SOHC.co.uk Forums > CB500/550
Carb jet size
Skoti:
Can feel my CB750F1 struggle a bit when over in the high alps.
It feels like the choke is on a bit, probably because the air is thinner up there.
So smaller main jets, not larger jets would probably be the cure for constant high altitude riding.
But when riding my newer BMW with electronic fuel injection management system, the fuel mixture adjusts automatic so no problems there.
taysidedragon:
I would guess that the PO just used what they could find, or was blind as a bat so couldn't read the jet numbers.
Sesman:
Err..is that correct. The school I went to taught that the atmosphere is composed on 78% nitrogen, 21% oxygen and 1% other gases at all altitudes. The atmospheric density however lessens with altitude, consequently this is why the motor struggles and loses power. The solution is intake compression management (supercharger) and fuel injection.
I suppose a smaller jet might help to maintain the optimum combustion ratio, assuming of course that intake vacuum is accurately compensated for as this lessens as you gain altitude affecting both fuel volume and atomisation. Basically, for any given jet size fuelling will lessen as you gain altitude and power is reduced.
I think that’s correct, but welcome any comments.
K2-K6:
I usually have to count backwards on my fingers to get my understanding in line with this ;D a little like my golf, as I total my shots up from how many zig~zag has been involved down one fairway.
Isn't it because air mass drops whereas fuel mass stays the same , causing it to move towards rich as the attitude accumulates. Then needing correction to bring equilibrium in AFR and hence combustion.
Sesman:
Nearly. Atmospheric density falls and hence vacuum drawing fuel also falls, hence less fuel, less ‘air’ and poorer atomisation resulting in less power. I have no idea if the combustion due to these effects is linear, but I somewhat doubt it due to the dissimilar fluid characteristics of air and fuel….i think🤔
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version