Paging the diesel-engine-isti - long-ish.

I've been playing about with a nice generator I got cheap, sold as
spares or repairs. It's a 6kW 'silent' type with a Yanmar L100 engine.

At some point it's been fuelled with petrol. The PO had fiddled with it
a little and got it running, but in the end had bought a new one. He
didn't do much as he was obviously not mechanically inclined.

I started it up, loads of white smoke, backfiring flame every now and
then[1]. Sniffed in the fuel tank, still smells of petrol, so I made
sure it was completely empty then put fresh diesel in.

I ran it for a while and after a little bit the backfiring reduced, as
did the white smoke. Leaving it running a little longer and I notice
sparks coming out of the exhaust, though most of the smoke has gone.
Look a bit closer, and the whole exhaust is glowing red hot, right
underneath the (plastic) fuel tank.

Oops.

So it's obviously still got a lot of unburnt fuel getting through. What
say the FOAK - a valve? Rings? Something else?

[1] making some really nice smoke rings

 

Probably both and/or piston/s /bore. Fuel wash with the petrol has
fucked it properly. Whether Yanmar spares are beneath the economical
repair point for this model is yet to be found - not a clue, myself.
It's up to you how much you want to spend on it, but I'd look for
another good used one.

 

Very often this is just unburnt fuel which has accumulated in the exhaust
with prolonged running at no load.
First give it an oil change then hook it up to a couple of electric fires
to give it a rated load and run it. If it will carry its rated load
there will not be much wrong, give it an hour or so to clear the
cobwebs.

If it will not carry its rated load it is probable that the pump and/or
injector have been damaged by misfuelling. They are easy enough to
replace, have fun bleeding the air out.

 

In older diesel powered cars, 'shit in the fuel' of a petrol nature
normally equated to various seals in the fuel pump then letting go.

Might be whatever this uses as a pump has the same problem.

 

You sure about that? A glowing exhaust could be a sign of running lean,
which might be the case if the petrol wrecked a pump seal. I'd try
partly blocking off the air intake to see if it improves things.

 

Diesel engines do not run lean or rich as you understand those terms
in petrol engines. They take a full deep breath of air every
time[1] and compress it to get a high temperature which ignites the
fuel. Only the amount of fuel injected changes.

The exhaust will normally glow when the engine is working hard under
load. If there is no load this could imply a fucked generator which
will most likely start releasing the magic smoke after a few minutes.
OTOH there are other reasons why the engine could be working hard.


[1] Unless the air filter is blocked, which makes them smoke under load.

 

Absolutely. In fact, a Diesel runs 'lean' by petrol standards even at
full chat; trying to achieve anything like a stoichiometric ratio
generally results in unacceptable amounts of smoke, though modern high
pressure injection engines can get closer.

Sounds as others have said like unburnt fuel in the exhaust. The fact
that it starts at all from cold implies adequate compression; one
tankful isn't going to **** the bores anyway.

I'd guess that it's the injectors (poor atomization) or fuel pump
(fucked seals somehow causing low injection pressure). This assumes
that absolutely nonthing else has been done, like taking the pump
apart to flush it.

Also, petrol has a low cetane rating as someone here pointed out a few
months ago, so it might just not want to ignite all the time but would
improve as the engine warms up.

 

Indeed, but having started it again is still has lots of white smoke - I
think the only reason it stops smoking is when the exhaust gets hot
enough it ignites the unburnt fuel.

I omitted the fact that I used a squirt of ez-start to get it going. I
was looking for some kind of cold start device but gave up looking and
just sprayed some in the air intake. So, it could be low compression.

It really looks like nothing's been done apart from take the fuel lines off.

 

Oil change - good idea.

Thanks. I haven't got around to checking the generator part yet. If that
doesn't work then it's probably not worth spendng much on.

 

Yes I do need to watch the economics, though I think a working one is
worth quite a few bob.

 

I've seen header pipes glowing red hot before, but never the tail end of
the silencer, as in this case.