air/fuel

[Ratters]

can anyone shed any light on this air/fuel ratio please?? it's the dotted line btw. ie: how bad it is, what it should be etc


thank you

[Graham]

if its the more bumpy line, ok in the middle far to rich at either end

[Ratters]

thanks graham what should the ratio be then as an ok average?

i've always thought it was rich at the top end, always said that to trig/denz/etc but i've always just gone by the plug colour which when i've changed them in the past have always been an ok colour.

[Graham]

the plug colour isnt a great way to check mixture, plug colour as much proves the plug is the right grade for the engine, change the plug grade and the colour will change even though you havnt touched the mixture, that said the plugs can give an indication of mixture but only if you use new plugs and drive at a steady throttle position for a mile or so, then symaltaniously switch the engine off and dip the clutch and coast to a halt, the plugsbwill then show you the mixture at the point you shut off, the tricky bit is finding a road long and empty enough to checkout big throttle openings

i'd say your motors rich enough at th top end its probably costing you some power and its definately costing you economy wise

mixture wise your looking for around 14.1 most of the time maybe a bit leaner say 14.5 light throttle, and richer at full throttle say 12.5-13.1,

the only real exception to that are silly horsepower turbo engines which have to be run really really rich at high boost

[alladdin]

i dont follow the mixture /road speed graph ?
is this basicaly an rpm graph with a constant (wide open) throttle ?

[Ratters]

yeah, as far i know it was full throttle from low revs upwards in 3rd gear.

...which isn't really how it's driven day to day driving is it?

[alladdin]

no but its an idea of you a/f ratio under full load across the rev range. its rich but safe i guess.

[Miniliteman]

yeah, as far i know it was full throttle from low revs upwards in 3rd gear.

...which isn't really how it's driven day to day driving is it?

3rd gear? Or 2nd? Or do you have a low ratio in the axle?
It's not that unusual for the lambda-reading to go walkabout at high rpm after peak-power. The mixture doesn't have time anymore to burn properly and fully, especially if the ignitiontiming at high rpm isn't correct.

[joe GSM]

Its runnig too rich at the end,reason why it drops of that much at top is that it so rich its blowing the spark out hence bore wash.

[razorass]

You are running way, way too lean from 35mph to 48 mph, that sort of AFR is ok for cruising, no way for for a wot pull. from 48 to 54 it's ok around 13-12.5 AFR, after that goes again way too rich resulting in loss of top end hp.

The over rich condition below 35mph could be caused by your carbs having abit too large pump jets, so when the dyno operator floors it, it goes briefly rich.

If it was my engine, i Would stick a wideband on it. Then change smaller pump jets, larger main jets and smaller aux airs and go from there.

..Assuming this is an carburated engine.

[razorass]

You are running way, way too lean from 35mph to 48 mph, that sort of AFR is ok for cruising, no way for for a wot pull. from 48 to 54 it's ok around 13-12.5 AFR, after that goes again way too rich resulting in loss of top end hp.

The over rich condition below 35mph could be caused by your carbs having abit too large pump jets, so when the dyno operator floors it, it goes briefly rich.

If it was my engine, i Would stick a wideband on it. Then change smaller pump jets, larger main jets and smaller aux airs and go from there.

..Assuming this is an carburated engine.

Sorry, BIGGER Aux airs.. my bad.

[Ratters]

yes carbed x-flow engine running on bike carbs. now that puts a new twist on everything side advice wise thanks for the info so far though guys