SOHC.co.uk Forums > CB750
Head Bolts
Martin6:
No cannister, it's only a removable paper filter onnthe 750s. Just cut the ends off with a Stanley and unravel. Do it over the catch can though :)
Edit: it's not diligence, more like lack of confidence I could have got it right 1st time!
K2-K6:
The oil level can "appear" a little variable on the 750 in comparison to other non dry sump type bikes.
As long as you put in the correct volume at change of oil it won't give problems, but may initially give a little confusion.
The bulk of the oil should be in the tank (as any dry sump system will be like this) with as much supply volume available to the pump, and then onwards to galleries as possible.
Dry systems work on having greater volume through scavenge, back to tank, than delivery to always ensure oil available to pressure side of pump. Interupted supply (depleted tank reservoir) leads ultimately to catastrophic oil starvation in extreme cases.
Manual says run until warm, switch off, then immediately (it doesn't say immediately) but you don't need a "settling" time on dry sump system, to check running level in tank.
There's no dipstick in engine as oil should not be reservoired there. If it is, then there's a fault and usually with stop valve that prevents flow from draining tank into engine while not running.
If checked after being out on a run, then left overnight and checked (before starting) again, with a drop between these two measurements you'd suspect the stop valve seals.
Usually dipping the tank at any point really should give virtually the same result, or very close in range. Big variation and you'll need to consider working on the pump to fix further potential problems.
Martin6:
Thanks. I have a dry sump system on my 850 Commando, so I know about 'sumping' :)
This was variations whilst still hot. I'll watch it, but I think it's probably fine.
The thing I'm most nervous about is still having signs of the sooty plug on no.1 and a bit on no.2 and not taking off when i more aggressively whack on the throttle. I think that suggests it's too rich, but not sure about that?
Along with the bad oil leak, this was one of the reasons i took on the engine refurb. The carbs were cleaned out thoroughly with carb cleaner and compressed air. Needles on middle grooves, bench synch'd to get reasonably close, using a drill bit method. Air screws initially at 1 turn out. Float heights double checked with a vernier guage on the inner flat area of the bowl edge. New rubber seals on the carb tops. No sign of splits in the rubber manifolds.
Can timing is fine and points / ignition timing (also no.4 is running clean). Tappets were set carefully when the cover was off.
Not sure where to go on this? It's a pain cleaning the plug every 200 miles, which is what I was doing. I've had one thought, I didn't clean out the exhaust headers, which were sooty on 1 and 2. Is it possible the sooty plugs could be due to transfer from the headers? But that wouldn't explain the bogging down. All a bit confusing...
Skoti:
Renew the needle jets and needles, that's what cured the sooty plugs on my F1 along with dodgy throttle response.
Although I first wasted cash on new main and idle jets which made no difference whatsoever.
Oh and BTW it's better to use genuine Honda needle jets and needles, after market stuff sometimes gives flat spots when accelerating as the needle profiles are not exact.
Good luck
Skoti.
K2-K6:
Unless it's a very unusual circumstance or peculiarity, then sooting of combustion chamber is always simple excess fuel to oxygen ratio.
Unusual circumstance......we had on here a partly blocked header pipe that did similar. Effectively this prevents full exhaust of burnt mixture, to combine new intake fuel volume with oxygen depleted mix and give incomplete burn. This is what exhaust gas recirculation does by bleeding in carbon monoxide to reduce the burnable mixture (accompanied by reduction in fuel injected obviously) and provide reduced effective volume under light loading. Clearly undesirable if present here though.
First suspect is always the air passages feeding the idle circuit, if not absolutely clear then the idle circuit runs at full "choke" as soon as you start it. With no air....or substantially restricted supply....the carb venturi sucks at maximum demand through only the idle jet dipped in fuel of float bowl. This will play havoc with any setup logic. Absolute certainty is required on this circuit to stop it running you ragged.
Crude test to see what response you get is too wind those idle airscrew in and out while running to gauge if there's competent response from each one that's suspect.
More advanced...with help from friendly MOT tester.....get each pipe measured when bike is working temp. Looking at HC to assess the unburnt hydrocarbon content should build you a picture to at least understand where it currently is in mixture terms.
Bench sync is fine for how you are, it won't generally correct anything jetting wise...unless very seriously out of kilter anyway. I wouldn't look at that as suspect.
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