Engine Husqvarna MZ52 skips at times and other times OK

[bjones]

Guys I have a 4 yr old Husqvarna MZ52 25 HP koler engine. Started missing and i cleaned plugs and it ran Ok so I changed the plugs out and ran Ok for a couple hrs of cutting and started again so I replaced plugs again with different brand and all was well for about 6 hr of cutting. Cleaned air filter and gas filter and always use no ethenol gas. Started skipping again and I could pull out choke and it would smooth out for a bit and then start again and I could reduce throttle and it would smooth out. I have ran sea foam in the gas as well. Any idea what it could be.

 

[bertsmobile1]

Yes,
The engine is not getting enough fuel.
If you reduce the volume of air & it runs fine but will not run without the choke at full speed then something is restricting the fuel supply.
Start by loosening the fuel cap.
If that does not work then time to clean out the carb, check the float & float needle.

 

[bjones]

Yes,
The engine is not getting enough fuel.
If you reduce the volume of air & it runs fine but will not run without the choke at full speed then something is restricting the fuel supply.
Start by loosening the fuel cap.
If that does not work then time to clean out the carb, check the float & float needle.

Thanks I will try the cap. Weird, after plug change it ran fine for 6 hrs and then started this skipping again but smoothed out after choke and reducing throttle. I too think it is gas related. Seems to do it when under heavy load when blades are engaged and in heavy grass or going up an incline. I had a rat eat a hole in the fuel pump vacuum hose a few yrs ago and replaced it and I wondered if it may not be getting enough vacuum to supply pump enough to pump properly. Wild guess. Thanks again

 

[bertsmobile1]

When the engine is under load it slows down so the governor allows the throttle to open wider.
A wider throttle of course needs more fuel.

 

[bjones]

When the engine is under load it slows down so the governor allows the throttle to open wider.
A wider throttle of course needs more fuel.

So I loosened the cap a little. My tank has the gas cap and two other components with hoses running to them. One is some type of check valve or PVC type valve, I pulled it out of top of tank, it just presses in and shook it and could hear it rattle, replaced it. Don't know what the other one is unless it some type fuel return line. Ran it under load for maybe 10 minutes and smooth as ever. This is nothing new, it may run for several grass cuttings (4-6) hrs and then act up again. Baffling. We will see, thanks for your reply.

 

[bertsmobile1]

EPA regulations requiring zero fuel fume emissions so the tank has an external vent with a charcoal canister on it plus a pressure relief that goes into the engine.
Basically the same set up as found on cars from the mid 70's on

 

[bjones]

EPA regulations requiring zero fuel fume emissions so the tank has an external vent with a charcoal canister on it plus a pressure relief that goes into the engine.
Basically the same set up as found on cars from the mid 70's on

I ran mower yesterday for about 30 minutes and it acted up 3-4 times. Pulled choke out for a couple seconds and back in and it cleared up for a bit and reduced throttle and it cleared up for a bit. I put in two new plugs and a new fuel filter and ran it wide open for about 1 hr in above average height grass and didn't miss a lick. Very odd. Talked to a guy at a high end lawn mower shop and he said they had seen problems with Kohler engines, said there was a electrical component box on side of engine that controlled timing and cylinder fire and I think he said it may take the place of the coil or coils and the fix was to remove it and install a regular coil or coils. Not sure if I have this correct or not but something to that affect. Every heard of this type setup. In hindsight I should have replaced the fuel filter and ran the mower before changing out plugs so I could eliminate one or the other.
Thanks for your response, evidently this is not a very active forum since you are the only guy to respond.

 

[bertsmobile1]

I ran mower yesterday for about 30 minutes and it acted up 3-4 times. Pulled choke out for a couple seconds and back in and it cleared up for a bit and reduced throttle and it cleared up for a bit. I put in two new plugs and a new fuel filter and ran it wide open for about 1 hr in above average height grass and didn't miss a lick. Very odd. Talked to a guy at a high end lawn mower shop and he said they had seen problems with Kohler engines, said there was a electrical component box on side of engine that controlled timing and cylinder fire and I think he said it may take the place of the coil or coils and the fix was to remove it and install a regular coil or coils. Not sure if I have this correct or not but something to that affect. Every heard of this type setup. In hindsight I should have replaced the fuel filter and ran the mower before changing out plugs so I could eliminate one or the other.
Thanks for your response, evidently this is not a very active forum since you are the only guy to respond.

The full time techs on this site have a bit of a protocol where we do not chime in on a thread that another one is working on.
Problem is while we all do the same things each one does it differently so it gets confusing for everyone.
The non-tech will often pop up with an "That happened to me & this fixed it " which is good & always welcome.

Now for starters, you have not told any one which engine you have.
Hp numbers mean absolutely nothing as several different engines can have the same Hp and the same engine can have 5 different Hp ratings.
Next you have a problem that responds to throttle and more important responds to choke.
These are both FUEL controls so if varying FUEL controls changes the symptoms there is 99% chance the problem is fuel related.

In my workshop I have an old Tecumseh tank which holds about 2 hours worth of fuel so I hook it up then go mow.
That allows me to separate problems between supply ( everything up to the carb ) and delivery ( the carb & valves ).
Further to this I pop in line spark testers on all plugs so I can confirm the spark is not breaking down.

Now ZTR engines run in very dusty conditions & for fuel to get out of the tank air has to get in and that air is full of dust.
Add some grass clippings, a little water and you have the ingredients for a plug forming in the fuel tank or delivery lines.
Because grass clippings float, when you stop the engine, the plugs break up and float away till the mower starts to run again and like hair on the bottom of the shower, they accumulate and form a plug again.

later models may have vent tubes that can block up.

A partially blocked float valve will cause the same symptoms.

Then we go to electrics.
There is a diode between the two coils to prevent them interfearing with each other and the coils themselves have a chip in them that replaced the points and they can break down with heat.
However if you have an electrical problem that should not change with the choke but may respond to throttle being reduced if they can not keep up 7000 discharges per second.

The last thing that changes with tie & heat is the oil switch, if your engine has one fitted.
Most Kohlers do not have them but a few do.
As for the timing module I have not seen one fitted for a very long time.
If you have one there will be 2 or 3 thin wires coming out of the coils.

Modern plugs are not very good.
At $ 7.00 ( aus) that ends up being about $ 1,00 / plug to the factory so not much quality control other than grading so the one sin single named boxes are better than the ones in blister packs.
Modern fuel is conductive so can turn a plug bad in no time flat which is why most engine makers recommend plug changes at very short intervals,
Toro Loncin engines call for new plugs at 100 hours, a plug should go for 1000 hours without problems.

When the problem is bad enough to stop an engine it is easy to eliminate electrics by using carb cleaner down the carb to see if it will fire right up again, but yours is just missing a bit.

Now if you only have a single kill wire on the coils then you can remove them and go mow.
If the problem goes away then it is 100 % electrical.
No change = fuel problem.

Doing this means that the mower is in a dangerous condition and you are relying on the fuel solenoid to shut down the engine.
So it is prudent to run a back up kill wire to the cab so you can shut the engine down bu manually grounding the coils.
If you have 2 coils you need two wires that are kept apart to prevent one coil back feeding into the other.
Note than blower housing must be refitted during this test.

 

[bjones]

The full time techs on this site have a bit of a protocol where we do not chime in on a thread that another one is working on.
Problem is while we all do the same things each one does it differently so it gets confusing for everyone.
The non-tech will often pop up with an "That happened to me & this fixed it " which is good & always welcome.

Now for starters, you have not told any one which engine you have.
Hp numbers mean absolutely nothing as several different engines can have the same Hp and the same engine can have 5 different Hp ratings.
Next you have a problem that responds to throttle and more important responds to choke.
These are both FUEL controls so if varying FUEL controls changes the symptoms there is 99% chance the problem is fuel related.

In my workshop I have an old Tecumseh tank which holds about 2 hours worth of fuel so I hook it up then go mow.
That allows me to separate problems between supply ( everything up to the carb ) and delivery ( the carb & valves ).
Further to this I pop in line spark testers on all plugs so I can confirm the spark is not breaking down.

Now ZTR engines run in very dusty conditions & for fuel to get out of the tank air has to get in and that air is full of dust.
Add some grass clippings, a little water and you have the ingredients for a plug forming in the fuel tank or delivery lines.
Because grass clippings float, when you stop the engine, the plugs break up and float away till the mower starts to run again and like hair on the bottom of the shower, they accumulate and form a plug again.

later models may have vent tubes that can block up.

A partially blocked float valve will cause the same symptoms.

Then we go to electrics.
There is a diode between the two coils to prevent them interfearing with each other and the coils themselves have a chip in them that replaced the points and they can break down with heat.
However if you have an electrical problem that should not change with the choke but may respond to throttle being reduced if they can not keep up 7000 discharges per second.

The last thing that changes with tie & heat is the oil switch, if your engine has one fitted.
Most Kohlers do not have them but a few do.
As for the timing module I have not seen one fitted for a very long time.
If you have one there will be 2 or 3 thin wires coming out of the coils.

Modern plugs are not very good.
At $ 7.00 ( aus) that ends up being about $ 1,00 / plug to the factory so not much quality control other than grading so the one sin single named boxes are better than the ones in blister packs.
Modern fuel is conductive so can turn a plug bad in no time flat which is why most engine makers recommend plug changes at very short intervals,
Toro Loncin engines call for new plugs at 100 hours, a plug should go for 1000 hours without problems.

When the problem is bad enough to stop an engine it is easy to eliminate electrics by using carb cleaner down the carb to see if it will fire right up again, but yours is just missing a bit.

Now if you only have a single kill wire on the coils then you can remove them and go mow.
If the problem goes away then it is 100 % electrical.
No change = fuel problem.

Doing this means that the mower is in a dangerous condition and you are relying on the fuel solenoid to shut down the engine.
So it is prudent to run a back up kill wire to the cab so you can shut the engine down bu manually grounding the coils.
If you have 2 coils you need two wires that are kept apart to prevent one coil back feeding into the other.
Note than blower housing must be refitted during this test.

I did indicate the type motor in my mower, (Guys I have a 4 yr old Husqvarna MZ52 25 HP koler engine.) although I did misspell kohler, LOL. Boy that is a lot of info and very informative and thanks for responding. I am a member of several other forums and if you have an issue you get a lot of response from everyday users not just the admins or full time techs on the site. I thought there would be a lot of users or owners that may have a similar problem that would chime in with their experience. Obviously I do not understand how this forum works but that is OK. Back to my issue, since we or I think it is prob. fuel related, do you think changing the fuel filter was the key since I ran it for an hr wide open with no issue or was it the plugs or both. I know that is hard to determine. Thanks again for all your help, I will post my results of the fix or comment on progress as I get more run time.

 

[bertsmobile1]

The Kohler engine has a model number that I would use to check what actual Kohler engine is fitted.
Not being a Husqvarna dealer I can not check what engines were fitted to your mower.
There could be several different Kohlers that are rated at 25 Hp.
Some might have a low oil cut out, some don't.
Some might have a SAM ( Smart Advance Module ) most don't.
Some have EFI although we can rule that option out.:laughing:
The key is the model numbers from the engine.
And yes there are a lot of mower forums out there and each one has it's own style.
I am on 9 of them + 4 chain saw sites + 7 motorcycle sites.
However I only post on a few.
Some are a total waste of time with lots of people posting me toos , or offering loads of encouragement & blessings but little in the way of useful help.
There are even some where totally wrong information seems to be the norm.
Some seem to specailize in restoring old mowers .
This site is much like Fix it.
People post a problem and some one walks them through it then they tend to vanish till they come up on their next problem.
I came here to learn about what I did not know ( more that I thought ) and of all the sites , apart from single brand sites, this had the type of responses I was looking for.

You seem like a person who knew their way round a mower and from you original thoughs can sit back & make objective conclusions, which I agree with, there is a fuel problem.

One thing I forgot to mention, put some WD 40 or similar goop in a trigger pack and the next time the engine starts to play up spray it liberally around the manifold ( not easy on a V twin ) annd see what happens.
Clouds of white smoke = air leak around the manifold.
Some Kohlers have a plastic manifold which can warp a bit when hot.

As for the information.
I do not believe in keeping secrets.
Teaching a person how to fix their mower is much better than telling them which nut to turn.
So the more you know & understand the better equiped you will be to diagnose future problems.