SOHC.co.uk Forums > CB750
re-jetting needed?
Greebo:
--- Quote from: El__burro on June 29, 2017, 10:37:06 PM ---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
--- End quote ---
I have 138 main jets & my needles are set on the bottom notch [5th] & it runs great & ticks over perfectly
I have also tried / experimented with the ignition timing, set to stock & also tried it 10deg' advanced but the 2 settings did not seem to make any difference in the way the bike runs.
I think when you first changed the jets you must have disturbed something else in the carbs settings...I say this because when you put the stock jets back you say it had the same problem, obviously it did not have this issue before you started tinkering.
neilg:
Do you have any one near who runs a dyno? When I changed the carbs on my BMW a few years ago I tried all the usual methods with runs and plug chops up and down the local by-pass but couldn't get it right. In the end I found the only way to get it sorted was to take it to a specialist. He ran it up on the dyno and sorted everything right through the range from tick over to full throttle. The work also included setting the optimum ignition timing etc. I appreciate the cost might be a put off but he did in a few hours what was taking me an eternity in guess work messing with buying and swapping different jets only to find it still wasn't right.
El__burro:
I've started by removing the carbs as i wanted to give it a clean anyway, put the 122 jets and drop the needle by locking it on the top slot, (see pic)
Not sure if should be the way around.
Hopefully I'll receive a confirmation before mounting it all back and do a timing check.
Thanks
el__burro
Sent from my SM-G935F using Tapatalk
hairygit:
Dropping the needle like you have makes it run weaker, which is what you need!
El__burro:
I have also realized that choke lever wasn't opening all the 4 shutters at the same level. Fixed this too.
Thanks
el__burro
Sent from my SM-G935F using Tapatalk
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