Carb sync - help needed - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 03-28-2007, 08:14 PM Thread Starter
 
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Carb sync - help needed

I am attempting to sync my carbs, the bike runs well, but i am thinking that the vibration may be from the carb synch, or lack of. i would be most thankful for any and all instructions in doing this synch job !!
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post #2 of 6 (permalink) Old 03-28-2007, 08:35 PM
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From another post:

"I built my own manometer by taping clear plastic tubing (1/4” id) to a yard stick and using automatic transmission fluid. I let it hang on the garage wall for several days to make sure all the A/T fluid had settled.

When it came time to do the sync, I ran the bike to let it warm up. I then shut it down and hooked up the manometer to the carbs. The bike was on its center stand. Since I was in my garage, I set a box fan in front of the bike to help with cooling.

My pre-determined approach was to run the bike, read the manometer, shut the bike down to make the adjustment, and then start it up again to see the effect of the adjustment. I used a small 9/32 wrench (I didn’t have a 7mm) to turn the adjusting screw/bolt. I had decided to make the adjustment with the bike off because I found that opening the throttle moved the adjusting screw/bolt to a better position for turning the bolt from the right side of the bike. I hooked the vacuum hose on the petcock to an external vacuum source to keep the fuel flowing.

Starting the bike with the manometer attached for the first time indicated that the carbs were very much out of sync. Before the A/T fluid got sucked out, I shut the bike down and made my first adjustment turning the bolt in the appropriate direction as indicated by the Clymer’s manual. I restarted and found that I had improved the sync, but not enough. I don’t know how many times I repeated this procedure because I tried to make small incremental adjustments and usually did something like this: not enough…..not enough….Oops! Too much! I would then adjust the bolt in the opposite direction and repeat the ”not enough…..not enough….Oops! Too much!” scenario multiple times.

The end result was that the fluid in the tube would stay at the same level on each side of the manometer at idle. I did run the throttle up to see what it would do and one side would be higher than the other depending on the throttle position. First, one side would be higher. I would then open the throttle a little more and then the other side would be higher. It was interesting to watch, but as long as they were even at idle I considered it good enough. After disconnecting the manometer and reconnecting the vacuum hoses to the carbs, I found that the RPMs at idle had increased. I adjusted the idle back down and the bike seems to run fine. At least I don’t think I hurt anything. For me, that’s a job well done…"

I have done just about exactly this. I used 2 cycle oil rather than ATF. Search the site for other "sync" threads for even more info. Post up any questions, we will be glad to help.

Jon

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post #3 of 6 (permalink) Old 03-28-2007, 09:02 PM
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Good find, Jon! I tihnk that's the one I used when I did mine the first time.

One other point that might be helpful is to know which way your turning to sync screw to what effect. The gist of the sync is that you are only adjusting the rear carb to be in sync with the front. That is, the front is stable, the sync is to bring the rear in line with that front set-up. So, if you hook up the manometer and your rear carb is sucking up the fluid (more vacuum in the rear than front), turn the adjusting screw out (left) to reduce the vacuum. If, on the contrary, you hook up the manometer and the front carb is sucking up the fluid, turn the screw in (right) to increase the vacuum in the rear carb. These really are gentle adjustments, even when it seems like one carb has all the vacuum!

good luck!

C
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post #4 of 6 (permalink) Old 03-28-2007, 09:21 PM
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Quote:
Originally Posted by Crobins365 View Post
Good find, Jon! I tihnk that's the one I used when I did mine the first time.

One other point that might be helpful is to know which way your turning to sync screw to what effect. The gist of the sync is that you are only adjusting the rear carb to be in sync with the front. That is, the front is stable, the sync is to bring the rear in line with that front set-up. So, if you hook up the manometer and your rear carb is sucking up the fluid (more vacuum in the rear than front), turn the adjusting screw out (left) to reduce the vacuum. If, on the contrary, you hook up the manometer and the front carb is sucking up the fluid, turn the screw in (right) to increase the vacuum in the rear carb. These really are gentle adjustments, even when it seems like one carb has all the vacuum!

good luck!

Cindy -

Good point.

I was doing this the other day and accidently left my choke slightly on. All of a sudden smoke is billowing out of the pipe as it is sucking down the 2 cycle oil. Felt like such a doofas. I found out the choke greatly affects the vacuum in one carb.

Jon

93VN750, under re-construction
vn750.com Member # 828

Rick's Stator and R/R
MF AGM Battery
Coastered
Degoated
Shaved & Jetted
Iridium's
MAC Tapered Staggered Pipes
Battery/Temp/Clock Gauge
Stainless Steel Brake Lines
Dunlop D-404's
23,XXX miles and holding pending gasket change (underway!!!)
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post #5 of 6 (permalink) Old 03-28-2007, 09:26 PM
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Quote:
Originally Posted by 93VN750 View Post
Cindy -

Good point.

I was doing this the other day and accidently left my choke slightly on. All of a sudden smoke is billowing out of the pipe as it is sucking down the 2 cycle oil. Felt like such a doofas. I found out the choke greatly affects the vacuum in one carb.

Jon
Ha ha ha - these lessons we have to learn, huh? Hey, at least it was 2-cycle oil and not mercury!!

C
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post #6 of 6 (permalink) Old 03-28-2007, 10:02 PM Thread Starter
 
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thanks for the info, I'll try it this weekend
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