Syncing the carbs

[Nol_one]

I’m new to a lot of this bike stuff but I’ve been working on a 1977 cb750k7 and fixing it up. Recently I took off the carbs to clean them and when I did messed with the pilot screws not knowing what they were. Knowing now I looked into the manual and backed them out each a turn and a half like it says but from here I don’t fully know how to sync them. It says I need a shop tachometer. Is this true and does anyone have any recommendations??

( for reference I don’t have a working tachometer on the bike)

 

[brettp]

I didn't use a delicate RPM gauge, just the stock one on the bike. But you do need something to set the idle correctly.

 

[madmtnmotors]

1-1/2 turns out on the idle screws is fine. Trying to set the idle mixture screws using the 50 or 100rpm drop method can be maddening since these don't always idle smoothly. Synchronizing the carbs using a set of vacuum gauges on the other hand will go a long way towards smoothing out the idle, improving throttle response, and quieting down the sewing machine noises at idle. After a good vacuum sync I can get mine to idle smoothly all the way down to 800rpm.

 

[brettp]

So true. That 500rpm is so ridiculous.
But at 800 RPMs, is your oil pump running optimally?

 

[madmtnmotors]

at 800 RPMs, is your oil pump running optimally?

Hard to say, no flicker from the oil light. I usually set the idle closer to the specified 1000rpm, just sayin' that with a proper vacuum sync that mine will idle smoothly down to 800rpm. Many people cannot get theirs to idle smoothly below 1200-1500rpm.

I don't spend much time at idle either!

 

[Nol_one]

I didn't use a delicate RPM gauge, just the stock one on the bike. But you do need something to set the idle correctly.

What would I need to do that?

 

[brettp]

To know the RPMs? I think there are apps out there that listen to the motor. Can't vouch for accuracy.

 

[madmtnmotors]

What would I need to do that?

https://www.amazon.com/Actron-CP767...words=dwell+tach+meter&qid=1714528774&sr=8-25

Tachometer tool that even includes a dwell setting for dialing in the points for those masochists that won't upgrade to an electronic ignition...