Suzuki gs750 1978 low compression

[SanderG]

hello guy's Quick question,

I got a haynes service manual to help me. ( see Picture )
https://photos.app.goo.gl/fWJjYlnzaWcURAT83
Now I wanted to work on my carburetors and saw that this manual has the CV Carburetors.
Is there an Haynes or other book on the VM carburetors that mine got?

Got an 1978 750B.

 

[Nessism]

On basscliff's website you can get a proper factory suzuki manual download for free with all the proper information. Haynes manuals are not very good. Basscliff also has a VM carb rebuild tutorial. It's strongly advised that you use it and go through your carbs completely.

http://members.dslextreme.com/users/bikecliff/

 

[SanderG]

@ nessism : I allready had a look at the VM carb rebuild tutorial. I am most certainly going to use it.
Just like to have something to compare. ( In the original service manual there isn't a whole lot on the carbs )

But nevermind anyway : Just opened the book and saw that they do explain the VM carbs, There's Just a wrong picture on the cover

Thanks Anyway!
Keep you posted

 

[Nessism]

When you go to take apart the carbs do NOT screw in the fuel screws and try to bottom them out. That sometimes results in the tip getting stuck and often broken off in the carb body. Just remove the screws and be sure to remove any thread sealant on the threads. When you go to install the screw after the carbs are freshly clean, then you can carefully bottom the screw before backing it out the proper number of turns (3/4 - 7/8 of one complete rotation).

 

[SanderG]

Sure will keep it in mind. Btw: With fuelscrew do you mean the mixture screw? Because in the manual for my bike it say's back out 1 full turn.

Will be taking them apart sometime next month. On my list for this winter:

- place weatherstriping on airfilterbox
- replace intake boots o-rings ( intake boots are fine I think, no cracks from the look of it )
- take apart carbs and clean/replace everything ( zlready ordered kits for gaskets and o-rings from robert.
- clean tank ( not sure how I'm gonna do it ) and properly prime it. ( Now when you look in the fillercap I see a bit of rust )
- while I have the carbs removed I'm gonna take the chain tensenor off because bike makes a litte rattling noise.

Do I forget something that you guy's would probably clean/check/replace or repare when I got carbs and tank off?

Further down the path I will need to adress the electric part ( coils, connections,... ) But first will probably come summer!

Thank ya guy's,
Nice to hear all this knowledge.
Kind of want me to get into it as fast as possible.

 

[Nessism]

There are two pilot screws: fuel screw and air screw. I think the screw you are referring to as the "mixture screw" is actually the pilot fuel screw.

 

[SanderG]

But fuel and air screw should be 1 turn out then?

 

[2BRacing]

But fuel and air screw should be 1 turn out then?

No, they are not both open 1 turn. Bottom screw is 3/4 to 7/8 turn open and side one is 1 to 1 3/4 turn open depending on engine number. Look here for good information: http://www.thegsresources.com/_foru...750-carbs-are-killin-me&p=2151222#post2151222

 

[Nessism]

The air screw is typically open slightly less than double that of the fuel screw.

 

[chuck hahn]

Actually his bike has VM26 carbs. bottom PILOT screw..which affects idle to about 1/8 throttle twist..get set at 3/4 to 7/8 ( I go 7/8 myself on my VM26s carbs ). Then it gets forgotten about. ALL fuel to air ratios are adjusted via the side MIXTURE screws....end of story. Initial setting for the mixture screws is 1 1/2 out to 2 out. And I find that on both my 750s and my 1000s the sweet spot is at or just a tad more than 1 1/2 out. I muse the Colortune and watch the flame color so Im pretty confident ive got it down rather well.

 

[SanderG]

so on my bike the pilot screw Goes out 7/8 off a turn
the side screw at 1 turn ( got it from the chart )

and then set Idle with mixture screw for the 4 carbs together ?

 

[jdvorchak]

Getting back to the original post of low-ish compression. I just have to ask. When you did the compression check did you keep pumping the starter until the gauge quit rising or just let it "hit" once per cylinder?

Proper would be:
Remove all spark plugs
Battery fully charged and starter not dragging
Throttle wide open
Keep starter engaged until pressure gauge won't go any higher which usually takes about 5 or more 'hits' or thumps?

 

[alke46]

I just wanted to chime in concerning the compression numbers. My bike also has a lower number in cyl. #3 versus the others. Yesterday as I was tearing my top end down for rebuild, I noticed two of the head bolts on the inward side of #3 cylinder was much easier to break loose than the rest of them.

I don't know if this would have an effect on the compression but my 1st thought was that just maybe those two bolts were not torqued to the same spec as the rest of them, thereby causing a possible lower compression in that cylinder. IDK, just an observation.

Good luck with yours SanderG

 

[jdvorchak]

I just wanted to chime in concerning the compression numbers. My bike also has a lower number in cyl. #3 versus the others. Yesterday as I was tearing my top end down for rebuild, I noticed two of the head bolts on the inward side of #3 cylinder was much easier to break loose than the rest of them.

I don't know if this would have an effect on the compression but my 1st thought was that just maybe those two bolts were not torqued to the same spec as the rest of them, thereby causing a possible lower compression in that cylinder. IDK, just an observation.

Good luck with yours SanderG

Twice now I've seen loose head bolts on these old GS bikes. Usually on the right side (#3 and #4) come to think of it.