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O.S. 46SF Carb Question

Old 09-04-2020, 05:05 PM
  #1  
BobHaley
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Default O.S. 46SF Carb Question

Hi Folks,
If someone out there has an O.S. 46SF on the shelf, and you could take a quick look at it, I'd really appreciate it. My old reliable 46SF has suddenly started to run horribly - in fact it barely runs at all.

When I look up the carb venturi, from the bottom (engine end) upward, I can see a "hair-line" split on the bottom of the spray bar, located in the middle third of the bar. The idle adjust needle normally rides over the spray bar, and opens and closes part of this split.

Since I've never looked at this before, I don't know what to expect.

Question: Is this a normal factory split? Or is it a crack in the spray bar?

If you would please look at your 46SF carb and tell me if you see a split or not, it would save me an enormous amount of time.

Thanks!
Old 09-05-2020, 10:10 AM
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H5606
 
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Too easy not to look - I happened to have one available without having to remove a carb.

What you're describing sounds normal if its the V-shaped notch on the spray bar I see in the picture -

Hope you can find cause soon and share your solution.





Old 09-05-2020, 02:16 PM
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tedsander
 
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From H5606 pic's pretty easy to tell if it is normal or not.

The very first thing is to try a tank of fresh fuel - from some other source than your current one! Open jugs can suck water out of the air, and the fuel is then pretty much ruined, except to kill weeds. This is the #1, by far, problem with an engine that suddenly won't run right.
Make sure all bolts are tight - don't super strong arm them, but everything should be snug
Is the carb fully seated on the body - compressing the o-ring? Is the high speed needle loose or wiggily at all?
We'll assume no crash or other way dirt got into it, but disassembly of the carb and looking for little "bits" in the passages may be of value. Sometimes you'll find vegetation, bug parts, or tiny bits of silicon fuel line (sliced off when pushing it over brass tubing).
Have you changed to a new glow plug?

Give us a description of what it is doing, or not doing, and we can give better advice. Does it run at high speed? Does it idle? Is it stumbling on transition from low to high? Does it smoke - if so, from where? Impossible to start? Run fine on the ground, but dies in the air (and how does it die - sagging, or something else)?
Old 09-05-2020, 03:15 PM
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BobHaley
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Thanks so much for the replies and pictures. Your V-shaped notch definitely looks "factory", while mine is much narrower and not a V at all. I'm pretty sure it is damaged.

I now recall that the last time this engine was running, it was on a plane that crashed hard. I cleaned the exterior of the engine and put it on the shelf. This is the first time I've tried it again, in a new plane. It's hard to imagine this internal part was damaged in the crash, but who knows.

With regard to how exactly it doesn't work right, it starts quickly but runs erratically, and needle and throttle adjustments have no logical effect, and except for one speed it quits after about ten seconds. It will run at the one speed forever. I did all the usual troubleshooting and when looking for dirt, noticed the spray bar split.

This morning I bought a 46SF parts engine on eBay. I intend to use the carb from that engine. But first I'll look at the spray bar on that carb and hope it looks like yours, not mine :-)

Thanks to everyone. I'll let you know how it works out, or not.


Old 09-17-2020, 12:50 PM
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BobHaley
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Hi Folks, I put the carb from another engine on mine and now it runs like a champ. A comparison shows the only difference to be the overly-narrow slit in the spray bar of the carb on the recalcitrant engine. My assumption is that the crash to which it was subjected caused the damage. That picture of a normal spray bar was the key to getting this resolved. Thanks to all for your help.

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