the Wasp

My Feedback: (1)

so we have a Magnum 180 4 stroker, with almost 4 gallons run threw it the engine is powerful and runs great so-far,,

but both it's High and Low Needles are very loose, is there another Brand's Needles that will fit tighter (and work) in the Magnum's Carb, or is there another Brand's Carb that will fit on it ??

anyone know ???

I am worried that in the future the Needs will loosen even more and create a problem, so I would like to fix it now

thanks guys !!
Jim

earlwb

Usually you can unscrew the needle and then bend the detent tab slightly and screw the needle back in. Sometimes it is as simple as replacing the little O-ring on the needle too.   The engine is a copy of a older OS design, so it is possible that a older OS engine carb would fit Ok too.

The problem is the single detent arm on the carb tends to upset the needle and push it to one side which can lead to problems where the needle moves around too much inside the spray bar.

If the needle is exhibiting false needle settings or it is changing and is very sensitive, you can put on a short length of fuel tubing to help make it easier to run.
It is like what I did in this pic here:

goirish

earlwb , good morning. Where did you get the aluminum slot on your engine mounting stand. I have looked all over and can't seem to find that profile. BTW, I have the same engine and my (knock on wood) runs like a champ. thanks

rambler53

My Feedback: (494)

I use teflon tape on the threads that plumbers use. It works and lasts especially on the idle screw that many overlook. This is common on a lot of engines from China. They all loosen up from vibration. The tape will secure it.

earlwb

I would be cautious about using teflon tape. The problem is that the treads are sharp and as you tweak the needle adjustments, the teflon shears off tiny bits and pieces and there is a risk it will clog up the spray bar on the inside.

The ideal setup is where there are two metal spring tabs pushing on the needle from opposites to each other, thus helping to keep the needle centered better.
But like I mentioned a new or slightly fatter O-ring might be the better way to go. The OEM O-ring may have simply gotten worn down or squashed out some and isn't holding the needle tight anymore.


gorish, I do not know where the aluminum extrusion came from originally, as it came with the engine test stand when i bought it.

Campgems

The Magnum loose needles isn't as much a thread issue as an O-ring grove issue. Iran into this on a 52 four stroke and a replacement needle with a new O Ring cured the problem.Every now and then, they cut the grove to deep so there is little to no drag which translates to little or no seal. For what it's worth, almost all Magnum engines use the same high speed needle. The idle mix is more specific to the carb. The replacement needles have a slightly longer taper than the original stock needle, so you get a little less touchy adjustment. It's worth the few bucks to get one that works right. When the O right is tight, the detent doesn't do much in the way of holding the adjustment, but gives you a click to count. When the O-ring is loose, the detent is the only thing holding adjustment, and a simple touch of the needle will change the mix until you let up on the tough. A

Don

earlwb

One thing some people have done is slip a few wraps of something in the O-ring groove on the needle valve. Then when you slip the o-ring back on, it can't compress down into the groove as far and you get a more tight fit. So one could use something like teflon tape in the groove to make the groove more shallow.

the Wasp

My Feedback: (1)

thanks guys for the help !!

well one good thing, is, that the Main Needle Assembly unscrews like on a OS engines, now only if the OS Needle Assembly will fit the Magnum, but the question is "what OS Engine do I buy the Needle Assembly for", that would take care of the Main Needle for good,,

as for the Idle Needle the treads are very loose, yet I can't get the Needle to come out, I may need to tare down the Carb to get it out

Jim

earlwb

Ok the low speed needle unscrews through the inside. You remove the throttle barrel and then when you screw the needle in, it will come out through the inside. They did it that way to prevent it from unscrewing and falling out on you.

Now there is a interesting thread here about some of the intricacies of the carbs. http://www.rcuniverse.com/forum/m_10..._1/key_/tm.htm

It is possible that the OS 4B carb needle holder might fit. It has a slightly smaller inside diameter to hold the needle better with, so it doesn't move around as much. But I am not sure if it fits or not, I don't have either carb to try it out with.
 
 

Campgems

I'm not sure the parts are interchangeable between O.S. and Magnum, but the carbs probably are. I know the carb from an O.S. 52 four stroke is a bolt on replacement for the Mag 52/61 four stroke. The carbs are quite different though, even the needle placement is different. Bot needles on the same side on the O.S carb and opposed on the Mag carb. Going to the O.S. carb may run into clearance issues behind the carb. The O.S needs about 1/8" to 3.32" more than the Mag does in front of the motor mount.

The O.S. carb is a much better carb than the Magnum carb.The carb off the O.S 56Ais also a bolt on replacement. Same body, just a different ramp on the barrel and a velocity stack which you can put onthe other carbs.

Don

SitNFly

My Feedback: (54)

I had a Magnum 30 many moons ago that had the same problem. Cut a small piece of fuel tubing and slip over the needle, covering the joint between the needle and the boss it screws into. You don't need the detent at all then. This works great for the high speed. Can't help you with the low speed.

the Wasp

My Feedback: (1)

SitNFly,, you know what,,,, I did that last night, took me a while LOL

and it works great for sealing the Needle but the Needle will still vibrate badly, I swear that Needle rock's back and forth a good 1/8 inch

slopoke

My Feedback: (16)

I used a o ring on the needle and detent to keep the needle from flopping around. Fuel tubing wouldn't stand the strain.


slopoke

the Wasp

My Feedback: (1)

I can see that but it wont seal it,

if you look in the link above you will see other guys have used the Fuel Tubing trick on other brands

Jim

earlwb

For many years I used to think that air would get sucked in or leak past the needle valve. But in reality fuel will tend to leak out from it instead of the air leaking in. On some engines it is very noticeable on others not. The problem is the needle rocking back and forth or jiggling around that causes false needle settings, rich and lean conditions. Around the needle's surface and the needle carrier's surface or spray bar a surface tension or resistance to flow effect occurs. If the needle moves a tiny bit to one side it increases this resistance resulting in less fuel flow past it.
You can readily see the effect if you go to touch and move the needle from side to side in the carrier while the engine is running. In some cases barely touching the needle can result in lean or rich setting effects, so that you have to be very careful when turning the needle.

so the trick is really to keep the needle from moving around in the carrier so that it stays still and doesn't vibrate or jiggle too much.
The fuel tubing has that effect of stabilizing the needle so it doesn't move around.  If you also have a dual tab spring clip on the needle to hold it centered better, that works too.

the Wasp

My Feedback: (1)

yes, I read all that on the other post,, thanks !!

Jim

Campgems

http://www.hobbypeople.net/index.php...-xl-15-75.html

This should fix your problem.

Don

cutaway

This is true for muffler (or otherwise pressurized systems). If you're running without that pressurization, or a uniflow system (very very slight negative pressure in the tank) it may not be true.

I had bought a used K&B .40 a while ago someone had jury rigged some homebrewed leaky remote needle lashup to and it wouldn't run reliably with classic uniflow venting and sucked all sorts of air bubbles. I fitted a line from the muffler tap to the uniflow vent, and even though it oozed fuel all over the place it ran OK in that configuration.

the Wasp

My Feedback: (1)

well I got thinking that I had once bought some new ORings for an OS Heli Carb and they didn't fit ,
so I went looking for them, and of-course I couldn't find them on the shelf because they were right in front of my eyes,
so about 3 hours later I went and looked again and (hey) there they were right there ,

well good luck they fit the Magnum's Needle and were a bit tighter in the Needle Housing [8D],
the Needle's threads are still loose but it should be sealed better, so I will be happy with it for at least the Summer

BYW, both the OS and Magnum Needle use the same thread, so did their Housings where they screw into the Carb, but the OS "Needle" was a good 2 or 3 mm shorter, so if I used it I don't think it would have closed enough to tune correctly..

Campgems,, I have to ask why you feel that Needle in the link will have tighter thread tolerances than the Stock Needle, I would hate to pay $8 for the Needle and $8 for shipping just to find it's just as loose as the Stock Needle..


thanks guys !!
Jim

Campgems

Jim, just giving you my experiences with the Magnum Carbs. They seem to have a bit of difficulty in keeping tolerances on the O Ring grove. Also, the needle shipped with the engine isn't necessarily the same as the replacement needle. The high speed needle fits almost every engine they make, not all but most. I had a 52 four stroke that was difficult to tune. Ipulled the needle out of a 60 2 stroke I had and things improved a bunch. Ditto on the idle mix needle.

Don't get me wrong, I've four or five Mag four stroke engines that I've run and a few more NIB waiting to be installed. They are a good engine, but the carbs seem to be the weak spot for them, The needles seem to be the problem is a lot of cases.

Those are my experiences, other's mileage may vary.

Don