Sick Engine

No, not the Ducati, the Briggs & Stratton lump in my mower.

It's a very simple 4 stroke jobby, but rcently just has no power, won't
run properly (slow and laboured). There's no manual throttle on it,
it's operated automatically via a sail switch.

I had the whole thing apart last night and couldnt find any obvious
clues. Cylinder head and valves were a bit black, but even after a
good clean up it still won't run right. Petrol is fresh, so it's not
that, and carb (such as it is) is clean too. Runs the same with the air
filter on or off, so it's not a clogged filter. Apparently good
compression (thumb over spark plug hole), and no nasty shards of metal
in the oil.

Any ideas?

 

Carb diaphragm? How old is it - does it have points, or one of those
electronic coils? Does it have a big fat spark?

Up until a few days ago I've found most problems on their engines easy
to solve. However, I've got one right now that just *won't* start. I got
it as a non runner - replaced the coil/magento thingy (removed the old
points) and it ran just fine. Left it for a while and now it will not go
- it has sparks, fuel and compression and barely manages to fire at all.
I'm completely stumped.

 

Mine has the carb above the fuel tank and the diaphragm is part of the pump
that works by engine vibration. The diaphragm should be replaced every
few years
as part of a service.

 

A blockage in the exhaust perhaps?

Tim

 

On 5 Jun 2010 06:37:35 GMT, "Dan L" <DONT SEND YOUR CRAP TO

What colour was the spark plug nose porcelain? That's usually a better
indicator of mixture etc.

 

It has one of those electronic coil things, appears to work okay.
Not sure about a carb diaphragm though, perhaps more carb investigation
is needed. I have a horrible feeling it's a seizing bearing that's
causing it to run slow mind.

Bloody things.
Even if I fix mine it's a moot point, the missus has ordered me a new
mountfield

 

So does mine, I think I need to investigate this carb diaphragm.

 

The throttle butterfly is operated by a sail switch, which is driven by
a finned rotor on the top of the engine. This mechanism all seems okay

Cheers for that.

 

Didn't check that... good point.

 

The plug, valves and combustion chamber where very black and oily,
looked more like a 2 stroke when I opened it up.

 

My wife did that last year, just before she divorced me.
It's got a Honda GCV135 engine - what a pile of crap!
That's the last Honda for me; I'll stick to Briggs and Stratton in future.

 

It has been run whilst on it's side before, which I know is not a good
thing.