Rough running petrol lawn mower help
Discussion
Folks, my old McCulloch m53-625 mower is not running right.
Fired it up for the first time this year over the weekend and when it finally started it ran rough.
It won't get up to full revs and when it runs the revs rise and fall and it then usually cuts out after a minute or two - but not always.
So far I have
Changed the fuel - no improvement
Cleaned up the air filter (even ran it without the air filter which made no difference)
Taken off the cab and cleaned it up as best I can - it looked fine before. No improvement
Taken out the spark plug and cleaned it - no improvement
I have taken it apart a few times and sometimes it runs a bit better than before, sometimes a but worse, but it never runs properly.
It is probably 15 years old and I have been keeping it going with various parts and fixes for a while now, but the engine has always generally run ok.
The rise and fall in revs suggest to some sort of fuel or air supply issue but the carb is very basic, as is my lawn mover engine knowledge!
I have not fully investigated the governor connection on the carb yet but it moves fine when I manually operate it. Actually I have not done this with the engine running which I should probably try.
Any ideas? Could it be the ignition coil? Would that result in a rhythmic rise and fall of revs?
Maybe I have buggered up the governor control on the carb somehow but it was acting up from the start.
Any suggestions welcome. It is not the end of the world if I have to get a new mower but I'd rather not spend £700 (I'd get a decent mower rather than a budget one) if I can fix the old thing with £50 worth of spares.
I can get a replacement carb kit for about £30 so that might be worth a punt.
If it is the engine side of the governor mechanism a big job to fix? I have not looked at the engine side of it yet, just the carb side.
Thanks in advance.
Fired it up for the first time this year over the weekend and when it finally started it ran rough.
It won't get up to full revs and when it runs the revs rise and fall and it then usually cuts out after a minute or two - but not always.
So far I have
Changed the fuel - no improvement
Cleaned up the air filter (even ran it without the air filter which made no difference)
Taken off the cab and cleaned it up as best I can - it looked fine before. No improvement
Taken out the spark plug and cleaned it - no improvement
I have taken it apart a few times and sometimes it runs a bit better than before, sometimes a but worse, but it never runs properly.
It is probably 15 years old and I have been keeping it going with various parts and fixes for a while now, but the engine has always generally run ok.
The rise and fall in revs suggest to some sort of fuel or air supply issue but the carb is very basic, as is my lawn mover engine knowledge!
I have not fully investigated the governor connection on the carb yet but it moves fine when I manually operate it. Actually I have not done this with the engine running which I should probably try.
Any ideas? Could it be the ignition coil? Would that result in a rhythmic rise and fall of revs?
Maybe I have buggered up the governor control on the carb somehow but it was acting up from the start.
Any suggestions welcome. It is not the end of the world if I have to get a new mower but I'd rather not spend £700 (I'd get a decent mower rather than a budget one) if I can fix the old thing with £50 worth of spares.
I can get a replacement carb kit for about £30 so that might be worth a punt.
If it is the engine side of the governor mechanism a big job to fix? I have not looked at the engine side of it yet, just the carb side.
Thanks in advance.
I had a petrol engine mower that would only run on the choke.
The main jet was blocked solid, and I cleaned it with some very thin wire.
You might have a partial blockage that might be removable with compressed air?
The gaskets can also tear, so air getting into the carbon could make it run rough as well.
Hth
The main jet was blocked solid, and I cleaned it with some very thin wire.
You might have a partial blockage that might be removable with compressed air?
The gaskets can also tear, so air getting into the carbon could make it run rough as well.
Hth
b14 said:
Is the fuel you've put into it fresh? My money would be on you needing to put in fuel straight out the pump.
Very fair point. It was last years fuel that I used, which does work fine on my ride on mower but maybe this little engine is a bit more picky. Will try some fresh fuel today.
If it ran fine before the winter lay-up and now doesn’t, then as has been suggested already, it’s most likely to be fuel related. Modern ethanol fuels really don’t do well being stored for extended periods as they absorb water. The fuel left in the carb/tank with cause corrosion of those components and any spare fuel stored separately will go off pretty quickly unless treated.
Get rid of all the old fuel and clean out the carb/tank properly with carb cleaner. Replenish with freshly purchased fuel and off you go
As an aside, you can get a fuel “stabiliser” (briggs & stratton do a good quality one) that can be used for the last fill of the year to avoid future problems.
Get rid of all the old fuel and clean out the carb/tank properly with carb cleaner. Replenish with freshly purchased fuel and off you go
As an aside, you can get a fuel “stabiliser” (briggs & stratton do a good quality one) that can be used for the last fill of the year to avoid future problems.
I picked up an expensive mower for a song which was described as a none runner. Checked it over when buying and it turned over and had compression so I thought it was worth a shot. Stripped and cleaned carb, fresh fuel, clean plug. It ran but really rough. Stripped and cleaned carb again no improvement. I thought it sounds like the timing is out, how's that work? It's just a magnetic pickup from the flywheel how can that be out of time. Went to remove the flywheel and sure enough the key was snapped so the flywheel was on about 15 degrees out. New key and I've got a £600 mower I'd paid £60 for!
TorqueDirty said:
It won't get up to full revs and when it runs the revs rise and fall and it then usually cuts out after a minute or two - but not always.
I have not fully investigated the governor connection on the carb yet but it moves fine when I manually operate it. Actually I have not done this with the engine running which I should probably try.
These two paragraphs.I have not fully investigated the governor connection on the carb yet but it moves fine when I manually operate it. Actually I have not done this with the engine running which I should probably try.
You've got to see what influence the governer spring has on it all.
It's fundamental to both the idle and the max performance of the carb.
The springs sometimes elongate over the winter and it's a dead easy fix with some needle nose pliers.
Or..... You try moving it when it's running and it's doesn't affect, and you move on.
And..... Never use E5, only super unleaded in it from now on. Much more stable.
Just off up to get some fresh super unleaded.
Will report back.
I'm doubtful because I have been lax with fuel over the years and it has always worked fine - but then on the other hand I'm usually wrong about everything so I live in hope!
If that does not do the trick I'll investigate the governor in more detail and also get a new plug.
Will report back.
I'm doubtful because I have been lax with fuel over the years and it has always worked fine - but then on the other hand I'm usually wrong about everything so I live in hope!
If that does not do the trick I'll investigate the governor in more detail and also get a new plug.
Fixed!
New fuel made no difference so I investigated the governor mechanism.
With the engine running I moved the governor connector on the carb to open the butterfly more. Engine roared in to life.
Then I noticed that steel plate that the governor spring hooks on to looked bent inwards in the direction of the carb, meaning that there was no spring tension.
Pliers out, plate bent forwards, spring tension restored, engine runs perfectly again.
And then I could not resist the temptation to "pimp my ride" so gave the plate an extra tiny tweak forwards to bring the revs up a bit more as it has always felt it needed a little more oomph.
Job jobbed. Thanks for all the advice.
New fuel made no difference so I investigated the governor mechanism.
With the engine running I moved the governor connector on the carb to open the butterfly more. Engine roared in to life.
Then I noticed that steel plate that the governor spring hooks on to looked bent inwards in the direction of the carb, meaning that there was no spring tension.
Pliers out, plate bent forwards, spring tension restored, engine runs perfectly again.
And then I could not resist the temptation to "pimp my ride" so gave the plate an extra tiny tweak forwards to bring the revs up a bit more as it has always felt it needed a little more oomph.
Job jobbed. Thanks for all the advice.
Edited by TorqueDirty on Monday 21st April 09:45
The other thing that's worth trying is revving it up and down repeatedly for several minutes. The ethanol makes the carb diaphragm go crunchy so it won't pump fuel properly. If you rev it you're essentially giving it a workout to make it more flexible again. I've seen this work a few times.
Edit - posted this at the same time as your last post. Glad you got it fixed.
Edit - posted this at the same time as your last post. Glad you got it fixed.
shtu said:
Glad you got it going, but how did those parts bend themselves in storage from last autumn?
You might have compensated for a partially-choked carb by opening it up more.
I probably rammed the mover in to the shed whilst trying to fight it past 4 tons of crap that had accumulated in there. You might have compensated for a partially-choked carb by opening it up more.
But yes, I may have bodged the fix, although the plate did look suspiciously bent before I straightened it to vertical. Time will tell.
At least I can mow the grass now and if the revs begin to rise I'll take another look.
TorqueDirty said:
b14 said:
Is the fuel you've put into it fresh? My money would be on you needing to put in fuel straight out the pump.
Very fair point. It was last years fuel that I used, which does work fine on my ride on mower but maybe this little engine is a bit more picky. Will try some fresh fuel today.
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