Gazza,

Have you had the head off the cylinder as it could also have a carbon build up if you are getting sparks coming from the exhaust port.

Yes you could have carbon build up in the muffler as well as the exhaust port.

The steps that I would do are:

1. Decoke the cylinder head.

2. Check around the exhaust valve for carbon and clean.

3. Check the valve and seat for pitting or flat spots.

4. If pitted or burnt valve reface the valve and seat then lap back in.

5. If refacing the valve then check clearance and reset.

6. Check exhaust port for build up of carbon and clean.

7. If the mower has the same problem with the fuel coming back out of the carby then you will have to replace the muffler with a new one.

Hope that this is of some help to you. I have had in the past when a machine comes from a farm or country area the mufflers being blocked by a wasp nest as it is hard to see and you go through hell try to work out what the problem is because the muffler looks new and you think nothing can be wrong with it.

I have been caught many time with this happening in the past. cheers2

Regards,
[Linked Image]

Bruce


Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.