Scooterotica

its funny that the more you read on a subject the more you realise that nobody knows what they are doing

i cant find where i read it at the momement but recently while looking around for a a/f ratio gauge i read "...optimum power is achieved with a afr of ?.? but in practice continued use at this ratio would ultimately cause serious engine damage"

it was on a snowmobile site/forum.

but in practice continued use at this ratio would ultimately cause serious engine damage keeps ringing in my head.

so i am assuming that what was suggested is that from the ideal afr it should then be richened up for safety

can anyone be more clear on this? or suggest what the safe afr is?

There is an ideal ratio for optimum power and there is an ideal ratio for engine longevity.
It's the same as timing. You could set your timing to say 14 degrees. You'd probably never blow your engine up but you would smash it up for being boring.

so wherefor the air/fuel ratio should be between 11:1 and 13:1, IMHO.

fishi

Taken from A.Bell's book:

Ratio of Fuel:Air
Starting 1:1-3
Idling 1:8-10
Low speed running 1:10-13
Light load ordinary running 1:14-16
Heavy load running 1:12-14

In the text he states that the required mixture is around 1:12 or 1:13 which is just right for WOT.

Safety is a relative statement...
To a racer on the very edge, which would probably be later on in a race meeting as the engine runs up to its maximum temperature at the end of a long straight, & then not quite blowing up is a margin of safety...
Mr Edmond's power-jet system that he uses, is probably aimed at a little enrichment more towards the second half of a race, because as the engine gets hotter (and I would assume its not in use all the time just when the EGT peaks at a certain temperature) its allowing the engine to be richened when needed, or to be leaned off to try to get the most power and then richened again when the temperature dictates...
But on the road normally a richer air fuel ratio would be considered safer...

The air fuel ratios have to vary, just to cope with the differing phases of carburation...with no one specific air fuel ratio that would suit every engine at all air speeds...
Theory & formula can dictate the most efficient A/F ratios to produce power with the most efficient burn... but in practice its not always ideal for a specific engine under load...

The good thing with two stroke engines is there are so many variables, but all linked... But with different approaches giving sometimes a very similar result...

Nick.. I think its safe to say some people know what they are doing. Come and watch the racing. Most of those guys know the score with the afr.

tony wrote:Nick.. I think its safe to say some people know what they are doing. Come and watch the racing. Most of those guys know the score with the afr.

im waiting for captain cruiser to get his act together then i will be coming out to offer my support, i dont have time or money to put a bike on the track and im still nursing injuries from enduro bikes but its worth coming out to watch and maybe fit some nice shopping baskets to your scooters when you are not looking.