Thread Tools
Mar 22, 2012, 09:56 PM
Registered User
Thread OP
Discussion

O.S. Surpass FS-120 Needle Valve Question


I've picked up a used O.S. FS-120 4-stroke. I can't figure something out. The engine runs with the high-end needle valve completely closed. Obviously, the valve is leaking, but the needle looks fine. I've compared it to a brand new needle and it's perfect. The odd thing is that when I tighten the needle down, the hub of the needle comes to rest on the carburator casing. There's no gap at the bottom as I see on another identical engine that I own. It acts like the needle is too short, but it's not. The needle must normally come to rest on a valve seat, but does this wear out, and if it does, can it be replaced without buying a whole new carburator?
Any help would be appreciated.
Sign up now
to remove ads between posts
Mar 22, 2012, 11:50 PM
TigreJohn
For whatever reason, it sounds like your needle holder has bought the farm. I haven't seen a needle seat wear out before. But I have seen a "unknowing person" (aka idiot) run a drill down the needle holder/spraybar to clean out junk and screw it up. Tower has the needle holder for your carb for $9; or the whole needle assy. for $17.
Mar 23, 2012, 06:10 AM
Registered User
Thread OP
Thank you for your help. But I checked the Tower website, and the needle/needle assembly are for the FS-40. The needle doesn't look like it's the same as the FS-120 needle, because this replacement needle has no o-ring, whereas the FS-120 needle does. Do you know if I could use the whole assembly on the FS-120?
Mar 23, 2012, 09:37 AM
Registered User
The easy way to confirm if the needle is leaking is to put a piece of tubing on the carb long enough that you can blow through it. If you can not shut it off by closing the needle then either the needle is the wrong one or the needle body is the wrong one or it is worn out. Here is the correct assembly from Tower, http://www3.towerhobbies.com/cgi-bin...?&I=LXCR62&P=Z . Since it is used you have no idea what may have been done here, could be worn out, or drilled out as suggested or most likely was replaced with the wrong part. These are great engines and worth the effort to make it right.
This is the SE version and not a pumped version of the engine, right?
Mar 23, 2012, 10:07 AM
Registered User
Thread OP
Yes, it is not pumped, and it does look like the SE. I looked at the Tower Hobbies link, but all these needle assemblies look the same. Also, I didn't recognize the carb, because the illustration doesn't show the vertical pipe that travels from the top of the carb into the cylinder chamber. I thought the pipe was part of the carb body. I'll do some further checking and then order the needle assembly. I hope that's all it is.
I was also advised to cut a short piece of fuel tubing and slip it over the needle to seal against the needle assembly to see if I could stop any leakage that way. What do you think of that?
Mar 23, 2012, 12:01 PM
Registered User
Waste of time get the needle assy Lane posted the link to.
Mar 23, 2012, 08:07 PM
Registered User
Quote:
Originally Posted by kpblau
Yes, it is not pumped, and it does look like the SE. I looked at the Tower Hobbies link, but all these needle assemblies look the same. Also, I didn't recognize the carb, because the illustration doesn't show the vertical pipe that travels from the top of the carb into the cylinder chamber. I thought the pipe was part of the carb body. I'll do some further checking and then order the needle assembly. I hope that's all it is.
I was also advised to cut a short piece of fuel tubing and slip it over the needle to seal against the needle assembly to see if I could stop any leakage that way. What do you think of that?
You don't have an air leak, you are not able to close the needle valve enough to cut off the fuel supply so the piece of tubing over the needle body won't solve that problem. If you want to be sure that it is the needle assembly why don't you take the one from your known good engine and put it on the one giving you trouble to see if that fixes the problem. If it does then you know for sure the new assembly will do the job.
The carb slips onto the intake tube and is sealed with an o-ring, the intake tube is not a part of the carb.
Mar 23, 2012, 09:21 PM
Registered User
Thread OP
Hi,
Actually, I tried that today and the same thing happened. The needle tightens right up to the hub and the engine keeps running. I also tried to tighten the low-end screw thinking that it might be too loose but it made no difference. The engine seems to run OK, but I just can't figure out what's going on. I could buy a whole new carb, but I'm not eager to spend the money. I'm thinking I'll send the engine somewhere for repair.
Mar 24, 2012, 02:58 AM
Registered User
gerryndennis's Avatar
I had the exact same problem with an OS 70, you could wind the needle in completely and still not get it lean enough.

I removed the needle and the needle holder and very carefully filed the needle holder down until the needle bottoms on its seat and not the outside of the holder.

Thoroughly wash (hot soapy water followed by hot water rinse and warm oven to dry then a compressed air blow through works for me).

I don't know why mine was like that but I don't think it's wear, at least mine has been perfect since I filed it.

Dave H
Mar 24, 2012, 06:08 AM
Registered User
Thread OP
Thanks Dave,
I think your idea is brilliantly simple. It's hard to understand how this engine could have been owned previously with this problem, but I'll try your solution unless someone can tell me why I shouldn't. At least I'll have a chance to take a better look at the carburator. Hopefully I won't find anything more serious wrong.
Mar 24, 2012, 08:27 AM
Registered User
Dave H you kicked the cobwebs out of my memory with this suggestion as I had done the same thing on an OS 70 in the past. It had a long extension wire hanging off of the needle and I think with time vibration on the needle wore the seat out a bit. Anyway it worked for me just as for you so it is worth a try.
Mar 26, 2012, 08:19 PM
dale

needle valve


I had the same problem with an OS 2 stroke...I did the sand it down part and it worked fine but I kept looking for the root cause..What I discovered was the valve seat was a sepperate steel part that was pressed into the carb casting and over time it had slipped to cause the problem you discribe. I was able to press the seat back into the carb..be carefull because I pressed it in to far and it cut off the opening to the carb. I was able to move it back down and have not had a problem since.
Mar 29, 2012, 10:00 PM
Registered User
Thread OP
Well, thanks everyone. I got a much more thorough answer to my question than I could have imagined.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold O.S. Engines O.S. FS-91 II Surpass (Pump) tom_sandiego Aircraft - Fuel - Engines and Accessories (FS/W) 1 Mar 19, 2012 07:44 PM
Sold O.S. .91 FS Surpass II 4-stroke Ohio lightwinds Aircraft - Fuel - Engines and Accessories (FS/W) 1 Mar 05, 2012 10:05 AM
Sold O.S. FS 120 Surpass w/Pump sid47 Aircraft - Fuel - Engines and Accessories (FS/W) 0 Jan 29, 2012 03:28 PM
Sold O.S. FS 120 Surpass II pumped Sdr Aircraft - Fuel - Engines and Accessories (FS/W) 1 Jan 26, 2012 02:14 PM
For Sale O.S. Engines O.S. FS-91 II Surpass $120 shipped sagomon Aircraft - Fuel - Engines and Accessories (FS/W) 2 Sep 21, 2011 07:29 PM