Poor mpg

I have checked the mpg of my slimline model 50 (59 engine) over many years. I check from full tank to full tank and it always comes back at 78 mpg, regardless of solo or two up riding.

My model 50 is standard gearing but using 18 inch wheels.

(The pre/fbed Model 50 with a 59 engine in the making will have 19 inch wheels and a 20T gearbox sprocket so I'm expecting even more mpg)

I use a Mk 1 Amal 626 26mm carb with a 210 main jet but no air filter to date. (Till I find it) Plugs are Champion N5 and a lovely colour, always have been.

Most importantly I use E0 petrol, currently ESSO Supreme Synergyy Supreme 97 RON BS 7800. If you have leaded fuel I should use it while you can. lead memory may protect your valve seats for years to come. Mine starts first time so it is in good tune.

My tyres are modern Avon's @ 30psi front and rear. If it makes any odds, oil is SAE 40 topped up with SAE 30 in the colder months.

As David suggests, you need to conduct your tests over a decent period but in different weather and include some longer journeys to give you a fair average. Some say damp weather gives a slightly better MPG but using ethanol will give a lower MPG.

Let us know how you get on please.

Worn needle jet and ignition timing are prime suspects. What colour is your plug? I could always tell when I needed a new needle jet when the mpg dropped noticeably. Retarded ignition is bad for mpg, as are binding brakes.

David:

Can you get your friend to post some info about the air filter he fitted to his ES2?

I have been looking for 20 years for an air filter that would fit my Model 50, but no luck.

The spare parts list for all models for 1961/62 lists an air cleaner p/n 18684 for all singles. I have asked before if anyone has information or photos of it and have received no replies.

Anyone out there now?

Mike

Mike / David,

I have said before that I have one, just not been able to find it. I hope to do an extensive search this summer and when I find it I will photograph it and post.

I can tell you that the threads are imperial and also fit the Amal 626 that I have on my Model 50.

when I find it, it may be worth having some more made, in stainless?

Maybe slightly rich then John. Are you sure the mixture screw on the carb is set right? Can't think of a lot else. Be very careful not to weaken it too much, you might be surprised just how much influence this has. I am assuming you have a 1" carb fitted, mine is a 26mm so about the same.

Even in your terrain, one would expect at least 60 mpg out of a Model 50 on decent petrol.

A bent needle won't be doing the needle jet any good. For all it costs, a new needle and jet would be top of my list. The dark plug does imply running slightly rich - or perhaps some oil burning. Check your advance/retard springs. Could they be weak and not retarding the ignition when the revs drop? THatcould explain the reluctance to idle.

Hi John

My 1960 (Slimline) M50 gets about 70mpg most of the time, even when I thrash it ! Plug is slightly rich, I always run on BP ultimate.Like Michael I would be very interested in the air filter Daves friend mentions, it would save modifying my cy head to get carb to line up with existing hole between oil tank and battery box! ( see my previous posts on subject)

At the moment bike is on trailer behind motor home ready for the trip to Italy for rally!.........Very excited......I sail tomorrow from Dover.

Regards John O

The said air filter has a very thin pancake, designed to fit between manifold and oil tank without modification.

Hi all:

I went out and measured my Model 50. There is only about 7/8" of clearance between the bell mouth and the oil tank. If you remove the bell mouth you will get more clearance, maybe 1-1/8"???

The problem with any type of pancake filter is that with any increase in diameter of the filter, the clearance disappears caused by the angle of the carb mounting. So, to physically fit, the filter would have to be quite small in diameter and short in stack height.

Hopefully, Neil Wyatt will be able to find his old one.

John, I agree about the carb but Mk 1 626 Amal works for me.

I don't think weight is much of a factor because my Model 50 still gives 78 mpg two up and even with luggage.

Your hills on the other hand will be a factor. Any chance of a test on flatter terrain?

Good Luck.