Briggs Stratton engine 5hp I/C starts ok, runs, but will not rev

Model 132232, type 0322-01, Pulsa Jet Carb.(Mechanical governor), remote throttle on rotavator.

The engine starts with choke, but will only idle on the fastest ‘Run’ setting and will idle without choke when warm. The throttle shaft on the carb body oscillates on its own, pulsing the revs at idle.

When I spotted this I found that if I operate the throttle spindle manually at the carb body, I can make the engine rev fully and without any misfire or smoke.

The engine stood unused for 3 years and the things tried so far are -

- Checking governor and throttle spring and linkages. Difficult to see, but I think they are all there and connected correctly.

- New spark plug, oil and air filter

- New petrol

- Throttle cable adjusted

- New diaphragm and cleaned accessible passageways with diaphragm cover removed

- Checked choke works as it should with air filter removed

- Removed and cleaned idle needle valve and jet

- Looked at lots of internet posts

This is the Atco Merry Tiller model where the remote throttle connects to the engine below the fuel tank close to where the governor shaft exits the engine.

Rather not strip the carb until all other possibilities explored, particularly as it runs ok when throttle on carb body is turned directly.

Any advice welcome please. Pete (1st post)

Briggs Stratton engine 5hp I/C starts ok, runs, but will not rev