SOHC.co.uk Forums > CB750

Fuelling or Not ?

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Greebo:
Hi Mark
You have got a similar set up to mine, I have 138 mains & then we had to play with the needles so we tried middle setting which did work on mine it was jerking constantly, but if I pulled out the choke while riding it was off like a rocket so we new it was lacking fuel, we then went to the next notch & it was only slightly better , so then we went for the last needle notch & bingo....this got us to where we are now.
What you have suggested in your last post makes a lot of sense,
I will give it a run today & try it at a constant 60mph in 4rth.
holding it at 60 in 5th when I get the slight missing, if I accelerate to 70 it goes past the missing & seems ok, but holding at 70mph I do still get a bit of hesitation, but again acceleration past 70 it goes really well right up to 90 no hesitation at all, obviously its much harder to hold it  constantly at higher speeds on country roads, but it dosnt miss a beat powering it through the gears.
going the other way at slower speeds ,say in 5th gear again cruising & holding it at 35 or 40 it as smooth as silk.. the problem occurs when approaching 60.

I will keep you posted

MarkCR750:
If you have PD carbs with an accelerator pump you'll get extra fuel as you power through the gears (if you wind the throttle open quickly) so that's worth bearing in mind when you are trying to figure out what's going on during your trial and error runs.

PS I think I'm right in saying that the accelerator pump doesn't operate (or not as much) with slower throttle openings and not at all when cruising at a steady speed, somebody please correct me if I'm wrong.

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