Still won't run

[TomB1]

I have a small mower with a 4.5 hp Tecumseh that has been hard to start for a couple seasons. Last week it ran for most of the yard and then wouldn't restart when I stopped it for fuel. I cleaned the carb running fine wire through all the little holes and the nut on the bowl. I also cleaned out the fuel tank and the screen is clean and the fuel line is good. After all these years I was amazed that the bowl had no debris in it when I removed it. It had gas when I removed the bowl screw. I read online and many said that replacing the carb cured their problem. I also was skeptical of the ignition. So I bought the carb that had the best reviews, the ignition that had the best reviews and a new correct plug. I replaced the air filter a while back and blew it out. Set the ignition with a feeler that fit the old one before I removed it.

Most said their mower started with one pull with the new carb. Not mine. It finally started and ran for a half minute and then slowed down and stopped just like with the old carb. Won't restart. Gas in bowl. It acts like it runs out of gas but everything is new or clean.

Any ideas? The carb has no adjustments except for the idle screw.

Tom

 

[tom3]

How strong is the magnet on the flywheel? Rare, but they do get weak. The screwdriver dangle test is good enough. Hanging by the handle the tip should pull in at 3/4 inch or so.

 

[Rivets]

First you need to check to see if you have an ignition or fuel problem. Remove the spark plug and have someone pull the recoil while you hold the plug against the block. If you have spark we can go after a fuel problem, which I suspect is the cause. My suggestion is to rebuild the carb which Tecumseh part number 631021B. Here is the procedure I use everyday.
[FONT=&quot][FONT=&quot]Needle and seat replacement.[/FONT][/FONT]
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[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]
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[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]
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[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]
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[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]

 

[TomB1]

The magnet is strong. I stuck an end wrench to it yesterday and had to pull it to get it off.

The ignition is new, just installed yesterday and it did run strong for about a half minute.


The carb is new, just installed yesterday. Everything inside appears clean. No gas in float and gas fills the bowl.

Tom

 

[Rivets]

Did you check for spark as I asked? Have seen many knockoff carbs for Tecumseh that are only designed for one type of engine, poorly made, and don’t work. Example, people have tried to use a carb for a lawnmower engine on a SnowKing engine. Won’t work as the jets are set too lean, and the customer needs to know how to punch the jets without ruining them. Working on carbs is like working on electrical problems, never assume anything is right until you have double checked it. If you need more help, you will need to post all engine numbers so we know which engine you are talking about.

 

[TomB1]

After reading your post I got to thinking about the ground wire again, even though I had looked at it before. First I gave it a short shot of starter fluid and it started after a few pulls. Then it stopped again. Had gas and the primer was working. Then I pulled out the spark plug and had wife give it a pull. No spark. So I pulled off the cover and looked at the ground wire. It looked fine as far as I could see but looking way back under the flywheel I found a bare spot on the insulation. I taped it up and tie strapped it away from the flywheel and the cylinder. Put it back together and it finally started after several pulls and a short shot of ether. Had to restart it couple times then it stayed running but rpm was lagging. I shut it down and filled the fuel tank, strapped the shutoff handle and started it again. Started with just a couple pulls so I let it sit and run for a few minutes.

I mowed awhile then the wife took over and it's still running and sounds strong now. I guess we'll see how it does next time I need to mow.

Thanks for the help and I'll update this thread as to how it's working out.

Tom

 

[TomB1]

Update

This is my trimming mower and I usually get all the trimming done on one tank of gas unless it is tall and growing fast over the whole yard. It's been dry for a couple weeks and hasn't grown much except in the shade. One tank should have done the yard easily. It ran out at about halfway. Filled it and it was hard to start. Had to give it a shot of starter fluid then it took off and ran fine again. It ran out of gas just as we were finishing the trimming. That's twice as much gas as what is usual.

The bolt that holds the bowl on is stamped 174 on the old carb and 189 on the new one. Could that be a larger jet size?

Tom

 

[sgkent]

you changed the carb. It is possible that the mixture is too rich now since you say the fuel consumption is high.

I usually try to keep original everything on engines other than when racing. That includes small mowers etc. My experience is that many small engines don't have a dedicated fuel pump and if they do it is not cam or electric driven but rather driven by the changes in air pressure inside the engine as the piston goes up and down. Those all rely on a gasket having a flap that seals up every pulse. Once the gasket warps then the fuel just sloshes in the carb or pump, and the engine does not get a steady flow of fuel as designed. The symptoms for me have all been the same - hard to start and not very steady at running. I did have an B&S engine on an edger do this lately where the primer bulb was leaking air in, and fuel out. A new primer bulb and off it went. However the symptoms were the same because although the carb had plenty of fuel in the bowl, it wasn't getting fed into the carb just right. I am a novice at smaller engines compared to many of the other folks here.