can you help walk a newbie through carb resync? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 18 (permalink) Old 09-12-2009, 12:26 PM Thread Starter
Members who have donated towards server costs
 
robardin's Avatar
 
Join Date: Jun 2008
Location: Flushing, NY
Posts: 344
iTrader: (0)
 
can you help walk a newbie through carb resync?

The engine vibration on my bike starts as the revs approach 3K, and by 4-5K it's very noticeable. This does not happen on another VN750 I have that is 10 years older, so I know it's not normal.

From reading the Verses and other threads, it seems to me it's very likely to be a carb sync issue. I did have to get the carbs cleaned when I got this bike in March (it had sat in a garage for several years) and I think the shop did not sync the carbs as they should have. (I had also told them to look into the sticky clutch on my older bike when I brought it in for inspection and a brake fluid change, something I haven't tried to do myself yet as it's supposed to be tough to do solo, and they said they lubed the cable and charged me the labor for it, but it felt EXACTLY the same afterwards and all it needed was a new cable... Not going back there... They also have never heard of "lubing the splines" as necessary maintenance, even though they're a Kawasaki dealership and have serviced "tons" of VN750s.)

Anyway, to try to make a long story short, I got a TwinMax and I'm not sure I'm using it right. I read about the hand-made $4 manometer but I'm leery of attempting to do two new things at the same time (jury-rig a device I've never used before, in a process I've never done before) without someone on hand to guide me. So, I found a deal on a TwinMax on Craigslist and figured it would make my life easier.

It came with two rubber hoses and an instruction sheet. The Verses helped me find the vac ports on the two carbs easily enough, and told me the front (left) carb is the reference one on our bike. Also with the help of the Verses, I found the adjuster screw under the fuel tank between the two carbs, labeled with a yellow stripe as described.

The directions for the TwinMax seem pretty simple. This is how I would summarize them, let me know if I'm missing steps or got any of these wrong:

1 - Ensure engine is warmed up before commencing balancing.
1b - (Kill engine, I suppose, since later they say to start the engine.)
2 - Connect the tubes to the carbs (use A for the ref cylinder) (left/front)
3 - Turn "sensitivity" knob to MAX (turn power on too I suppose), adjust ZERO knob until needle is at zero
4 - Turn Sensitivity back to MIN, start engine and let it reach idle.
5 - Turn Sensitivity knob until it starts moving off zero, then adjust back to zero.
6 - All done!

OK, sounds easy enough. But when I get to turning the engine back on, the needle on the TwinMax is shaking wildly, it's not settled on one number! It's centered on zero, but oscillating between -1 and 1. Is that normal? Or does that indicate some problem other than carb syncing?

But, if I fiddle with Sensitivity, somewhere around 3/4 to MAX the center of the oscillating needle moves over from zero to -1, and at MAX goes all the way to -2. This is indicating the carbs do need syncing, right?

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
robardin is offline  
Sponsored Links
Advertisement
 
post #2 of 18 (permalink) Old 09-12-2009, 02:20 PM Thread Starter
Members who have donated towards server costs
 
robardin's Avatar
 
Join Date: Jun 2008
Location: Flushing, NY
Posts: 344
iTrader: (0)
 
Also... how the heck is one supposed to reach and adjust that 7mm carb adjustment screw?! There's no space for even my smallest socket wrench, and as far as I know they don't make very small, thin, L-shaped screwdrivers to slot into the flat head screw...

I'm thinking of buying a pair of thin longnose pliers and using them to hold a flat head screw drill bit to reach and turn that screw, but there must be a more normal way to do this. I mean, nothing I've read on this forum seems to comment on it at all, just says "turn the screw slightly to adjust". The Verses says it's easier to do from the left side, which I can see why, but that's not much help in and of itself!

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
robardin is offline  
post #3 of 18 (permalink) Old 09-12-2009, 02:37 PM
Members who have donated towards server costs
 
Crobins365's Avatar
 
Join Date: Jul 2006
Location: Kennett Square, PA
Posts: 3,505
iTrader: (48)
     
Hey - I use the homemade manometer, so I can't be of any help on how to set that between min and max. My guess, however, is that the oscillation is exactly what you'd see on the do-it-yourself version when the carbs do indeed need syncing. Essentially what you want to do is balance out the vacuum pull so that the front and rear carbs match each other, i.e., no jumping around. The idle adjust knob (on your left carb, as sitting on the bike) affects the vacuum on the front carb only by adjusting how the throttle plate sits in the carb body; the carb sync screw (the one that's impossible to reach) affects the vacuum on your rear carb only - same deal, it adjusts the positioning of the throttle plate.

You do want the idle set at about 1100 rpm before you start syncing - this will ensure that you've kinda got the front carb set where you want it. When you turn on the engine, if the front carb is drawing up more than the rear, you want to INCREASE the draw on the REAR by turning the carb sync screw clockwise. Conversely, if at 1100 rpm the rear carb is drawing more than the front, you want to DECREASE the draw on the REAR by turning the carb sync screw counterclockwise.

I've found the easiest way to make these adjustments (if you don't have a carb sync screw tool - they do make one!) is to turn the bike off, twist the throttle until you can see that screw, then reach in with a long, thin flat screwdriver. Adjustments should be made in very SMALL INCREMENTS - your carb is very delicate flower.

C
Crobins365 is offline  
 
post #4 of 18 (permalink) Old 09-12-2009, 02:45 PM
Senior Member
 
Join Date: Jul 2009
Posts: 686
iTrader: (0)
 
small screwdriver

take 2 minutes and make one...
Cut the end off a small screwdriver and bend the remaining piece.



I keep mine with registration & insurance cards on the bike.
VoIPDoc is offline  
post #5 of 18 (permalink) Old 09-12-2009, 02:48 PM
Members who have donated towards server costs
 
Crobins365's Avatar
 
Join Date: Jul 2006
Location: Kennett Square, PA
Posts: 3,505
iTrader: (48)
     
Quote:
Originally Posted by VoIP Doc View Post
take 2 minutes and make one...
Cut the end off a small screwdriver and bend the remaining piece.
The actual tools, though, have a coupler so that you can turn the end and the screwdriver or socket - sitting perpendicular to the shaft - turns accordingly. Any chance you can increase the size of your pic? I may be missing something.

C
Crobins365 is offline  
post #6 of 18 (permalink) Old 09-12-2009, 03:29 PM Thread Starter
Members who have donated towards server costs
 
robardin's Avatar
 
Join Date: Jun 2008
Location: Flushing, NY
Posts: 344
iTrader: (0)
 
[QUOTE=Crobins365;114859]You do want the idle set at about 1100 rpm before you start syncing - this will ensure that you've kinda got the front carb set where you want it.
[/QUOTE=Crobins365;114859]
Yep, got that set already as my standard engine idle.

Quote:
Originally Posted by Crobins365 View Post
When you turn on the engine, if the front carb is drawing up more than the rear, you want to INCREASE the draw on the REAR by turning the carb sync screw clockwise. Conversely, if at 1100 rpm the rear carb is drawing more than the front, you want to DECREASE the draw on the REAR by turning the carb sync screw counterclockwise.
Well, I don't see any imbalance at idle. The oscillation centers around 0. I have to dial it up to 3/4 of the way to MAX to see any drifting, towards the negative side (left of zero). If I dial it all the way to MAX then it's definitely to the left of zero, clustered around 2 (-2). Does that indicate that it's my front carb drawing more, I suppose?

Also, I've found that with the two vac ports re-routed to hook up to the TwinMax meter, after about five minutes the engine dies (presumably due to lack of air intake?). I read in the Verses mention of some kind of "T hose connector" which was not mentioned in the directions for using the TwinMax. Would that help? This way I keep having to unplug the TwinMax and restart the bike to let it idle for a few minutes before retrying.

Quote:
Originally Posted by Crobins365 View Post
I've found the easiest way to make these adjustments (if you don't have a carb sync screw tool - they do make one!) is to turn the bike off, twist the throttle until you can see that screw, then reach in with a long, thin flat screwdriver. Adjustments should be made in very SMALL INCREMENTS - your carb is very delicate flower.
Aha, twisting the throttle moves that screw downwards, eh? (Told you I was a newbie) I figured that out in reverse, when I pushed the screw down while trying to adjust it I revved the engine as if throttling

(Sorry for the cluelessness; I can't seem to pick anything practical up from a book, I need a master to sign on with as an apprentice, so to speak. I signed up for a Continuing Ed motorcycle maintenance course at a local college that offers it, but it got cancelled for the summer session due to lack of enrollment. Let's see how the fall semester goes.)

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
robardin is offline  
post #7 of 18 (permalink) Old 09-12-2009, 03:31 PM
Senior Member
 
G3P0's Avatar
 
Join Date: Aug 2009
Location: MN West Mpls
Posts: 116
iTrader: (2)
 
I use a long 7mm 12pt wrench, worked well enough, found a ratcheting 7mm wrench a couple weeks ago at autozone while killing time between jobs
G3P0 is offline  
post #8 of 18 (permalink) Old 09-12-2009, 03:32 PM Thread Starter
Members who have donated towards server costs
 
robardin's Avatar
 
Join Date: Jun 2008
Location: Flushing, NY
Posts: 344
iTrader: (0)
 
Quote:
Originally Posted by VoIP Doc View Post
take 2 minutes and make one...
Cut the end off a small screwdriver and bend the remaining piece.



I keep mine with registration & insurance cards on the bike.
Clever. But I have no metal cutting tools or tools to bend stuff except my two hands. I have metal cutting shears, like bolt cutters and one for cutting thin aluminum strips or something.

Looks like I'll have to defer adjusting my carbs until I can find this special tool, or see if my "needle nose pliers + flat head drill bit" combo will work.

I am worrying though that I am barking up the wrong tree on my vibration problem.

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
robardin is offline  
post #9 of 18 (permalink) Old 09-12-2009, 03:34 PM Thread Starter
Members who have donated towards server costs
 
robardin's Avatar
 
Join Date: Jun 2008
Location: Flushing, NY
Posts: 344
iTrader: (0)
 
Quote:
Originally Posted by G3P0 View Post
I use a long 7mm 12pt wrench, worked well enough, found a ratcheting 7mm wrench a couple weeks ago at autozone while killing time between jobs
I went out and got a 7mm wrench at my local hardware store, as part of a set of metric wenches, but it's pretty tiny. Doesn't ratchet either. Maybe I need to hit Home Depot or Autozone to look for this one.

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
robardin is offline  
post #10 of 18 (permalink) Old 09-12-2009, 07:01 PM
Members who have donated towards server costs
 
Crobins365's Avatar
 
Join Date: Jul 2006
Location: Kennett Square, PA
Posts: 3,505
iTrader: (48)
     
Quote:
Originally Posted by robardin View Post

I am worrying though that I am barking up the wrong tree on my vibration problem.
Again, hoping someone who's used a real manometer pipes in, but if you're osciallting around zero, methinks you might be pretty close to sync'd.

Say again what the vibration feels or sounds like? Is it a deep 'thunk thunk thunk' sound? If you use a breaker bar or screwdriver, you can set one end (for the screwdriver, go with the pointy one!) against the engine block and put the other end in your ear. It'll work like a stethoscope and you can try to pin down from where in the engine the sound is coming. On the left side (as you're sitting on the saddle), try putting your new-found stethoscope to the lower front of the engine block - see if the noise is coming from there.

C
Crobins365 is offline  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Once registered, your User Name"cannot be changed". We can make exceptions within 7 days, but after that, it is set in stone.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome