1997 cb750 carb set up

[Kernow]

Hi,
First post here so be gentle

I bought a 97 f2v around a month ago. Good condition and low miles. It started running rough at idle a couple of weeks ago so I've stripped and cleaned the carbs including the pilot screws.
I put everything back where it came from including the setting of the pilot screws and guess what.....it's running fine!
I'd like to make sure everything is just as it should be so could someone please explain idle screw adjustment for me please?
I have the official Honda manual which shows how to adjust them using rpm changes at idle but says its for the Swiss version only (SW) which seems odd!
I have a colourtune kit on order but being the impatient type I'm keen to get on with it!

Any advice appreciated!

Thanks,
Pete

 

[amc49]

Generally they give you a number in turns to set them at...............and don't screw with it. That number can be lean for emissions, you simply open a bit more and match them all for a little richer and possible smoother idle. Rolling off idle to go faster very slowly is affected by the screws too. So, open them a bit more if getting like a small balk or hesitation going off-idle.

The old school norm has you opening them more for richer or CCW. Depends on idle air type, that for a screw between engine and throttle slide, or, a true pilot screw. Some have AIR screws which do NOT meter fuel with the air, those are generally BEHIND the throttle slide and you turn them opposite (CW) to richen. I don't know your type but probably the former one, a true pilot.

Old school method say car has you turning the screw to rich or lean enough to begin to lower the rpm, then back the other way to raise it, the going lean has much more effect and easily noticeable, rich sometimes not noticeable at all due to modern very lean carb circuits so you tend toward using the lean side, mess it up to try to die then back until you reach the highest rpm you can get and stop there. Harder to tell that with 4 cylinders and 4 settings though, why it's better to take them all one way or the other in 1/4 turn amounts, then easier to tell the difference. Any question and err to the rich side. A screw that has zero effect or less than others points toward dirty carb, they all should have an effect.

Any mention of using a tach to get idle drop of any sort is for emissions only, they commonly mention get to best fastest idle then tell you to drop it say 50 or 100 rpm after that using a tach. You'll get better smoother idle ignoring that part to simply stay at the highest rpm the screws can give you. RPM drop is for the birds.

 

[Kernow]

Thanks for that. Makes sense. My pilot screws are between the throttle valves and cylinder head. What's concerning me a little is that the original position for the screws weren't all the same. They were something like
2 1/4
1 1/8
2 1/2
1 1/4

I've put them back in their original positions and it seems to be running fine. Perhaps I should do a plug chop.

 

[Scooterboy]

Hi Kernow, another Cornwall member here (Looe) I'd set them all to 2 1/2 turns tbh, I've just ordered a stage 3 jetting kit for mine from the states, pilot and main jets as I'm running pod filters with a shortened exhaust (1996 f2n)

 

[Kernow]

Thanks scooter boy. Maybe I'm overthinking it!

 

[amc49]

If Dynojet kit then they really aren't spit, you can repro the results without spending all that money. The stage 3 needles can be a tuning issue too. Anybody read the very small note that says often the kits do NOTHING on modern highly oversquare motors? Food for thought there. I bought a couple kits when they were discounted to $25 once and still not impressed. The OEM parts worked better. That was on a 1st gen DOHC though.

To OP, yes, common to open all screws same amount and a bit more to richen idle off the super lean EPA setting if mentioned. Try up to a full turn a 1/4 at a time to find what you feel is the best at pure idle and off-idle roll-on throttle and then leave it there. If doing any light backfire at decel it'll help too.