On Sat, 30 Apr 2016 16:51:34 -0700 (PDT), wrote:

snip

Thanks...

You are welcome. ;-)

The instructions tell me to hold the throttle fully open while startung the engine.

Ok, but have you tried other throttle positions when starting OOI?

Yes, it has a carb primer: a rubber bulb thing that you push three times.

That's the badger.

I *think* this sucks petrol up up out of the tank enough to fill a little resevoir that feeds the jet, as far as I can make out.

Yes, or fill the float bowl if it has one etc. Basically, to get a
decent fuel feed up to where it counts. When you pump it, does it stop
(pressurise) or can you just keep pumping? If you can keep pumping, I
wonder if you would see a spray of fuel from the plug hole if you take
the plug out and spin it over after 'over priming'?

I'll try cranking it over with the plug out, but touching the engine and see if the spark is bright.

Ok. Is this mower electric start?

If not I will buy a new plug.

One of the first things to change as it's easy and cheap. As a quick
and dirty check, most plugs in these things are gapped at around 25
thou and that's about the thickness of a thumbnail. ;-)

If that doesn't help, I'll perhaps try a new coil.

You can get coils where some of the windings become shorted so that
you get enough spark to run the engine but not a good enough spark to
start the engine *easily*. The manufacturers sometimes offer ohms
check readings and whilst they can help if the coil is badly out, it
may not if it's intermittent (under load etc) or a thermal problem
(unless you heat the coil with say a hot air gun when testing).

If that doesn't work, I may just modify the air cleaner with a gas blow lamp permanently attached to it so I can implement Another John's lifesaving tip each time I start it - without needing to grow a third arm!

I have seen people mod such things with a small (typically) silicone
tube passed though a hole (drilled in) the air cleaner and facing the
carb inlet. The outer end of the tube is plugged under normal
conditions and therefore giving good / clean access for a squirt of
'Easy Start' or whatever when required.

That said and given all the right circumstances, that shouldn't be
required (of course) but sometimes it is the simplest option.

The fact that it does start (easily?) when given something slightly
more flammable than fuel (say gas or ether) may indicate a general
'fuelling issue or mask the fact that there is a (minor) issues that
is being masked by the 'starting aid'.

It's like having a weak battery on a car. It may not have enough
'guts' to start the car on the starter motor but may have plenty to
run the engine (and I experienced on many_an_occasion when starting my
Morris Minor with the starting handle). ;-)

Daughter was given an old 2/ leaf blower that wouldn't run, apparently
had been 'check out' by a mechanic and that 'needed a new carb'. A
couple of pulls on the starter cord suggested it had no compression
and quick strip down reviled a seized piston ring and a fairly scored
bore. Just to prove that it wasn't the carb, I got her to put a new
ring in it, put it back together and whilst it did indeed start and
run, it was obviously f'd. ;-(

I have a Honda GX200 powered generator and that became quite
intermittent, mainly on starting (although like yours, would start
with some Easy Start etc). Once running it generally carried on
running and would re-start ok. One day it simply wouldn't start at all
and I managed to pin it down to the coil (weak spark). I fitted a new
coil and it's been fine ever since. ;-)

At least 4/'s don't suffer with the same issues as 2/ where leaky
crankshaft seals can also have a big impact on starting and running
(other than leaking oil all over the place). ;-)

I love the challenge of a recalcitrant utility engine as you can
generally go though it all quite easily and if it's common / modern
enough, replace they key components (like coils or even CDI units)
quite cheaply. The very common engines (like Honda specifically) also
have a good supply of pattern parts, or in the case of engines also
used on things like go-carts, 'racing parts'. ;-)

Cheers, T i m