Sovereign XSZ40 lawn mower starts then stops

[Jon Freeman]

I have recently fitted this mower with a new ignition coil and plug, and replaced the gaskets on the carburettor, because it was not starting at all. Now it starts really easily, better than at any time since purchase, but it runs for about 5 seconds - revs highly, corrects back, hunts again at high revs, then drops back and cuts out. Will restart and repeat the cycle over and over, but doesn't change to any stable pattern.

This is a quite primitive device with not much that can be adjusted. Any suggestions as to what I might do to fix this please? All suggestions received with gratitude.

Jon

 

[Burnerman]

With this one, the primer bulb causes a squirt of raw fuel to shoot down the carburettor choke, directly into the engine - hence quite reliable starting so long as you don't overdo it!
Obviously the carb can't pass fuel through its jets as there looks like there's an obstruction somewhere. I'd start by removing the carb, cleaning the outside of it thoroughly with an aerosol cleaner and then taking the float bowl off - marking its position first. This will reveal the float needle valve, the float itself and if you delve deeper, the main jet and emulsion tube which is located centrally. All of these parts need to be removed and made absolutely clean - a compressed air supply is very handy here, but the carb cleaner will do.
John

 

[Jon Freeman]

John, thanks so much for this clear and incredibly quick response. Just checking a couple of things. The re-starting is working multiple times even though I don't repeat the priming process. Does that alter your advice at all? I will clean it out anyway. Also, I assume that to get the carb bowl off, I undo the nut (bolt) on the bottom?
Jon

 

[Burnerman]

Sure, the nut on the bottom of the float chamber releases the bowl, and there is a rubber gasket there in a groove which seals things up. Check for water and other debris in there if you can. Check to see that the petrol tank can supply a good flow of fuel with the fuel pipe disconnected......if there is no external filter then there will be a nylon gauze one in the tank, covering the fuel outlet.
The float is released by pushing its hinge pin to one side, and this pulls the needle down with it.....where its tip goes is a popular place for an obstruction.
I think the engine is using up some fuel from its float chamber at every start - and I think the fuel isn't being replenished quickly enough - hence the restart without a prime.
These carburettors are largely non adjustable, and they rely on excellent gasket seals between the carb and the cylinder and also between the air filter inner and the carb to work well.....you seem to have attended to these.
Hope this helps!
John

 

[Johannnb]

hi, Burnerman. same symptoms for me, i figure its lacks of fuel but, cos i'm getting on, do you have any video to walk me thru the removal an cleaning repair of the carb ? ps i used to do it on cars but that was 40 yrs ago, lol

 

[lonner]

Often mowers sit for a few months throughout winter.
Unleaded fuel can gel up or its water in the fuel and why they often get this poor starting prob.

Empty float bowl as said and if possible unblock the jet with a bit of fine wire.

 

[Burnerman]

Sorry I don't have any pics of this maybe Youtube can help?
Anyway, if you have sorted car carburettors before you have nothing to fear from this one......a tip or two, assuming this has the carb with the priming button at the front, and a conventional float bowl.
Have an aerosol of carb cleaner ready if you don't have compressed air available.
The bolt on the bottom of the float bowl is also the main jet, often enough......if it is drilled on its side, check the drilling through the bolt is clear;
If the float bowl is dimpled, mark its position;
The emulsion tube is above the main jet position, use a well fitting screwdriver to undo it, and check the many drillings are clear - the horizontal holes line up and you can see through them;
If the machine just wont tick over, you'll see a hole drilled to one side of the carb choke - air filter side. Blow some carb cleaner through this as it bypasses the other jets;
With the float pin removed, let the float fall out and make sure it brings the needle jet with it.....look up into the needle jet housing, and if you can see a red sealing ring up there make sure it doesn't get lost.
Best of luck with it....nothing to fear with these.
John