I had originally toyed with the idea of turning this into a GS150 replica and had started collecting GS parts when I could find them. In the interim I had changed the original Puch style seat that came with it and installed a PX based 177 engine. The seat was period correct for this type of scooter and looked good but I didn’t like the riding position and it would “bounce” a bit when riding on rougher surfaces. When a GS seat came up at a good price, I replaced the single seat pretty quickly.
As time goes by and you collect more parts and scooters sometimes you get lucky. Not always but sometimes. I got a GS150 VS3 engine as a part trade. It had been reconditioned by a friend and had some expensive engine upgrades installed. There is a niche market for performance parts for these older 1950’s engines and frames, however they can be fairly pricey. This wasn’t running when I got it but was reasonably complete and looked in very good condition. One of the best upgrades for this engine was a 12v ignition and lighting system by Pinasco. It was really the only option available at the time this engine was rebuilt but now the SIP vape system has proved to be an excellent alternative. The plastic CDI unit had a broken mount but that was easy to replace with an aftermarket one. It had an aftermarket intake and a Polini CP23mm carburetor both upgrades to the factory Dellorto fuel system. I had never used one of these tiny carburetors before and had to have a read up on them before getting the engine running.
Luckily getting the engine running and installing it into the Douglas frame was pretty straight forward. There were some issues with the throttle cable as the cable for the PX carb was too short and the Polini only had a pull choke and not a cable operated one. Replacing the pull choke was easy enough and the wiring was pretty straight forward as well because there had been a 12v system in place with the PX engine, I only had to modify a few things to get the lights working. A new, longer throttle cable, fuel line, angled foam airfilter and a homemade choke assembly, sorted out the fueling system and I had a brake switch off a Honda motorcycle in my cack stash. While investigating how to get the brake switch working, I discovered one of the bolts for the rear suspension mounting bracket had stripped. As it turned out these were both UNC bolts and were very hard to find locally so were replaced with longer metric equivalent ones. The longer bolts made for a good mounting point for the brake switch and the brake actuator had a tab with a hole in it for just this sort of thing.
One of the issues (and there are a few) with doing engine swaps on these older scooters is the room available for things like the carburetor and throttle/choke cabling and the airfilter. The side pods on these Douglas scooters are quite small in comparison to GS150 ones so there can be issues getting everything to fit inside the pod. Also because the suspension on older scooters is usually not too good then that can cause clearance issues as well when the spring is compressed and the engine pivots in the frame. I was recommended a Pinasco rear shock absorber for this set up which has turned out very well so far. The shocks for these scooters are quite a bit longer than your average largeframe or PX ones and there aren’t a lot of options currently available. With the current set-up the Polini carb sits up higher than the bottom of the fuel tank so there may be some problems as the fuel level drops. On other bikes I have used electric fuel pumps to overcome this but may just keep a spare fuel bottle in the sidepod for emergencies.
Hurry up summer.