OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Tecumseh / Kirby Engines Tecumseh HM80 8HP

What is the push mower???


Perhaps the volume of the little filter cannister has something to do with it. Im thinking a vacuum lock.
It could be the head pressure. How high above the carb is the tank on the HM80?? As opposed to the mower??

You could maybe try a slight enlarging of the breather holes in the fuel cap.
On a different cap is probably a good idea.
Or rather than removing the filter/hose, plow some pressure in the tank before trying to restart.

Is the motor running lean?? Perhaps the fuel delivery when running is not good enough to keep the float level right.



Im sure its got a filter in the tank, perhaps filter the fuel before or when you are filling the tank.

Hi Bob the push mower is a Quantum 55 motor. I reckon you are on the money with the fuel cap call.

For the record the tank carb height difference is greater on the ride on and chipper than the push mower.

I have switched to the red Briggs filter and they have run perfectly so I'll stick with them. The problematic filters did seem to collect a lot of fine particles that the others let through.

Theoretically the filter only has to filter out anything that would not fit though the smallest passage in the carb.


As a precaution as the fuel should be clean.

Bob, it doesn't really work that way with fines in the fuel. There is usually a small amount of gum some of the time, and the gum glues the fines together. This all happens in a small passage of course, especially right upstream of a seldom-adjusted mixture needle, where a sudden drop in flow rate causes particles to get deposited (like on the inside of bends in a meandering river). Once a few grains of fines stick together, they make a base for a blockage that just grows like a vegetable from a seed. That is why carb cleaner has such a profound effect: once you take the gum out, you just have loose grains that will fit through the passage under air pressure.

The Briggs red filter is intended for gravity-fed fuel systems, and the black one for systems with a fuel pump. You shouldn't expect to be able to use a black filter in a gravity system: there is just too much restriction.

Hi folks, just a question on whether or not I am following a correct fault diagnosis path.

The HM80 has not been run in over a year. Last time I used it it ran fine for around 20 minutes then cut out and would not restart. A day later I checked purely to see if it would fire and it did on first pull so I turned it off drained the fuel and put it away.

Today I had a lot of stuff to put through the machine. I put in some fresh fuel and it fire and ran from the third pull.

After about 20 minutes of running fine it stopped as if running out of fuel. After 20 or so pulls I gave up and decided to check a few things.

Fuel in the tank
Carb was getting fuel
There was spark
Plug burn looked perfect
Fuel was purchased less than 3 days ago
Magneto air gap was fine
Compression felt strong

I decided to check the valve clearances. They were minimal at best, about .005 thou. By specs exh is .020 and inlet is .010

I pulled the valves and adjusted them accordingly.

Could the valves being tight have caused the problems I experienced? I have yet to start and run the machine as I had to make a gasket up for the valve cover.

The valves looked good as did the seats and were tight in their guides. The bore looked excellent.

Hopefully I will get to run the machine by the weekend.

There isn't much to go on in that description, Aldo. I'd begin with three possibilities that are easy to deal with.

First, tappet clearance just about always decreases when the engine warms up, due to metal expansion at high temperatures. That is the main reason to have tappet clearance in the first place. Since the engine stopped when it got warmed up, there is a fair chance it was holding the valves slightly open, at those highly inadequate clearances.

Second, have you removed the cowls and checked that the air intake passages and cooling fins are clear, and the flywheel has all its fins? Poor cooling air circulation is prone to causing the fuel to boil in the carburetor, whereupon the fire goes out in the engine due to lean mixture.

Third, have you checked the rate of flow of fuel into the carburetor? You can get upstream problems that cause the fuel flow to stop after a while - in particular, blocked vent in the fuel tank cap, or a floating mass of grunge in the tank or outlet pipe that moves down the pipe when fuel flows, but goes back up when the engine is stopped. By checking that fuel flows full stream out of the needle-and-seat when you remove the float bowl, and keeps on flowing while you empty the tank through the needle-and-seat, you can check for that problem.

There are other things it could be, in particular high temperature breakdown of the ignition system, but there we get into stuff that is more difficult to test for, and way more expensive to fix. Would you mind checking those three things, making another test on the engine's behaviour after a long run under load, and reporting back please?

Thanks Grumpy I will look at those. I did try the fuel cap but no change.

I had a play and I think, as you say Grumpy, there was a fuel restriction blokage of some sort. I have a fuel tap and inline filter and removed the filter and it ran just fine. Started and then retarted it many times with no issues.

Its a gravity feed and when I pulled the hose from the carb inlet fuel would only very very slowly dribble out. I used a second piece of hose with no tap or filter and the fuel poured from the hose at any level below the tank level. Very strange. All these tests were done with no fuel cap.

We have had a couple of floating-mass fuel hose blockages just like that reported here in the past couple of months, aldot. I think it begins with water in the fuel tank, which grows something like algae. The algae dies when the water is drained and the tank is filled with petrol, but it continues to drift around in the tank. Eventually, when the machine is run out of fuel, it finds its way through the outlet fitting into the hose, and then it causes problems - it doesn't float back into the tank, but stays in the hose.

IIRC, we had one that lodged in the fuel tap and another one that plugged up the in-line filter. Both were delayed-action problems: the machine would run normally for a time, then stop mysteriously, but would start and run again after the floating mass had floated back up the fuel line.