SOHC.co.uk Forums > CB750

re-jetting needed?

<< < (5/16) > >>

El__burro:
Plug reading with 110 jets was almost perfect.
The only problem was poor top speed. Since (this morning) I swapped the jets it's been worse, niw it struggles even to start in 1st gear.
i have put the old jets and cleaned replaced the plugs but the problem i is still there.
The needles are in the second gap (stock position) if i remember well.
I guess (and hope) that a good carb clean will sort the problem.
Is 122 is too big or i need to look at other settings?
Thanks
el__burro

Sent from my SM-G935F using Tapatalk

hairygit:
Float levels may be worth checking again, and check float valves are shutting fuel off as they should. No way should it be running too rich on 110's unless it is flooding!

Sent from my X6pro using Tapatalk

K2-K6:
There's something odd there as switching the jets back to 110 should get it back to where it was.

Are you confident that the ignition is advancing? Have you anything to check that?

El__burro:
I thought about checking the ignition, could swapping the jets could have caused it?
Shall I put the 122 and look at ignition timing then?
Float levels looks ok. (I have about 30ml of fuel in each carb)
Thanks
el__burro


Sent from my SM-G935F using Tapatalk

K2-K6:
No, swapping the jets will not make a permanent change to the bike as if you swap them back as you've done it should be back to what you had before.

If it was in front of me I'd run it on the 110's as that gave reasonable plug colour and then look to see if anything else is a problem.

What the ignition does is to start at low revs with the static setting you adjust the system to in setting it up, as the revs rise the advance / retard mech brings the ignition point forward. If this doesn't happen properly the engine will struggle to gain rpm much over about 5000rpm and prevent making much power up there. You'd check this with a strobe to see if it moves and returns as you run the engine up and down revs.
You need to verify this to avoid chasing other things, if ignition checks out then you can work through carb issues more logically.

The two systems are not mechanically related,  they only come together in combined effect in the combustion chamber to make it run but each must obviously be ok to get the motor to respond well.

Navigation

[0] Message Index

[#] Next page

[*] Previous page