Correct carb sync sequence??????

[GS750GUY]

Dear GS'rs,
I'm in the process of syncing my carbs on my 78 GS750EC with a set of vacuum guages and I'm not sure of the proper sequence for tuning and syncing the carbs. Do I do as follows:
* First....... adjust the side air screws for each carb until I have the highest idle minus 1/8 of a turn.
*Second.....sync the carbs with the guages.
*Third........adjust the fuel screw for each carb by reading the condition of the plugs after riding a while.

When I rebuilt my carbs I set eveything according to factory settings when I did a bench sync. To my surprise when I put eveything back together and hit the start button it fired right up.

I borrowed a set of sync guages from a friend and found that just one carb was only off by one hash mark on the guages. Darn close.

However, after I returned the guages my friend asked me what sequence I used when I did the sync. I told him all I did was sync the carbs with the guages and did not even consider the side air or fuel screw adjustments under the float bowl.

Do I need to get the guages back and start over? Or, can I tweek the fuel or side air screws after I have used the guages to sync the carbs?

The bike seems to run great except that when my brother follows me on his bike he says my GS seems to be running a little rich.

Thanks again for your wisdom concerning this.
GS750Guy

[TheCafeKid]

Ahhhh welcome to my world!! Hahaha. Actually i learned this weekend that the gauges have nothing to do with the air/fuel adjustment screws. so you should be pretty good to go...just gotta figure out why you're running rich...i have the same problem as well tho i am running pods and 4into1 pipe which makes it a bit more difficult. Try one and half turns out from seat on the fuel screws, and the air you want to adjust based on best idle. one thing i noticed is as your are turning your screws, go slowly and give the engine time to compensate, a little turn can do alot, but you have to wait to hear it happen. Do you have problems with smoke from the exhaust? Just wondering, as i have a bit of that problem on my 77 750B

[Jd Powell]

You may want to take a look at what your doing. Your carb will have either an air screw or a fuel screw. And if it has an air screw it is probably a Two stroke The fuel mixture screw is on the bottom of the carb on the engine side. (not the airbox side) adjust for Highest idle but you must keep turning down the idle to stay on that circuit (below 1500 RPM)
The idle screw is the big one between the carbs underneath on the airbox side.


The syncing screws are between the carbs on top also on the eng side of the carbs sync 1&2 first by adjusting the left screw, Then 3&4 with the right screw, finaly sync 1-2 & 3-4 by utilizing the center screw.


Be sure to have a fan blowing over the cylinders while doing these procedures or you will cook your bike. Hope this clarifys a few things for you.

[GS750GUY]

Thanks for the tips CafeKid!
I believe you are correct. The fact that the syncing with the guages has nothing to do with the fuel and air screws now makes sense after thinking about your explanation. After syncing with the guages is done the instructions I have mention fine tuning the fuel first and then the air screws last but says no more about the need to re-sync again with the guages after fine tuning the fuel and air.
I'm running a stock air box and stock exhaust. Initially when I first fired the bike up it had quite a bit of smoking but I was told the bike just probably needed to be run on the road a while to kick the cobs out of it since it had been sitting for four years. And they were right the more I rode the bike the smoking subsided considerably. It still has just a very slight smoking problem but hardly even noticeable. The bike only has 11,000 miles on it. I will try taking a look at the plugs and try some adjustments and see what happens.
GS750Guy

[GS750GUY]

Thanks JD Powell!
My 78 GS is a 4 stroke and actually has both an external air mixture screw on the side of each carb just above the float bowls as well as a fuel mixture screw on the under side of each carb in front of the float bowls.
Thanks for your help. I will remember the fan.
GS750Guy

[Jd Powell]

I stand corrected on your air screws. Did not realize you had mechanical slide carbs.

[TheCafeKid]

No prob sir...having just learned a thing or two about it myself, i will gladly pass on the info...thats what makes this place great! A bunch of knowlegeable guys to teach the ones that arent so they in turn can teach others...to bad the rest of the world doesnt work so smoothly..:-D

[GS750GUY]

Thanks JD. I'm not sure what you mean by mechanical slide carbs.
GS750Guy

[GS750GUY]

Thanks CafeKid!
I agree GS is the best group of cycle enthusiasts around. I have learned so much from the veterans. When I started this GS750 restoration project a year ago I knew nothing about motorcycles. It's because of the GS family that I was able to see it to completion successfully.
I pulled all four plugs and found I definitely have a rich running situation going on. Three plugs were badly black encrusted including the insulator and the fourth indicated a slight rich condition with a fairly clean insulator. I turned in the fuel screws 1/4 turn on the three badly rich carbs and just 1/8 turn on the slightly rich one. Now I will readjust the air screws for best idle, re-set the main idle screw to normal idle and then ride a while and take another plug reading. I will keep you posted on the results.
GS750GUY