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Toro 421 Model 38010,TECUMSEH MODEL HS40-55513G

This is a discussion on Toro 421 Model 38010,TECUMSEH MODEL HS40-55513G within the Small Engines forums, part of the Tech Support Forum category. I've gotten my snow blower fixed up a bit but I've got one more hurdle. But first let me give


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Old 12-14-2010, 02:21 PM   #1
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I've gotten my snow blower fixed up a bit but I've got one more hurdle. But first let me give you some background info. This thing is older than I am and it sat for a while. Over the last 15 years its been used a handful of times and always started. I've actually had it for 3 seasons and I've had very little problems with it. Up until now just a leaky fuel line. I fixed that last season. This season I pulled it out of the shed and it started within 4 or 5 pulls. That was normal even on really cold days. The first snow it worked fine. The second snow it would die every so often, but if I primed it no problem it would fire right back up.

I suspected an air leak of some kind. So I decided to tear it apart and clean up the carb (since it hasn't been for a long time). I did the carb service and fixed a leaking fuel hose which I suspect was the issue. Now when I prime I can feel the fuel being sucked in, before i could feel/hear it really just sucking air. I thought I was in the clear, then after I got it back together it won't start very well.

Right now if I get the engine started it will stay running if I have it choked until is starts to choke itself out. This seems normal to me.

The problem is when I take the choke off. The engine seems to rev up extremely high. I'm not really sure because I don't really have a good way to test the RPMs but they seem extremely high. I think I found someone on this forum say that the idle rpm should be 1700 and the high should be 3800.

As it runs I'd guess that the idle is closer to 3000-4000. Now thats a total guess based on the sound of it and what I know of other small engines (not much).

My initial thought was I just needed some carb adjustment but so far I'm not having any luck. I can get it started and keep it running but it seems like it is running way too fast.

So far I've mainly tried adjusting the power screw. Its labeled as part 22 in this diagram. I turned that down until it seems more normal but then it dies on me.

I haven't adjusted the idle screw (#24 in the diagram) really but I could try that too I suppose.

I tore it apart again and checked the throttle linkage and it seems to be hooked up correct. But I can't tell for sure.

The short version of this long story.
It starts really hard and revs up way high without the choke.

Does anyone have any ideas?

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Old 12-14-2010, 02:23 PM   #2
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I should add, with a little adjustment I got it to sound a little more normal but it would surge. Run for a second at a normal sounding rpm and then surge to high rpm. That just kept going.

The one time I got it to sound the best I let it run for a bit then hit the auger lever and it died instantly.

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Old 12-15-2010, 04:08 AM   #3
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Are you sure the carb is adjusted correctly?

Since your engine does start and run decently now, if it is mixture related, it'll simply be a slightly lean Hi needle. Opening the Hi needle about 5-10 degrees (ccw) would likely solve it, but i'll include the full tuning rigamarole so you understand what we're up to.

The carb will have (hopefully) 2 needles for setting the mixture, the Hi for running wide open and the Lo for idling and midrange/transition. The Hi one will be further from the engine, and the Lo will be closest to the engine. Most any Walbro carb'ed engine will start and run (very richly, tho) with both screws between 1.5 and 2 turns out from gently closed. Newer engines use special caps on the needles to stop you from adjusting them, but you can get the tool to adjust them with at your local small engine shop, I'm told, or you can mod the screws for normal slot heads with some creative dremel work(damn you EPA! Dontcha know an engine needs to be tuned to run properly!!!) Sorry. Once she fires, she should run with the choke open, tho the engine will be down on power and smoke alot. Time to start tuning.

First, hold the throttle wide open, and slowly close the Hi needle (further from the engine). The engine will smooth out and speed up. Note where the engine begins to sound smooth, and continue closing the needle (called leaning) until the engine begins to stumble and get rough again. Note this position, and then set the Hi needle to a little to the rich side of the middle of the 2 points you noted..... Hope that's clear... It is important that it be just to the rich side of center to ensure a good mixture and adequate lubrication to the engine. Instead of halfway, it's more like 60/40 towards the rich side.

Now, go to idle. Let the engine idle a little bit (30 seconds or so). Open the throttle and see how it performs. Probably it'll stumble, sputter, smoke and maybe quit. If so, lean the Lo needle a bit (closest to the engine) and try again. If it simply quits immediately, it's idle is lean and you'd need to open the Lo needle slightly. Repeat this until the engine accelerates from an idle cleanly to full throttle.

Because the idle jet has some effect on the main jet, after you get the idle working right, just revisit the Hi needle as described above to fine tune it. You want it set a bit towards the rich side of the 2 stumble points for best performance and engine life. The engine will run smoothly 90% of the time, and burble every few moments when it's right.

If needle twiddling doesn't do the job, then it's time for a carb kit and some more twiddling.
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Old 12-16-2010, 07:06 AM   #4
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Thanks bozodog. I'll give that a try as soon as I can. I think the problem is the carb adjustment like you said. I've just been struggling to get it right. Now I know the process so hopefully I can get there.

Thanks.
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Old 12-16-2010, 09:19 AM   #5
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I did it by ear for years before I found this guide. My stable of lil' engines are always needing attention.

I keep'em running, hubby runs them into the ground.
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Old 12-16-2010, 11:12 AM   #6
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I'd be inclined to think that it may be a problem with the linkage, if it did not do this before you had the carburetor off. Adjusting the hi or lo needles should not make that big a difference in the speed if the engine is running smoothly.
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Old 12-17-2010, 04:52 AM   #7
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From the description of your problem it sounds like the governor is not controlling the engine speed as it's intended to do.

When you re-install the carburator the throttle has to be held in the full position and the governor arm has to be held all the way to one side of it's travel, I don't remember to which side of the travel, I would have to look it up (can't remember everything about all of them).
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Old 12-21-2010, 08:39 PM   #8
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I've done everything you guys have mentioned but I still can't figure it out.

I think one of the problems was like jrrdw said. The I didn't realize that that arm was something more than just the arm that controls the throttle linkage.

I reset that to the proper position but still no go. I'm afraid that the governor is broken. No matter what I did with that thing and the carb adjustments its the same result. I can get it to start really easy but the engine runs really fast and when I adjust the carb it only goes basically on or off. Nothing in between.

Could I be doing something wrong or is there a good chance the governor is broken? I don't think it was before I started.
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Old 12-22-2010, 03:38 AM   #9
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Is your throttle valve moving freely? Can you control the engine speed at all with the dash board control or by hand? If your getting any control at all you need to find the fast idle screw up on the linkage controls above the carb. Inspect the little spring on the screw because these Tecumseh's are notorious for that spring not holding the screw in place and the end result is way fast engine speed.

Here's a link to a diagram to help you identify all the parts, you will need the engine numbers stamped in the blower housing.

http://www.jackssmallengines.com/help.cfm
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Old 12-28-2010, 09:04 AM   #10
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jrrdw-

I found someone to help me in town who knows more about it than me. We got it to idle down a little bit but still not great. He works at a John Deer dealership and brought it into the guys at the shop and they basically said the governor isn't working properly. When you change the governor you either get it to not start at all of it runs wide open.

I'm not in the process of looking for a new snow blower but I still might tinker with this one. Rip it all apart and see if I can figure out why its not working right. My guess is I'll have to rip all the way into the motor.

Thanks for your help.

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