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1983 GS750e carb main jet and O-rings

maxredline

maxredline

Forum Newbie
I have a very sweet 83 GS750e. The only mod is a period correct Vance and Hines 4 into 1 pipe. I didn't realize how loud the pipe was but I totally rebuilt is with ceramic packing and paint. The engine ran fine but I figure it is running a little lean. Near the end of the summer the carbs engine was sputtering on throttle until hot then started surging. I now have the carbs apart and am chemical cleaning. I am still trying to figure out the main jet sizing. Stock is 117 so I figure going up 2 if that is possible but 120 should do. From what I have read the jet type is a small round style. I do not know if this is true or not so I am stalled on this point. I am also stalled on mixture screw O-rings.
I have read to install a 2mm washer on the main needle to richen that circuit up so I plan on doing that if I can not find a larger main jet.
Any information that can clear this up for me would be greatly appreciated.
 
Read this... https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Towards the back, there is information on how to lift the needle. Hint: putting small washers under the needle clip won't lift the needle.

Regarding pods, you will save a bunch of time and trial and error if you buy either a Dynojet kit, or some of member Zed's "air correction" jets. Oh, and make sure your pods are not the cheap junk Emgo/chinesium cheepies. Get proper K&N's, UNI filters, or similar.

Lastly, the main jets should be the N100.604 size

​
 
Hi there, can you give a little more detail on what throttle position/operation (constant, snapped open and held WFO, rolled-on?), the rev range and and under what load the bike was misbehaving? Different fuel circuits take charge at different loads and rpm and with the CV carbs fitted to an 83' the throttle only indirectly controls the position of the slide and thus the operation of needle/needle jet and main jet. Understanding the exact conditions under which the bad metering occurs can go a long way to determining what to look at.

Have you tried the carbs running in the bike after cleaning to see if that fixed the issue? Or are you looking to re-jet as the carbs are apart on the bench? You said "the engine ran fine" so was wondering if anything happened or was done to cause the spluttering and surging. Or has this always been a niggling problem?
 
A little history, the 83 GS750e was stock as far as I know it when I got it used (under 9k kms) Meaning stock 4 into 2 pipes, stock air box, filter and jetting. The main jet is a 120 main when I got the bike and from what I understand stock is 117. There is no reason for me to believe the previous owner has changed them to the 120's.

I did not run it much with the stock pipe and found a parts bike with a 4 into 1 Vance and Hines that I rebuilt. Bike was running a little lean but I road it that way for a short while. In between the engine was running on 3 cylinders until it got warm and then started surging on the throttle.

The parts bike with the 4 into 1 has 130 mains in the carbs which seem a bit large from what I have read.
The carbs are apart. I in the process of chemically cleaning the carbs and then ultrasonically afterwards. From there install new O-rings and put in larger mains without installing any washers on the main needle. I have been contemplating installing 125's but I do have the option of installing the 130's that came with the parts bike.
 
Not sure but thinking you're using stock air box and filter. 117.5 to130's with only a 4 into 1 pipe seems too much. If you're using pods may be fine. The pods affect the jetting way more than a 4 into 1.... Just my opinion.
 
I agree with your assessment of using pods.
I am hoping Ed chimes in. Maybe the 120 with the needle clip one position lower may work.
 
I have chemically cleaned the bs22 carb set, untrasound washed and replaced parished o-rings. The only change I have made was move the main needle valve up one notch as the spark plugs looked ok. Put the carbs on the bike and it fired up. Found it was only running on 3 cyclinders. Then I believe the same cyclinders carb float bowl was over flowing. Thats what you get for not testing floats on the bench. Out the carbs come. I did buy a remote aux fuel bottle so I can test with the tank off. I tried to cheap out and got burned.
Another thing I did learnt was to take the carb rubber boot clamps off. They get damaged easily pulling and pushing those carbs around.
I am going to check all sparks once I get the dry carbs back on the bike before fire up.
 
APE pods look and perform as well as K&N for half the price. And get Dynojets!
 
I test with a gravity bottle too but i use water as to not waste gas or get it all over the place. Then drain bowls via the drains and blow a lot of air down the fuel line to force out residual water.
 
So cleaning the carbs and replacing the O-rings has done the trick. I used all the jets that came with the bike. I did move the needle one clip more open. After starting it a couple of months ago I insured the bike as the weather has been really good here on the west coast of Canada. I got my gear on to go for a ride. Initally the engine did not want to start but then did on 3 cyclinders. I got the temp gun out and found the non firing cylinder. I gave the float bowl a tappy tappy with a socket extension bar and the bike ran great. Then for a good burn with good results.
 
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