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Discussion Starter #1
Hello!

In a previous thread, I mentioned that I'm trying to get our old '89 Lawn Boy lawn tractor running again (12 HP Briggs & Stratton engine).

I intend to rebuild the carb, and have already gotten the kit (with instructions, so that should help). I don't think I've ever rebuilt a carb before, and have a couple of questions.

First of all, the kit includes a replacement Welch plug. It's about 1 1/2" in diameter. I was wondering -- is it customary to automatically replace the Welch plug, or is it better to leave the old one in place? And if I do replace it, do I use a sealant around the edge of it? I recall reading some generic rebuild instructions which suggested applying enamel nail polish along the rim before putting the plug in place. The instructions with my specific kit don't mention anything along those lines, though.

Also, what is a good solvent for cleaning the interior of the carb? I have some lacquer thinner on hand -- would that be good? (I've already cleaned the grime and gunk off of the exterior using regular paint thinner.)

Thanks for any ideas -- I'm sure that I'll have more questions when I actually tear into this thing.
 

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If the current welch plug is sealing fine then leave it. They are a bit of an art form to get to seal properly. You shouldn't need to use any sealant if you do it right but you could use gasket sealant with it if you needed to.

Most mechanics use "brake cleaner" as their go-to solvent. If the paint thinner is working for you then I'd just stick with that.
 

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If the current welch plug is sealing fine then leave it. They are a bit of an art form to get to seal properly. You shouldn't need to use any sealant if you do it right but you could use gasket sealant with it if you needed to.

Most mechanics use "brake cleaner" as their go-to solvent. If the paint thinner is working for you then I'd just stick with that.
Thanks very much for the replies!
 

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If the current welch plug is sealing fine then leave it. They are a bit of an art form to get to seal properly. You shouldn't need to use any sealant if you do it right but you could use gasket sealant with it if you needed to.

Most mechanics use "brake cleaner" as their go-to solvent. If the paint thinner is working for you then I'd just stick with that.
:ditto:
 

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Unless you are talking about the big welch plug in the end of the carburetor (like briggs had), I believe there are ports behind the welch plug in that carburetor. If there are, then the welch plug need to come out to make sure that the ports are clean. That is the reason why it is installed, so it can be taken out and replaced.

I know with the Tillotson diaphragm carburetor you are wasting your time if you don't pull the welch plugs.

I have a shop and have been rebuilding carburetors for a long time. I always pull the welch plugs
 

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Discussion Starter #7
Unless you are talking about the big welch plug in the end of the carburetor (like briggs had), I believe there are ports behind the welch plug in that carburetor. If there are, then the welch plug need to come out to make sure that the ports are clean. That is the reason why it is installed, so it can be taken out and replaced.

I know with the Tillotson diaphragm carburetor you are wasting your time if you don't pull the welch plugs.

I have a shop and have been rebuilding carburetors for a long time. I always pull the welch plugs
bobr, thanks for the reply -- sorry I didn't acknowledge sooner, but I hadn't checked in here the past few days.

Yes, the Welch plug I mentioned is the large one on the end of the Briggs & Stratton carburetor. It's about an inch and a half in diameter.

On a side note, as I've been disassembling this carb, I'm having trouble removing the the main nozzle and the jet nozzle. Of course, I haven't soaked the carb in solvent yet (was going to do that after removing the jets -- rebuild kit includes brand new jets).

I went ahead and used some spray carb cleaner around them for now. Maybe that will loosen them a bit...
 

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Dave,

I guess I should have read your post closer the other night, but it had been a long day. Since you said 12 HP Briggs, that is an updraft carburetor. Has a long jet that goes up through the body and into the throat of the carburetor

Be careful, that carburetor body is zink. The threads come out of the carburetor with the jet sometimes. Zink gets a powdery corrosion that just keeps expanding and jams the jet so bad that the zink tears in the threads before the brass jet comes free.

that carb is probably replaceable (Briggs knows they corrode bad), but I bet the cost would absolutely scare you.
 

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Dave,

I guess I should have read your post closer the other night, but it had been a long day. Since you said 12 HP Briggs, that is an updraft carburetor. Has a long jet that goes up through the body and into the throat of the carburetor

Be careful, that carburetor body is zink. The threads come out of the carburetor with the jet sometimes. Zink gets a powdery corrosion that just keeps expanding and jams the jet so bad that the zink tears in the threads before the brass jet comes free.

that carb is probably replaceable (Briggs knows they corrode bad), but I bet the cost would absolutely scare you.
I have 11 and 12 hp verticals with flo jets on them
 

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I have 11 and 12 hp verticals with flo jets on them
Yes, vertical shaft engines usually have flo jet carbs, but the carb body is still zink, and prone to corrosion around the jet, especially if water gets into the fuel.

OP didn't specify vertical or horizontal shaft, so I was guessing.
 

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Discussion Starter #12
Dave,

I guess I should have read your post closer the other night, but it had been a long day. Since you said 12 HP Briggs, that is an updraft carburetor. Has a long jet that goes up through the body and into the throat of the carburetor

Be careful, that carburetor body is zink. The threads come out of the carburetor with the jet sometimes. Zink gets a powdery corrosion that just keeps expanding and jams the jet so bad that the zink tears in the threads before the brass jet comes free.

that carb is probably replaceable (Briggs knows they corrode bad), but I bet the cost would absolutely scare you.

Thanks for the "heads up" about the carb body...as I mentioned earlier, I haven't really soaked the body in any type of solvent yet. Perhaps if I soak it for a while, I can loosen the jets...I'll give it a try, and post the results (knock on wood :duh:).
 

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Discussion Starter #13
UPDATE:

About a week and a half ago finally got this project finished.

I finally ended up drilling out the old main nozzle using a bit just slightly smaller than the threads, then peeling the remainder of the brass nozzle away from the threads in the carb body -- apparently the problem was the corrosion that bobr mentioned.

I ran a tap through the threads in the carb body to shape them up a bit, then put the carb back together.

The engine fired up on the first try after sitting idle for 14 years!

Thanks for all of the help everyone!

:thThumbsU
 
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