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running straight pipes

  • Thread starter Thread starter moochx5
  • Start date Start date
M

moochx5

Guest
Ok guys I am building my GS 750 into a stretched bobber. What I dont know is if I run 4 straight pipes do I need different needles in the carbs to handle the pressure diffrence? Each pipe will be about 3 1/2 feet long but no baffles in the pipe.

Thanks guys and here she is

picture.php
 
You might need to re-jet. I would just install the pipes and see how it runs. If it runs like crap, you know you need to change something. Also, before riding it make sure you lengthen up those pipes so cold air wont reach the valves and warp them.

Good luck,
KT
 
It's like any other exhaust modification. Put on the exhaust you want, then tune to match. No one can tell you what you'll need ahead of time.
 
Yiu'll need a kit for that

Are you going to run filters?

CV carbs need some restriction
 
Hey Mooch,I agree with the other posters you will need to re-jet. Also be aware that with no baffeling in the exhaust you will lose back pressure so you won't have optimum combustion ( the back pressure helps to hold the incoming air/fuel charge back from leaking out of the exhaust valves while both inlet and exhaust are open for a split second)you'll get nice flames when the unburned fuel vapour builds up on the overrun though!!. As for re-jetting be safe and go for really outlandish jetting say 165 to start with assuming you have standard jets of say107.5-110 (not sure what the GSX750 runs as standard but that should be close),ALWAYS start rich and lean down, you'll know without a plug chop if it is too rich as you'll not be able to rev out in top, it will have a ceiling say 6,500RPM that it won't go past no matter how much you try, this number is just to give you an idea not a definitive number to work to,I assume you know how to tell from the colour of the plugs how well each cylinder is running black is obvious,chocolate is getting there but not quite, light tan is good,grey is a little lean and white is too far unless you intend to race it.Sorry if you know all this. I re-jetted my GSX1100EZ from scratch after I had to fit pod filters( the engine is in a GS1000 frame so no room for a standard airbox) with no help and having some advice would have saved me weeks of work and lots of frustration- when I phoned any of the tuning shops all I got was "bring it in we'll put it on the dyno"-great if I lived in England but not much use to me 300 miles away in Northern Ireland!!. One more thing if you are going to play with the jetting, the jets as you know are brass and don't like rough treatment get the closest fit of screwdriver you can then dip the end into the rubber solution for fixing patches to punctures in cycle tubes, you can get this in any cycle store or tyre fitters let it dry then if you are careful you won't damage the jets when you unscrew them.Good luck and happy riding!.Johnny
 
Johnny Drummond said:
...( the back pressure helps to hold the incoming air/fuel charge back from leaking out of the exhaust valves while both inlet and exhaust are open for a split second)...
Click to expand...

That's actually not what backpressure does...and I don't think any GS motors have valve overlap from the factory...
 
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