GR650 "air induction system"

[Big Rich]

More specifically, what to do with it.... Years ago when I got my GR I had the normal "old Suzuki" problems. But even after everything was cleaned / tuned / etc, I still had issues with a wandering idle. Come to find out, the rubber tubes used in the GR650's air induction system had not held up to 30 years of neglect either. Here's a picture of the system for those that haven't seen it:



For a quick fix, I just used rubber vacuum caps on the carbs and cylinder head. Naturally, the rubber would go thru some heat cycles before it failed as well so I started replacing them yearly.

 

[Big Rich]

After replacing the original CV carbs for some good old VM34's, I no longer had the option of using the air induction system. Which meant replacing vacuum caps on a regular basis, and when they developed a leak it became a hassle. What to do? Get some 1/4" silicone tubing and connect the air induction ports:



Now here's what I'm getting at.... with the tube connecting the intake ports, I noticed the idle had increased slightly and didn't put 2 and 2 together. I was poking around near the carbs while the engine was idling and grabbed the silicone hose, pinching it with my fingers - and the idle dropped slightly!

Obviously, I'm no mechanical engineer or anything. But my best guess is that the intake pulse from one cylinder is pushing a small amount of air thru the silicone hose and into the other cylinder.

Small increase or decrease in power? Better or worse fuel economy? I'll find out eventually, but just wanted to share my experience with the collective here.

 

[Jedz123]

Rich
Likely the vacuum from one cylinder is pulling from the non vacuum from the other side ( I think the pistons are on an opposite firing pattern on the crank, so as one is in intake stroke creating vacuum the other is in exhaust stroke with the intake valve sealed)... Quite odd. I remember seeing this on my GR650 and thinking why they did this... Good to know. Thanks for the diagram!

 

[Big Rich]

Yep, we are on the same thought process Jedz. Once my bike is back on the road full time I plan on experimenting a little with the inductions system. I've been reading for years about how people just cap off the ports (like I have myself) and everybody always said "it didn't effect how the engine runs". Heck, I've said it myself plenty of times.

 

[barnbiketom]

Hi Rich!
my hoses were bad too, and I got BLUE silicone hose on the stock setup now.. the color alone makes it run much better! heehee.
I tried it both ways and felt no difference..

 

[dorkburger]

I've never owned one so cant add anything but to say what an odd setup. I wonder what happens on the compression stroke. Is a small amount of mixture blown back into the carb, or is there a check valve somewhere in line? I really cant see it forcing much if any mixture thru there in a large throtthe opening position. Could it be an emissions thing?

Pretty forward thinking of Suzuki to add factory nitrous lines.

 

[Big Rich]

Mr Burger, I was thinking about that as well.... if air is passing between cylinders via the silicone tubing, there is a chance that fuel could be as well. I might have to see about routing the tubing above & over the carbs to be certain anything would drain back.

I certainly didn't consider nitrous though!

 

[Big Rich]

Bump - I have found out one other thing since adding the tubing..... it's impossible to sync the carbs when each port is linked.

Duh.