Carburetor adjustment no 3 to no 4

[jetts68]

Hi all I have a question relating to my 79 cbx1000. I'm in the process of completing the rebuild of my carbs. A little background I have just completed an engine rebuild, I have a compression of 145 psi on all cylinders and the timing is spot on. The engine has not been bedded in yet. I fitted the carbs to the engine but have ran into a problem while trying to synchronise them. I could not get no 3 carb to reduce it vacuum to match up with no 4 carb. I removed the carburettors and inspected them again. What I can tell is with all the butterfly adjusters screwed all the way in, "this should open the trottle plates to there max adjustment", all the trottle plates except for the no 4 and no 3 have a gap of about 2 to 3 mm. The no4 should not have any gap as it's the master carb. But I thought no3 should have a gap similar to the other 4 carbs. With the no3 adjuster fully screwed in the no 3 trottle plate is fully closed before the no 4 trottle plate closes.
Firstly is my theory above correct that all the carbs should open to appropriately 2-3mm except for the master no 4 with the adjusters screwed in fully.
Secondly if I am correct any suggestions as to how to adjust it.

[Larry Zimmer]

As I best recall, set #4 with the idle adjust screw. Then, set #3 to be the same as 4. Then set #2 same as 4. Then set #1 same as 4. Then, set #5 same as 4. Then #6. Your reference is NOT a gap to the throttle bore. The reference should be edge of the throttle plate to the small hole in the bore near the plate(s) when the throttle is essentially closed. Be certain after adjusting each one to open and close the throttle a few times to be certain that the plate(s) returns to the same setting. Do this well enough and you won't have to mesh with on-bike synch.

[jetts68]

Yes you are right that is correct for setting the plates up. The problem I'm having is that no3 has no adjustment because it's plate is fully closed with its adjuster in it's fully open position before no 4s plate is closed. I do not see anything bent or misaligned. Come Monday I'll split the carbs again and inspect them again. Something is wrong with them.

[Devonian]

Are you sure the no.3 throttle plate isn't installed backwards?

[daves79x]

You have one of two problems - (1) the adjuster arm that the adjuster screw goes into has the incorrect bend, not allowing for the proper adjustment. You need to remove it and bend it slightly, (2) the throttle plate arm on #3 has two parts, the adjuster arm/ring and the shaft itself. Sometimes the adjuster arm ring freezes onto the shaft and will not allow for movement. Requires disassembly and cleaning. Beware - that arrangement is quite fiddly to get back together correctly. Or (3) you have some parts assembled incorrectly. But I think from what I'm understanding that you are not attempting the bench sync correctly. As Larry said, starting at #4, match 5, then 6. Then match 3, making sure 1 or 2 are not too far shut, holding 3 open. All downstream throttle plates from the one you are adjusting must be open at least as far as the one you are adjusting.

Dave

[jetts68]

Thanks for your reply. I found two problems. Firstly no 4 linkage plate the one with the little ball on it, the centre that slides up on the trottle plate shaft is ovaled causing it to be located incorrectly. Secondly the trottle cable rotating plate has a slight warp in it. I've replaced them and hay presto sorted. As I enquired earlier with trottle plate no4 closed and all the adjusters screwed in fully you get a gap of between 2 to 3 mm on the rest of the carbs trottle plates. I'll bench sync them tomorrow as you suggested and see how it goes. This bike teaches me something new every day. Again thanks for the guidance.

[Larry Zimmer]

Good news. Be meticulous with your settings on the bench. Operate the throttles several times. Might even close them with a little snap to be certain that everything is tight with no slop/lash anywhere. As I mentioned above, you might find things very smooth without having to do a synch on the bike.

[daves79x]

Just one thing - I never loosen my sync adjusters when separating carbs. That way they'll be sort of close when I go to bench sync. 'Turning the adjusters all the way in', doesn't mean anything other than you'll be in for a lot of adjusting when bench syncing. That was what I was confused about.

[jetts68]

Hi daves79x
I would agree with not messing with the adjusters. But when you buy a bike that's completely dismantled and in boxes and was sold as parts only. You can't trust anything. A lot of help from the specialist out there. And Two Wheels Spares. I now have a complete original 79 cbx1000z. Not the prettiest machine on the block, 45 years has given it some visual scars. but its mechanically perfect.