Trouble with Honda GX530

We have been in business for 25+ years.


We have a Sears mower in the shop that has
a GX530 Vtwin.
We serviced this mower earlier this spring and
delivered back to the customer. It was running fine.
They mowed with the mower about 4 or 5 times and
then it started running like the choke was part way on.

We picked up the mower and thought the air cleaner might
be plugged - it was fine.

Checked valve - ok

Checked the plugs and they were sooty but ok, put new ones in.

We removed the carb and went thru it several times - no improvement.

Changed fuel pump - no improvement.

Ordered a new carb - same thing

No excessive blow by. If you pinch off the supply
line the engine will run as it should.

We are stumped. Hate to start tearing into the engine
without due cause.
ANY IDEAS are welcome.
Thanks olf20

SO what was the leakdown test like and what were the numbers from your wet/dry compression tests. ?

In times like this the colour tune comes out to test for oil or excessive fuel

My son done the leak down test and told me everything look ok.
I did not pursue the results as he has done this before.

No gas in the oil. No test. Oil on dipstick was on full mark
We have seen crankcases well over filled with gas and engine still ran fine.

That's the funny thing about this engine, everything looked ok except the
running as if the choke was on.

Thanks for the reply!
olf20 / Bob

Tried draining the tank & running on fresh fuel ?
You said you pinched off the breather and the mower ran properly
Does that mean with the breather pinched off it no longer 8 strokes ?
"Runs like the choke is on " I presume you mean it 8 strokes and blows black smoke form the exhaust ?
Have you tried running it with the kill wires disconected from the coils to isolate the engine from the mowers electrics ?

We pinched off the fuel line from the tank - It ran fine.
We pinched off the fuel line to the carb - It ran fine.
We pinched off the crankcase line to the fuel pump - It ran fine.

Yes it is blowing black smoke, definitely over fueled.

Will isolate the engine this morning.

Thanks for the reply

olf20 / Bob