Honda CB750k2 main jets

[Pauarc]

Is it possible to check needles on the bike or is it a carb strip off bike

[Trigger]

Is it possible to check needles on the bike or is it a carb strip off bike

Carb strip 

[Pauarc]

I have put the 110 main jets in I think I will see how it runs before I strip carbs and see how the plugs look. Thank you Trigger
 

[Oddjob]

I've done needles on the bike on a 500/550, tricky but can be done. Might not be possible on the 750 though due to differences in carbs but TBH they look the same type of arrangement.

[Trigger]

Can not be done of later 750 carbs as the lifter is on top of the carb. Can be done on early 750 carbs with cables to each carb 

[Pauarc]

110 jets in Been for run for about 30 miles runs ok tick over a little rough air screws now 1 turn out. was 1 and half going to look at plugs tomorrow morning

[K2-K6]

110 jets in Been for run for about 30 miles runs ok tick over a little rough air screws now 1 turn out. was 1 and half going to look at plugs tomorrow morning

Certainly interesting as the use of airscrew resetting when using the smaller mains shows that it's really asking to run with the needle lifted one notch (needle up, clip down one)  to get it in the right place now.

This would bring the initial phase of needle taper and richer mixture down towards the idle circuit flow to stop it dropping into a bit of a lean flat spot about third throttle opening, then leave the idle back where it was to enhance that smoother running when they were set slightly further out.

Subtle difference, but places the elements more accurately.

[Martin6]

1 turn out on the airscrew is around where the service manual suggests. I wondered if carbs on and off and jet changes, just affected the balance? Maybe re-balance the carbs, to see if that improves the idle?

[Pauarc]

All plugs are now running a bit on rich side

[Pauarc]

All air screws are working correctly all set to best tick over

[Nurse Julie]

All plugs are now running a bit on rich side

I always set mine to run very slight on the rich side rather than the lean side.

[K2-K6]

All plugs are now running a bit on rich side

What that is showing is the richer mixture of idle circuit only.

Changing from 120 to 110 main jet, you'll see at wide open throttle specifically. You have to run them absolutely wide open and pulling maximum torque to assess this, nothing else will show the effect.

Its classic "plug chop" routine. Warmmup, then getting it pulling "balls out" and hauling it's maximum torque in something like 3rd or 4th gear, pull clutch, switch off, then exhamine the plugs to see what the maximum demand is telling you. Nothing else will fully inform you about accuracy of main jet mixture than that, even if you never want to ride it like that 
Main jet size is about peak flow through that with the needle fully retracted (wide open) the taper controlling all the rest of intermediate mixture below that.

If it goes flat as you come up on the throttle in low speed with 110 installed, that's telling you it's going lean in the region where idle hands over to needle taper, hence the response you get when you turn the airscrew inward, it just brings idle mixture slope to a more steep gradient in getting the two to attach.
Now it'll show rich at low rpm use, because of this.

Raise the needle, leaves the maximum alone at full throttle broadly, but "fattens" the mid to low range slightly, and avoids the need to run idle too rich.

It's "mapping" but with a carburettor.

[Pauarc]

How the plug’s looks now

[K2-K6]

The colour doesn't look too far out from those plugs as far as I can see.

The ceramic collar around the central electrode is what I'd use for primary judgement, it'll probably take more lengthy run at load to see accumulated view from the outer surround near the threads.

Picture is a little blue bias, masking the yellow content (opposite to blue and significant part of brown hue on plug carbon ) to judge more accurately. 

Was wondering what drives the decision to turn the idle circuit more rich initially  ?

[Pauarc]

It idle better about 1turn and rev up ok and good response up to 65 to 70 from stand still. It just the tic over I would like to get better