Lawn mower running rich

[laserblazer]

My cheapo Homebase Sovereign lawnmower has never run that well. Now it has packed up altogether. The plug is very sooty, if I clean it the engine runs for a minute or so then stops. I've cleaned the air filter and I cannot see any adjustment on the carb. I'm reluctant to start stripping the carb down as I have no manual for it. Looks like I will have to get it serviced

[carvjo]

an occasional oil change, fresh spark plug and good fuel was all the servicing I ever did on my mower!

Petrol does go stale.. try it with a fresh drop of fuel and see if it will run..

or - take the air filter off and squirt some WD40 into the air intake and then try to start it..

or - get some sheep, they keep the grass trimmed nicely..

[plexer]

if you take the air filter off next to it you should see a linkage with some sprngs on it? if so this is the centrifugal governor perhaps the springs are too weak to stop this shutting it off all together?

Ben

[laserblazer]

You could be right @plexer. I did think the springs looked a bit flimsy. Trouble is, how do you tell? I'll try google.

Edit: Google is my friend http://repairinglawnmowersforprofit.com/tutorials/

[Sirbendy]

Be very careful fiddling with the governor....

What make is the engine? Briggs and strat, Tecumseh, Honda etc? I've never got on with Tecumseh lumps..run like poo, very maintenance sensitive. Briggs..well...I've looked after a lot of those..in fact, I still am, heh. Every season a plug clean, fresh 30w oil, air filter clean in fuel and re-oil, carb cleanout with cleaner and float bowl off to airblast out, and she just runs.

Runs for a minute, then stops with a sooty plug says rich mix based on the plug - either overfuelling (stuck float on the carb or gunk in the jet), or lack of air (whip off the air filter and clean/replace it). When it runs, does it smoke? does it rev up and down, or is it lumpy? Usually the engine should be pretty constant - I wind mine down to a lower idle as a rule, unless the grass is long...but it's always a pretty constant speed.

To free a sticking carb, gently tap the bowl with a spanner and see if it starts again...if the carb bowl has a brass nut on the bottom, take it out after shutting off the fuel feed/clamping the hose, gently remove the bowl and wipe it out..they tend to accumulate muck which plays havoc. Blat the whole lot with WD40, or carb cleaner or similar, and make sure the float pivots smoothly. Reassemble carefully.

Air filter, if a foam sponge job - wash it in petrol, squeeze and loo tissue it dry/mostly dry, and lightly oil it with some SAE 30 oil (don't use multigrade in a mower), stick it back in.

Really, that's about it...air and fuel, plus spark..should work. Check the throttle linkage for kinks and obvious damage..the governor I would leave well alone. Last stop would usually be the points inside the flywheel (PITA to do, if you even have them)..old Briggs had them, as did Suffolks. They may be obsolete now.

Usually points/magneto issues are a non-start/b1tch to start/major kickback job. I've had it with engines that have gone from full throttle to dead halt when they've hit a lump of concrete or a hidden immovable object - the flywheel mass keeps it spinning and shears the woodruff key, putting the thing well out in terms of timing. Always a fun moment.

[plexer]

I had thi with mine last weekend cleaned the air filter as it ws well and truly gummed up not just lightly oiled and seemed to want to cut so I tightened the governor spring ever so lightly in order to get it back to the operating speed it should be at that was all that was wrong with it.

Ben

[Oaktech]

i expect it will be the wind vane governer or associated parts.

I have a sovereign mower with the briggs 3.5 on it and when i got it the previous owner had tried to service it and cracked the carb body, so i replaced the carb and had a go at it...

I ended up taking the plug out and running neat petrol down the inlet, sloshing the mower around and then turning it over untill the fluid ran clean out of the plug hole, I then let it dry overnight, then changed the oil, which looked a bit watery, then fired it up.

It did exactly what yours was/is doing, the solution in my case was to buy a set of governor springs for about £3 from ebay, then a governor vane itself as when i took it apart there were big chunks missing!

[laserblazer]

Thanks, it is a B&S 3.5 with an auto throttle. I have cleaned the filter and plug. The governor springs look very slack. I'm also told that the carb diaphram can get distorted and should be replaced. I'll have a look for springs on ebay.

[mac_shinobi]

or - get some sheep, they keep the grass trimmed nicely..

Or a goat - have some goats milk as well if you like that sort of thing :P

[synaesthesia]

Running a tecumseh lump on my mountfield freebie. Mower is literally the same age as me so quite pleased it still runs rather well with the exception I need to hold the throttle shut with my foot to get it to turn off (Must get round to sorting that.) Exhaust is nackered, bolts are sheared/missing where it's been repaired before but it still cuts grass and runs oddly well!

[alexyarm]

Ditch the engine and strap a Yamaha R1 lump on it.

[synaesthesia]

If someone has one going begging then I would

[pcstru]

R1 - naaaa. You want a nice CBR900. After all, every lawnmower needs a Blade.

[HaleStorm]

If its got a Auto-Throttle, does that mean it also has an auto-choke? perhaps the choke is jammed open, allowing too much cack into the combustion chamber....which would be why your spark plug is coming out covered in carbon dust.
The choke in theory should only be open for a cold start for the first 2-3 mins until the engine warms up...which doesn't take long on a small mower engine.

My Honda had an auto choke and it was a pain in the a***, had to clean the spark plug really regularly - like once every 2-3 cuts

[Sirbendy]

I was looking at the bay of E...some old petrol flymos on there....I recall those quite well...wouldn't like to use one now!