New here

[mblab]

Hi all
First post- Was fortunate enough to pick up a 77 gs750 last summer. Good price, good looking almost stock bike, Looks to have 4 into 2 MAC (?) mufflers. Ran way rich when I got it, had 120 mains, got some 110's, much better, still a little rich, but no plug fouling now.
Was going to get it to my local wrench for a tune up, found that he has retired. As there are no other old timers around here that know these dinosaurs like he does, and I don't trust the "unplug one module and plug in another" mechanics with it, I've got to work on this thing meself.
I've wrenched my Brit for 25 years, just have no experience with Jappa's.
Sooooo, Hopefully a little guidence from you all.
First, the bike runs strong, but idles at about 2000 rpm with idle screw backed out all the way. Syncronization?
Second, I've noticed a noise that might be a cam chain. Common on an 18000 mile bike? Should it be dealt with or left alone?
Third, the #1 spark plug is a bit oily. Do these bikes have a common issue with rings or valve seals?
Fourth, What the heck are the mixture screws on the bottom of the carbs for??? Book sez leave em alone.
All in all, the bike is a hoot to ride and I'm looking forward to getting it dialed in.
BTW, I've got the Clymer manual.
Thanks for any help.

[koolaid_kid]

Old timers?
Dinosaurs?
Jappas?
You must be a graduate of Dale Carnegie's "How to win friends and influence people". 8O :razz:
You are correct to doubt the parts replacers. They just keep replacing parts until it magically works again.
As to your manual, I personally use my Clymers Manuals when I am in the woods without a Sears catalog, if you catch my drift. But others on this forum disagree, and I respect their opinion.
The screws you speak of are called the idle mixture screws, and are used in the idle and low rpm cruise mode. Further than that, the carb experts here can help you more than I can.
But welcome to the forum, and your verbage is certainly, ummm, refreshing.

[deves3000gt]

welcome

welcome to the site. I have a 77 gs 750 they are great bikes. my #3 plug is the one that gives me some trouble with fouling. never really found out why i just put a new plug in every now and again. my bike only has 14k on it and has done it frome the begeing. But i saw you said you put 110's in your main jets, if it is still too rich the stock jets are 105's. good luck with the bike

[koolaid_kid]

I agree, it sounds like you are headed in the right direction, but not quite there. For some mysterious reason, people tend to put too large a jet in, thinking that it will give them more power. Not realizing that it is an integrated system designed by the factory. Best of luck.

[49er]

Hi all
First post- Was fortunate enough to pick up a 77 gs750 last summer. Good price, good looking almost stock bike, Looks to have 4 into 2 MAC (?) mufflers. Ran way rich when I got it, had 120 mains, got some 110's, much better, still a little rich, but no plug fouling now.
Was going to get it to my local wrench for a tune up, found that he has retired. As there are no other old timers around here that know these dinosaurs like he does, and I don't trust the "unplug one module and plug in another" mechanics with it, I've got to work on this thing meself.
I've wrenched my Brit for 25 years, just have no experience with Jappa's.
Sooooo, Hopefully a little guidence from you all.
First, the bike runs strong, but idles at about 2000 rpm with idle screw backed out all the way. Syncronization?
Second, I've noticed a noise that might be a cam chain. Common on an 18000 mile bike? Should it be dealt with or left alone?
Third, the #1 spark plug is a bit oily. Do these bikes have a common issue with rings or valve seals?
Fourth, What the heck are the mixture screws on the bottom of the carbs for??? Book sez leave em alone.
All in all, the bike is a hoot to ride and I'm looking forward to getting it dialed in.
BTW, I've got the Clymer manual.
Thanks for any help.

Hi mblab, welcome to the GSR.

At only 18000 miles, it sounds like your bike may have sat unused for a considerable period. That one oily plug could have been caused by the rings in that pot being rusted to the bore surface. When this happens, as the engine is turned over, a piece or ring can break off and gouge a groove on the bore. More damage is done with each additional revolution until the sharp edges have been smoothed with wear. From then on your compression and oil consumption is compromised.

Your main jetting is still too large at 110 for the VM 26 carbs. I have a K&B carb kit for your model that has 102 mains. This jetting is for a stock engine ie, OEM carbs, airbox and 4-2 exhaust. If you are running pods on your carbs then the 110's may not be that far out.

Your high idle speed could be caused by unsychronised carbs, or a sticking/badly adjusted throttle cables, or the slide height is set to high.

Those mixture screws should be removed when ever a carb clean is needed. Just make sure that you lightly seat them, counting the turns and recording each one seperately. When re-fiting the carbs, you have the correct settings to start your tuning from.

[chef1366]

Change the o-ring between the engine and your intake boots. This could be the problem with your high idle? Any mods other than your mac exhaust? Stock airbox? I don't think just a mac 4-2 should warrant you to use anything except stock jetting unless your airbox has been removed.
I would pull the head and check your cylinder wall for gouging as 49er stated. If not gouged change your valve stem oil seals.

[pasteurized]

Unfortunately 49er, I would have to disagree a bit the the jetting suggestion. I was just looking over the paperwork that came with my Vance & Hines 4-1 a couple of years ago, and their jetting suggestion was exactly that, a 110 main. Pilot Jet would be at 17.5 and moving the needle up a notch was also suggested. I figured I should chime in with this as I just saw that sheet a couple of hours ago.

Hi mblab, welcome to the GSR.
Your main jetting is still too large at 110 for the VM 26 carbs. I have a K&B carb kit for your model that has 102 mains. This jetting is for a stock engine ie, OEM carbs, airbox and 4-2 exhaust. If you are running pods on your carbs then the 110's may not be that far out.

[mark]

Fourth, What the heck are the mixture screws on the bottom of the carbs for??? Book sez leave em alone.

Those would be your pilot screws, that regulate the mixture for the pilot circuit (important just off idle, works with pilot jet). With a non-stock exhaust you may have to mess with them if just off idle your having carburetion problems. If your idle is high and the carbs are closing correctly, it could be synch issues, but I'd think more likely a vacuum leak as Chef suggested.

[mblab]

Hi again
Thank you all for the replies. Koolkid, hope it wasn't the refrence to oldtimers that ruffled you. I resemble that remark myself.
Ok, as for the screws on the bottom, I strongly suspect that they are not in the factory positions. What kind of black art must be invoked to get these right?
Sync is generally done with the 4 tubes and hoses, right? Short of getting these, is there another way?
Put braided stainless lines on it yesterday, changed fluid, cleaned the caliper up. Any suggestions for a set of pads with a little more bite?
Mike

[mblab]

Oh, one more thing I forgot to mention about the high idle speed- I have the stock airbox and a UNI foam filter, but the horns are a loose fit (not sealed to the box) obviously leaking air. I know this is not a good thing regarding filtration, but maybe affecting idle as well?

[koolaid_kid]

Hi again
Thank you all for the replies. Koolkid, hope it wasn't the refrence to oldtimers that ruffled you. I resemble that remark myself.
Mike

No ruffling involved. I found your post amusing, at best. I wish you the best with your bike and hope you find GS Resources helpful for your bike.
As to brake pads, there will be many opinions. I use EBC pads with excellent results.
As to the leak at the air box, it will also affect idle. Are the clamps still in place?

[mblab]

Yea, the clamps to the carbs are intact and tight. Its loose where the horns enter the airbox.
Read some other threads here, guess I'm not the only one who has pilot screw issues. I did close them down , and opened them 3/4 turn and viola! idles smoothly at about 1000 rpm.
So, on to other issues and a bit of riding.
Cheers!