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How does this carburetor work?

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Old 03-30-2019, 11:20 AM
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brickwoodward
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Default How does this carburetor work?



Iíve been flying fuel over 40 years. Mostly .40 size and under, except for an occasional four stroke. Iíve never tinkered with this carburetor before. May I ask if anyone has some instructions on it? Itís on an OS Max 61 and it says 7mm on the front of the carb body. Thank you so much, bill
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Old 03-30-2019, 11:36 AM
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Right away I recognized it as an old OS carb. The upper adjuster with the slotted head is the low speed needle. The forked arm surrounding it is essentially an adjustment limiter - the head of the needle is offset, and as you turn it, it moves the fork one way or another. That fork has limits, supposedly preventing one from adjusting the needle too much in either direction. It was a pretty poor carb, and was ripe for replacing with a Perry or SuperTigre. The engine itself was great, once the carb was replaced. Ran mine for many years.
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Old 03-30-2019, 12:06 PM
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A. J. Clark
 
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The screw directly below the one in the fork holds the fork from moving against vibration. If you make an adjustment on the low needle you'll need to loosen the holding screw.
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Old 03-30-2019, 06:17 PM
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the Wasp
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Originally Posted by tedsander View Post
Right away I recognized it as an old OS carb. The upper adjuster with the slotted head is the low speed needle. The forked arm surrounding it is essentially an adjustment limiter - the head of the needle is offset, and as you turn it, it moves the fork one way or another. That fork has limits, supposedly preventing one from adjusting the needle too much in either direction. It was a pretty poor carb, and was ripe for replacing with a Perry or SuperTigre. The engine itself was great, once the carb was replaced. Ran mine for many years.
that's funny, cause today all the OS Heli engines uses that same type of carb.. with that, the OS "40E" Carb, that came on the OS 50 Heli engine did have some problems going lean after a Heli came off full throttle and go into a hover, but there is an easy fix for that today

Jim
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Old 03-30-2019, 06:23 PM
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Thank you both! That will work. I thought the offset screw head and fork were probably for the idle. It was my uncles but I never talked to him about it. Iím going to start looking for one of the other carbs you mentioned and in the meantime Iíll mess with it.
Thank you again, bill
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Old 03-30-2019, 06:27 PM
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Wasp, I posted my reply just before your post. Would you be willing to share the fix? Or it might not be as critical for a plane vs. a helo?
thank you, bill
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Old 03-30-2019, 07:41 PM
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Originally Posted by the Wasp View Post
that's funny, cause today all the OS Heli engines uses that same type of carb.. with that, the OS "40E" Carb, that came on the OS 50 Heli engine did have some problems going lean after a Heli came off full throttle and go into a hover, but there is an easy fix for that today

Jim
They sure should have improved them if still in production! My knowledge came from the ones I had back in the 90's!
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Old 03-30-2019, 09:21 PM
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Iím pretty sure thatís the time frame for this one.
thanks again, bill
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Old 03-30-2019, 10:59 PM
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Originally Posted by brickwoodward View Post
Wasp, I posted my reply just before your post. Would you be willing to share the fix? Or it might not be as critical for a plane vs. a helo?
thank you, bill
I am very sorry, I would very much like to tell you about that modification, but the Heli forum it was posted on (RunRyder) has been shut down and I could not find the information. I looked on Heli Freaks and RCG for you and still I could not find that info..
the problem was with the "Original" 40E Mixture Control Valve inside the Carb.
if you ask on Heli Freaks about the Run Ryder post about "Like Magic for the OS 50" may-be you will get replies

see my link below, it tell that the newer and larger 60L Carb has an updated Mixture Control Valve, I have to wonder if this 60L Mixture Control Valve will fix the problem with the 40E Carb ??? but never the less, we have to understand that he 40E was a Heli Carb, so we also have to ask if the stock 40E Heli Carb will run the same or better on a plane with a prop instead of a Heli with a gear reduction ????

you may have to copy and past the link ??
OS-60L-Carb-screen.pdf

good luck
Jim

Last edited by the Wasp; 03-30-2019 at 11:02 PM.
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Old 03-31-2019, 01:55 PM
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Thanks Jim, I just looked and the carb number is 7M. Iím going to do extensive search for this and see what I can find based on your notes. Iíll also find what I can from heli sites and past sites. I sure do appreciate yours and all the comments I recurved.

Thanks again, bill
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Old 03-31-2019, 05:14 PM
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you are welcome. you know
A) I have to wonder if the newer Mixture Control Valve from the OS 60L Carb will work for you, I am sure it will fit, you can find out by checking the O-rings part number or OD/ID sizes..
B) most likely the OS 65AX Carb will fit your engine, or, if your Carb has the same ID/OD may be you can use a Heli Carb, there are a lot of used ones around, even new ones, ask me how I know ,,, don't buy the OS 61FX Cab !
C) you should remove the Carb and muffler, and back plate and G-plug, or for that mater remove the head and soak it all in hot Antifreeze (not on high) for 6 hours and then clean off the Antifreeze well with WD40, it will be clean as new, if it comes out dark grey don't worry the WD will bring back it's color if you rub it in

Jim
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Old 03-31-2019, 06:16 PM
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Thanks Jim, this was my uncles so Iím not sure how old it is? It has, ď7MĒ stamped on the front of the carb and I havenít been able, yet, to find parts and ďOĒ rings yet. Iím sure theyíre out there, I just havenít hit the right spot yet. Iím very familiar with the antifreeze treatment. We learned that in the 80ís. I was always buying somebodyís throwaway and rebuilding them. I have an OS 120 with the Hemi, Saito style valve arrangement Iím rebuilding. Iíve never seen one so this is a pretty neat thing for me. I have two of the Enya 90, 4 strokes from when AMA changed the engine size rules for pattern in 1983. These things are powerhouses!!

thanks again and Iíll keep you posted, Bill
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Old 03-31-2019, 07:23 PM
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I've got one of the same 7M carburetors. I bought a complete used engine to get the carburetor. I used the carb on a Nelson short stroke .40 racing engine. The round barrel that goes into the crankcase had to be modified extensively, so that the carb will no longer work on the OS .60 it came from. I'd like to find a serviceable carb body to return my carb back to stock. Finally these 7M carburetors are great carbs. They were developed for helicopters, and essentially have high speed, mid range, and idle capability.
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Old 04-01-2019, 06:35 PM
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Thank you Greg! Iím going to go ahead and work with this, mainly because I havenít let one get the best of me yet! Now I have more hope!!

Thanks again, bill
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Old 04-01-2019, 07:59 PM
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Clean it good, and give it a try. I think you will like it. Because it's a helicopter carburetor, it a little more sophisticated then the standard aircraft carburetor, but that can be a good thing. Good luck, and if you have problems come back here for solutions.
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Old 04-02-2019, 08:09 AM
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A lot of those eccentric adjusted carbs were very sensitive, tiny adjustments made big changes.
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Old 04-02-2019, 11:01 AM
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Thanks Greg, I will keep you posted. Now to see if I can find an ďOĒ ring kit or source?

Hobbsy, thanks for your input. I think back in the 80ís K&B had a black body Perry carb? The idle/ low speed adjustment was a large brass disc that only required ďtickĒ one way or another to bring it in? Very sensitive. I watched many a person turn that disk sixteenth, eighth or quarter and it never idled until we could teach them to move in very tiny increments??

thanks again to all, bill
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Old 04-02-2019, 01:11 PM
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hummm I have to wonder if the 60L Mixture Control Valve will allow a richer idle and mid range making the idle screw less sensitive

Jim
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Old 04-02-2019, 06:58 PM
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Bill, I've found most of my O rings at my local Ace Hardware store. Perry made a lot of carburetors either as OEM stock, or replacements. John Brodbeck, and John Perry were good friends, so K&B's had Perry carbs for many years. The story is that K&B decided to make their carburetors in house, when John Perry bought a new full scale airplane. The carburetor was the most expensive part of the engine, and K&B decided it was time to reduce their up front costs. Over the years I've run a lot of Perry carbs, and yes the idle disc is very sensitive. Perry carbs are still available.
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Old 04-04-2019, 06:43 AM
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Hi!
The carb works like any other two needle carb except this one has an exentric screw that moves the fork (which governs the idle needle) either to the right (leaner) or to the left (richer). You don't have to loosen any screw to adjust the idle ,just turn the idle screw and the fork will move.
This OS carb is a much better carb than the old perry carb.
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Old 04-09-2019, 07:50 PM
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Originally Posted by GREG DOE View Post
Bill, I've found most of my O rings at my local Ace Hardware store. Perry made a lot of carburetors either as OEM stock, or replacements. John Brodbeck, and John Perry were good friends, so K&B's had Perry carbs for many years. The story is that K&B decided to make their carburetors in house, when John Perry bought a new full scale airplane. The carburetor was the most expensive part of the engine, and K&B decided it was time to reduce their up front costs. Over the years I've run a lot of Perry carbs, and yes the idle disc is very sensitive. Perry carbs are still available.
thanks Greg, my ACE told me theyíre for plumbing, ďwaterĒ, and not chemical tolerant?? You have any long term issues?
thanks, bill
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Old 04-09-2019, 07:52 PM
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Originally Posted by jaka View Post
Hi!
The carb works like any other two needle carb except this one has an exentric screw that moves the fork (which governs the idle needle) either to the right (leaner) or to the left (richer). You don't have to loosen any screw to adjust the idle ,just turn the idle screw and the fork will move.
This OS carb is a much better carb than the old perry carb.
thanks jaka! I kind of figured that out but you just made it good!! Thanks, bill
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Old 04-11-2019, 05:09 PM
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Bill, You may remember that the idle disc on the Perry carburetors had two small black "O" rings. I've used Ace Hardware Story O rings in that application. The only problem I've had with their O rings was in a gasoline application. I tried them in a Bing slide valve carburetor on my Mini Max ultralight, and they swelled up.They are cheap enough that you could get a couple, and soak them in glow fuel to see if there are issues.
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Old 04-11-2019, 07:10 PM
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Originally Posted by GREG DOE View Post
Bill, You may remember that the idle disc on the Perry carburetors had two small black "O" rings. I've used Ace Hardware Story O rings in that application. The only problem I've had with their O rings was in a gasoline application. I tried them in a Bing slide valve carburetor on my Mini Max ultralight, and they swelled up.They are cheap enough that you could get a couple, and soak them in glow fuel to see if there are issues.
yep, Iíll get a couple and soak them in fuel and see! Thanks Greg! I think we have an automotive parts supply in town that keeps a range of O rings.
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Old 04-11-2019, 07:59 PM
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Bill, Yes another good source. I've gotten O rings at my local O'Riley's, but I don't remember if I used them in a model airplane application, or some other project?
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