Hi all - wondering if there are any of you who may have a good conceptual understanding of the elements in play for my engine problem.
The problem is that the machine struggles to start and runs rough. A quick check of the plug confirms rich too dark and not tan colour.
Today I went into it in more depth.
At first I thought it was the ignition so I got a spark tester and I can see a good spark all the time.
The plug was wet with fuel so I thought the bowl could be stale.
I swapped out all the fuel and replaced it with treated fuel since the machine doesn't get run very often - this is best anyway.
It then did start but still ran poorly - so I started to think I had a carb problem, since its about 10 mins to remove it I decided to do that.
Once I had the air cleaner housing off I decided to run it again and it ran and it ran nicely.
So thinking the air filter was clogged I cleaned it and re-oiled it and decided to re-assemble it with the engine running and this is how I know that attaching the crankcase breather is when the engine becomes upset and goes really rich. The revs drop off from 1200 rpm idle to about 700 and if I run it faster it runs lumpy as you would expect with too much fuel.
There is no pressure I can feel in the crankcase breather either out or in with the engine running so how that can be affecting the carb I don't know.
It makes no sense to me - the same jets are in play and the breather could be robbing or adding air [hypothetically] but in either case the fuel will still be proportional to the quantity of air so I am not sure why the crank case breather attachment is causing this issue ?
The engine is this
A B&S vertical 500cc air cooled side valve motor. 12.5HP.
I will say the engine generally runs well but has been starting to get progressively worse over the last couple of times I have used it.
On the parts diagram it isn't obvious whether the breather can be detached and cleaned.
The breathe pipe itself is sound and not oily.
Thanks in advance for any thoughts.