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I've got a Stiga Park 740 PWX with the 18hp V-twin. I haven't run it for about 3-4 weeks and came to start it today and no go.

The engine turns over normally on the key but it doesn't fire up.

I carried out the normal checks before starting and when it wouldn't fire I checked the following;

Air filter is clean.
Removed, cleaned and check the gap of the plugs before refitting. The one plug was black and sooty but the other was nice and clean (*See note below). Both gaps were slightly over.
Tested ignition to both plugs with an inline tester and confirmed spark present in both plugs.
Plenty of fuel in tank
Worked through the fuels line from tank to the pump.
Fuel passing easily through fuel filter.
Passes through the fuel pump to the left cylinder (looking from the front of the mower, air filter at rear) but nothing passing out of the right cylinder outlet. *The black, sooty plug was from the right cylinder.
I've blown through with my mouth again air passes to the left cylinder outlet but not out of the right cylinder.
If I suck on the right cylinder outlet, air comes through but very little in comparison to the left.

I tried attaching a compressed air line but blew the cover of the pump so either way, I now need a new pump

Any thoughts on why it's not firing up please?

Adjust valves with engine cold to .004- .006.
Big Block Vanguard Engine same procedure & specs. above, take your time & let us know if this helps, thanks, Mark

mechanic mark said:

Adjust valves with engine cold to .004- .006.

B&S VANGUARD ENGINE VALVE ADJUSTMENT - Google Search

Big Block Vanguard Engine same procedure & specs. above, take your time & let us know if this helps, thanks, Mark

Click to expand...

Thanks Mark, I'll give it a go.

What was the outcome? Not likely that both cylinders would suddenly have valves so far out of adjustment, that engine would not start. Engine will start and run quite happily on one cylinder.
Walt Conner

Try mixing Star Tron Fuel Treatment per instructions on bottle with 93 octane gasoline & give it a try. Let us know how it goes, thanks, Mark

Unless rings or valves stuck because it was over heating when you last used it
There is little that can cause a no start condition in a month
If I was presented with your mower in the shop I would be putting a short shot of carb cleaning spray down each plug hole ( or 1/4 teaspoon of known good fuel ) then cranking the engine.
If it fired a few times I would then do the same down the card.
If it fired again I would then remove the carb solenoid & check the plunger was retracting .

Smunkey said:

I haven't run it for about 3-4 weeks and came to start it today and no go.

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Stale fuel alert.

Smunkey said:

The engine turns over normally on the key but it doesn't fire up.

Click to expand...

Again stale fuel alert. Now water in the gas.

Smunkey said:

Removed, cleaned and check the gap of the plugs before refitting.

Click to expand...

Knew this was coming. Normally plugs are at the top of the replaced parts list. This one made it to number 2.

Smunkey said:

one plug was black and sooty but the other was nice and clean

Click to expand...

Ah-ha. Time for parts swapping. Plugs, ignition coils if possible on this engine. Valve inspection time.

Smunkey said:

Both gaps were slightly over.

Click to expand...

Put the gaps back to recommended spec.

Smunkey said:

Tested ignition to both plugs with an inline tester and confirmed spark present in both plugs.

Click to expand...

Spark present but is it enough to fire under the cylinders heat and compression? Need to load test the coils and plugs.

Smunkey said:

Fuel passing easily through fuel filter.

Click to expand...

For how long? Will it empty the tank into a 5 gal bucket?

Smunkey said:

Passes through the fuel pump to the left cylinder (looking from the front of the mower,

Click to expand...

Sides are determined from behind the wheel. Cars, trucks and mowers.

Smunkey said:

but nothing passing out of the right cylinder outlet.

Click to expand...

Need to see why.

Smunkey said:

I've blown through with my mouth again air passes to the left cylinder outlet but not out of the right cylinder.
If I suck on the right cylinder outlet, air comes through but very little in comparison to the left.

Click to expand...

Could there be a clog of some kind here? Probably want to remedy this one.

Smunkey said:

I tried attaching a compressed air line but blew the cover of the pump so either way, I now need a new pump

Click to expand...

What engine manual was this stated in exactly? Compressed shop air at probably 150psi into either a gravity fed or pumped supply at around 3-5psi. Something .... here.... doesn't.... add..... up.

Air, fuel, spark and compression.

slomo said:

Stale fuel alert.

Again stale fuel alert. Now water in the gas.

Knew this was coming. Normally plugs are at the top of the replaced parts list. This one made it to number 2.

Ah-ha. Time for parts swapping. Plugs, ignition coils if possible on this engine. Valve inspection time.

Put the gaps back to recommended spec.

Spark present but is it enough to fire under the cylinders heat and compression? Need to load test the coils and plugs.

For how long? Will it empty the tank into a 5 gal bucket?

Sides are determined from behind the wheel. Cars, trucks and mowers.

Need to see why.

Could there be a clog of some kind here? Probably want to remedy this one.

What engine manual was this stated in exactly? Compressed shop air at probably 150psi into either a gravity fed or pumped supply at around 3-5psi. Something .... here.... doesn't.... add..... up.

Air, fuel, spark and compression.

Click to expand...

Comprehensive reply slomo. I'm going back to the beginning. Draining off fuel, working through the system and replacing service items, fuel filter, plugs etc.
I'm then going to look at the valve clearances and ignition.

It'll take me at least another week to do this but I'll try and post back with results after each element is done.

Smunkey.
Please don't do it like that
Very important technique is to replace only 1 thing at a time so the root cause can be identified .
Otherwise you will end up doing a full end of season service 5 times a year till the root cause is identified .

don't compound the problem with new ones. figure which of the three things are missing, It is really easy to troubleshoot any engine that does not run if you just focus on figuring which of the three are missing.

fuel to air
Spark
compression