Kitchen Garden Forum

Firstly, I have read pretty much all the related posts and must say that I have learnt a lot, so thanks in advance:



Suffolk Punch 30S
Atco 114?
Dellorto carb

Bought from new some 15 years plus but it stopped working many years ago and has now become one of my resurrection projects


Cleaned carb/fresh petrol

Starts on choke needs to warm up before moving choke lever

Pilot/mixture jet flush with body

original fixed main jet

no air filter element fitted as yet

Problem: No throttle action

That is, I can only get the mower to run and cut the grass by fiddling with the pilot/mixture and throttle stop screw

the regulator/govenor function appears not to be working

Can I check the theory of operation of the Dellorto carb/Regulator/Govenor?

Is the throttle butterfly opened by the engine vacuum and then backed off by the regulator/govenor (R/G), this seems to be the only way that I can see it working

looking at the rear of the engine the R/G lever is at 21:00 and does not seem to move as engine speed varies (manually moving throttle butterfly)

I cannot see how this system should work unless the R/G lever has a starting point more like 22:00-23:00 and then moves anti-clock to back off the throttle

I would appreciate any help provided

Hello Mikec24,
The carb butterfly would be pulled open by the action of the throttle (governor) spring being tensioned. This is the spring that, if I recall correct, fits between the loop in the vertical link and the throttle arm....The arm, on the other end of which, the throttle cable acts.
The action of the governor would be to regulate revs by opposing the spring tension....such that an equilibrium? is set up at the desired revs. If the load from mowing starts to slow the revs then the spring tension would be more powerful than the governor action and the spring would pull the carb open some more to, within reason, maintain the revs at a constant.

A114 had a mechanical fly weight in sump governor, earlier A98 had an air vane external governor worked by forced air pressure from the flywheel fins.

It is very difficult to describe the action, it does sort of defy some logic especially in the specific case of A114 and I am trying to visualise it from 20+ years ago. I reckon the Dellorto fit finished in about 1991? It would all be easier to determine a fault if the machine was in front of me.!

A114 in sump governors could be problematical...and could drop to bits in several ways. The internal parts could become unclipped and move out of line and another regular one was for the spindle that the governor bobbin spins on coming loose and moving forward from the crankcase side...not good news and needing careful dealing with given that I suspect such parts would be obsolete. Often though an in sump failure can lead to a frighteningly screaming over revving engine rather than not reving.
Hoping it is an external failure with yours...but if it continues to puzzle I would think a local machinery agent would be able to quickly ascertain if it was a viable repair...but do look for a long established agent given the now age of Punch 30S.

I hope I have recalled it correctly. long time now since I've seen one.

Clive.

SOLVED

Thank you Clive
Turns out my logic was correct, in that I deduced thing were working back to front. On the top of the carb, the throttle butterfly is actuated by a plate with two holes in it, one for the spring return for the butterfly and another for I thought, the feedback from the actuator mechanism
In fact the feedback mechanism is fed back to the same hole as the return spring!
Reassembled, adjusted the mixture and idle screws and it all works as it should
Need to get a new air filter before final adjustments
Not typical of me to make such an error but many thanks for your assistance