Dying Rotorvator

[JimmerG]

Are there any petrol heads here?

My rotorvator has just started dying on the spot. I've found the problem but don't really understand it.

Its a Webb, with a 4HP Briggs and Stratton. The throttle cable seems to attach to a bell crank on the under the air filter, attached to the bell crank is a very flimsey looking spring which seems to attach to a wire attched to the throttle itself - difficult to tell excatly what happens as the spring/throttle wire union is inside some casing, that I haven't had a chance to remove yet. What's happening is the flimsey spring is so flimsey, its allowing the throttle to reclose and consequently the machine stops.

Does anyone know why this flimsey spring is used, could I attach the throttle cable direct to the throttle?

Am I making any sense?

J

[taff]

not to me, but here's a manual page if you know the number?
Operator Manuals, Illustrated Parts Lists & Wiring Diagrams - Briggs & Stratton

and if no-one else knows,I'm sure thesepeople will

http://en.allexperts.com/q/Small-Engines-Lawn-1746/

[JimmerG]

Thanks for your help Taff,

I'll get the codes and have a good read.

J

[jacob marley]

When did last clean the air filter out? and do you put the petrol through a filter when filling the tank that is usually the problem .
And the flimsey spring you talk about is the govenor control spring and you can run without it being connected but you will not have to much control either flat out or just above tick over leave the spring where it is and check others out first....jacob

[geoff]

at the moment I'm restoring an old mountfield rotovator fitted with an aspero/tecumseh engine
Our library has a haynes manual on restoring lawnmowers. I have found it very useful as the same engines were used for mowers and rotovators
also our local lawnmower service dealer was very helpful with advice
you could also take the thing apart carefully making sketches and give it a good clean out
the lawnmower manual has a service schedule and a fault finding guide

[JerseyJimbo]

I work on all sorts of engines and Honda being one of them, they are of very similar ilk to a B&S... firstly forget about that spring, its is designed to be like that... as Jacob M points out it is the speed governor and nothing really to do with the running of the engine...

When you say dying on the spot, how is the engine, cold on choke, warm off choke properly warmed up? All of these will make a difference. Will it rev freely with no load on it, ie not in gear or drive but just revved from the throttle?

When did you last change the air filter or spark plug or oil? What is the condition of the oil and is the level good? Do you turn off the petrol every time you finish using the machine as like a Honda, you can get a very small flow of petrol from the carb into the crankcase and engine oil over time if you dont, so as the crankcase vents into the air intake during running can act as 'rich' running which can stall the engine under load?

Basically, stick a new air filter in it, change the spark plug, put in new oil, it will prbly cost you £10-15, and your machine should run like new...

If none of these things solve the problem ( it wont do any harm to do them anyway) then you are possibly looking at a blockage in the main carb jet (not uncommon) or an air leak on the gaskets after the carb, easy to fix if you have some basic tools and a bit of spanner knowledge...

or if you really get stuck feel free to send me a pm

[JimmerG]

Thanks for all of this guys - this is top notch help.

I haven't changed the filter for years so that might be somthing to do with it - I can imagine the airways are a little choked. The spark plug is new, the oil old but full, and there's apparently no way of shutting the fuel off. The only way of stopping the engine is by closing the throttle as far as it'll go and waiting....!

The curious stalling happens once the engine is warm and the choke is fully in, and when both under pressure and not under pressure, usually ony at high revs.

What I don't quite understand is the difference between this speed governor and the throttle. The control that is directly operated by the flimsy spring (and thus indirectly via the throttle cable) seems directly to alter the revs, its this control that seems to shut on its own accord (against the pull of the spring) and shut the revs and eventually the engine down.

Maybe I should try holding this spring actuated rev control in one place, and operating the throttle at the same time - to see what happens...

Have I made all this more complicated than it really is? - I only half understand what I'm talking about!!

J

[JerseyJimbo]

The spring is there to act as a damper between the speed governor and the throttle, im not sure of the exact set up in a B&S but in a Honda there are a set of centrifugal ballast weights that are actuated to move when the engine reaches a predetermined rpm. These weights will act on a lever that acts on the shaft that comes out of the block and attaches to the spring,then on to the throttle lever. The only way to control the rpm of these simple single cylinder engines is to open and close the throttle, there is no engine management to speak of.
If as you suggest, hold this governor and open the throttle the engine will rev, and rev, and rev. Then the only thing that will stop it revving will be the engines inability to supply enough fuel, or the valves bouncing unable to keep up with the engine speed...! Either that or the noise and vibration from the hard revving engine causes you to let go through panic

Stick a new air filter in it, it will thank you for it no matter what. Dip the oil and wipe it on the back of your hand, wear latex or nitrile gloves if you can and give it a sniff, if you can smell a hint of petrol then i suspect fuel contamination of your engine oil, id change that as well, even a small amount of petrol in your engine oil can affect the way it will run, especially when you say the problem happens when the engine is hot....

[geoff]

Make sure the vent to atmosphere on the petrol tank is clear, otherwise as fuel is used it will create a vacuum and prevent fuel from flowing into the engine