CB750F2 carbs/running

[blackeagles]

ok, new question.  I finished a bit of work on a 400f2 so thought I would have a go at a 750f2.  Its very little work needed (well, a noisy primary chain but I will ignore this) but I'm having a real problem with the carbs/running so would appreciate any suggestions on the following.

It was not running when I got it but with a new  battery it ran but this problem was there from day 1 - bike will tick over but if you 'blip' the throttle the revs do not want to drop back even though I can see the carbs have snapped back shut ok and the arm has contacted the tickover screw.  I took the carbs off and they seem to be opening and closing ok and the jets are all clear so I set the pilot to 1 3/4 turns out and put it all back on but the problem is still there.  I then thought it was one of the cables sticking but they run freely and even with both undone I can start the bike but still the revs will not go back to idle unless I adjust the tickover screw at which point the bike will stall!!

I don't think I explained this very well but hopefully you will get the idea and any suggestions (before I take the carbs off again) would be appreciated.

[K2-K6]

The carbs on these are paired with K7 and differ substantially from previous numbered 750 models.

They have a throttle lifter mechanism when choke is used that will allow up to about 3000rpm,  so needs to be fully off choke to assess it's tickover.

Confirm your idle set screws are as per manual,  so ok for start point.

Check for leaks on carb to head rubbers as that will give you inconsistent tickover.

They also have accelerator pump on these if you are not aware,  but that wouldn't compromise tickover even if not working.

Check timing is also ok and not advanced.

[blackeagles]

ok, thanks I will recheck them

[blackeagles]

well the ignition timing is ok but the choke will not get anything like 3000rpm yet the adjustment screw is all the way in (but the cam looks worn) and the 'screw' setting which is 1 3/4 turns out is also ok (not sure if this is correct for this carb, I've got PD41Bs but I was told they should be PD42A)

Anyway the problem continues with the revs going all over the place even with the carb closed!!

[K2-K6]

OK,  it's got a setup "peculiarity" that some get caught out with.

The #2 carb linkage should be fixed / non adjustable and you can get a combination in which adjustment of the others conflicts if routine setup is wrong.

http://www.sohc.co.uk/index.php/topic,17769.0.html

Above Link should help get them correct if you are in doubt.

[blackeagles]

ok, thanks.  I will have another go when I get time.