jhunter

My Feedback: (20)

I had given up on getting my old FS-1 to run again, it needs a new carb body, which has been discontinued by OS. I was looking at a friends new Magnum 91 and the carb dimensions looked pretty close, we tried it and it fit the OS perfectly. That was about a year ago, and of course the carbs were back ordered with no date in sight. Last week I hit the Global site and they were in stock! I ordered the carb and intake pipe, got em in 3 days. Put them on tonight, had to move the slow speed needle 5 3/4 turns from full out to get the motor to start, pretty smoky but it was running. The problem is the engine peaks beautifully with the high speed needle valve completely closed. I took the carb apart to make sure I didn't unseat any O rings and everything looks OK. We did not try and run it with my friends carb the year before, we just figured if it fits, it's gotta work, right.Not. Any ideas on what I can do? I think I can uses it as it is, but I would like it to peak before the NV is closed. I use Magnum 28% fuel and I had an APC 13x4 on for the test. Maybe if I went to a prop with more pitch I could get it loaded and maybe peak earlier? I don't know. If anybody has any ideas please let me know, thanks.

Campgems

The carb will be just fine. What it sounds like is that you have the idle and high speed way out of sync. My Magnum 70fs was the most contankerioius engine straight out of the box. It started and ran sort of with the factory carb settings, but as soon as I started tuning, things fell apart. It isn't an O.S carb and it doesn't tune the sam way

The O.S carb idle mix has you screw it into a stop then back out X turns for the start point. The Magnum carb will let you screw in the idle mix to the point it falls out of the threads. You have to start from fully unsrewed to the stop, then in x turns. Pull up the Magnum 70 manual and set your carb to the starting points suggested and then tune from there. It will work out just fine. Sorry, it's been about 5 years since I went down this path and I don't remember the exact settings. Seems that the idle was 2 1/2 turns in from flush with the throttle arm. and the high was 2 1/2 turns out from a screw in to stop.

Don

carrellh

The Magnum manuals are on http://globalservices.globalhobby.co...als/Magnum.asp

jhunter

My Feedback: (20)

Thanks for the manual link. I had set the low speed at 4 1/4 turns the first few attempts and had a lot of fuel blowing out the exhaust pipe and no light off. I did not get the motor to start until 5 3/4 turns on the low speed. I replaced the fuel line to the carb already, tonight I will try another tank, maybe that will help. I cannot think of any reason why this setup wont work, a 4 cycle carb of any brand should work, fuel just gets atomized! Some time ago someone suggested putting the original OS carb back on and use a remote needle valve. Any thoughts on that? thanks.

Campgems

A remote needle valve should work OK. I think. However, did the OScarb have the idle and high speed needles on the same side? If so a remote may not work.

You should reset both the high and low speed valves to factory stock settings then try again. Your description of things are exactly like my Mag 70 was after I first got it running and the "experts" at the field helped me adjust it. Resetting both valves to stock setting and then go from there solved my trouble. Don't touch the idle until you have the high speed set as you will screw up the balance between the two.

Also, did you put a gasked on the intake to head? OS doesn't use one, but Magnum needs one.

Try a tank of Omega 15% 28% seem way high.

You may wan't to check wiht Global and see if they have had any problems with the carbs.

Don

jhunter

My Feedback: (20)

Campgems, The OS does use an intake gasket also, it's in good shape. The OS carbh as the needles on opposite sides too. I have used nothing but 28% in all my 4 strokes for the last 6 years, including another OS 70, and the motors love it. I think your tip about setting the high speed needle first is a good idea, I'll try that this weekend. Thanks.

wcmorrison

My Feedback: (2)

Carbs are different, different in how they spew the fuel into the throat.  Some use a split, some use a diamond cut and so on.  I found Magnum uses a split.  Some time ago, I disassembled the carb and forgot to get the settings before doing the disassembly.  I contacted Global Hobby and they said take the carb off the engine, turn it over so you can see the split.  Set the idle needle half way across the split.  And then reinstall the carb on the engine.  I always set the highspeed needle at 1.5 turns out, a bit more maybe two turns out is usally rich.  Did that and fired up the engine, the idle was perfect, never changed it again.  I used a tack to set the high speed to the max and then back it off about 300 RPM.

So were I you, I would remove the Magnun/AS carb, set the idle needle at half way across the split.  I think that will be near perfect for you.

jhunter

My Feedback: (20)

Thanks WC, Ill do that tomorrow, I like the sound of that fix. I'll post the results.

jhunter

My Feedback: (20)

Setting the low speed needle to the half way point, re-built the fuel tank, checked every bolt on the engine for tightness, engine still peaks with the HS needle fully closed. Started right up with the slow speed halfway in the spray bar. I also get a lot of exhaust smoke untill the HS is closed and the moter leans out. I must have a bad carb. Carb O rings are all in good shape, tried reversing the carb mounting 180deg, I put it on backwards so the HS needle was opposite the muffler. Stood on one leg and hopped around, everything. Guess I'll call Global in the AM.

jhunter

My Feedback: (20)

OK, found the old OS carb and put it back on, this one has a worn HS needle valve seat, this is where this all started a year ago. Confirmed that that amount of time on the healing shelf did no good, motor runs with the HS closed. Removed the throttle spring and replaced it with some fuel tubing that also encompassed the HS nv. Motor ran great with engine peaking with some lean adj still remaining, aha! Removed a remote needle valve from an OS 46 AX, installed that in the fuel line and opend the OS 70 carb HS 4 turns, had to open the remote needle 3 turns before the engine would start, ran perfect, better than the first repair, peaks nice with room to spare. I will order another remote NV and use it and should be OK. All the mid range smoke dissappeared too, just smokes a little at idle. I still think the Magnum carb is bad, I will send it in for replacement, also is there any other condition, internally, that would cause this problem? Smoked like a maddog with the Magnum carb. Valve adjustment? Piston ring? etc. Thanks everybody for your help.

Kimhoff

My Feedback: (22)

Why are you concerned about smoke?  You should concentrate on getting the needles set correctly.

jhunter

My Feedback: (20)

Magnum 91 4 stroke carb bolted right on and works perfectly/

jeffie8696

You sent in the old one and they replaced it?

jhunter

My Feedback: (20)

Yes, I called them up and talked a man in the customer service dept. and told him I felt it was bad from stock, he gave me a return authorization number, asked that I send it to his attn. He actually called me 3 days later and said he had my carb on his desk and was sending a replacement the same day. I installed the replacement on a new Magnum 91 and it ran fine, stuck it on the OS 70 and it ran perfectly, touchy on the adjustments, but solved my problems. I believe the CS man's name was Russell, Global Hobby in LA CA.

jeffie8696

Russ is a good guy, I have dealt with him before.

jhunter

My Feedback: (20)

I was surprised at the personal service I got from him and the quick turnaround from Global Hobby. Very good place to do buisness.

NM2K

My Feedback: (14)

Your 13x4 prop is way too small for that engine. It needs something on the order of a 13x6 to run properly, in addition to having whatever problems it has brought into line. I don't believe in lugging down engines with too much prop, but a 13x4 is way too light for a .70 four-stroke. Good luck.


Ed Cregger

jhunter

My Feedback: (20)

I disagree, I have, and my friends, have used APC 13x4 props on the OS 70 in planes like the 40 size Funtana with superb performance. Might not be by the book but they worked for us. This particular motor is being put into a Sig Ryan STA, and I will use a 12x6,7, or 8 there, can go up to a 14x7 also.

NM2K

My Feedback: (14)

A 12x6 is a .52 sized prop. The 12x7 - 8 makes sense to me.

Then again, I'm used to flying Enya four-strokes, which are very strong once broken-in and not over-nitroed (my own words).

Oh, and while I'm nit-picking, they aren't motors - they are engines.

Seriously, as long as you are enjoying yourself in your hobby, that is what matters most.


Ed Cregger

jeffie8696

Ilike to see my 4Sengines turning about 10,000 static on my choice of prop.

NM2K

My Feedback: (14)

Me too. Although, it is not a hard and fast rule.

As the OP has expressed, we tend to go by our own experiences, which is as it should be.


Ed Cregger