A gsx750e tuning challenge

[Maarten]

Hello,

I hope you Suzuki hero?s are up for a challenge!

I?m building a motorcycle for my girlfriend (sinds I crashed her gs550 in spectaculair fashion about a year ago) and have come to the point i?m almost ready to start en tune.

Because she wished a little upgrade, i?ve bought a separate gsx750e with the following specs:

- 750cc, 16v engine with electronic ignition.
- Ignition timing: done!
- Sparkplugs: brand new!
- Carburators: ultrasonic cleaned!
- Valves: set!
- Intake boots: good condition!
- Compression: good!
- Exhaust: 4:1 Marshell.

But now it get?s challenging! I really really like the VM carbs, but the gsx750e had CV carbs so? I have fitted VM gs1000 (vm26ss) carbs and it fit?s like a beauty! Furthermore i?m using K&N filters and live in The Netherlands (sea level).

According to the bikeCliff chart, the basic setting of the gs1000:
* Main jet# 95
* Pilot jet# = 15
* Pilot air jet# = 1.2
* Pilot screw = 1

What would be a good starting point for this bike?
And, anybody any experience with this setup?

After I get it running she will go for a dynorun.

Thanks in advance

Maarten

 

[Maarten]

Hello again,

Perhaps this is a harder to answer question than I thought.
So, a new proposal!

I was thinking, the gs750 had VM carbs and has the same amount of cc's as the gsx750e.
Is it a good idea to start with the standard setup for the gs750? Despite being carburetors for the gs1000.

Thanks!

Maarten

 

[Steve]

You have too many variables there to make a reasonable guess. The 16-valve motors have different flow characteristics, which require different jetting. Yes, the 8-valve 750s came with VM26s, but I think the jetting would be different for the 16-valve engine.

Why desire for VM carbs? What is your intended use for the bike? I see this is your girlfriend's bike. Is she a racer?
The BS series (CV type) carbs are so much more friendly for street use. VM carbs are better on the track, but do "OK" on the street.

.

 

[Maarten]

I see what you mean Steve.

I have some experience with both type of carbs (CV/VM), and found the VM such a treat to work with! Especially in combination with K&N filters. Her previous gs550 had VM carburetors and worked great.

She will be using the motorcycle on the normal road.

Thanks for your reply. Any suggestions about where to start are appreciated.


Maarten

 

[Guest]

From a friend...........

Tell him to start by JUST replacing the main jets with 117.5's and leave the pilot stock and needle in the center position.
Adjust air/fuel screws to fine tune.

.............that knows what he's talking about.:encouragement:

 

[Maarten]

Hello GSRick,

Thank you very much! Sounds like a friend with experience
I'll let you know how it works out. I'm going to start with these specs.

Maarten

 

[jdvorchak]

Just my 2 cents worth. I have an 81 GS750E with Mikuni BS32 (CV) carbs. Complete stock setup with OEM airbox and filter. Starts instantly, idle is perfect, takes throttle well with no hesitation or flat spots and pulls like a freight train when you get happy with the throttle.

This bike sat for 13 years in a guys back yard and was horribly neglected. Cleaned the carbs, replaced the O-rings and set the float levels. That is all I needed to make it run great.

 

[Maarten]

Thanks for your reply John,

I see what you're referring to
But since it's a balance between 'fun project for me' and ' becoming an aesthetically pleasing bike for her', i'm willing to give it a good thorough try.

I'll remember what you've said here!

 

[jdvorchak]

Pulling the carbs is only about a 10 minute job so playing with the jetting isn't a bad idea. Just make sure you buy quality pod filters. One tip is to use Vaseline or silicon, like dielectric grease, on the intake boots so they slide in and out easily and reduce the risk of tearing one.

 

[Maarten]

So, I promised an update but study got in the way (as usual). Luckily the weather in The Netherlands is getting better and the girlfriend is getting impatience, so that’s pushing me

Let me start with; Steve, you are a legend! I used your tips about the initial setup and it fired up right away. And after a little tinkering she idles perfect and revs up like a beast!!

She kept smoking heavily but after abstracting almost 6L (you guys use the ounce I believe, so that’s 203 ounce), even that issue was resolved ( '' thank you PO'', although, I should have double checked).

I need to resolve a small problem with the brakes, after that I’ll start with tuning it for real. The photo included in this message is like she sits right now.

Again, thank you all!

 

[thebrandonbeezy]

So, I promised an update but study got in the way (as usual). Luckily the weather in The Netherlands is getting better and the girlfriend is getting impatience, so that’s pushing me

Let me start with; Steve, you are a legend! I used your tips about the initial setup and it fired up right away. And after a little tinkering she idles perfect and revs up like a beast!!

She kept smoking heavily but after abstracting almost 6L (you guys use the ounce I believe, so that’s 203 ounce), even that issue was resolved ( '' thank you PO'', although, I should have double checked).

I need to resolve a small problem with the brakes, after that I’ll start with tuning it for real. The photo included in this message is like she sits right now.

Again, thank you all!


View attachment 50350

Thats a very nice looking bike pal!

 

[Maarten]

Thebrandonbeezy, thank you very much! Still a lot of little jobs to accomplish (like leaking carbs), but she's fast!! (see photo below).

Cheers!

 

[jdvorchak]

6 L? It only holds about 4L ... no wonder it smoked.

Those Mikuni carbs will leak if you don't replace the O-rings that are on the float valve seats. Also known to leak if you don't replace the O-rings on the interconnecting fuel lines. Next time you have the float bowls off, check very carefully for cracks in the over flow pipes. That's the brass pipe in the center of the float bowl. If you find a crack it is easily repaired by clean and soldering the crack closed.

 

[dowser81]

Damn that is one mighty fine ride your girl is a lucky lady, if mines looks anywhere as nice as that when im finished i will be one very happy chap.

So, I promised an update but study got in the way (as usual). Luckily the weather in The Netherlands is getting better and the girlfriend is getting impatience, so that?s pushing me

Let me start with; Steve, you are a legend! I used your tips about the initial setup and it fired up right away. And after a little tinkering she idles perfect and revs up like a beast!!

She kept smoking heavily but after abstracting almost 6L (you guys use the ounce I believe, so that?s 203 ounce), even that issue was resolved ( '' thank you PO'', although, I should have double checked).

I need to resolve a small problem with the brakes, after that I?ll start with tuning it for real. The photo included in this message is like she sits right now.

Again, thank you all!


View attachment 50350

 

[Maarten]

@jdvorchak, thank you for the advice. I replaced all the O-rings and that cleaned the little filters inside the carburetor. They contained some gunk and the rubber O-rings where perished. Unfortunately they keep leaking, so the search continues

@dowser81, you sir, just made my day Thanks! To achieve a strait line in tank and seat I ''cracked'' the frame and welded solid triangular pieces in place. I don’t know what you envision, but I wish you luck!

So, been tinkering for a few weeks and made some progress!

I replaced the main jets to #110 what made a big difference! Sparkplugs have a great colour but.. (there is always a but): she pulls hard, but the maximum speed isn’t great. The bike makes a lot of RPM when riding fast and has a very (!) short first couple of gears (especially first and second), so I was thinking sprocket ratio.
I’ve counted 17 in the front and 52 in the back! After some calculations and some reading on gsresourches, I’ve ordered a 43 tooth sprocket.

This will make a drive ratio of 2.53 in stead of 3.06. A streetbike instead of a dirtbike ;-)
I like to know what you guys thinks of this.

Cheers!