Today I went for a spin on the bike, first trip since Remembrance Sunday, I did just under 70 miles before I decided I was chilling down quickly due to an annoying mist type of rain

On the way round, I did something I hadn't done for years, I filled my fuel tank with genuine 4 star leaded fuel !!

With about a 1/4 tank, I filled it to the brim & off I went

Bike ran very well all day, but felt that after filling, it was that little better than before - previous fuel was 98 unleaded

Does anyone else manage to fill up with 4 star - there are a few retailers who still sell this or has anyone noted a better running motor with 4 star

Just asking

Best regards

Jo'b

email (option): Jonnyob1@googlemail.com

Not really an answer but a fuel related comment...

Yesterday I started up the B33 after it had been laid up since mid August (My broken ankle wasn't much use for kickstarting for 5 months or so)...

I thought this would be a good test for the 'stale fuel in a fortnight' theory.....I'm happy to report it started on the third kick...Ian

email (option): ian@wright52.plus.com

I have started up vintage bikes on unleaded fuel 18 months or even older.
Never any bother.
Old fuel doesn't bother any of the Honda engines in my mowers or generators etc.

Anything really suspect goes into the TVO tractor.

anotehr reason to keep using obselete machinery.

My attitude is...if it'll burn it'll do.


effinol bothers me more, filthy corrosive stuff.

I went out on mine today with the air temperature hardly above freezing and couldn't believe how well it was going along a duel carriageway, but coming home it seemed to struggle up the long hills. then I noticed the trees and grass bending and realised it was the wind direction which allthough not very strong made a big difference.

My Commando started easily with 15% ethonal fuel from the USA after standing over a year. It ran a bit lumpy at low speed, so I cleaned the pilots out and was as good as gold

I normaly run my bikes on the the cheapest petrol I can find, usually with no problems. But once when I put expensive Shell stuff in the Commando the carbs iced up.

For me going unleaded and then with ethonal has been no problem on any old bike. I think petrol now is better than it has ever been.

Cold air temperatures make for a more dense fuel/air mixture...That improves effective cylinder filling and more fuel in means a bigger bang and more power out...
It's a good argument for using an M20 in the winter....or on a wet, cool day.

Ironically most people ride them in the summer mainly, when the bike gets slower with rising temperatures as the opposite effect comes into play... ...

I suppose a slow ride on a sunny day might be better than a fast ride in the winter though... ...Ian

email (option): ian@wright52.plus.com

they was a subject on the forum and it was suggested that the m20 would run better on super unleaded mine seem to

email (option): roger.beck@node6.com

On the subject of octane rating at least, putting a higher octane fuel into an engine will not make it go any faster unless the fuel originally used was a lower rating than that required by the engines design...

An engine must be designed to take advantage of the different anti knock characteristics etc. of a higher octane rating before any more power is produced...

If you put a low octane fuel into an engine with a high compression ratio the result will be predetonation...

However, if you put a high octane fuel into an engine with a low compression ratio, nothing will change...The fuel itself has no more potential to produce power in an engine designed for low octane than the lower octane fuel itself...

It's the changes made to an engines design to take advantage of the potential of a high octane fuel that result in a power increase...not the presence of the fuel itself.

If that wasn't the case there would be no need to fit high compression pistons etc...You would just increase the octane rating...

How to assess the impact of modern fuels on an old engine I'm not too sure about...I'm not really convinced that a 'seat of the pants' impression from riding the bike is a very accurate or useful measure...

Even if you do accurately identify and quantify a difference it does nothing to explain the reasons for that difference.
Therefore, if performance is worse, it leaves you with no information to consider in contemplating alterations that might lead to an improvement....Ian

email (option): ian@wright52.plus.com

If any one has any old fuel they are dissatisfied with I will collect it FOC.

Just a thought. Would modern "leaded" petrol, probably unleaded with a lead replacement additive, result in a leaner mixture than unleaded petrol?

email (option): pvlietstra@gmail.com

I've tried to resist it but I'm afraid I'm slipping into lecturer mode, sit back and be prepared to be bored.
There are two main trouble that aflict engines relating to fuel, they are; 1) pre-ignition and 2) detonation, a brief explantion follows;

1) Pre-ignition occurs when the air/fuel mix starts to spontainiously ignite before the spark has happened. It is mainly caused by local over heating in the cylinder of things like exhaust valves, sparking plug electrodes or carbon build up.
2) Detonation occurs when the already burning air/fuel mix pressurises a unburnt portion of the mix sufficently to raise it's temperature enough to cause it to ignite in an uncontrolled way. Common causes are over advanced ignition timming and too low an anti- knock value (Octain rating) of the fuel.

As far as M20's are concerned pre-ignition can happen as there is a lot of surface area exposed the the burning gases and like all large sidevalve cylinders they have only adequate cooling.
Detonation is unlikely to occure due to RON (reaseach octane number)of the fuel, more on this if you are interested, but ignition timing is often vague to put it mildly.
When I snap my fingers you will wake up.
Richard

email (option): richard177smith@btinternet.com