[ricster]

whilst starting my 3 hp B&S engined rotavator, the engine speed raced to full RPM and was unable to reduce the speed using the throttle control lever even though the cable and linkages are moving.  It worked perfectly the day before! Any ideas/suggestions would be appreciated, many thanks.

[R Tallentire]

I suspect that not all the linkages are moving otherwise the throttle would close. Check the lever on top of the throttle butterfly, this usually has an adjustment screw on it to set the tickover speed. With mechanical governors, when the engine is not running this is normally in the open (full speed) position irrespective of where the control lever is. You should be able to move the butterfly lever into the closed position against the spring pressure exerted by the governor or control lever mechanism, (is the spring broken?) If it was just stuck it will now probably be OK so oil all pivot points and try the engine again. If the lever is jammed solid, or the lever can be lifted out, the screw inside the carb may have come loose and the throttle disc displaced, this could be serious as the screw will have gone through the engine. If it appears that the governor, at the other end of the wire link(s), is jammed (mechanical governors) a strip down of the engine is needed to check what is wrong inside. Air vane governors rarely stick, removing the fan cover and cleaning out dirt etc. should have an air vane working properly.

[grendel]

if the engine has a governor check that you havent got a lump of dirt wedging the governor open.
Grendel

[ricster]

tahnks for the replies. i know it has a governor fitted but dont know if its a mechanical or air vane type - how does one tell the difference betwwen the two and where would i find it? sorry for sounding daft but im not very mechanically minded but do understand the theory behind the workings of an engine.

[grendel]

my aspera has an arm coming out of the side of the engine, linked to the throttle valve, speed control is by tensioning a spring acting on that arm, not sure of the B&S. just check the throttle valve is working, not jammed wide open.

Grendel

[Bigbadfrankie]

the briggs is air vane. check the springs. Gwiz will be along with help check the previous posts

[Gwiz]

As the other chaps have said, check that the govenor links and springs are attatched and that there isn't anything holding the links in the full rpm position, Check also that the carb assembly hasn't become loose or that the gasket isn't damaged in anyway as this will allow a weak mixture and could also increase rpm. Check the throttle shaft in the carb as if this is loose (worn) it can also allow excess air in to weaken the mixture also.
And while you're looking at the machine, check to see if the throttle cable hasn't smply slipped so that you can't move it back to idle......

[ricster]

Once again, many thanks for the replies and advice. Ive looked at the entire mechanisms and none of linkages/springs are broken, however, Im unsure if something could be missing or has snapped off while using the machine. The governor spring extends all the way out when throttle lever is pulled back.
What was of note is how 'slack' the throttle shaft is - I can easily pull it out of the top of the carb although not fully as it comes to a stop - Im assuming there must be some kind of screw, rivet or whatever attached to the other end of the shaft which is inside the carb. I'll try and locate a engineers drawing of the whole assembly and go from there. Once again, many thanks for all your help.

[grendel]

sounds like the throttle plate may have become detached, you shouldnt really have any movement up and down as the plate on the shaft should stop that, might be time to take the carb off and look, then you will have to find the plate and screw as if they are inside the engine they can cause further problems.
Grendel

[ricster]

Thanks Grendel, I think the week-end will be spent stripping the carb and related assemblies. Ive managed to source a technical drawing of the componenets from the official B&S website.