compression

Hi John,

I could only dream about figures like that, I had a thread running a while ago about the same thing, my psi figures were way below yours, and I can easily kick it over (hot or cold). To try and improve the psi reading I even fitted a new head + valves etc, but it didn't improve much. I have to say that my M50 (Slimline 1960) performance seems ok, ie 55-60 ishon the level but I do tend to ring it neck a bit.As its only a 350 with a lightish short stroke I always tend to drop a gear(or two) to maintain momentum on hills......................It is what it is!

âRegards John O

Original thread April 2017

I'd suggest a rev counter (so you can see that it's really not revving too hard - they all sound like that) and a pair of ear plugs. Ear plugs are good for at least +10mph in every gear.

As Jo Craig is supposed to have said: "an engine has no sense or feeling...."

My model 50 is still in boxes and missing a few important parts so I can't comment, but I took my poorly running jubilee out at the weekend and that comfortably managed 45, so I guess your 350 should do a bit better! Have you checked the gearing?

I think you may be barking up the wrong tree here. Try checking your ignition timing and points gap. Give it a bit of advance them try a retard and see what happens. Easy if you have manual advance system on a magneto.

Next try feathering the throttle a bit or give it a bit of choke to see how it behaves. Then change the jetting to suit.

Yes, low compression makes it flatter than a fart, but so do a combination of other things too.

Try testing your compression gauge on various other bikes for comparison and get some sort of bench mark.

Hi John,

Boo-cock? has good points,....check the timing, etc mine was a little bit retarded, and correcting it improved performance. I achieved a genuine 68 mph on Saturday (Our last Yorks branch ride out) but it was on the A59 coming to Bolton Abbey down hill ! I have a sat-nav on the bike to confirm speeds.(the chrono reads about 8mph fast at 60!)

Regards John O

Have you checked the valve timing?, not whether the marks line up but with a timing disc , It seems it can be out enough to turn a sloth into a slug.Without substantial modification it will never feel happy trying to keep up with A road and motorway traffic. However it is an ideal mount for club runs round muddy lanes and trips to the shops. I don't have a bike that will do less than 90mph but none are relaxed when cruising over 60 , its all relative.

You cannot expect a 350 single to be happy, flogging up hill in top gear, better to change down, and use a few more revs. that being said, my old BSA B31 would hold 65 m.p.h, on the flat, the equivalent Norton should be capable of, at least, the same.

The smaller engines are happier when they have good RPMs. Slogging the engine as it sounds like you are will not make it last any longer. Give 'er some stick and she'll love you for it.

Sounds a little rich probably on the needle position.

Interesting, I know nothing about Amal needles but wonder if a new needle and needle jet would help? Is the cutaway standard?

Apart from the carburation, ignition & valve timing issues already discussed here are a couple of things that took the edge off my 19S performance in the past:

At one point I thought it would be a good idea to fit a carb bellmouth with gauze to act as a spark arrestor. It took me a while to realise that it also presented a significant resistance to air flow.

At another time the silencer developed a bit of a rattle which I ignored for a while but eventually decided to treat the bike to a new exhaust. This gave a noticeable increase in performance, I can only assume that the rattle was due to a loose baffle which was restricting gas flow.

Ian McD

are the chain/sprockets in good condition

are there any brakes sticking

tappets ok

check the chainguard see if its sitting on the chain when you get on the bike

is the fork oil leaking from the top nut and running down dripping off the bottom

Barry

Most of my enjoyment in running old bikes stem from the oppertunity to tinker and "improve" things .

I must admit all the 350s I've had have felt gutless. I had a B31 in the 70s that wouldn't do more than 60 realistically; more recently a Velo Viper which went well but only if it was wound up till the valves nearly bounced.

They all suffer from having to lug about a heavy frame etc usually well capable of handling their 500cc stablemates.

I much prefer the lazier power delivery of the bigger engines.

I got to "test ride" a Yamaha MT09, the instant power from any revs or speed is enough to get the front wheel up so fast that you could ride it like a unicycle (well --someone could!) , bloody terrifying , and impossible down some muddy lane without electronic gismos to manage it, bit like a jet fighter that is uncontrolable without a computer to help. Give me a 350 Norton anytime, or a test ride in a Supermarine Spitfire!.

My 59 NH 350 Ariel would do about 75mph and hold 60mph loaded with luggage two up. To be fare though it would struggle on hills so I just changed down.

Check other things as suggested.