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JimH

Briggs & Stratton Updraft Carburetors

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JimH
I need some help with getting the float level correct when I rebuild these carburetors. I am using a new needle and seat and all parts are clean but I still get gas dripping. This is not my first attempt as I have rebuilt several carburetors with much success. Are these carburetors trickier to set? Thank's in advance for any input.

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Simplicity314
You might want to try bending them so there is a slight incline when carb body is upside down. That will cause a better seal when it is turned back over in the right position.

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HubbardRA
Make sure you have the correct needle valve to match the seat. If the needle has a neoprene tip then it mates with the solid metal seat. If the needle is solid metal, then the seat has a rubber "o-ring" made into it to seal with the metal. A metal needle will not seal with the metal seat. Been there done that. Just make sure you have the matched pair.

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andrewk
If you have the neoprene tip, you can lap the brass seat to get a better seal. Take the OLD needle, and put a dab of lapping compound on the needle, insert, and lap away. Then wash it out real good in some soapy water, dry, and it should be better- Hope this is of some help- Andy

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olcowhand
It may not be the needle/seat leaking at all. It could be the emulsion tube that runs at angle from main jet up through carb to the carb throat. Where this tube passes through it seats against the carb. If there is any roughness where it seats, or the threads in carb are not allowing a tight seal, then the carb will drip gas as it allows gas past this seat, into the intake.

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TimJr
If the the brass tube is leaking, take your old one, grind off the threads, and use it to polish the seat where it meets the carb body. Use something like a car cleaning type wax, a final buffing compound like 3M Finesse-It II, or even a polish type tooth paste. You are better off spending extra time with these very fine grits rather than gouge things with the wrong lapping compound. These work on the float needle and seat also. Even using these compounds with a Q-Tip will help remove any stuck on gunk that carb cleaner alone won't wash away. Also, where is the gas dripping from? - those carbs are also notorious for leaking where the upper body meets the lower body. They warp from either water and freezing at some point, or improper tightening of the hardware. Some very careful filing can help that at times. Hope it helps, Tim

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HubbardRA
On one of the last carbs I worked on, I thought the emulsion tube was leaking and worked on that. Turned out to be a pinhole in the brass float and it was slowly sinking. Pays to check all the possibilities.

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andrewk
quote:
You are better off spending extra time with these very fine grits rather than gouge things with the wrong lapping compound.
I honestly don't think there is much difference- Lapping compound is used to make valves "air tight" when they are closed, and is a very fine grit. Or do you mean something else?

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TimJr
There are different grits of "valve lapping compound". Plus, valve lapping compounds are meant to be used on steel valves and seats - some valves and seats are made of even harder materials. Carb parts are either aluminum, brass, or not so special steel. So, using too aggresive of a grit could quickly ruin what you are working on, therefore my suggestion of something pretty mild such as the paint buffing materials and Q-tips for application. A cordless drill with the Q-tip mounted in the chuck makes for a quick job of polishing the inlet needle seat. Doesn't require pressure - let the compound do the work for you because you don't want to change the angles of anything, just buff off any varnish or minor imperfections that are causing a leak. Tim

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andrewk
I didn't realize there were different grits of lapping compound... The stuff I have isn't very agressive at all- I'll have to look at it when I go into work this afternoon. I use the old needle when polishing these, to help ensure the angles don't change- I also don't use any power tools, just back and forth movements with no pressure... Anyway, now that I know there are different grits, I'd sure like to get some thats a bit more agressive for the valves I do b/c they take forever!

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Dark
The briggs valve compound has two cans on the same package top and bottom heavy grit and lighter grit tooth paste works great for carbs so does Brasso polish and a q tip I have used talc powder and water also

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TimJr
Isn't this club just the best? Where else can somebody get so many good answers and learn new things from other people who are "in the know"? Jim - how is that carb coming along? I think we are all holding our breath and hoping that one of our tricks keeps you going. Tim

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JimH
Tim, I'm waiting on a new throttle shaft and bushings. I am just as excited as you guys are for the final outcome. I really appreciate all your pointers and info. Hopefully when it's back together that will be it. I will definately post an update.

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TimJr
Jim, did your carb originally have throttle shaft bushings? Many of the updrafts don't, like on a 7016 or 7116, but bushings out of a one piece Flo-Jet (like what a 4211 would have) will work if you drill out the throttle shaft bore very carefully. Seems like the old 3 bolt updrafts like on the 6hp Broadmoors had bushings - I would have to check that though. Tim

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JimH
I finally got my carb parts and got it back together. Eventhough, I used a new needle and seat, I polished the inside of the seat with a Q-tip and fine polishing compound. I turned the fuel shut off on and let it sit for awhile. No leaking! Next I fired it up. Motor ran good, no adjustments needed. Accelerated good and no black smoke. So I concluded that the float is set right and is doing its job. BUT, when I look in the carb intake there is wetness and a slight drip. Now I'm wondering if the gas is coming from the nozzle tube that protrudes from the bowel and into the upper body? It is seated securely. Also, I noticed I do have warpage at the rear of the upper body but I have remedied that for now. What are your thoughts on the wetness I am seeing at the carb intake? Thank's, Jim.......

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HubbardRA
This picture shows the primary leakage paths of these carbs. The blue path is from the emulsion tube seat. The green path is from a float that is set wrong, or is sinking because of a leak in the float. Either leak will put gas in the intake. This picture is a 4-bolt carb but the principle is the same on the 3-bolt units.


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TimJr
If it is leaking past where the brass tube meets the carb body, there are two possible fixes. One, is get the tiny plastic/nylon washer from the carb kit for say a 3.5 horse engine that has the carb mounted to the tank. Sorry I don't know the part number - saw this trick years ago. It fits around the tube, and sandwiches between the taper of the tube, and the seat of the carb body. Takes up any imperfections and seals it. Another trick is back to the polishing. You will need another emulsion tube, grind off the threads to is just slides up in there, and use it to "lap" the tapered seat back smooth. I have done that before and had it work. Just be sure to rinse the area out good before reassembly with the new tube. Tim

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JimH
Tim, thank's for the tips. I am convinced that my problem is the brass tube. Reason I am saying that is that with the motor off and the fuel on to the carb there is no dripping at all. If there was that would indicate to me the float level is not right or a hole in the float. I have water tested the float and it does not leak. By holding it under water or letting it float. no water getting in the float. Will keep you posted.

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HubbardRA
Both of those leaks shown in the picture I posted will occur with the engine off. The tube will leak with the engine off, because the seat is below the level of the fuel in the bowl. If it doesn't leak when sitting with the fuel on, then neither the float, nor the emulsion tube are leaking.

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