# Tecumseh HM100 carburetor



## nt40lanman (Dec 31, 2012)

I've finally had it with my carb. I've been through it a number of times. I finally ordered a kit for it online but wanted to get some feedback on my issue. It idles perfect. At full speed or under a load, it sounds great. The problem is part throttle without a load, it's like store brand dog food. I assume I'm going to find plugged ports or something behind the welch plug on the side but what?


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## mkd (Dec 31, 2013)

how did you adjust the high and low speed mixture screws? once you start the machine up how long before you can take the choke off completely? explain the "store bought dog food symptom?


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## nt40lanman (Dec 31, 2012)

I adjust the low speed mix by getting it hot and screw it in until it starts to surge then back out till it smooths out, and a touch more. The high speed I adjust at full speed, the same, then tweak it a touch if I notice a problem while blowing.

Off idle, it will surge erratically, not rhythmically. If these carbs have "part throttle" fuel ports like cars used to, that's where I think my problem lies. I'd say it's the idle circuit if it didn't idle so well.


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## mkd (Dec 31, 2013)

I will get back to you in a bit! selling my old snowblower now.


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## nt40lanman (Dec 31, 2012)

So stop fooling around on the internet and get that equipment moving!!!!


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## mkd (Dec 31, 2013)

nt4! snowblower sold! what I did to set the carb up when I rebuilt it was to start with the idle mix screw at 1 turn out and the high speed at 1 1/2 turns out. once I got the engine started I had to enrichen the high speed till it smoothed out and didn't stall from a cold start because 1 1/2 turns was too lean. once it ran enough to be completely warm I turned the curb idle rpm's down as low as the motor would run and still run smoothly. at that rpm I ran the idle mixture screw in a 1/4 turn at a time (lean) till the rpm started to drop. take note of the screw position and back the screw out (rich) till the rpm starts to drop again. set the idle mixture screw midway between the lean rpm drop and rich rpm drop screw positions. now set the curb idle to your liking ( I think around 1500 rpm?) . with a warm engine run the throttle to high position and do the same thing with the high speed jet under the carb in the center of the bowl. turn it in till it drops off rpm's then back out till it drops off and set the high speed mixture at the mid point between lean and rich drop off mixture screw positions. that should get you a starting point to fine tune from. to fine tune the high speed mixture I started with a stone cold engine. use your normal starting procedure and the minute the motor starts take the choke off and see how it runs. if it dies the high speed is still to lean. I have mine set up so at start up with the engine on high speed I can take the choke off right after it starts and it will run without balking or dying. once your high speed is done run the engine to fully warm. once warm position the throttle to the slow speed setting. the slow speed is about 1/3 throttle position not all the way to the bottom. from the slow speed setting advance the throttle briskly to high speed . if it balks or spits turn the slow speed or idle mixture setting one way or the other till throttle advancement from the slow speed can be done without any engine sputter or balking. generally a tad richer will be what you need to do. you will have the carb settings correct when it starts and stays running at high rpm with the choke let off very soon after starting and when the throttle is lowered to the low rpm setting for 5 seconds or so and advanced to high speed without the carb balking. there is no accel pump so the idle mixture setting running a tad rich has to make up for the opening of the throttle plate and lean mixture caused by the plate opened up. hope this helps!


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## nt40lanman (Dec 31, 2012)

Wow, that's a procedure. I guess I do most of that without thinking much about it. I've set up many engines and carbs, there's something WAY wrong with this one. I've never pulled welch plugs before. I just hope the holes for the throttle shaft aren't worn.


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## nt40lanman (Dec 31, 2012)

Pulled the carb tonight and will disassemble it when I get a chance. Anyone pull welch plugs before? How do you get them out?


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## Kiss4aFrog (Nov 3, 2013)

Did you happen to price out a new carb at the time you were looking for the kit ?? In most cases a whole carb is often less than the rebuild and your time.

But there are times I do like the challenge and it's more about rebuilding then saving money.


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## td5771 (Feb 21, 2011)

The plug on the bottom under the float is easy. There is a hole to the side and you just pry it our there is nothing underneath. Its just a cavity for the primer inlet.

The one on the side is a different story. There is only a 1/16 or so of space between the underside of the plug and the carburetor body. To make it harder on the body are the tiny holes that need to be cleaned and if they get messed up the carb is junk. 

Some use a chisel to tap them out. I don't because its a pain to try to hold the carb down.

I use a very, very sharp drill bit. I drill a hole very slowly in the upper right quarter of the plug. There usually aren't any ports/holes under that portion. Drill very slow so the drill point doesn't poke through and hit the carb body. After you have a small hole use an awl or small screwdriver in the hole to pry the plug out.

To put them back in just lay them in the body with the arch or bowed side facing out. Support the carb and using a blunt object and hammer just tap them flat. Don't make them concave, just flatten them a bit.

I avoided doing them for a whlie when learning but after you do it you will wonder why you were worried. Its a piece of cakea bit bit


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## nt40lanman (Dec 31, 2012)

I figured it would be easier than it seems. Going to whack it now.

Frog, I got the kit for about $9 including shipping. Small price for a shot at a repair. I like the work anyway.


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## nt40lanman (Dec 31, 2012)

Here's a pic with the plug out. You were right, easy peasy!!!

There's 5 ports.

2 in the center straddle the throttle plate at idle. 
1 around 10:00 at the edge is slightly downstream of the throttle.
1 around 5:00 pointing towards the idle mix
1 in the lower right looks like a shiny line, no idea where this goes.

The one at 10:00 had a chip in it that I had to blow out but I can't imagine it wouldn't have come out the other 5 times I blew compressed air through there. Maybe it was trapped and kept settling in there.


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## mkd (Dec 31, 2013)

nt4! if you still have the welsch plug out go find yourself a piece of fine copper extension cord wire and use a couple of strands to route thru the passages. once done blow them out with cleaner and then air before you install the new welsch plug. works good for the small holes in the bowl bottom nut also.


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## nt40lanman (Dec 31, 2012)

I have an acetylene torch tip cleaner I'll use. I can see light through them. I know what they all do except the last one. I'll wire that out in the morning and see if I can figure it out.


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## Grunt (Nov 11, 2013)

Have you seen this tutorial?
Disassembly, Cleaning and Repair of Tecumseh Series 1 Carb 632107


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## nt40lanman (Dec 31, 2012)

That's a pretty good one. I'm very familiar with these carbs and cleanup of mistreatment. The only thing I've never done is take out those plugs. I hope that chip (which could have been from drilling) was the problem. I'm going to wire out all those ports and replace the rest of the parts just for good measure.


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## nt40lanman (Dec 31, 2012)

Finished


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## nt40lanman (Dec 31, 2012)

Well that didn't work. Runs about the same. Everything in the carb seemed perfect. The only thing that was odd was while I could make cleaner spray out of the idle port down in the center near the main jet, I couldn't see the port. I dug around with a pick and couldn't find it. I'm going to pull the carb off and get that port wide open somehow.


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## ranvette (Jan 5, 2014)

Went threw the same thing with a Tecumseh 8HP carb.I must have had it apart 3 times.Never could find a thing wrong with it.I replaced it with a Oregon replacement carb and the engine has never run better


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## Grunt (Nov 11, 2013)

The parts you removed look pretty corroded, a new carb may be the needed fix if you can't clean all the passages out.


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## nt40lanman (Dec 31, 2012)

They looked corroded but were just gunky. I wired out and now understand all the ports. The only problem was the end of the idle circuit port in where the main jet screws in and holds the bowl on. I could get a new Oregon carb but I feel like I really want to fix it.


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## nt40lanman (Dec 31, 2012)

I have an update on this. After trying to open that port up in the middle and breaking the tip of a pick off in there, I realized I'm cooked so I go at it. I got the tiny ball out (circled in green) that plugs an idle circuit drill port. Getting in there I realize the plug in the hole above (in red) is pushed down too far, partially blocking things. I may go medieval on it just for fun and see how it goes. Anyone know of an epoxy that's suitable for gasoline immersion?


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## Kiss4aFrog (Nov 3, 2013)

_*Anyone know of an epoxy that's suitable for gasoline immersion?

*_Maybe auto parts store gas tank repair ??


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## Tote-M-Pole (Feb 1, 2014)

I bet that the throttle plate bushings are also yorked out.


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## db9938 (Nov 17, 2013)

Good old JB weld is fuel safe, or so the package says.


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## nt40lanman (Dec 31, 2012)

I'm set to get a used one from jackmels but I might try and fix this.


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## nt40lanman (Dec 31, 2012)

I cut that side of the main jet housing apart and got the plugs out. I drilled all ports, cleaned it up with a file, and sealed it up with JB Kwikweld. I'll see how it flows tomorrow. If I got epoxy where it shouldn't be, I'll carefully re-drill and seal the ends of the holes.


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## Shryp (Jan 1, 2011)

Yay, for future projects I wounder if some solder would work. Not a small iron, but with a propane torch like plumbing.


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## nt40lanman (Dec 31, 2012)

Mission accomplished!!! It runs like a top. I was assured by the JB Weld site that gasoline won't eat the epoxy so we'll see what happens.


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