Tarpen Generating Set

The Evolution of A JAP Powered  Tarpen Generating Set

A History

Back in 2014 I purchased a Tarpen 110v DC Dynamo at Kingsfold .
I had in “stock” a JAP O series 34cc 2 stroke taken off a “Jobber” motorised garden tool .This original Dynamo saw service with a succesion of engines (Petter AS,Petter A1, Petter AA Diesel and at one time A Lister D) Then it gave up the ghost and stopped generating,at which point it was retired into storage,the engines having been moved on to others as time went by. Then A couple of years ago I was lucky enough to find another similar Tarpen Dynamo and Petrol Tank on ebay (locally) and purchased it for the bargain price of £9. This 2nd Dynamo was paired up with the JAP O series ( 34cc 1/4 HP ) and the story begins .


JAP O series powered Generating Set and home made Switchboard on show at the Chequers Laddingford in 2018
A You Tube video of the above setup can be found HERE

This setup worked quite well , the engine would run all day quite happily and with the large Tarpen tank did not require re fueling during a show .Being a 2 stroke it was a bit smoky at times but it was OK in the main .

If you look at the photo above, the bulbs are low wattage 50 volt ones and the engine is running a 400w  Dynamo so it was OK but a little underpowered
The speed could be increased to provide the full 110 volts but it would “scream” a little at such high revs .

When the opportunity arose to purchase a JAP 4/2 engine ( 245cc 2 1/2 HP)
at a reasonable price I saw it as a suitable replacement for the small O series .

JAP 4/2 version with the same Switchboard and a home made Control Box  at Kempton Great Engines in 2019
A You Tube video of the above setup ( without control box) can be found HERE
notice the 100w larger light bulbs .

This setup/version appeared to be the answer -however after 2 hours or so of running fine  the engine would suddenly stop /stall for no apparent reason ?
If it was left to cool down for 5 mins the engine would start again no problem so it was thought to be caused by fuel evaporation when the engine got too hot ?but nothing could be done ( a lot was tried ) to rectify this problem but it just was not to be which is no good for shows if the engine keeps  stopping .

At this time I also had a JAP 4/3 ( 288cc 3 1/2 HP) running a pump
with exactly the same problem so obviously JAP engines were not designed to be runall day ??  at least thats my opinion ! .

Part 2 – Beginings

So having tried all sorts of things to try and fathom out why (my) JAP Engines would not run continuously for more than a couple of hours without stalling and given up when no specific reason could be found ,they were almost consigned to the for sale section ! however before this happened a moment of inspiration occured . The only possible reason for the engine stopping was evaporation of the petrol ? so what would happen if the engine was run on propane gas ? – IE nothing to evaporate !

One of my other engine interests is ex GPO propane powered engineering plant -in GPO terms “PED” or Portable Engine Device , I currently have 2 Villiers Pumps and a number of 24v Generators with 2 different Villiers,Honda G20 ( very early import) Kohler and JAP engines -none of which ( Including the JAP ) fail to run all day with out missing a beat .

I also have in stock a couple of spare Villiers Gas carburettors .

Now as previously stated in part 1 – I am not an expert engineer but I know someone who is – what if the Villiers Carb could be adapted to fit the JAP 4/2  hmmmm I wonder? So in late 2019 In steps friend and fellow group member Phill Sheppard who is an expert engineer in no uncertain terms ! – Phill was duly commissioned to make me an adaptor plate from scratch – the story progresses .

Villers Gas Carburetor fitted to JAP 4 series manifold with Phill Sheppard designed and built adaptor plate

Circumstances dictated that the duly modified carb setup (as seen above) was not delivered until the re scheduled Paddock Wood Crank up , which was just before the “lockdown” was put in place, so this instantly became the first project to be developed whilst “staying at home”

One of the first things that needed to be sorted was the gas inlet , the normal vertical hose tail  inlet would have to be changed for either a right angled one or a banjo type fitting as the existing inlet would foul the adaptor plate .


Early version of the Carburettor setup with banjo type gas inlet
giving about a millimeter of clearance to the adaptor plate

A suitable banjo was in stock so that was the way to go !

The other casualty of the setup was the original Villiers Air Filter and its fitting plate  which just would not fit in the gap afforded between the manifold and the JAP governor housing also a cm of metal had to be removed from the rear of the oval shaped plate at the bottom of the carb to clear a part of the crankcase ribbing .

A simple mesh  covered by a thin aluminium sheet was the replacement air filter solution .  Then It was time to try it out !


Gas primed – first pull of the rope and away she went !
so far so good –