# Craftsman 9 HP with Tecumseh HMSK90 Motor



## Carguy8486 (Nov 12, 2019)

Hello everyone,
I'm fixing a friends 9 HP Craftsman Blower (1999 Tecumseh HMSK90 motor), Craftsman Model #143.019003, and have a few questions, hopefully someone can answer them for me. The motor was surging, so I bought a carb kit, used the ultrasonic cleaner to clean it, installed the carb kit, and reinstalled the carb (new plug, as well). It runs well at low RPM in the shop which is heated. At higher RPM's it is backfiring slightly, which is one problem. Also, when outside in the cold (mid 20's farenheit), it starts hard and also exhibits the backfiring. 

The questions are:
1) Could it still be the carburetor? I know it was cleaned very well, but perhaps there is some small orifice that is plugged, but don't think it would cause the backfire issue.
2) Could it be backfiring due to a leaky exhaust valve? 
3) Does this motor have adjustable valves, or do I have to take the head off, remove and grind them? I do realize I could take off the exhaust and intake stuff to look, but if someone knows, I would appreciate any intel.

Any help would be very much appreciated!


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## JLawrence08648 (Jan 15, 2017)

You need to remove the Welch plug in the side and clean the holes with a welding tip cleaner then buy a new Welch plug, seal it with nail polish.


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## paulm12 (May 22, 2015)

can you run a compression test or better yet a cylinder leak-down test? That will help determine if you have leaking valves. If so, the cylinder head should be cleaned and the valves should be lapped. I bought a leak-down tester (used) a few years ago and use it all the time now, especially on the older engines.


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## Carguy8486 (Nov 12, 2019)

RE: Craftsman 9 HP with Tecumseh HMSK90 Motor

Thanks to Paulm12 and JLawrence 0648 for some advice. I didn't take the welch plug out when I cleaned it, so will do that today, and see how it functions. Regarding the compression, I believe it is fine, but if removing the welch plug doesn't work, I'll check it. I don't have a leak down tester, but found one pretty cheap, so will try it. I did figure out that the motor doesn't have adjustable valves, so if the leak down test shows the valves are leaking, I'll take it apart, lap the valves and take it from there. I may also replace the carburetor with one that I can adjust the air/fuel mixture, too, to help with the cold start issue. 

Thanks again for pointing me in a direction that may help.


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## Toro-8-2-4 (Dec 28, 2013)

Carguy8486 said:


> RE: Craftsman 9 HP with Tecumseh HMSK90 Motor
> 
> Thanks to Paulm12 and JLawrence 0648 for some advice. I didn't take the welch plug out when I cleaned it, so will do that today, and see how it functions. Regarding the compression, I believe it is fine, but if removing the welch plug doesn't work, I'll check it. I don't have a leak down tester, but found one pretty cheap, so will try it. I did figure out that the motor doesn't have adjustable valves, so if the leak down test shows the valves are leaking, I'll take it apart, lap the valves and take it from there. I may also replace the carburetor with one that I can adjust the air/fuel mixture, too, to help with the cold start issue.
> 
> Thanks again for pointing me in a direction that may help.


Sometimes it is just better to buy a new aftermarket carb on EBAY for $15 to $20 for these Snow King Engines. If there was a lot of the white colored aluminum corrosion it will just come back. But I have still cleaned them and got them running. I have been able to clean the idle jets with out removing the welch plug. 

I Dont have an ultra sonic cleaner. If you have one, great. make sure it is an industrial style. The cheap ones for jewelry are not powerful enough.

I remove the emulsion tube, main idle jet and both choke and throttle plates. I do a cursory clean with carb cleaner and compressed air using a rubber tip on the nozzle to get a good seal and good pressure. It is the idle circuit you want to focus on clearing out. The blind passage ways. The main jet is easy to clean.

I soak it in Kroil for a bit. An hour or longer. Other solvents may work as well. I know some people use gun cleaning solvents. It is just that carb cleaners do not remove that white powdery crap very well.. I then get a fine wire and bend a 90 degree angle in it. Then carefully poke it through the 4 Idle circuit jets in the carb throat to make sure the are not blocked. More compressed air and clean away the kroil with carb cleaner. Cycle through a few times. It does take time. If you are doing this as a for profit business you need to just buy a new carb. I do it for myself and some customers I dont mind taking a loss on when they need it back fast.

When using the compressed air I block the top of the main jet passage with a finger in the throat in order to force more air through the idle circuit. If the pressure is real high it can be a bit uncomfortable. 

I will use carb cleaner with a straw through the idle jet port and watch to see if I am getting flow trough the 4 idle jets in the throat. You have to be careful you don't get it in the face. It does not taste to good. .
Not a perfect process but I have been able to get stuff working well with out buying a carb kit. 

Definitely check the valve clearance. Make sure the seats are not worn such that the valve can move side to side. A crude test is to run it at night and see if the muffler glows red. A little bit is not too bad. A lot is not good. It made be an indication of a too lean condition. Or it may indicate a poorly sealing exhaust valve.

It is tough to compression test these engines because of the compression release valve.
Good luck.


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## Dillon21 (Jan 4, 2020)

I have a very similar machine but a little newer. Just replaced the fixed carb with an adjustable one from auction site for about $12 with shipping. Works great. Checked RPMs to find it was running around 3250. Did some research, there were three diferrent crankshaft setups with this engine. The one for MTD (Craftsman) was set to run at max goverened speed of 3600, not 3250. I turned it up to 3500 +/- 20 and it is a noticiable difference. Surging was a combination of carburation and govenor spring tension for me. I added an impeller kit also, I have to say I now enjoy it when it snows. It is a totally differrent machine now.


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## ou2mame (Dec 23, 2019)

if you buy a cheapo aftermarket carb, make sure you get one that is adjustable. The fixed carbs might work, might not. But if they don't, there's nothing you can do about it.


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