The International CBX Owners Association

Hi Guy's, just been syncing the carbs, As the book says using number 4 as the base carb. 1-2-3--5 all adjustable and seem to be working as they should.
Problem with number 6 what ever way you adjust the screw no difference, and showing very little vacuum. Not responsive.
Pressure checked the cylinder, all OK.
No leaks from the rubber inlet, tested with WD40 while running.
But when connecting a tube to the vacuum outlets, then sucking or blowing! no resistance. Where as all the others you can feel a resistance on all the other carbs !
Thanks in advance

Phil, this could only be the result of a blockage in the port or the intake tract. Probe the open port, after shining a strong light into it. If there is a blockage, you need to remove the carbs to investigate or risk whatever it is being suciked into the cylinder.

Tight intake valve ? Check valve clearances ? Try pulling the choke all the way closed then see if
there's any change in resistance in the vacuum hose.

Thanks for that

What puzzles me is that you said the (compression?) pressure checks out good.
You might also try turning the motor over by hand while sucking/lowing the vacuum tube to see
if the resistance (or lack of) changes. One last thing, look at the throttle linkage connection
between 5 and six carbs for mis assembly. If the washers that go on either side of the off the
lifting fork are out of place* it could be holding the no. six butterfly open making adjustment
nearly impossible.
*compare to the other linkages.

Are you sure #6 is firing? Never tried to sync without all six firing, so don't know what you'd see.

Dave

Preview: Re: very little vacuum on number 6 Help please
Sorry it's been some time.
I've been busy removing the carbs ! well found out what it was. But as you said the butterfly was not closing !!
1 to 5 all fine, 6 slightly open due to the adjusting screw worn thread. Changed now and adjusting looks good.
But until the carbs were removed, not a chance of seeing the problem.
a few other things found as well ! 1-2-3 choke plates not closing correctly. A noticeable difference between 1-3 and 4-6 the latter closing correctly, 1-3 not fully closed ! due to number 2 choke plate slightly miss aligned by about 1mm.
Now that's also done.
One other problem I have found !!! all main jets removed. Standard 98# but for number 4 this is a 110 ???? any thoughts on this please.

These are the trials of working on 45 year old carbs that several guys before you have touched. What you discovered about the throttle plates is quite common and why those need carefully checked when assembling/bench syncing.

Dave

As Dave said, bench sync'ing would have identified your problem.

daves79x wrote: ↑

Thu May 30, 2024 7:01 am

These are the trials of working on 45 year old carbs that several guys before you have touched. What you discovered about the throttle plates is quite common and why those need carefully checked when assembling/bench syncing.

Dave

I'm sure you are correct. Thanks Dave

Tip: Do a very meticulous bench synch and a 'live' synch is almost gilding-the-lily. Be certain to use the jet hole nearest the manifold as your reference point when bench synching. Work the throttles several times after each adjustment to be certain things are 'seated'.

Thanks Larry, will do. But do you have any idea why number 4 is running a 110# main jet all the others are 98#

What model are these carbs? VB60, VB62, VB64? They each have different size main jets as standard, but not different between each carb on the rack.

Dave