where else to look carb leak

sgkent

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I have a craftsman edger 536.797430 probably made by MTD for them with a Tecumseh engine 143.963515 about 1996 - 1998 or so, . Starting about a year ago the tank was empty each time I go to use it. Usually it showed signs it came out the carb. I've rebuilt the carb 4 times using new factory parts and tools, new hoses etc.. Everything checks out - I can invert the carb and the needle seals. I see no cracks. Am out of bullets how the fuel may be bleeding down. New needles, new seats installed the correct direction, new bowl, gaskets, etc.. Anyone else run into something like this? carb # is 640049. I even replaced the brass float a couple times, one new one had a hole. Put the last one in a pot of water and boiled the water to see if it had any bubbles.
 

Fish

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If memory serves me correctly, the 536 prefix, was for a company called Noma, which was absorbed by Murray.

But your problem is with the engine, so the equipment brand doesn't matter here.

After you go through the carb, does the engine run OK?
 

Fish

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If it runs good, just put on a fuel shutoff.

shutoff.jpg
 

Rivets

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The only two things that I can think of that could be the cause. The float needle and seat not sealing properly or the bowl gasket not installed properly. The first will allow fuel to continue to flow and the second will not seal the float bowl. The part number for both is Tecumseh number 631021B. This is the procedure I use to solve this problem.
[FONT=&quot][FONT=&quot]Needle and seat replacement.[/FONT][/FONT]
[FONT=&quot][FONT=&quot]Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.[/FONT][/FONT]
[FONT=&quot][FONT=&quot]I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.[/FONT][/FONT]
[FONT=&quot][FONT=&quot]With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. Next check to make sure that the float does not have any liquid in it. If it does, replace. If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.[/FONT][/FONT]
[FONT=&quot][FONT=&quot]PS: On the side of some Tecumseh carbs you will find a plastic cover. Under this cover will be an idle jet. Remove it and check to see that the jet is open both horizontally and vertically. You should be able to push the old float needle wire through the vertical opening.[/FONT][/FONT]
 

sgkent

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yes it runs super. Starts first pull most of the time. Only issue it has is that the tin hits the starter sometimes and goes clink when pulling it. The quills used to break every few years but the last time I took the replacement part to a good welder, and he replaced the small spot welds with a full 360 degree weld all the way around the quill. All my carb problems started about 4 years ago when the idle jet unscrewed itself. It's a California carb so it does not have an idle mixture adjustment. I replaced the idle jet that was lost and that problem was solved but then others began occurring. I've rebuilt hundreds of carbs of all kinds in my life so this is unusual for me to not be able to fix the problem. That said, I'll put one of those fuel cutoffs in and see if that stops it. The tank didn't look to have any cracks so that should do it.
 

Fish

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Yeah, just use the shutoff and be done with it.
 

Fish

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Take a real close look at the fitting going into the carb.
 

sgkent

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Take a real close look at the fitting going into the carb.

you mean that it could be leaking from the threads or a crack?
 

Fish

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yeah, worth a peek at it.
 

sgkent

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posting results. Bought a new carb as a spare and added a shutoff on the old one since the mower runs fine with it. Found a crack in the plastic fuel tank but it did not appear to be leaking but I replaced it too. The new tank came with a shut-off too, so now I have a spares.
 
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