without it, for not having been thoroughly broke in yet, at about 3 grand. I will try to post a pic later on, and try connecting it to the crankcase to see what that does...


Thanks...Drew

Its just an open air hole as-is. I doubt you'll ever get a stble idle below 2500 without connecting it up to the crankcase breather nipple. Its a low-tech version PCV... no check-valve.

chk this out it may help it sounds like what your describing is a pvc http://media.hobbypeople.net/manual/210970.pdf also known as a crank csae breather

See page 2 (by the numbers on the pages) at the bottom left. In that pick,,, appx 1/3 inch above the carb body on the right side of the intake manifold is a little flat spot on THAT engine.

I assume right there is where the "PCV" nipple is. (thats where it shows one in the 1.20 manual. Thats where I have seen them on other 4-strokes...) If there is a nipple there.. its "PCV" and you route the lne from the crankcase breather to it instead of just routing it out of the model as mentioned in that version of the manual.

The "PCV" nipple does not HAVE to have a little check valve thingy in it (simulating a zerk fitting) They just have less effect on idle tuning if they do.

The problem may just be that you have one version of the engine... and another version of the manual.

This style PCV is really close to the original PCV systems found on appx 1970's automobiles.

Sounds like a PCV (Positive Crankcase Ventilation) setup to me too. But if you run a line from the PCV to the intake manifold, I would add a filter to that line.

Connect the breather to the nipple on the intake manifold with a tube and
retune your engine.

I have an old OS Surpass 120/pump that does the same thing.
It sounds like Magnum is a copy of the old OS Surpass engine.

California Smog laws strike again!!!!!You guys in So. Cal will soon be having mandatory inspections next year......Good luck. BTW no Nitro in two years.

Thanks for the input, I connected the intake to the crankcase and was able to get the idle down to a stable 2500 from 3000.

Thanks again...