Topic: K1 carbs air screw setting.

[_mark]

Hi everybody.

I'm going to restart my CB750 K1 and I need to check the carbs with the vacuum gauges.

It is unclear to me the air screw check.

From the manual I see: " Turn the air screw slightly at a time within 1/8 turn in both directions from the original setting, pausing for about 5 seconds to locate a point of highest engine speed by the tachometer. Perform this adjustment on all carbs. If it takes over a full turn more or 1/2 turn less the original setting to change the engine speed check the following possibile causes...

Priorly is written that the starting point is one turn to open from the fully close position.

What is unclear to me is this:
- when i will find the position of maximum revs, will I leave the screws permanently in this position  ?
- the rotation check of +/- 1/8 turn must be done at same time on all 4 carbs resulting in the same setting on all 4 carbs?


sorry for the maybe stupid questions. Thanks and Regards.

Edit : I found the K1 supplement manual; Adjust the respective air screw so that the engine RPM is smoothest with maximum vacuum pressure. The standard adjustment which gives the best performance is 3/4 to 1 & 1/4 turns open from the full close position.

[ekpent]

I use 1 turn out as a base setting for those on the earlier 1976 or older 750's. I've never really fiddled with them too much after that.

[Scootch]

+1 on the 1 turn

[_mark]

+1 on the 1 turn

what? 

[RAFster122s]

+1 on the 1 turn

what? 

Scootch is saying he uses 1 turn out as well...
That's what 1+ means


David

[newday777]

Hi everybody.

I'm going to restart my CB750 K1 and I need to check the carbs with the vacuum gauges.

It is unclear to me the air screw check.

From the manual I see: " Turn the air screw slightly at a time within 1/8 turn in both directions from the original setting, pausing for about 5 seconds to locate a point of highest engine speed by the tachometer. Perform this adjustment on all carbs. If it takes over a full turn more or 1/2 turn less the original setting to change the engine speed check the following possibile causes...

Priorly is written that the starting point is one turn to open from the fully close position.

What is unclear to me is this:
- when i will find the position of maximum revs, will I leave the screws permanently in this position  ?
- the rotation check of +/- 1/8 turn must be done at same time on all 4 carbs resulting in the same setting on all 4 carbs?


sorry for the maybe stupid questions. Thanks and Regards.

Edit : I found the K1 supplement manual; Adjust the respective air screw so that the engine RPM is smoothest with maximum vacuum pressure. The standard adjustment which gives the best performance is 3/4 to 1 & 1/4 turns open from the full close position.

"I'm going to restart my CB750 K1 and I need to check the carbs with the vacuum gauges."

Is this a normal spring restart from a winter storage or is this a restart from a long neglected bike and did you rebuild the carbs after stripping them bare of all parts for a total cleaning and rebuild??(you didn't make that clear or include any history of your bike and what you have done so far to this point)

If a total rebuild of the carbs and removed the air screws from the carbs, then as the others have said, the 1 turn out is the initial setting, then once you start the bike then you begin with the 1/8 turn at a time to find the sweet spot.
Does that help?

[Deltarider]

Syncing and setting the airscrews are two things. Adjustment of the airscrew, say within 1/2 turn, will not change the underpressure. You could even temporarily lean them out for the time of the syncing, so you will not be in poisonous fumes too much. 

[pjlogue]

When I set my carbs up and dialed in the air idle screws I started at the 1 turn out setting.  After the engine was fully warm I tweaked the sir screws one at a time to get highest idle rpm.  I did find that this gave me an engine that was very difficult to start and would bog down when trying to launch from a stop.  Enriching the air idle circuits on each carb about 1/8 turn alleviated the hard starting and bogging down at launch.

-P.

[HondaMan]

Here's a [sort of] simplification, given our modern gasolines that burn a little differently from when that manual was written:

1. Start with them all at 1 turn out.
2. After 50-100 miles of riding, pull the sparkplugs and look at them for color. If they are getting too much fuel they will be dark and fouled. If so, turn the air screws in to 7/8 turn and try again.

Today I find that most of the 750s need to be set to slightly less than 1 turn out, usually around 7/8 turn. This is due to the slow-burning nature of our modern fuels as compared to 1970s gasolines.

[_mark]

Thanks everyone.