SOHC.co.uk Forums > CB750
Carbs Install
Martin6:
I would appreciate more advice, please. I thought I'd give it another go on the carbs. I did a 25 mile run, to warm it up on the whole, a nice little ride. But, hesitation on a light throttle, before it pulls and idle is lumpy below 1500rpm.
So, I tried to adjust the carbs. I don't really detect a sweet spot on the pilot air screw. I started at 1 turn out and hesitation is apparent gently rolling on the throttle (less then 1/3 throttle). At 3/4 turns out of the air screw, the hesitation was worse, but the idle initially seemed, 'perhaps' smoother but very difficult to be sure. I can turn the screw all the way in on individual carbs and not really notice much difference at idle. Idle seems lumpy below 1500rpm even with the screw out from 3/4 to 2 1/2 turns. I think it is running on all 4cyls.
Any thoughts?
Slide adjustment? I'm wondering if the slides may not be seating fully. I thought they were when I had the carbs off to clean. I hear a clack from them going back down and it seems to be in unison.
Float height or stuck float(s)? I measured and adjusted to service manual spec. I measured from the rim just inside where the gasket seats, to the float, at the float position when the needle just gently starts to seat. There is nothing coming out of the carb overfow pipes. But might this be connected to the oil level issue below?
Pilot jet blocked again? But it does idle and starts OK without throttle when warmed up.
One other significant finding. The bike had just had an oil change. When I checked the oil, the level was fine and it was clean. I checked it again after my run and it is now half an inch over the upper line, with a slight emulsion and an odour not quite of pure oil. It seems thinner, but it was hot. There was dripping from the end of the valve cover breather pipe, which seemed almost clear, not really oily. Could this be fuel contaminating the oil? What could cause this? I did forget to turn the fuel tap off when I filled the tank and paid. Maybe 5mins at most.
Appreciate advice / commiserations/ encouragement! :)
P.s. my tyre stayed up, the back brake now works, as does the starter button! :D
McCabe-Thiele (Ted):
Are you comparing the change of oil levels whilst on the center stand on level ground on a cold engine?
Breather pipe might just be doing it's job venting off from a warm engine?
I would not panic just yet.
Oddjob:
Have you checked the float level height?
Nurse Julie:
--- Quote from: McCabe-Thiele (Ted) on April 02, 2023, 07:34:55 PM ---Are you comparing the change of oil levels whilst on the center stand on level ground on a cold engine?
Breather pipe might just be doing it's job venting off from a warm engine?
I would not panic just yet.
--- End quote ---
It's a 750 Ted, it's a dry sump system, it has a seperate oil tank. You check level when engine hot. On a cold engine, there is a higher possibility the oil has sumped and not returned up to the oil tank.
McCabe-Thiele (Ted):
Forgot about the tank system - just trying to ascertain if the oil levels were checked in identical circumstances. If I do an oil change I fill it close to level, fire it up to ensure filter is full of oil then check it again & top up if needed.
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