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I am trying to repair a old toro snowblower. Has a 5 hp tecumseh. Carb looked good but cleaned and rebuilt. Started right up and runs fairly good except is pulses, will not run a steady speed unless the motor is under load and blowing snow. I have not had that happen before. Any suggestions on how to stop this? Thanks

That engines carburetor has a soft plug on the out side of it located on the side of the carburetor. When you cleaned that carburetor did you remove that soft plug? Under that plug is some very small holes which is part of the slow speed circuit and if they are plugged in any way it will run just like you described.

Thanks for the quick reply, I am not familiar with this soft plug? There is a low speed adj screw that was removed and cleaned. It this plug inside the bowl?

Dreamen said:

Thanks for the quick reply, I am not familiar with this soft plug? There is a low speed adj screw that was removed and cleaned. It this plug inside the bowl?

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Facing the carburetor from the air cleaner side it will be on the left outside of the carburetor. Yes I (think) there is a soft plug inside also but that isn't the one I am talking about. Sometimes it just looks like a flat aluminum plug but it can be removed and replaced with a soft plug.

Ok I know about that, I have never replaced that one. I have a new aluminum plug. "The carb was so clean inside it is hard to believe that is the problem. I have never had to remove that. Will check it out

Thanks

Just some things that com to mind.

Can you stabilize the surging or hunting by adjusting the choke?

When surging happens it is because the engine is running out of fuel. The carburetor is not able to meter the appropriate amount of emulsified fuel. If you can stabilize the engine with the choke there is a pretty good chance that there is a fuel delivery issue and not a governor problem. I believe that the other poster is referring to the welch plug that covers the intermediate and high speed circuit. If you have that plug from a kit, it is never a bad idea to pull the old to inspect and clean. Is the screw on the side of your carburetor actually an adjustment screw? does it have a spring, brass washer, and o-ring on a removable screw that forms a point at the tip? Or is a a brass screw that has a few holes drilled threw it horizontally and one hair pin hole in the tip, and this screw would have a plastic cap on it? I ask not to be insulting, only to help clarify. The first is a "low speed adjustment screw" the second is a fixed jet that is not adjustable. Either way, I would bet that the problem lies in the carburetor. When the carburetor was rebuilt, did you pass fluid through each of the passages and orifices? If the bowl jet is not adjustable, I would check that again. One thing I have learned is Tecumseh main jets can never be too clean. They can be too dirty. Lastly I will mention the float height. When the float is installed it should be set to 11/64" With the carburetor inverted or upside down, you should be able to set an 11/64" drill bit between the casting and the float. Tecumseh made a great tool for overhauling their carbs (tool number 670377) It has a hook to remove old seat, a drift to install new, and the handle is 11/64" for setting the float height. I hope some of this helps, if not we can try again.

I'm betting the carb is set too lean and you never replaced the float needle seat. The seat is in Tecumseh kit #631021B. Here is the procedure I follow, even though you have an adjustable carb, it should work for you. Combine this procedure with the one last posted.

Needle and seat replacement

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.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

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.

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.

Thanks for the reply, I did remove the aluminum I think they call the welch plugs. It was clean. Will take it apart again tomorrow. Has to be something plugged as now it has to be on choke to run. Did not have to do that before. There may of been dirt in the gas line. This has sat for 5 years. Tank was empty and clean and there is a screen in the tank were the gas line attaches. Will check the seat again, it is a new seat but I did not change the needle valve as it was clean. Float seem to be ok, does not rattle. Will follow up tomorrow

The one post did not show up before I replied, yes the low speed adj screw has a spring and gaskets. I removed all the screws and sprayed carb cleaner thru all the jets and blew out with compressor. There is also the high speed adj on the bottom of the carb bowl. Both are clean and jets free. Will take apart again tomorrow.

It is always a good idea to change the needle and seat when rebuilding a carburetor. When overhauling a Tecumseh carb, I always do it. The previous poster gave a good description. Just to clarify though, a failed needle and seat will not cure a "running lean" symptom. ( that I am aware of) If the needle and seat has failed it may show signs of running "rich", not "lean". You may also see fuel coming out of the air cleaner, or worse, fuel may be leaking out of the carburetor and ending up in the crankcase. There is a chance that if the needle and seat has failed, the carburetor will flood and the excess fuel can go through the intake manifold, into the combustion chamber, and end up in the crankcase. If this happens the gas will act like a solvent and cause the viscosity of the oil to change. Could end up thinning the oil to the point where the engine overheats. Pull the dipstick, does the oil smell like gasoline? Does the oil appear to be over full? Is the gas tank dry, even though you filled it? The easiest way to check if the needle and seat is functioning is to use a pressure testing gauge. If you don't have one, the next best thing would be to hook the gas tank up to the inlet, look through the throat of the carburetor and see if gas is coming out of the emulsion tube. (usually a brass or plastic tip sticking up in the throat.)

Anyway, back to my original point, replacing a failed needle and seat will not cure a "running lean condition", but properly setting the float height can. So can properly cleaning the carburetor. As the previous poster suggested, ultrasonically is the way to go. Even after that I still pass carb. cleaner through each passage so I can visualize that it is open.

Lastly, I don't believe that you stated weather or not this surging happens at high speed, low speed, or both. If it happens at high speed, no-load, I will also suggest that the you check the rpm's of the engine. If the rpm setting is in excess of the recommended setting it could cause surging. I.e. if Tecumseh says the setting should be 3,600 rpm and it is set closer to 4,000, then that over-speeding can cause the surging and other, more serious problems.

I really appreciate all the input. Took apart again today, cleaned, wired and blew out every port. Seat and needle valve look good. I hook up the gas line and take bowl off and hold the float to make sure the needle valve seats. I have no gas running out the carb or drips anywhere. Oil is fine. It started right up, surged a bit, but with a little high speed adj it smoothed right out. It is a touchy needle valve from most of the tecumseh I have. This is a beater, one rusty blower, I think it has seen little use as wear pads have little wear. But it blows snow!! I have not adj the low speed only opened it up 3/4 turn. Does not seem to do much. Not often that you are running at low speed. How do you check the rpm. To me it seems to run much slower at full throttle than any other blowers I have.
Thanks Again.

The low speed screw should change the pitch of the engine when manipulated. If you set the throttle to the low position and manipulate the screw and it doesn't change, then something is not right.

The rpm has to be checked with a tachometer. There are several variation that work. The most cost effective is a vibra-tach. Briggs markets on for about $25. It works great.

http://www.barrettsmallengine.com/manual/tecumsehlheadmanual.pdf see carburetor troubleshooting page 14