SOHC.co.uk Forums > CB750
First ride misery.
Graeme77:
First ride of the 750 today, took it for MOT and it passed.
However, there were 'issues' LOL.
Bike stutters, power comes in fits and starts. It did smooth out a little after a while, but not great.
Then, it cut out and wouldnt re-start. It did this a couple of times, cutting out dead when pulling up to a junction.
It would re-start, but only with a bit of choke, then off choke imediately as it doesnt like running on choke.
First thing felt like it was lean, or maybe ignition.
Then, stopped for petrol and it wouldnt re-start. Eventualy drained the battery. There is no way this bike will start on the kickstart, but normaly starts straight away on the starter.
Got it trailored home, pulled a plug, and its properly sooted up. Didnt get a good run on the bike so hard to tell, but my guess is its fouling up the plugs to the point where there not firing.
Air filter is suspect, ill remove it for now, see if that helps, but ill look into the carbs again.
Do you think the dodgy power thing could be running rich?, plugs fouling? It did feel a bit like that.
When i went over the carbs i noticed i have 2 different types of emulsion tubes. One set where the row of 4 holes are all the same, and another set where the bottom 2 holes are a fair bit smaller than the top two.
Any idea which ones my 750F1 should have?
As the chains are a bit noisy, and the starter clutch chatters, the AA man thought it had slipped the timing chain. I find this highly unlikely though. I think he just didnt want to know.
Ill look into the starter clutch though.
Graeme77:
Oh yeah, and the clutch bite point changes as you turn the bars ::)
Cable routing around the fairing bracket must be suspect. You can feel it in the lever. Makes pulling out of junctions 'interesting' ;D
K2-K6:
Good stuff getting your test done.
Sounds from the plugs as if it's rich. It would be sensible to have the emulsion tubes the same as a good start point.
Rich usually gives the feel of abruptness and sort of chang, chang, chang as it tries to tick over then eventually dies if badly rich, also you get a much stronger unburnt fuel smell from exhaust.
Lean usually feels much less precise and sort of wafty with delayed response and usually gets very hot.
Don't let the clutch cable compromise your safety especially moving out of T junctions, that's gonna hurt you if you get caught out.
At least you can now ride it to get it sorted.
Graeme77:
I posted on the other site, but ill add my new findings here.
I have been trying to sort the running issue.
Its hard to start, have to play with the choke then get the choke off quick. It never has liked running on choke.
If i turn the idle up to 2500+ it runs fine, but try and turn the idle down and as soon as it gets to around 2000rpm it just dies.
Ive checked timing, tappet, and had the carbs apart agian. All the passageways are clear, all jets are fine, float heights are all spot on.
116 main jets and 40 idle jets.
It did idle ok at 1200rpm before this first ride. I dont get what could have changed.
Clutch cable will be sorted, but need to get it running properly first.
I have no air filter in it right now as i thought maybe its clogged.
Maybe i should mess up the float heights again, stick the mix of 132 and 152 mains back in and unbalance the carbs. It at least ran when it was like that (but badly)
Runs great, on all 4, above 2000 ish.
Spitfire:
If it is a CB750F1 then the main jets should be #105's, my F1 hates running on choke, it needs it to start but then I push it down as fast as possible and get moving.
Got this from the US site I think.
Float Main Slow JN Screw
75 CB750F B750A & 7A 2-Jet Mechanical Slide Pre-EPA 26 105 40 3 1
657A & 657B 2-Jet Mechanical Slide Pre-EPA 26 105 40 4 1
76 CB750F 069A 2-Jet Mechanical Slide Pre-EPA 26 105 38 2 1
Cheers
Den
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