Ploughman

Rich, The fuel tap has an integral sediment bowl, and as you expected, a simple mesh coarse filter. It has all been cleaned out, looks dirty because the bowl is old and lost is translucency. Not sure what you mean by vacuum the fuel tap. It is cleaned out and flows freely. There is no vacuum forming. The engine switch off is the ignition key. it seems to work OK, engine on and off. Definitely does not start if key is in off position !! Unfortunately, much as I would like to have a parts diagram, I do not have one. Ace kindly supplied manuals, but my engine is later MAG model and different. is looking more like valve issue, and I will look at compression etc It has been a long established problem, probably there when I purchased the machine from a mower machinery supplier

I have saved vid as MP4 suffix, hopefully more accessible now sorry for convenience for non-Mac users. Thank you all for valued comments. Fuel tap may refer to "Open" and "shut" , but will double check. Filter is recent addition to ensure that fuel is clean. It is after the tap however, gravity feed. Can see the petrol running through into the filter where it hits the magnet . I have had it running out of the pipes - it just keeps running with no hold ups - all of which have been replaced with new fuel pipe, as I was concerned that fragments of old pipe could have been blocking jets. Have tried emptying out all fuel, replacing with Aspen 4 . Then changed back to standard 95 octane ( just purchased ) as there was no benefit and might cause unforeseen issues with neoprene or other seals, eg the needle seating. Fuel cap is very clean. Unfortunately, I do not have manual for this particular engine ( GS300 7.2 HP Electronic ignition ) , as Ransomes used Briggs, and also Honda whereas this is a Swiss MAG , later rebadged as Kubota mechanical rattling is because I had revs above idle and the centrifugal clutch starts catching and ringing like a bell. I will start her up again, wait till fails and attempt video when pulling the cord, when assistant available, as video was not a success with one hand pulling ( 7.2 HP ) and the other pointing at the neon ! I think that could be very instructive. She will definitely not start again once failed until cold. There is a brief no-glow at the first call for full throttle. Does seem to be sparking as engine dies however. Neon Light intensity and frequency seem to correlate with revs. 1613509510_lowerrestrimmedMAGGS300stallonmainjet11_09_2023.mp4

Morning Martin,Ace, Rich . Thank you for your further suggestions. I have attached a video clip of the MAG GS300 engine which reluctantly started this morning ( normally second pull ), then responded OKish, did go to main jet, but then died on asking more throttle from the idling position. The neon light seems to light up OK , and there is still spark even when the engine is dying, I think ?? Glad of your views on the light indications. My limited knowledge points to maybe not electronic or electrical after all. The time taken to failure at higher operating throttle has reduced over a period months. from 30 mins to 15 mins, then 5 mins or so, but this morning was less than 2 mins. So engine was relatively COLD. After assuming coil or condenser ( has new NGK BP6ES) , my suspicion is sooty valves ( but no engine smoke ). All thoughts very welcome. I have cleaned out carb several times, removed jets etc, changed fuel, inserted filter. As engine was cold, no time for any excess heating up of the air/fuel mixture although engine has in the past run hot. I will send details of old model plane and bits separately many thanks Ploughman 1782913265_lowerrestrimmedMAGGS300stallonmainjet11_09_2023.mov

Hi Martin, thank you for checking on this. And very good to be able to join your forum on a shared problem. I agree, all points to fuel starvation , so efforts so far have all been towards that, including air jetting out the filler cap. The issue is associated with being hot, or a passage of time ( eg filler cap, blocked filter, jets ) . I have a neon light, so if I can see that when she is hot it will help the diagnosis before attempting access to electrics. I have an old home-made model aircraft, with ic engine and ancient controller all for "renovation" - would there be interest on your forum somewhere ?

Ace, very many thanks for your help with the manuals. Will download shortly. Yes, the symptoms are exactly as per your video. But I imagine that the electronic ignition also requires a coil, and maybe even a condensor ? In fact, I did have that model, and I notice your trick with the weights, which is a good idea.I had a lead pipe across the front arms at the time,only issue is turning after short runs, and our grass is bumpy !

Ace, if you are able to share the manual it would be a great help. The mower is a GS 30" mastiff serial 00493 I did sell my mark2 36in from 1980 , but kept one 36 in which is a difficult wrestling match, and this 30inch ride on with GS300 MAG engine , does have electronic ignition. It is the GS ( ride on) that has the trouble

Hi John, yes it does have governor. I had considered this as issue, but when cold the response is fine. it is only when hot that no power available, so would that rule out governor is potential cause ?

Hi Ace, Brian & Nick , very many thanks for your thoughts. I have taken off the carburettor many times, and cleaned it out, including both jets, were dirty to start with but are now really clean ! Plus in-line filter, aspen petrol , new correctly fitting air filter, so I feel prob unlikely on that side. The issue is that she runs fine, full power on main jet, but only for around 6 minutes, was 10mins plus, but then will only idle and eventually fails altogether if too much throttle applied. Needle has also been replaced, as the little neoprene ( ?) point may have deformed slightly. In fact, changing that needle - by the commercial mower supplier, was in response to a fluttery sound , and seemed to cure at the time, but on reflection probably had the problem from day one. Otherwise the machine is in unusually excellent condition

Thank you very much for responding so quickly, especially after a two year hiatus. Thank you also for mentioning the work tried on valves . I had also thought next job would be to look at valves, expecting reseating etc But as you say, plenty of compression, and so if I can get access , will change coil and condensor . Not sure if it maybe electronic ignition. Will let you know if I manage to sort this frustrating issue, present in various degrees since acquiring the mower, and think the failure on main jet has occurred more quickly over the period. Yesterday’s trial was to use a new NGK BP6ES , clean carb again, no joy at all. But the ancient standby 36” walk behind , same engine but earlier Heikin carb, old stale fuel, rusty plug, started immediately after all year in the barn and no problems at high temp…

Ace, I have exactly same problem with 7.2 HP MAG engined 30” Ransomes Mastiff. Runs on idle jet only after about 5 or 6 mins, splutters and pops if given more throttle and then finally stops and won’t start again until cold. Tried most things, cleaned carb several times, installed fuel filter, tried Aspen 4stroke , changed plug , cleaned out tank and shut off valve etc Will try the neon spark test. Did you resolve the problem? Thread seems to have terminated. Thanks, P