Intermittent problem - engine starts missing and cutting out, almost dies.

[Marty Singletary]

Since the motor runs fine for an hour, Bertmobile 1 answer makes the most sense to me. Rust in tank gathers to plug fuel exit. I have a tractor that does this. I would blow an low pressure air line back from the fuel filter into the tank to push the sediment away from the tank outlet.

There is no sediment. There is nothing in the old or the new fuel filter. The gas tank is also made of plastic. No rust. No anything else. The fuel filter is new and clear plastic, gas is passing clear and clean.

 

[bertsmobile1]

There is no sediment. There is nothing in the old or the new fuel filter. The gas tank is also made of plastic. No rust. No anything else. The fuel filter is new and clear plastic, gas is passing clear and clean.

Just so you have this clear in your head, and it might not be a contributing factor.
Grass clippings end up in the fuel tanks of most mowers along with all sorts of other strange things.
The fuel displaces the water in the clippings so they sort of float in the fuel , not on top of it, much like alge scum in a bottle of water.
When fuel is being drawn out of the tank they get dragged to the outlet by the current in the tank where they can form a plug.
Come tanks are known for having a casting fin which partially blocks the outlet & snags all of the floaties passing by it, Cubs are notorious for it.
This can take anywhere from 15 minutes to several hours.
Because they do not pass through the tank outlet, they do not end up in the filter.
When the engine stops, there is no flow so they float off and disperse sort of evenly in the tank again.
So after a 1/2 hour or so enough of them have dispersed to allow full fuel flow & the mower starts right up & runs like a pearler.

Two tests for this
1) the instant the mower cuts out whip off the fuel line from the tank, before the filter or pump and blow back through it as the previous poster mentioned with his rust clogging tank.
IF the mower starts back up right away in place of waiting the 1/2 hour or whatever is the normal recovery time then a plug becomes prime suspect
2) use a auxiliary fuel tank either for the whole mow or plug it in the instant the engine stops.

Remember you are there describing what is happening in words.
We have nothing to go on but those words
People use different words to mean the same thing and the same words to mean different things , they often overlook things that tech would pick up on if we were there looking at your mower & drinking your beer.
Every tech can tell the difference between an electrical stall & a fuel stall by the actual sounds the mower makes and the sequence of those sounds.

Like a lot of things, mower repair is the art of eliminating what the problem is not rather than waving a magic wand and pronouncing what the problem is.
There are very few instances where a single set of symptoms define a specific problem and in many cases the actual problem can & does have several problems at its root cause.

Now you have a problem that you have not encountered before so you don't understand what is happening.
We are all trying to assist you and any one else who chances upon this thread with a similar set of symptoms.

You might also like to take note that no one has fobbed you off with a "change this part " as if we are the Gods of small engine repairs.
We have simply asked you to do some investigating and get back to us with the results.

If we were there we would have recognised that the valve lashes were way out of spec by the way the engine starts and the sounds it makes running.

You may or may not have a plug but we do not know that until it has been checked.
If your problem was nothing more than the valve lash they lucky you just try to remember to check them every couple of seasons.

 

[Marty Singletary]

Just so you have this clear in your head, and it might not be a contributing factor.
Grass clippings end up in the fuel tanks of most mowers along with all sorts of other strange things.
The fuel displaces the water in the clippings so they sort of float in the fuel , not on top of it, much like alge scum in a bottle of water.
When fuel is being drawn out of the tank they get dragged to the outlet by the current in the tank where they can form a plug.
Come tanks are known for having a casting fin which partially blocks the outlet & snags all of the floaties passing by it, Cubs are notorious for it.
This can take anywhere from 15 minutes to several hours.
Because they do not pass through the tank outlet, they do not end up in the filter.
When the engine stops, there is no flow so they float off and disperse sort of evenly in the tank again.
So after a 1/2 hour or so enough of them have dispersed to allow full fuel flow & the mower starts right up & runs like a pearler.

Two tests for this
1) the instant the mower cuts out whip off the fuel line from the tank, before the filter or pump and blow back through it as the previous poster mentioned with his rust clogging tank.
IF the mower starts back up right away in place of waiting the 1/2 hour or whatever is the normal recovery time then a plug becomes prime suspect
2) use a auxiliary fuel tank either for the whole mow or plug it in the instant the engine stops.

Remember you are there describing what is happening in words.
We have nothing to go on but those words
People use different words to mean the same thing and the same words to mean different things , they often overlook things that tech would pick up on if we were there looking at your mower & drinking your beer.
Every tech can tell the difference between an electrical stall & a fuel stall by the actual sounds the mower makes and the sequence of those sounds.

Like a lot of things, mower repair is the art of eliminating what the problem is not rather than waving a magic wand and pronouncing what the problem is.
There are very few instances where a single set of symptoms define a specific problem and in many cases the actual problem can & does have several problems at its root cause.

Now you have a problem that you have not encountered before so you don't understand what is happening.
We are all trying to assist you and any one else who chances upon this thread with a similar set of symptoms.

You might also like to take note that no one has fobbed you off with a "change this part " as if we are the Gods of small engine repairs.
We have simply asked you to do some investigating and get back to us with the results.

If we were there we would have recognised that the valve lashes were way out of spec by the way the engine starts and the sounds it makes running.

You may or may not have a plug but we do not know that until it has been checked.
If your problem was nothing more than the valve lash they lucky you just try to remember to check them every couple of seasons.

Did not wish to insult of say you are wrong, just do not see and evidence of sediment or debris and fuel filter. If after my next run (mow) if I still have the problem with the now rest valves. The certainly this sounds like the next step to solve my mystery. Sounds like ultimately if this were the case I would then have to look at a way to clean out the fuel tank.
Thanks for your comments, Marty

 

[bertsmobile1]

You would have to work very hard to insult me.

If you are lucky the valve adjustment will get you out of trouble

If not check the tank

To clean it out drain the tank, remove the filler cap them blow compressed air back up the fuel line.
Once the tank is dry the escaping air will take the light stuff with it.

After that things start to get expensive.

 

[Marty Singletary]

You would have to work very hard to insult me.

If you are lucky the valve adjustment will get you out of trouble

If not check the tank

To clean it out drain the tank, remove the filler cap them blow compressed air back up the fuel line.
Once the tank is dry the escaping air will take the light stuff with it.

After that things start to get expensive.

Thanks again sound like a plan.
Marty

 

[Marty Singletary]

Thanks again sound like a plan.
Marty

I am glad I reset the valve to the values to what they should be at but that did not turn out to be the ultimate problem. I admit I was a skeptic since the Cat is 13 years old and I have always used a funnel with a screen to put gas in the tank. But you were the man with the correct answer. I guess I was being lazy since I had to get the mower up on blocks to get to the fuel line under the mower. With that said a partial fuel line block is what the problem was. Although it took 13 years the block was created by plastic shavings that must have been in the tank since the day it was built. Looked like the same black plastic as the tank, that must have been created when they drilled the hole for the gas outlet fitting. Any way was only getting a dribble when emptying tank until I blew backward and instantly got a pop as the plug blew back into the tank and then as you know now I got a good flow. Tank drained to the bottom of outlet port, then I made a mop from paper towel and an aluminum stick and started to mop the remainder of gas from the tank. The paper towel not only picked up the remaining gas but also all the plastic shavings stuck to the mop and was able to get the tank cleaned.
Thanks again for your experienced input, it solved my problem.

 

[bertsmobile1]

Thanks for getting back.
It is always good when not only some one fixes their mower but also comes back on to tell everyone what worked.

So now with a clean tank & correctly set valves you are good for another long run.
Listen to the sound that the engine makes when it is cranking, when that starts to become lumpy, time to do the valves again.

As for your tank. I find it easier to use compressed air from a vary long air duster.
Got a couple with hooked ends to get into the corners but id does require a lot of air to push the gunk out.
You wouldbe amazed at what comes out of some tanks,,, I am.

 

[Marty Singletary]

Thanks for getting back.
It is always good when not only some one fixes their mower but also comes back on to tell everyone what worked.

So now with a clean tank & correctly set valves you are good for another long run.
Listen to the sound that the engine makes when it is cranking, when that starts to become lumpy, time to do the valves again.

As for your tank. I find it easier to use compressed air from a vary long air duster.
Got a couple with hooked ends to get into the corners but id does require a lot of air to push the gunk out.
You wouldbe amazed at what comes out of some tanks,,, I am.

Yes i did use compressed air also. I can tell when I start the engine that it was requiring that I choke it and keep the choke on until it really was getting gas to keep running with out the choke on. Now It starts with out the choke, and gets up to rpm fast and clean.
Again you all are great. Thanks again.