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Repair Zenith Stripped Main Jet


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#1 mrf1002u OFFLINE  

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Posted December 14, 2012 - 11:57 AM

I am looking for suggestions, or better yet, previous experience with repairing a stripped main jet hole in the lower body of this Zenith 9711 carburetor. It is on my Standard Twin and obviously leaks gas. The brass needle and its nut are fine if I remember right, but the hole on the bottom of the bowl is stripped.

After a little research, I am considering using JB Weld's SteelStick on the threads and then clean them up with the original size tap. This would have to be done carefully as there is obviously a jet further up in the hole that the needle must seat into. Doesn't seem like a helicoil would be practical here, but I have been wrong before. I have the carb torn down, but I do not have pics of it in that state.

Your thoughts and previous experiences would be appreciated!

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#2 HDWildBill OFFLINE  

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Posted December 14, 2012 - 01:00 PM

I'm not sure it can be repaired. Should be interesting what others come back with.
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#3 mrf1002u OFFLINE  

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Posted December 14, 2012 - 01:40 PM

I am sure I could at least get it to work, even if I just epoxy the needle assembly into the carb, but I am hoping to make it a little less permanent.

#4 LilysDad OFFLINE  

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Posted December 14, 2012 - 01:46 PM

Is it the carb body that's stripped? Is it die cast or iron?
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#5 mrf1002u OFFLINE  

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Posted December 14, 2012 - 01:59 PM

Yes the carb body is stripped and it is aluminum or potmetal.

#6 Alc OFFLINE  

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Posted December 14, 2012 - 07:33 PM

That stinks , I guess JB Weld or similar is what I would try first , Al
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#7 LilysDad OFFLINE  

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Posted December 14, 2012 - 09:19 PM

How about rethreading the body for an insert which is threaded for the jet? Just like an insert for a spark plug. All you need is a guy with a lathe.
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#8 mrf1002u OFFLINE  

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Posted December 14, 2012 - 10:25 PM

How about rethreading the body for an insert which is threaded for the jet? Just like an insert for a spark plug. All you need is a guy with a lathe.


I'm not sure there is enough material there for that option. Also the threads between the body and the insert would have to be sealed somehow. I will take a better look at it over the weekend and maybe post some more detailed pics. The carb is still soaking in the carb cleaner right now.

#9 WNYTractorTinkerer OFFLINE  

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Posted December 15, 2012 - 02:12 PM

That sure is a toughy.. My gut tells me JB would be the best way to go.. Is it one of those long-needle jet jobbers? Aluminum isn't real easy to work with as the melting temp is pretty low.. Inserts will be hard to place properly and will possibly compromise the little bit of metal you have to work with.. I would consult a engine shop machinist myself and maybe there's a product available to do this type of repair.. I have seen carbs from time to time with some sort of epoxy built up around needles on the outside. I'm not sure what product that was though.. But it worked and that was the main thing!! Good Luck!

#10 mrf1002u OFFLINE  

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Posted December 17, 2012 - 11:53 AM

Ok, here is what I did.

There wasn't much material to work with on these things to start with, and to make it worse, there is a hole directly above the high speed jet that lets gas in from the bowl. Can't block that. There is literally about a 1/4 inch inside the threaded hole to work with. I noticed that the end of the hole had a little flare to it. So I took the smallest ball peen hammer I had (very small) and slowly worked my way around it with the hammer, just slowly and lightly tapping it. I also chucked a brass drift with a pencil size (unsharpened) end on it in the vice and used it as an anvil in the tighter spots. I did this very slowly and very lightly until I could tell that I shrunk the hole a little. I filed the end of the hole somewhat smooth again afterwards and removed just enough to level it back up. This still didn't allow me to retap the hole, but it did let me get a barely finger tight connection between the 2 parts. I removed the sealing washer and laid a small amount of JB weld on the threads and tightened it up by hand. Removing the washer let it go into the hole a couple extra 32nd's to get a better bite on the remaining threads and it wouldn't tighten enough to to make the washer seal anyway. I put my mouth into the bowl and blew to make sure the gas would get past the hole in the bottom and into the main jet and it did. I will let it set until next weekend and as long as I dont torque the screw in against the seat too much, it may hold.

An insert would be impossible on this carb I think. There just isn't enough width or depth to work with. You might fill the hole with JB or other stuff and redrill and tap it, but remember, the needle has to line up with the jet above it. I may be possible to tap it up a size to a different needle assembly and size the needle to the jet hole if needed. If this fails that may be something else to try. But here again, the hole would have to be tappped on the same centerline as the jet above.

Larry

#11 olcowhand OFFLINE  

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Posted December 17, 2012 - 11:58 AM

I just remembered having one similar many many years ago. I also did the peening trick to shrink the hole, but I also found a thin lock-nut that would screw up on the aluminum real tight, which further shrunk it, and kept it from spreading. Then I tapped the threads & all was fine. You speaking of peening it jogged my memory.
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#12 mrf1002u OFFLINE  

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Posted December 17, 2012 - 01:52 PM

Good idea olcowhand.




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