Topic: 750 K3 - verify 657B carb settings for tuning

[Chachi]

I have my K3 on the road now; first time it's been on the road in about 15 years. It's running OK, but not 100%. It levels off/lacks/hesitates in the mid range (around 5k). I haven't checked plugs yet and I've only put about 30 miles on it so far. Before carbs, I know to verify point gap, timing, tappet clearance, spark plug gap.

Bike set up:
750 K3
Stock coils
New NGK D8EA plugs with new NGK 5k caps
Stock airbox, boots in good condition, new Honda air filter and airbox gasket
4-1 exhaust
657B carbs with new Honda float valves, needles, seat

I know it has 110 mains as they were stamped. The idles were not visibly stamped. Are all jets stamped? I'm pulling rack again this week to hopefully verify idle jet size and recheck needle clip position and float height.

I want to confirm the best foundation for tuning, recheck everything and adjust if needed and then if I'm still having issues I can at least provide the correct details here for feedback.

Mains: 110 OK? (stock says 105 I think)
Idle: 40
Needle clip: 4th position from top
Float: 26mm
Air screw: 1 turn out?

[Davez134]

I know this is not going to be 100% helpful right now, as my desktop computer is being repaired and that is where my shop manual is saved... I could swear the chart/ specs I have seen for that year/carb casting called for 120 mains. Everything else seems spot on. I only say so because on my 72 with same carb casting numbers, I started tuning with 120's and was following manual.   Everything else seems spot on.  At 5000 rpm's, what would you say your throttle position is when it hesitates?

[Dream750]

Idle jet cutaway pic is a genuine Honda (Keihin) #40 idle jet, you want to ensure they are 100% clean for best performance. They should have the letter "K" logo and size stamped on them.   
 
657B carb settings and perhaps some other useful 750K info which comes from the Honda service specifications manual for US models.
 

[Chachi]

Thanks Dream750. Those are great to have. Davez134 - I was just looking through my Shop Manual and K1-K4 are listed with #120 main, except K3 which is #105 and all with #40 slow. In my case I needed to verify jets specific to carb model vs. bike model (K3) because my carbs did not come with my bike. I have 657B, which turns out to be a good match to my K3 - both call for #105 main.

I do not have any jets on hand to change out - are the #110 mains OK with my set up? Stock airbox, 4-1 exhaust. Or am I going to be better off with #105? This is my first time getting into this.

[Chachi]

This was from another thread:
#120 used up to engine #2200000
#110 from 2200001-2304500
#105 2304501 and later

My serial is in the #110 range according to the above if it is accurate. But more importantly, I'm looking for the best starting point with my set up (which is stock except 4-1 vs. 4-4).

[Duke McDukiedook]

110 should be ok for your setup but you would have to do a plug chop at the rpm you are having trouble with.
I have found on my K3 I had better luck with Denso spark plugs than the NGKs.

Like Dream alluded to, have you completely cleaned your crabs (every orifice with compressed air and crab cleaner and wire)?
You did not mention whether you had points or electronic ignition. If you have points I would check to make sure that is all up to snuff first.

[ekpent]

This was from another thread:
#120 used up to engine #2200000
#110 from 2200001-2304500
#105 2304501 and later

My serial is in the #110 range according to the above if it is accurate. But more importantly, I'm looking for the best starting point with my set up (which is stock except 4-1 vs. 4-4).

FWIW the jetting specs per serial number I posted in an earlier thread were taken from an official Honda parts fiche I use from my local Honda dealer. Usually they are correct but have found a blooper or two over the years.

[Chachi]

Cool, thanks ekpent. My parts fiche also lists #110 as main for K3. It's the old scanned PDF version.

Dukie - I've had the rack off once so far and cleaned, but pulling again this week and re-confirming everything. I have points.

[Chachi]

Also... my mid-range symptom could possibly be traced to user error. While riding yesterday I realized that the choke lever was not 100% open (lever down). I thought it was, but I realized I needed to push it down a little further to fully open it. I am going to be checking that adjustment as well. And with only having 50 or so miles on it since getting it back on the road, it probably needs to blow a few cobwebs out. But, before I start dialing in issues and troubleshooting them, I need to verify my major carb settings (needle clip position, float height, etc.). That way I can report back here with all of the needed info for adjustment suggestions.

[Chachi]

It turns out that if you follow the available documentation and advice from here your bike can run well. I had two different idle jet sizes and my jet needle clip was in the 3rd from the top vs. 4th from the top and my air screw was out 1 3/4 turn.

Anyway, now I am running:
110 mains - had a matching set in there, so left them alone
40 idles - picked up new set at my local Honda in addition to fresh carb-to-airbox boots
Needle clip 4th from the top
Float 26mm
Air screw 1 turn out

[Vin750]

Idle jet cutaway pic is a genuine Honda (Keihin) #40 idle jet, you want to ensure they are 100% clean for best performance. They should have the letter "K" logo and size stamped on them.   
 
657B carb settings and perhaps some other useful 750K info which comes from the Honda service specifications manual for US models.
 

@dream750 this information is amazingly useful. Thanks for sharing.

Would you know what service manual would contain this info?