V4 Carb Sync Guide

Forum rules
Please can you post items for sale or wanted in the correct For Sale section. Items / bikes for sale here will be removed without warning. Reasons for this are in the FAQ. Thanks
Settled in member
Posts: 38
Joined: Thu Jul 03, 2014 11:38 am
Re: V4 Carb Sync Guide

Post by Johannes » Thu Jun 14, 2018 11:33 am

Just reviewing this very informative thread and having not done this before a question came to mind (given that i'm taking my carbs off my 24 this weekend to clean, new pilot jets and new intake rubbers), which is "what is the synch screw doing?" I am assuming that it is adjusting the mechanical linkage to the butterflies??? Am I correct?

I'll go hunting for a similar thread for the NC24, but assume that the process is very similar.


Posts: 9353
Joined: Fri Jul 04, 2008 1:01 pm
Bike owned: ZXR400 / VFR400
Re: V4 Carb Sync Guide

Post by Neosophist » Fri Jun 15, 2018 5:10 am

Yes, it just changes the freeplay between the linkages. The NC24 has 4 separate vaccum ports, one of them is not shared with the vaccum tap as the NC30 is so you can leave the tank connected or if you remove the tank and use a dummy tank make sure that you block the vaccum hose.

There are only 3 adjustment screws and one fixed carburettor... adjust all the screws to ensure that all 4 carbs are pulling the same vaccum just off idle.

give the bike time to settle after adjustment and blip the throttle occasionally.

Try to sort it quickly, if the temp gets really high it can throw off the adjustment so best to wait for the bike to cool back down to normal running temp before continuning.
xivlia wrote:i dont go fast on this bike so really do not need a rear brake.. /
vic-vtrvfr wrote:Ask xivlia for help, he's tackled just about every problem u could think of...

Settled in member
Posts: 2
Joined: Mon Dec 15, 2014 11:35 am
Re: V4 Carb Sync Guide

Post by blackvtwin » Thu Nov 14, 2019 9:05 am

crookzy1 wrote:
Sun Mar 13, 2016 10:44 am
If you either don't have a carb balancer, or you don't have the tools/skill to adjust the screws whilst the carbs are on the bike, you can do the following.

Take the carbs off the bike and observe the butterfly valve for carb 4. Adjust the idle screw for carb 4 until the butterfly valve reveals the first of the very small holes inside the carb. Adjust the idle screw it until all you can see of this first hole is a minuscule crescent. Adjust the screws for the other three carbs so that they match this crescent as precisely as possible.

This was recommended to me by Rick Oliver and it seems to have worked a treat. Of course you'll only be able to tell for sure by checking with a balancer but they sound right to me.
Ah man I messed around with the carb sync tool and had a hell of a time trying to make a tool that could get to the sync screws for adjustment. I just can't get my hand in under there to properly adjust with the socket or otherwise. I thought i'd tuned it but I don't trust the sync tool I got, idle was also too high and ran out of idle adjustment, so I ended up pulling carbs out and starting again with your method. The bike seems good now, got some play in the idle adjustment now and it was much easier to do so thanks for the post.

Settled in member
Posts: 238
Joined: Fri Aug 26, 2016 10:17 am
Bike owned: 3 x NC35, 3x NC24, NC29, RC46
Location: London
Re: V4 Carb Sync Guide

Post by Suzuki416 » Thu Nov 14, 2019 4:38 pm

A quick note to follow while using the Carb synch is :

Adust the front pair together
Adjust the rear pair together
Then adjust the 2 pairs to each other
Start with the NON Adjustable carb & the carb next to it (be it front or rear banks - depending on model)
Synch that
then move to the other bank..

I use the Morgan carb tune pro (love it) & connect the front pair as 1 & 2, & the rear pair as 3 & 4.
Ignore the fact that the cylinders are NOT numbered that way...

He also sells a terrific tool - NOT THE CHEAPEST !!!!!! but you dont burn your hand & it really speeds up the process
http://www.carbtune.co.uk/bevel.html - I wish I'd bought it 15 years ago.. 400cc V4 bikes really suck as the inside of the V gets damm hot.

Post Reply