Tecumseh LH358 governor adjustment - Snowblower Forum : Snow Blower Forums
 
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post #1 of 8 Old 03-25-2018, 08:24 PM Thread Starter
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Tecumseh LH358 governor adjustment

Hi -

I’ve been trying to adjust the governor for a new Tecumseh LH358 block, replacing a LH318SA, and it’s so finnicky. I bought this blower for $60 and want to use it to replace my smaller snowblower. Figured it would be a good winter project when I saw the guy post it for sale on Facebook.

I tried to rebuild the LH318 which had a bent valve but i guess it was too abused and died again. I had the same problem adjusting the governor on the old engine, too. I watched a vid on YouTube from Donyboy73 on governors and I don’t really feel like I’m doing anything wrong.

https://youtu.be/SSwSIA8qgR8

Maybe my cheap rpm gauge is crap and not working right? The max RPMs for this engine is 3600 but I can never make it past 2100. I adjusted governor just the slightest more back, adjust high idle screw, and I get a surging issue. I might just have to take it to someone to complete the final adjustments I guess...but figured I would ask for advice here first.

I rebuilt the OEM non-adjustable carb (replaced the main nozzle and the o-rings) and also tried a brand new adjustable carb. The new carb was from amazon...it was missing the Welch plug under the bowl but i had one from another carb rebuild kit and punched it in. I feel pretty darn confident that my carbs are good. I’ve rebuilt plenty of them. With either carb it’s running stable but only at max 2100 RPMs.

When I check my 3 Amp stator’s AC output at 2100 RPMs I’m getting 36 volts. That’s pretty darn good and what I’m supposed to get at 3600 RPMs. According to the Tecumseh manual, At 2500 RPMs, my stator is only supposed to dish out around 24 volts AC.

I made some vids in case you want to see that she’s responding pretty good with either carb. Just not anywhere near max RPMs.

https://youtu.be/nus25qfWsjM

https://youtu.be/p5b-3ET9-tE

Thanks in advance!
Kevin
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post #2 of 8 Old 03-25-2018, 08:30 PM
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Are you sure you have the settings on your tach correct?

It sounds to me like the engine is running at the correct speed or maybe even a little fast. I suspect the tach may be reading 1/2 of the correct number.

It also could be the tach is picking up a weak signal... try winding the tach wire a couple more turns around the plug wire and/or more tightly and see if the reading changes.

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post #3 of 8 Old 03-25-2018, 08:46 PM
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I'm with ELaw. I think, from your videos, it's running at the proper speed, or even a little too-fast, as he said.

Do you have something of a known RPM, that you can use for checking the tach? A generator would be ideal, since it should be running right around 3600 RPM. But even a lawn mower should probably be around maybe 3200-3600, somewhere around there. If the tach showed more like 1600-1800, that would definitely make me think it's reading half of the actual RPM.

If the tach can be set for single-cylinder, or two-cylinder, it's possible that it's in two-cylinder mode, and therefore dividing the observed number of ignition pulses by 2, to calculate the RPM.

When your tach showed ~700 RPM, I really don't think that's 700 RPM. I think it's reading half of your actual RPM, or at least something close to that.

If it is low by half, then you're already at 4200 RPM, and Tecumseh engines are known for being sensitive to over-revving. It can make them blow the connecting rod. So for now, at least, I'd probably adjust the carb to drop the RPM to an indicated 1800, in case that's really 3600. You can always raise it again later, that's way easier than dealing with a blown rod

Regardless, great deal on the blower, hopefully you can get the nice shiny engine sorted out!

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post #4 of 8 Old 03-25-2018, 09:01 PM
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i agree thats not 2 grand but its not 4k either
check tach settings
iam set at 3720 his sounds lower

Last edited by 1132le; 03-25-2018 at 09:05 PM.
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post #5 of 8 Old 03-25-2018, 11:05 PM Thread Starter
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Quote:
Originally Posted by 1132le View Post
i agree thats not 2 grand but its not 4k either
check tach settings
iam set at 3720 his sounds lower

OK, I was suspect maybe the tach could be the problem because, I agree, it sounds pretty good, right? I do have a Harbor Freight 8750 generator that runs at fixed speed so I will check the tach against that. I'm also reaching out to a couple of friend mechanics to see if I could borrow something to check it. I definitely don't want to blow it up running it above 3500 or 3600 RPMs.

When I read the voltage coming out of my stator and saw 36v, I knew I needed to get a 2nd opinion on what I was seeing!

ALL -- Thanks so much for replying!
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post #6 of 8 Old 03-25-2018, 11:31 PM
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Perfect. Just make sure to disable the auto-idle feature first, if the generator has that. Or put enough electrical load on it that it comes out of idle, and goes up to the high speed.

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post #7 of 8 Old 03-26-2018, 07:11 PM Thread Starter
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Hi - So this morning at work, I was thinking about tachometers...shopping! Of course all the cheap tachs like the one I bought popped up. Well, there was a youtube video that I decided to watch about mine and that's when I found out I did not have it programmed for single cylinder engines.

Changed the settings after watching this video...

Now I'm golden. I was right on the money at 3600 RPMs actually so I lowered it to like 3450 because these tachs probably have a +/- 100 RPM accuracy.

Thanks again for the replies!

Kevin
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post #8 of 8 Old 03-27-2018, 09:56 AM
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Awesome! I'm glad you got it sorted out. Good thing you didn't keep trying to reach 3600!

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