Welder-generator revs going up and down...

[hot_anvil]

My welder-generator is normally great and reliable. Starts first pull, nice welds etc. Recently it has started playing up: the revs have started to rev up and down a bit - not a big swing - when there is no load, but the revs go up and stay constant when a load is applied as normal. After a few hours (of discontinuous use - I tend to run the genny for a few minutes of welding and then turn it off while I set up the next series of welds etc) the revs go up and down more decisively - even when attempting to weld - resulting in crap/no welding. Have to give up at that point. Plenty of fuel. Oil in sump. Air filter looks clean. Any ideas?

Here are the details on all the various plates:

HILTI
110.240V
pf 0.8
Hz 50
Serial 22720-3
200 Amp
240 4kW
110 2.2kW


Engine:

Honda 13.0 GX390


Syncro (alternator):

Type: EW 200 DC
Code: 96201180FA2
SN: 2260987
PO: 58637000
Ins: F/H
Phase: 1

Looks a lot like this http://www.sip-group.com/acatalog/S...at_P200W_DC_Petrol_Welder_Generator_2328.html , but I’m assuming it was supplied by Hilti? I bought it secondhand 2 years ago, but it was 5 years old then.

 

[cumbriasteve]

I am probably wrong but worth a mention...my lawnmower engine did the exact same thing, I messed about for ages with no luck, then stripped, cleaned and replaced the seals on the carb...no problems since

 

[the snooper]

it will be a carburetor fault, most people leave their genny stood with petrol in the carb and it does them no good. the petrol goes bad and starts to block the main jet, take the bottom off the carb and clean out the main jet and float bowl when you are not going to use it for a while leave it running and turn off the fuel and let it use whats left in the carb then it cant go bad