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My Snapper 422 snow thrower with a Tecumseh HS 40 engine was working but acting as if it was too rich and using fuel much faster than it should. First thing I found was that the fuel supply hose had a slit in it. Replaced hose, but engine was still not working properly. It would start, and then begin acting as if it was too rich, and shut down. So I decided to check out the carb. Removed it, cleaned it and checked all settings. Float floated, and when I blew through the "fuel in" port, and pushed up on the float, it sealed. Put it back on the engine. It started immediately, but then bogged down and quit. With the engine off, fuel would drip out of the choke end of the carb. Obviously the needle and seat were not shutting off the fuel. After messing around with it off and on for about two weeks, I purchased a new carb. Works great. Snow thrower starts immediately, and seems to run well, except that at full throttle, it begins to miss a little. If I reduce the throttle slightly, it smooths out. Maybe too rich at full throttle? But the new carb does not seem to have an adjustment for the mixture. No adjustment for the idle mixture either:



Is there a way to adjust this type of carb? Perhaps I can remove the adjustment screw from my old carb and install it on the new one?

Thanks for any help, Bob

I would say the new carb is slightly too lean in the complete full throttle position. Could try using the bowl nut off of the old carb and see what happens. The main fuel jet is in the bowl nut. And would bet the rubber float seal tucked up inside the fuel inlet has either swelled or cracked/damaged which is what is causing the rich run issue and the flooding.

Thanks for the reply. I thought to replace the needle and seat of the original carb, but seat did not seem to be replaceable. When I purchased the new carb the description stated that it was for a 5.5 hp, 22 inch snow thrower. My 422 model is 4 hp, which is what leads me to believe that if anything it would be too rich rather than too lean. But now that I think about it, you are correct that if I can back the throttle off and it runs better, that would be a symptom of too lean at full throttle. Maybe in the Spring I will take the carb apart and see if an adjustable main jet can be substituted, and if that makes any difference. Right now I want to leave things alone so my wife has a working snow thrower!

The float seat looks like an O ring of sorts as illustrated in this picture


The rubber seat will swell or crumble when exposed to carb cleaner. Also on Tecumseh the float when properly adjusted for height doesn't sit level. you should be able to slide an 11/64 drill bit between the float and the carb body without the bowl gasket installed opposite from the hinge pin. And also be aware that a carb set at warm temperatures will run lean when operated at cold temperatures. Back when we had adjustable Tecumseh carbs the procedure when setting them in the fall during tune up was to set the main jet to run smooth and then turn it out 1/4 turn to compensate for the denser air in winter. Otherwise it would run poorly when the customer started it to blow snow.

As I already said, I installed a new carb. I don't need any information on the seat or how to adjust the float level. The question I have is: Is the main jet mixture adjustable, and if so, how?

The main jet is the bowl nut. It is not adjustable. On some tec carbs you can swap in an adjustable bowl nut with a needle. Some you can't

Don't know if this fits but it has the adjustable main jet.

Thanks for the comments. The one that I ordered used that same stock photo of one with the adjustable main jet, but the one I received did not have it. It says it is compatible with the HS 40 Tecumseh.....I may try that in the off season. Right now the machine runs OK, and I don't want to mess with it. Warm this week, but with my luck if I take the snow thrower apart again, we will have 2 feet of snow!

Bob

Looks like scamazon strikes again.

We are off to a good new year!...
Happy new year everyone

Here is a link to view some Tecumseh carbs with repair tips.

You can also download a FREE Tecumseh L-head service manual that cover several model and Hp of the L-heads.
You might try these links for the free manual:
I have not visited these links lately.
I think the smallengine link is a direct download.



https://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_L-Head_Engines_Service_Information.pdf

Take care of your old adjustable jet carb, they are NLA and are good carbs.
Pay attention to the little o-ring on the bottom of the bowl where the High speed jet screw is located. If it's bad or gone and the little flat washers that is used to keep from worrying and damaging the o ring is gone the carb will have a aggravating leak.

Sometimes you can clean up the seat using a q tip and tooth paste.

Thanks for the comments.

I have a soft bound Tecumseh book called "Mechanic's Handbook" for 3 - 10 HP engines. On the back it says "R2/93" which I presume means "Revision 2, 1993. I also have a Tecumseh "Technician's Handbook" for 3 to 11 HP L-Head engines dated 1998 that I downloaded from the internet at some point. I also have a CD titled "Tecumseh Repair Manual" dated 2005. All are good for explaining how to adjust the original carb, but none mention a carb with no idle or main jet adjustments.

I will check out the link on repair tips, but as I said, right now all I wanted to know was if there was a way to adjust this carb without a main jet adjustment screw, since in my close to 60 years of messing with theses small engines, I have never seen one before. According to Hammer, the answer is that maybe I can install an adjustable bowl nut on my new carb, or maybe not. For now the engine is running pretty well, and if it is a little rich, I am going to live with it for this Winter.

Bob

Run what you brung'...it's a snowblower, not a Heart-Lung machine....now for some snow!

AirMaster flyer asked:
I will check out the link on repair tips, but as I said, right now all I wanted to know was if there was a way to adjust this carb without a main jet adjustment screw, since in my close to 60 years of messing with theses small engines, I have never seen one before.

You say you have never seen one.
The non-adjustable jet replacement carbs for small engines came about due to emission regulations. Al Gore type carbs.

You think maybe yours is running too rich. I've modded several of the non-adj jet carbs so as to make the engine run smoother but usually I had to enrichen them by modding the idle jet circuit BECAUSE the idle ckt is also used to enrichen the High jet area on those emission carbs.
On some of the Tecumseh non-adjustable carbs you can remove the low speed idle jet tube and play with modding it. If your replacement carb cost very much in $$'s I would suggest leaving as is and fix your OEM carb, because you stand the chance of ruining your replacement carb and having to spend more bucks. (Some replacement carbs
Some of the Tecumseh carbs fixed low speed jet brass tube could be taken out of the carb with the carb on the engine and they have a color code plastic cap indicating their size. When I first started modding the carbs i made sure that I could get a replacement low jet tube BEFORE I started modding the carb. (if the carb was the expensive type replacement)

"The non-adjustable jet replacement carbs for small engines came about due to emission regulations. Al Gore type carbs."
That explains a lot. This snow thrower was purchased in 1987!

Happy New Year to all...Today it is warmer outside than it is inside! But there is bound to be snow sooner or later.

Edit: This new carb does not have a low speed adjustment either. The spot where it would be is plugged. Next Spring I may remove it and see if the adjustable bowel nut from my old carb would be direct screw in replacement. If not, I will just leave it alone.

I had replaced the carb at some point, and so I have two old ones. One does have a brass sleeve for the needle seat, but it is not obvious how it would be removed as there is no slot for a screwdriver or flats for a wrench or socket. Appears to have been pressed in. The other does not have a separate brass sleeve at all, as if the carb is a throw-away.

Today afternoon high of 67F, so no snow!