SOHC.co.uk Forums > CB750

float levels k6 wont fire 1+2 choke side

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hairygit:
Personally I feel it's unlikely to be electrical, as if it were, you would have problems with 1+4 OR 2+3, as these cylinders share common points and coils. So fuel is probably the area to be looking at. Is it a K6 tank and tap setup? If it is, you'll have a single fuel line from the tap, going to a T piece which has 2 pipes coming from it, one feeding carbs 1+2, the other feeding 3+4. Are you sure the plugs are wet with petrol and not oil? Use a bit of clean white rag to wipe some of the wetness onto, if it's black it could be oil, (some pattern part valve stem seals are absolute crap! >:() if it was just petrol it should evaporate away in the sun quite easily

davepainter:
To bryan mick hairygit cheers imfo-very usefull,
i,did take 1+2 plugs out of head,an hour ago and started up, looked like GOOD spark to me,
REF battery its recently been charged OK.
REF oil or petrol,since putting new 3rd set of plugs in yesterday and only starting bike twice for less than 3 minutes it immediatly only fired on 3+4?? rrrrrr
points to float height? i,ll try again tomorrow! thanks details 26mm.
a mate at work told me this today-26mm-he was right! he,s got a late model cb650 reckons float heights a bit critical.
REF valve stem seals thats scary?/ not suprised after recieving pattern inlet rubbers-david silver/ not there fault its gen honda from now on pricy yerr!
I,ve read other carb-running faults on probs page massive usefull thanks guys.
Its double piss of because when she does run on all four plugs she,s great-fek me it even ticks over at 1000 revs WITH almost no camchain slack rattle bang. MIND you if taking 750 carbs off becomes an olympic sport i,m a contender!!
i,ve even taken the plugs out after a good 30-40 mile ride and they look like the ones in the haynes manual showing perfect.
 AH yes when i took plugs out today after trying to run
No sign of oil some clear wetness-petrol on plugs 1+2 ,i,ll post when i,ve set float heights cheers DAVE.

Bryanj:
Some parts you are stuck with pattern, like those inlet rubbers mate---Honda don't make them anymore!

davepainter:
Still no go, yesterday Sunday i fitted the new carb to head inlet rubbers, and set the float levels to 26mm,
bit gutted still only firing on 3+4???? 
i think its got to the stage of putting the bike into a local specialist ex honda centre mechanic based in fareham near portsmouth.
unless its electrics or an engine-valve-piston-fault there is,nt much more i can do
i,ve read other posts and guys have even got another set of carbs.
i,ll post again if i get this sorted out cheers dave.
any ideas on a postcard!

hairygit:
There is one more serious thing that could be wrong, and I've only seen it twice in 30 years of playing with sohc 750s, snapped camshaft, caused by incorrect re assemly of the cam carriers, it happened on a mates rat bike, using cam carriers from different bikes, cylinders 3+4 died, so he rode it 175 miles home on 2 cylinders :'(( But I certainly hope that isn't your problem!) You can eliminate this possibility doing a compression test on the duff cylinders, or possibly removing the tappet covers and running the engine, oil WONT spray out if the cam is broken. If oil sprays out, the cam is still in one piece, so see if someone will lend you a compression tester and check all 4 cylinders, that will give a good idea of the state of the valves (silly question, you have checked the valve clearances? because if theyre too tight the valves wont close properly ???) Still think it will not be an electrical fault though!

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