# MTD Snowblower runs full throttle or not at all



## BrokeBlower

Hello all,

I've got an MTD Snowblower, it has a Tecumseh HMSK100 10 HP motor. 

I got it when my dad passed away, it had a broken muffler, and it would either run wide open or not at all. 

I went to the small engine shop, to pick up a new muffler today and explained to them what was happening. They told me to clean the carb. 

I didn't do a complete carb tear down as I didn't have a rebuild kit on hand so what I did do was:

1. Remove float bowl
2. Remove float/needle
3. Cleaned the float/needle/bowl/pin with carb cleaner/ with a copper brush
4. Shot a bunch of carb cleaner into the carb
5. Cleaned the main jet in the float bowl, the 2 bigger holes, and the small one (I do not have an adjustable jet)

I put everything back together, started it up and it ran like it was supposed to, I adjusted the speed and that was working as it was supposed to, so I let it sit and idle for maybe 45 secs to a minute and it went wide open, and the speed adjustment is back to not doing anything at all, so I'm back to where I started. It either runs wide open, or not at all.


Thanks in advanced for any help you give.


----------



## jfmtnbiker

One thing you missed with your carburetor cleaning which causes people a lot of problems is the idle restrictor screw. On the choke side of the carburetor you will see a small rubber black cover. Take a flat head screwdriver and pry off this rubber cover. Then, you will see a brass screw. Unscrew this and be sure to clean the two holes and the one on the end. The holes are very tiny, so be sure to run a thin piece of wire through them. Typically, I remove this screw before even spraying any carburetor cleaner. This way it is yet another escape passage for the carburetor cleaner and debris that may be inside.

The idle restrictor screw must be fully installed for the unit to run properly. Unfortunately, people think that this screw allows for adjustment of the idle speed. This thought process is incorrect. If you do not make the screw reasonably tight, it will actually fall out due to the vibration of the engine. If a screw this small was to be an adjustment screw it would have been installed with a spring to maintain its tightness during operation.

I have worked on Tecumseh engines that surged when I put the screw in after cleaning. My experience has been that sometimes the screw is threaded slightly off and if that happens, it doesn't tighten in such a way that the holes are lined up inside. So, if at first you don't succeed, be to remove and re-insert the screw.


----------



## jfmtnbiker

I should also add that you may have debris in the emulsion tube. If the emulsion tube is corroded on a tecumseh snow king engine, this often requires replacement of the carb. But, try cleaning the idle restrictor first.


----------



## BrokeBlower

Here is a video I took, it finally uploaded. 







Thanks for the posts, I'll be sure to clean that tomorrow.


----------



## BrokeBlower

I did as you said popped off the cover, unscrewed it, soaked it in cleaner, and cleaned it. 

Started it back up, and had the same results as the video above, so I took it out again and same thing again.


----------



## sboricic

I had a similar problem with mine. Same engine and HP. It turned out to be the throttle mechanism itself that was causing the problem. Perhaps the spring that leads to or on the mechanism itself is broken on yours not allowing the governor arm to work properly? Here's a video with a bit of info.





*Here's another link with some useful information.*
https://www.youtube.com/watch?v=16lQOZF3e84


----------



## HCBPH

*Throttle Control*

Based on the video, I'm less inclined to believe it's in the carb. I'm betting it's either in the throttle/linkage or governor itself.
This photo is a 10 HP with a different carb though. First thing I'd do is pull the heat shield over the carb. As you look at the carb, the governor is on the left side of the carb with linkage that connects to the throttle and carb.
Start the engine and with the throttle open around 1/4 - 1/2, move the governor to the right (towards the rear of the blower where the rope starter is). If the rpm changes as it should between full vs partial speed, then I suspect my diagnosis is correct.

If my suspicion is right, start with the linkage then the spring on the throttle and insure they're correct. If those look right, insure the engine is off and see how the governor moves by hand and it's not stuck.

Let us know.


----------



## CarlB

HCBPH said:


> Based on the video, I'm less inclined to believe it's in the carb. I'm betting it's either in the throttle/linkage or governor itself.
> This photo is a 10 HP with a different carb though. First thing I'd do is pull the heat shield over the carb. As you look at the carb, the governor is on the left side of the carb with linkage that connects to the throttle and carb.
> Start the engine and with the throttle open around 1/4 - 1/2, move the governor to the right (towards the rear of the blower where the rope starter is). If the rpm changes as it should between full vs partial speed, then I suspect my diagnosis is correct.
> 
> If my suspicion is right, start with the linkage then the spring on the throttle and insure they're correct. If those look right, insure the engine is off and see how the governor moves by hand and it's not stuck.
> 
> Let us know.


+1 on what hcbph said


----------



## td5771

have a blower now that does that. I believe I narrowed it down to the spring between the governor and the throttle. Its obvious on mine that at some point the end of the spring broke off and it stopped functioning. no low or middle, off or the tension is so much it pulls wide open. havent gotten to change it yet.but everything else seems right.


----------



## jfmtnbiker

I understand your description now when you say full throttle or nothing. I was thinking as though it struggled to run in the lower throttle position. The video definitely clarifies things. I am inclined to believe it is the throttle spring or the throttle adjustment. If it ran fine before and all of a sudden isn't running right, whatever you do...do not adjust the actual governor. Replace the springs first and the adjust the governor. Typically I find that the actual governor is not in need of adjustment.


----------



## Shryp

My guess is the throttle linkage or butterfly is stuck open. Take the heater box cover off the carb and check for binding.


----------



## BrokeBlower

Thanks for the responses.

I completely tore the carb down, pulled the butterfly valve out cleaned it with 000 steel wool, and really cleaned the carb and I got everything running/working properly.

One last question. For the Bowl nut, since I have a non adjustable one, do you just tighten it to a positive stop, or just make it snug?


----------



## jfmtnbiker

The bowl nut must be tightened very snugly in order for the bowl to properly seal. Every so often, I see a bowl or two where someone does not tighten the bowl nut enough and additional air gets sucked into the carb. It is almost impossible to strip out the bowl nut unless you go crazy with force when tightening it.


----------



## Shryp

Just snug it up.


----------



## CarlB

I only snug the bowl nut. Over tightening the bowl may distort the bowl and cause a leak. these bowls are O-ringed and need not be overly tight. I tighten finger tight then another 1/4 turn.

Carl


----------

