[boardy]

Hi,

I recently borrowed a Merry Tiller Rotavator that had been sitting in a barn for at least ten years. I think its a 70s  model and has a briggs and stratton 4hp engine. I managed to get it running and have given the carb a bit of a overhaul with new diaphragms etc and a new spark plug. The engine starts ok and runs well but as soon as it comes under a load i.e. when the tines go into the ground, it dies. The problem also happens when throttling from a low speed to a high speed quickly. I tried to clean the fuel tank out as it was a bit dirty and made sure the fuel filters were clear. I have also tried adjusting the carb but the problem still seems to occur. I don't really know much about engines etc and my knowledge extends to about all I have tried above. Does anyone else have any suggestions as to what might be wrong?

Thanks
James

[smud6ie]

The symptoms you describe suggest that the mixture could be  weak.warm up the engine ,then open the throttle to the run position,screw in the mixture screw until the engine starts to die,then open it until till engine splutters then back in till the slightly rougher side of smooth.(rich mixture)
With it set slightly rich it should run ok when the engine comes under load when digging
smud6ie

[boardy]

Hi,

Thanks. I did try messing around with the mixture but will give it another go tomorrow and report back what happens. Thanks again.

James

[boardy]

Hi,

I have tried adjusting to a richer mix and it does run better than it did but still seems to bog down too much i.e. I am having to either lift it out the ground or stop the tines. After doing this it hesitates then manages to get back up to full speed. I havent used a tiller before, am I asking too much of it? The ground here is pretty good only slightly clay but not that heavy, as I say though I am not sure what to expect of it power wise, it feels like its bogging down too easy.

James

[smud6ie]

Can you see the if  governor is operating correctly ?You are not expecting too much,with 4 good horses it should be almost impossible to stall in soil.
smud6ie

[boardy]

It appears to be, I can see it opening the throttle fully when there is load but the engine still slows until the load is taken off. When its idling there isn't any 'surging' etc.

[smud6ie]

has making the mixture richer cured the stalling when quickly opening the throttle?
smud6ie

[boardy]

It definitely improved it a lot, it seems to respond most of the time but occasionally would still cut out.

[globetrotter]

It definitely sounds like fuel starvation. You should never stall the engine however deep the rotors go. I suspect fuel is not pumping properly possibly due to not adopting the correct procedure when fitting the new diaphragm.
Loosen the screws attaching the carburettor to the fuel tank then re tighten whilst at the same time holding the choke butterfly open by three eighths of an inch. This will allow the diaphragm to flex and therefore pump petrol properly.
Hope this helps.

[boardy]

Thanks for the reply, im away at the moment so will try again when i get back. Does this work the same with the pulsajet carb choke as it is a pull out push in type rather than a butterfly, so if i pull the choke lever out an equivalent amount or are we on about the throttle ? Its got a lot of work to do so hopefully I can get it running properly! On another note do you know why the choke lever is sucked back in when starting the engine?

[globetrotter]

Hi.
The procedure I outlined is for the pulsa jet carb. You have the older version with the semi automatic choke which should and does pull in when the engine starts. However the procedure is similar but hold the choke open when tightening the screws, jam it with a screwdriver if necessary. Be sure that there are no air leaks between carb and tank as this can cause the problem.

If you are fairly certain the carb is OK, remember the old adage "most carb problems are electrical". Check the points and condenser.