Abby’s Guide > Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) > Discussions > Stalling under load; Tecumseh HSK70 7 Hp

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grump

Joined: Jan 14, 2008
Points: 58

Stalling under load; Tecumseh HSK70 7 Hp
Original Message Dec 20, 2008 10:13 am

Have an HSK70 7 hp engine that's been used about four years which is mounted on an everlasting and loved old Ariens chassis from 1971.

Ran great until first use this season. I'll preface this by stating that last spring I shut off the fuel line and drained the carb. It's the first year I've done so little for seasonal storage. There was about 1/4 tank of fuel. The snow blower has seen light use with only one curb cut and 20' of driveway. My estimation is maybe 16 hours of use.

This year I filled the tank, it started right up and made it about 100' from the shed to the driveway. There's where the problem began.

It stalled under load. Ran fine at idle but as soon as I engaged the drive belt and demanded something from it; stall. Setting the choke to 1/4 (the first notch) seemed to help, but the problem persisted. I tried tweaking the needle adjustment on the carb. It started at 1 5/8 turn from a gentle bottom, and seemed to run best at that position. I tried tweaking it both with the drive belt engaged and disengaged.

It idles fine but just plain stalls under a load.

What should I do?

This message was modified Dec 20, 2008 by grump

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mkd55

Location: wisconsin
Joined: Dec 16, 2005
Points: 155

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #1 Dec 20, 2008 10:56 am

does it run at full throttle at all? if it idles fine and runs to full throttle and stalls it sounds like a full throttle fuel problem.could be needle bound or stuck partiallly closed,needle could be not properly seated on float arm,dirt or blocked high speed jet. if the engine runs at full speed you should be able to richen the mixture and notice a drop in rpm's or it will shut down. i would take the high speed jet out or better yet take the bowl off and remove the brass tube the high speed jet screws into. get a magnifying glass and look for the small orifices in this tube.they could be blocked causing your high speed shutdown. the holes are very small and hard to see but they are there.use a very small strand of copper wire to clean them out and shine light thru the holes to see they are open.by draining the tank crude in the bottom could of found it's way into the passages and these holes. here is the link for the below information .Basic Carburetor Pictures

Briggs & Stratton Carburetor Picture Breakdown ... Tecumseh Carburetor Picture Breakdown · String Trimmer Carburetor Hose Hook-up ...
www.la

Tecumseh Carburetor Picture Breakdown

This is a basic Tecumseh old-style float type carburetor.

This is a basic Tecumseh new-style float type carburetor.

When installing the rubber seat for some of these carburetors be sure it is like this.

From, http://www.repairfaq.org/sam/lmfaq.htm, the following info was used.

The small hole in the hollow bolt on the bottom is most critical. Make sure it is cleaned down to the shiny brass and that this hole is unblocked and fully open:

I first use carburetor cleaner inside and out with cotton swabs to remove all traces of gunk from the inside. Use as many as needed till no more discoloration shows up. Then, use the broken end of a wooden toothpick or pop sickle stick to clear the .5 mm diameter hole in the side. In severe cases, this hole may not even be immediately visible due to the varnish and gunk buildup.

If this hole is narrowed or clogged, the engine may start but then die in a few seconds. Gas enters the reservoir in the nut slowly or is forced in by priming but the normal suction cannot replenish it quickly enough.

This was submitted by one of my readers:

The small hole in the hollow bolt on the bottom is most critical. There is one hole that passes through the bolt from side to side and one hole that extends up the center of the bolt from this hole and into the bottom of the well of the bolt.

From the Lawn Mower Repair Man's site: "Another tip that is just for Tecumseh is how the needle is hung from the float. The picture I took for this didn't come out clear and when I get one it will be added here as well. The wire clip that connects the float needle to the float is what is of concern here. The open end of the wire that hangs from the float must aim towards the air intake or air filter side of the carb. If it's pointing toward the engine side, the needle won't center correctly and may leak. This makes absolutely no sense to me but it's an advisory from Tecumseh I picked up on years ago. Once I started following their advise, the vast majority of un-explained flooding carbs (after being rebuilt) mysteriously ended. So although the reason isn't readily apparent, it does work.

This message was modified Dec 20, 2008 by mkd55

grump

Joined: Jan 14, 2008
Points: 58

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #2 Dec 20, 2008 6:08 pm

Just to clarify, it runs great at slow and fast speed if there's no load on the engine. I can engage the drive belt and it'll be OK, It's when there's a demand on the engine from snow that it just hopelessly studders to a stop. Does that classify as a high speed shutdown.

I'll try taking apart the carb and checking the small orifices. The link above the illustration you posted leads to a great site with detailed information.

Is there anything else I can check for?

Haven't seen anything about a fuel filter. Is there a hidden one on this engine and, if so, could it be the underlying problem?

friiy

Location: Las Vegas, The Desert
Joined: Apr 12, 2008
Points: 600

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #3 Dec 20, 2008 7:17 pm

More than likely there is no fuel filter, Still sounds like you have a jet plugged. The amount of fuel required to run the engine at full speed no-load and full speed under-load is quite diffrent. your throttle shaft on the carb should hardly move from low-speed-no-load to high-speed-no-load... Only when when the engine is under load trying to maintain high rpm under load will the throttle open fully... When the throttle opens fully (under load) the carb pulls from a main nozzel of the carb... I bet Number 18 and four of the pictures is what is some what clogged..

Good Luck

Friiy

mkd55

Location: wisconsin
Joined: Dec 16, 2005
Points: 155

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #4 Dec 20, 2008 7:32 pm

grump! you say the high speed is set at 1 5/8" and it runs best at that setting.before you tear into the carb adjust the high speed 1/8 turn or so richer and see if it still stalls.it is possable for the mixture to be somewhat ok at no load and have the machine be too lean under loaded conditions. if the high speed jet is sensitive to adjustment you should be able to richen the mixture till the rpm's start to drop. at that setting lean it in just enough to bring the rpm's back up and try it under load. i rebult my carb and used the initial settings and the slow speed was pretty close but the high speed at 1 1/2 was too lean.didn't find it out till i started the machine when cold and had to keep the choke partially on for longer than what i was used to. if you have someplace warm to tear into it it's not too bad to take apart. if you do take the carb off make sure the intake manifold is sealed and tight to the head. an air leak would also cause a lean condition. take note to the way the needle pin is installed hanging from the float arm! the round end goes towards the motor and the point goes toward the open air entrance of the carb.

This message was modified Dec 20, 2008 by mkd55

grump

Joined: Jan 14, 2008
Points: 58

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #5 Dec 21, 2008 11:44 am

Success!!

Took off the carb bowl and found some specks of black crud that looked like fuel line material. Quantity wise maybe two shakes of a typical salt shaker.

Inspected the bolt with the two holes. The larger was visibly open, the smaller looked OK but I ran a single strand of wire from an electrical cord through it and wanting to be compulsive about it used a neighbors compressor to blow it out. I think it was OK to start with but that small hole; well I guess anything can impair it.

Ran a few ounces of fuel through the carb into a jar while it was open and it came out clean. Polished the needle just a tad with an SOS pad, probably not the right thing to do but I rinsed and dryed it well.

Hardest part was getting the float needle part back on with the open end of the spring facing the air intake. It didn't want to stay under the lip on the float (which inspected AOK) but eventually went into place. Am sure with practice it'd be easy.

While I had tools out I cleaned the spark plug and closed the gap a bit to .030

Ran it through the hardest packed curb mound I could find and it didn't hesitate a bit. Let is run awhile (admittedly admiring how well it's doing) and ran it through some more packed curb snow. Just like new. Will check it in awhile for any leaks I might have missed.

Am going to change the fuel line, check that the tank is spotless, and have a carb gasket onhand just in case this happens again.

Is it advisable to add a fuel filter to this, or would that impede something?

Thank you many times.

ExCompost

Joined: Jan 1, 2009
Points: 2

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #6 Jan 1, 2009 11:20 am

Thanks Grump, Frily and everyone else for this thread. My 20+ yr. old Ariens w/ a 7 hp Tecumseh and bowl carb had the same problem of faltering and stalling under load. It took a rebuild kit and cleaning of the idle and main jets w/ copper wire to solve the problem, and a cutting and tightening of the governor spring to the throttle plate seemed to help.

One of you mentioned removing the main fuel jet and inspecting it. Do you mean the passage that runs up the center of the carb body and protrudes into the throat between the choke and throttle plates? Can that te removed? If so, please let me know how to do it for future reference.

Do you guys think that 87 octane works ok w/ these older engines, or is mid-grade or premium recommended? Thanks a lot and Happy 2009.

MacLorry27

Joined: Dec 23, 2008
Points: 54

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #7 Jan 1, 2009 11:59 am

ExCompost,

87 octane works well in all these small engines, however, you want to avoid gas that has alcohol in it, as it does in many states. Newer engines can handle it, but alcohol attacks rubber and plastic parts that have not been formulated to withstand it. Where I live I buy premium alcohol free gas for all my power equipment even though the 91 octane is not needed. It’s only sold at a few gas stations as it’s not legal to put it in cars (other than classics).

Mac

mkd55

Location: wisconsin
Joined: Dec 16, 2005
Points: 155

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #8 Jan 1, 2009 5:28 pm

excompost!! if your carb is like the illustration in the post above it has the main jet screwed into the bottom of the brass high speed bowl nut that holds the float bowl on. to remove the nut just turn it out counterclockwise with the appropriate wrench. once out you can inspect and clean the two holes. make sure you don't bend the float tang.the bowl gasket is in place, and the needle is hanging off the float tang where it should be, and the indent or sloped side of the bowl position is noted and positioned in the same place when you put the bowl back on. i believe there is a little dent in the bottom of the bowl facing up and that needs to be under the float so the float can't stick to the borttom of the bowl if it runs dry and is left like that. the float then rests on the dented bump rather than the full length of the bowl.

This message was modified Jan 1, 2009 by mkd55

ExCompost

Joined: Jan 1, 2009
Points: 2

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #9 Jan 2, 2009 10:47 am

Hi mkd,

Thanks for the advice on positioning the bowl, as I wasn't sure where in relation to the float to put the deep or dented end.

In my earlier question, I was referring to part 11 on the diagram, the fuel well spacer, which appears to be permanently installed in the carb body. The jet screw and the bowl nut are no problem to remove and clean. What's your take on using reformulated regular (10% ethanol) or higher octane gasoline, such as we use here in NH?

mkd55

Location: wisconsin
Joined: Dec 16, 2005
Points: 155

Re: Stalling under load; Tecumseh HSK70 7 Hp
Reply #10 Jan 2, 2009 7:18 pm

i have been running no more than 10% blend for a few years now in my 1986 tecumseh ariens 824 8hp, so far no ill affects. the spacer has a larger orafice than the brass jet nut so if anything is going to clog it's the holes in the nut. i found out the hard way about clogged jets on a new 40hp evinrude two stroke outboard. the bottom carb high speed jet had a piece of gasket clogging it that worked loose when it was assebled when new. i ran it on one cylinder back to the landing probably five minutes max. it's a 1987 motor bought new and in 2001 i had to have the cylinder head rebuilt with the bottom cylinder bored and a new piston and rings. i t took me a while of thinking why the cyclinder went bad and i figured a did some damage when the jet was plugged. if you have no gas you have no lubrication for the cylinder either. the boat gets used in canada once a year and thats it and i'm still going every year and have had no problems since. nock on wood!

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