Out of control Tecumseh

[INTJ]

Maybe someone knows something about a very unstable engine run.

I have a 9HP Ariens sno blower, and the motor races up and down in a continuous cycle. It races up and it races down, ad infinitum.

When under a snow throw load, it normalizes, but once you are in a no load situation, it races, such as in a turn or at idle.

It does this with the tines engaged or off.

One clue is if you apply the choke at halfway, this cuts the extreme RPM range in about half.

Vacuum leak?

 

[JimPghPA]

What brand engine is on it. Model number would also be of help.

 

[cancov]

I have a Briggs that does something very similar on a garden tiller. However, it DOES NOT do it when the fuel tank is at maximum. These symptoms, again, only occur when the fuel drops below 2/3 - 1/2 the capacity of the fuel tank.

 

[Nick R]

Originally Posted By: INTJ

Maybe someone knows something about a very unstable engine run.

I have a 9HP Ariens sno blower, and the motor races up and down in a continuous cycle. It races up and it races down, ad infinitum.

When under a snow throw load, it normalizes, but once you are in a no load situation, it races, such as in a turn or at idle.

It does this with the tines engaged or off.

One clue is if you apply the choke at halfway, this cuts the extreme RPM range in about half.

Vacuum leak?


Probably a plugged jet, if it's a tecumseh. Rebuild the carb, and do use new manifold gaskets.

 

[johnachak]

My MTD single stage does the same thing. It gets better when warmed up and under partial (Maybe 25%) choke. Under load it is fine. After working a while, it stops surging completely unless I completely open the choke. Then it surges ever so slightly.

 

[charleshickman]

I wondering if there is a governor, maybe centrifugal? How old is the engine?

Disclaimer: I know nothing about this subject matter so please no LOLs. It just sounds like maybe the engine races the governor cuts what ever it cuts, probably fuel and then when it slows the governor opens the throttle again.

 

[INTJ]

Tecumseh 9hp. LH318SA is engine #.

Thanks

 

[INTJ]

It's 2007-2008? Maybe 16 hours on the clock.

 

[TylerL]

I was thinking air leak/vac leak too.

 

[oggb]

Did one of the governor springs come off? Seen this happen with many a lawn mower.

 

[INTJ]

I'll have a look tomorrow.

I don't know the schematic of it either, as what I'm supposed to be looking for.

My 6.0 HP Craftsman/ Tecumseh mower had a sliver of silicon stuck in the needle jet/ seat area, and this flooded the motor.. easy fix because gas flowed out of intake and an easy hallmark symptom for float/needle seat..

I recall the governor springs to be a pain to set back up in the right position. I had to get a web page picture to get it right.

 

[INTJ]

If it's a partially plugged jet, then I'd guess the 'half choke' would compensate for the lack in fuel, by "choking" the air supply.

 

[tomcat27]

It's running lean. certainly could be a carb gasket leak but most like a dirty jet (as others have stated). could also be an incorrect float level

 

[The_Eric]

Has it always done this? The few Tecumseh engines that I've had have been pretty unstable until under load, then steady as a rock. Maybe it's just the nature of the beast?

 

[INTJ]

Not to this extreme Eric. I should youtube it, but I just changed the oil in it with Rotella synthetic, and I don't want to dilute the oil with fuel from the surge.

 

[punisher]

Governors do not cause idle speeds to fluctuate. Usually a broken governor will cause an engine to go WOT.

Listen to above and clean the carb jet(s) and ck for vac leaks.

 

[INTJ]

My Briggs pressure washer did the same thing. A rapid up/down surge.

My neighbor fixes small engines as side work, and he happened to be over at that time, and kindly showed me it to be the gasket under the carb. I noticed this gasket was orficed or holed with many holes, like a metering block on the Holley carburetors. This gasket had a fold in one corner that eventually tore, making a vacuum leak. It was an assembly defect.

 

[The_Eric]

I don't think you'll have to worry about fuel dilution. If it's running like this primarily at low throttle settings, then maybe there's a blockage in the low speed circuit, or maybe the low speed needle just needs a tweak. Also take a peak at the governer spring/linkage and throttle shaft.

Remember that the governer is trying to close the throttle and the spring/linkage from the throttle lever is trying to jack the throttle blade wide open. As engine speed increases, the force the governer exerts increases, balancing the force of the spring and consequently the engine speed. As the engine speed drops due to imposed load, the force exerted by the governer drops and is temporarily overpowered by the throttle spring, opening up the throttle blade in an attempt to bring the engine speed up. Once back up to speed, the governer is able to balance out the throttle spring and the engine rpm levels off.

 

[INTJ]

Oh, it wont run at anything below 80 percent throttle.

It will go lower, but under choke.

 

[The_Eric]

Gotcha. Sounds like it's time for a tear down and cleaning.