Carb balancing starting point.

[ReaperVmax00]

Hello! So, in getting my Vmax running and riding, I cleaned and rebuilt the carbs, replaced all 4 mixture screw assemblies as all of the washers were missing for some reason, and replaced all the rubber boots. The bike has the dyno-jet stage 7 kit and a UFO 4-1 exhaust, I see on Dyno-jets instructions you set the mixture screws at 2.5 turns out on all, then follow normal balancing. I have watched plenty of videos and read how-to's all over as well as having a dealer service manual. I don't see any mention anywhere about adjusting the mixture screws before or after syncing the carbs. Would that not be necessary on at least cylinder 2 where the linkage isn't adjusted? Thanks in advance! Id love to get the tuning right the first time and either haven't found the info, or haven't been looking in the correct places.

 

[MaxMidnight]

Balancing the carbs is to ensure a similar air flow (or restriction) in the venturi.
The mixture screws set the volume passing through the idle circuit.
Whilst I stand to be corrected they operate independently of each other.
That said if you are inclined to tinker with the idle mixture I'd be inclined to do this after balancing.

Does your S7 still have V Boost?

 

[ReaperVmax00]

V-boost valves are present but locked in full open position. I know how to adjust idle mixture when referring to 1 carb feeding 1 cylinder but not 2 carbs feeding two cylinders together. Adjusting them after doing the sync makes sense to me, however!

 

[Fire-medic]

V-boost valves are present but locked in full open position

Is the VBoost round plastic connector under the left Yamaha scoop unplugged? That's one way to 'lock' the VBoost full-open, when they cycle to full-open (unplug the round VBoost connector now!) and then closed once the ignition is turned-on.

The advantage is that you can use the VBoost closing so you can balance the carbs easily and then return to full-open by the above method. I have Dynojet Stage 7 and I use VBoost in its normal function.

 

[ReaperVmax00]

It is unplugged but the valve is physically tied to full open with a custom made looking bracket. When I had it apart I verified it was all the way open. So I'll likely do the balance/sync with it in that position.

 

[Fire-medic]

If you read the sync instructions, you'll see that you need the carburetors to be able to have only one pulling the partial vacuum you're measuring, but with the VBoost open, that cannot be. You will always be pulling vacuum on two at once.

 

[Parminio]

It is unplugged but the valve is physically tied to full open with a custom made looking bracket. When I had it apart I verified it was all the way open. So I'll likely do the balance/sync with it in that position.

And as Firemedic says, that's going to be very, very difficult.

The reason is that with V-boost in the full open position, you have in effect an open plenum chamber for both carburetors, so one carburetor will be effecting the other.

The physical image: Imagine two people, each with their own paper towel roller, blowing air through it on either side of your face. It would be pretty easy for you to tell which person is blowing more or less air. Now imagine both of them blowing through the same paper towel roller into your face. You're going to feel more air, but how do you tell which one of them is blowing more or less air?

You can't.

That's how it's going to be with your V-boost in full open.

 

[dannymax]

You may want to do a little more investigating regarding the washers & o-rings. Almost a certainty they are in place and you missed them...it's easy to do.

 

[ReaperVmax00]

Interesting! That was very well explained thank you! I will get that valve closed for balancing! Dannymax, believe you me, I searched high and low, inside the carbs and out for those washers, thinking maybe I missed them or I somehow dropped them all on disassembly. But all of the o-rings were worn like they were sitting directly against the spring so I chocked it up to improper assembly by whoever did the stage 7 kit or the last cleaning.

 

[dannymax]

I was unaware you had found and removed the o-rings. You are correct, you would have certainly have seen the washers if they were there.

 

[Fire-medic]

A suggestion, remove the bracket holding the VBoost open, and do the 'unplug the VBoost connector as it cycles full-open upon turning on the ignition key' method, when it comes time to put things back the way they were (VBoost held-open). It's the round plastic M-F connector beneath the left scoop below the faux gas tank cover, which will need to be removed to remove the screws for the scoop.

 

[ReaperVmax00]

Thanks for the help guys! Just waiting for it to warm up outside then I’ll get the sync done!

 

[ReaperVmax00]

I couldn’t wait on the weather, it’s almost 60 degrees today so I went ahead and synchronized the carbs. MY GOD is this thing smoother than I ever imagined it would be. Could NOT be happier! Only thing I noticed, is when at steady rpm and steady engine load, I.e. cruising, I can hear an irregular “slapping” from the exhaust. It’s not a pop, or a backfire, but a “slapping” sound. Doesn’t seem to affect performance at all, but I’m a mechanic by trade and it caught my ear. Is that the “sloppyness”People refer to with the stage 7? Or is there something else I can look for. Thanks!