77' GS750 Vacuum Leak

**Larry D** · 08-26-2009, 02:27 PM

Yes, there are gaskets there and they're probably shot. Go to the homepage of this site and look for the Carb Rebuild section on the left column near the bottom of the page. The gaskets and complete o-ring sets are available to rebuild your carbs. Highly recommended.

**Nessism** · 08-26-2009, 02:32 PM

Originally posted by miles28

Hello all, I'm relatively new to both this forum and my bike. I did STF, but didn't quite find what I was looking for. Heres the problem:

I have a high mileage 1977 GS750 that continually fouls the plugs out (every cylinder) and seems to have some vacuum leaks on the two outside cylinders. At least that is what I'm thinking.
I sprayed starter fluid on the carbs, and the two places that it made the idle change were where the carbs meet the block at the intake. I can also see gas sputtering out of these places from time to time.
My question is, are there supposed to be gaskets at these junctions? Or do I just pull the carbs and check the boots and tighten the mounts? Or am I completely wrong altogether?

My bike doesn't seems to have any real "pep", nor does it pull very hard (which I'm guessing are other issues as well).
Thanks so much for any help you may be able to give me. Please free free to asks for specifics if I have forgotten something.

_C

Well _C,

You didn't search very hard or you would have found that intake boot leaks are one of the most common problems with these old GS bikes. Pull the carb boots and replace the O-rings underneath. Some of the earliest 750's did not have the O-rings in which case you should replace both the boots and O-rings. While the carbs are off it's recommended to rebuild those as well - get parts from cycleorings.com

Good luck

**TheCafeKid** · 08-26-2009, 02:33 PM

If its fouling the plugs, there are other things going on, but to your specific question: There are ORINGS behind the intake manifolds/boots/pipes whatever you choose to call them. They need to be replaced after many many years as they dry out, crack, flatten and get brittle and turn to dust. These, along with the orings you're going to need to clean your carburetors from www.cycleorings.com To put it bluntly and to the point, if you dont plan to clean your carbs, and that means completely disassemble, soak, and replace the orings in EACH ONE, then you might as well quit messing with it, because it wont run right, ever. Period. You also NEED to adjust the valves. There are a list of things that SHOULD be done if you want to succeed in getting the bike running properly. Not to sound like a jerk, but there are alot of people that come on here, ask a question, then when they dont get the answer they want to hear, ignore it, and ask it again. Or, they tell the people on the board here, whove been working and restoring these bikes for god knows how many years, they dont know what they are talking about. But, I digress on this...

IF you have true interest in getting that mighty machine running properly again, do the following:

Break down, soak, clean and re-ring the carburetors
Adjust the valve clearances. (should be done every 3-5k miles)
Check all of your wiring for dirty connections, clean and replace connectors as necessary.
Assure you have NO VACUUM leaks, both in your intake boots (which you're working on) and your airbox (it does still have the airbox right?)
Check and repair your charging system as necessary.

DO THESE THINGS, and do them all, and that mighty 77 750B will run for many many many more miles without fault. They are truely bulletproof, if you do the necessary maintainence. But, if you dont do just ONE of these things...much like a scorned woman, it will treat you ever so badly, and you will get angry, frustrated, and disgruntled...and then you can sell it to me

BTW, Welcome to the GSR, wipe your feet at the door, prepare to get your hands greasy, and then hang on for the ride...

**miles28** · 08-26-2009, 02:34 PM

Thank you Ed, maybe I was searching the wrong sections. Appreciate the help

-Chris

**miles28** · 08-26-2009, 02:37 PM

Lol, great advice. Truly appreciated. So am I to assume my model is a "B"? It only has the single front disk, and I could never find what letter designation it is. But I do so love that bike!

**Larry D** · 08-26-2009, 02:44 PM

Originally posted by miles28

Lol, great advice. Truly appreciated. So am I to assume my model is a "B"? It only has the single front disk, and I could never find what letter designation it is. But I do so love that bike!

Don't mean to beat you up, but, this is from the homepage too. There's alot of great info there.

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http://www.thegsresources.com/gs_modelchart.htm

**TheCafeKid** · 08-26-2009, 02:44 PM

Originally posted by miles28

Lol, great advice. Truly appreciated. So am I to assume my model is a "B"? It only has the single front disk, and I could never find what letter designation it is. But I do so love that bike!

If your bike was manufactured in late 76 (june or july on) or early 77, it would be a "B"...if its later than that it could possibly be a "C", though im not sure if technicly speaking the "C" had wire wheels and single disc, or if it went to the mags and dual disc before it would be constituted a "C" model...

**miles28** · 08-26-2009, 03:56 PM

Hmmm, Sept. of 1976. . .I guess (according to the chart), it's an "A"

**SqDancerLynn1** · 08-26-2009, 04:49 PM

You can make some gaskets for the old style. Gaskets were never offered.
As said the best way is to replace them with the O ring style boots

**TheCafeKid** · 08-26-2009, 05:05 PM

Originally posted by miles28

Hmmm, Sept. of 1976. . .I guess (according to the chart), it's an "A"

There were no "A" models in the US market. Sept of 76 would have been a 77 model year, as around june or july Suzuki started tooling up for the coming model year. This is the reason there are so many odd bikes out there with parts from two different years on them. A late 81 650 might have stuff left over from 81 on it, as well as some upgraded stuff due out with the next model year or something like that... Its sometimes tough to decipher when you're hunting for parts what you actually need sometimes...

77' GS750 Vacuum Leak

77' GS750 Vacuum Leak

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