SOHC.co.uk Forums > CB750

CB750 F2

<< < (2/4) > >>

blackeagles:
an interesting idea and i assume my 'local' has a gas tester although i have not seen one when there.

i just read a post you did back in 2017 where you were quoting 'honda manual' about syncing then adjusting slow running no 2 screw to max rev then back 100rpm, readjust and then do the others likewise.  i cant say i have tried this, just set them all the same setting so maybe i will try although i have got to get the syncing right/checked first and find an electronic rev counter to do the final adjusting as i doubt the bike one is accurate enough (or maybe it is goo enought as i'm not looking for the last bhp!)

K2-K6:
The car mot equipment usually has to have a decent calibrated meter so maybe a scource if they are friendly  :)

Was my previous post (referred to  by you above) the one with a photo from the Honda manual in it?

The routine is their official one and it does indicate that the factory carries out this routine during production to give accurate running at low speed.
They also state not to move the screws in normal service,  but only re-established them after carb rebuild.  What it's doing is normalising each individual cylinder's combustion process until they are equal,  irrespective of the final screw position as it's combustion parity that counts in smooth running.
It's a very neat routine that effectively "micrometer" adjusts the low speed running to refine it,  but as you point out,  main throttle syncing needs to be correct before this stage.

I think its just as accurate if you sync them first with Bryan's bench method,  you don't need gauges for it this way.

Rev counter,  if you've a DMM ( digital multi meter) that reads frequency,  that will give you an accurate rev counter when connected to one points set as one revolution produces one pulse. 

blackeagles:
i don't think it had a pic, just a requote from a post you did earlier but it still hold good today and something i will try.

bike is not fully insured so can not run it down the bypass to test out the changes, or go to the local garage, although i don't think i am that far away as things stand.  i am going to reset the gauges by using one cylinder so they should all  show the same afterwards (i did do the bench set but it ran badly so may have screwed that up) and anyway i guess they only need to be close not necessarily spot on - i may see if i can borrow carbtune pro or such if i feel it will help.

K2-K6:
The exhaust analysis would be to assess if you've a basic mixture problem in regard to uncontrolled fuel faults.  By reading O2 C0 and HC, it would be clear if there's an underlying issue. 

It won't be necessary if you can work through and get where you need conventionally though.

royhall:
There should be a non return valve in the accelerator pump body (the removable cap)  that prevents fuel flow until the diaphragm is pumped, could that possibly be stuck slightly open. They are still available from CMS. https://www.cmsnl.com/honda-cb750f2-super-sport-england_model14689/diaphragm-pump_16021393004/#.Xw6z8puSmUl

There are no restrictors as such in mine just small bore brass tubes inside rubber tubes (I assume to prevent the rubber tubes collapsing). There's a small air vent in the side of the carb bodies, if one or more is blocked it's impossible to get even running. The vent is hard to see and cannot be cleaned with carbs assembled. Also, I have never seen that vent mentioned in any manual.

My F2 runs spot on after the second carb rebuild to clean the vents, where previously it would not balance up at all. And don't forget, the air screws work in the opposite direction to earlier 750's.

Navigation

[0] Message Index

[#] Next page

[*] Previous page