Ruggerini MD151 hunting

[Michael Gilbert]

Hi All , I've recently got my Ruggerini 151 engined Enfield on the road and after a lot of playing with the gearing I've now got a bike i'm happy with
apart from the engine is "hunting" (like when you leave the choke on) on tickover and at low revs. The air cleaner is the correct one for the engine and is clean. I run a separate spill pipe back to the tank. I contacted the company that reconditioned the pumps and injectors and was told that it could be an air leak, so I annealed every copper washer and made sure all the tubing was new with the correct size clips. No improvement.
Has anyone had/overcome this problem, or any ideas. I would be delighted to hear from you. Michael.

[Diesel Dave]

Firstly congratulations on getting the bike back on the road.

If by ‘Hunting’ you mean an uneven tick over producing a bit of black smoke then this is usually caused by setting the idle too low and the fuel screw too high.

Also if you have an ‘overfuel’ plunger on the end of the rack limit, this will cause problems on a motorcycle fitting.

Remember the timing is fixed so you cannot set the idle too low, it should usually be around 1200 rpm.

If you retain the overfuel plunger (this is fitted to allow the engine to cope with short term high demands such as someone throwing shovelfuls of wet sand into and empty concrete mixer). When fitted to a motorcycle it’s possible to overheat the engine by forcing it into ‘overfuel’ constantly when pushing hard down the motorway.

[Michael Gilbert]

Dave, I believe the hunting was caused by the timing on one cylinder being slightly different to the other. When I checked the timing by the fuel rising up the tube at the start of injection I found the two cylinders varied. I tracked it down to the working area of the "buckets" that go between the camshaft and the injector pumps were slightly different sizes when tested with a micrometer. I sorted through the buckets I have (from four engines) and found two the same, I then shimmed under the pumps accordingly and hey presto a smooth running engine.
I'm actually quite pleased with myself. Michael.

[Diesel Dave]

Well done, grand job