Topic: Syncing Carbs, 72 cb750 - Throttle Valve Screw?

[mcswny]

I've had my bike for a few years and never really "needed" to sync my carbs. Sure it could have used it but I was running under the premise of if its not broke dont fix it. Well I'm finally wanting to learn to sync them.

So I've been reading and re-reading the manual about syncing them and I'm just not 100% understanding. The manual keeps talking about adjusting throttle valve screws and my bike doesn't have them on any of the carb bodies. (photo attached). The idle is adjusted by just adjusting the own single screw above carb number 2. With that being said, do I basically just attach the manometer (I have the Motion Pro) and then adjust the air screw and sync via that? Am I missing anything else? (If youre wondering, the plug screw is already out in this photo)

Also, if anyone has used the Motion Pro Carb Sync tool I have one more question. You have to sync the tool off your "master carb" and I read it's usually either number 2 or the one that can't be adjusted. It seems like all 4 carbs look the same, so should I just go ahead and sync it off number 2?

If I need to get any more photos, I can snap them in the morning.

Thanks!!!
Tim

[mcswny]

It looks like on cmnsl there are two 1972 carb schematics, one with the throttle valve and one with? Am I mistaken?

One without:
http://www.cmsnl.com/honda-cb750k2-four-usa_model14362/partslist/E26.html#results

One with:
http://www.cmsnl.com/honda-cb750k2-four-usa_model14362/partslist/E25.html#results

If anyone has any info on this I'd love to learn.

Thanks!!
Tim

[Dream750]

Try this reference ...

http://manuals.sohc4.net/CB750SB/750_25.pdf

Lots of good info to get your carbs adjusted correctly.

[mcswny]

Thanks dream, I'll look through these first thing in the morning! Thanks!

[mcswny]

Hey dream this all seems pretty straight forward thanks!

I think my last question is this. It seems like the only thing that's specified with tr air screws is that you seat them and the turn back out 1 full turn from the seat. Is there any way to gauge how accurate this has been down, and if it hasn't been done, won't it affect the idle, even though these carbs have the easier operating bar with single throttle stop?

[evanphi]

You air screws are easy to see how much they are turned... turn them in until they gently stop and then turn them back out the same amount. Make sure they all match!

Also make sure that your idle mix (which is what you're adjusting with these screws) isn't too lean/rich at the current setting. Check your plug colour.

Adjusting your air screws shouldn't affect idle speed too much, you just don't want to be bogging or starving when you open your throttle!

[mcswny]

You air screws are easy to see how much they are turned... turn them in until they gently stop and then turn them back out the same amount. Make sure they all match!

Also make sure that your idle mix (which is what you're adjusting with these screws) isn't too lean/rich at the current setting. Check your plug colour.

Adjusting your air screws shouldn't affect idle speed too much, you just don't want to be bogging or starving when you open your throttle!

Thanks so much for the response Evan!

Cheers!

[mcswny]

Try this reference ...

http://manuals.sohc4.net/CB750SB/750_25.pdf

Lots of good info to get your carbs adjusted correctly.

Hey dream, I was looking to print this PDF out but it seems to no longer linked and I can't seem to find it. Do you still have it??

Thanks,
Tim

[Restoration Fan]

This page has all the links for the CB750K's on the forum.
http://manuals.sohc4.net/cb750k/

[Dream750]

Hey dream, I was looking to print this PDF out but it seems to no longer linked and I can't seem to find it. Do you still have it??
Thanks, Tim

Tim, you’re right. And it looks like ALL the CB750 service bulletin links are now dead, but I don’t know why.

They are found inside, bottom of the page of the CB750 FAQ link: http://www.sohc4.net/cb750/ and you used to be able to click on the individual bulletin subject to open them.

All I have at the moment is the early shop manual supplement which is close, but not as detailed as the later service bulletin.

[mcswny]

Hey dream, I was looking to print this PDF out but it seems to no longer linked and I can't seem to find it. Do you still have it??
Thanks, Tim

Tim, you’re right. And it looks like ALL the CB750 service bulletin links are now dead, but I don’t know why.

They are found inside, bottom of the page of the CB750 FAQ link: http://www.sohc4.net/cb750/ and you used to be able to click on the individual bulletin subject to open them.

All I have at the moment is the early shop manual supplement which is close, but not as detailed as the later service bulletin.

Hey Dream, another member passed along the link here and I just downloaded them all for future reference.
Here you go. http://greenbushacres.ca/Motorcycles/Technical/Technical.html