Carbtune

[Guest]

I Just used my new Carbtune for the first time yesterday. What a joy! Flat readings across all four in less than ten min.

[spyug]

That's good news. I'm actually going to try mine for the first time tonight.
Do you have any words of wisdom?

I'd be interested in any insights on these gizmos.

Cheers,
Spyug

[crapwacker]

Not really. They are pretty easy to use. Set them up with the restrictors they supply. I numbered my hoses for fool-proof setup. Move the slide up to drop the rods, and down to raise them. My lowest reading was on #3, and I knew from last year that this slide was already on bottom, so I lowered the others to match.

[BassCliff]

Hi,

I use the throttle cable adjustment at the handlebar to raise the idle to about 2000 rpm when synchronizing the carbs.

I started here:



And ended up here (my bike has the pre-muffler/crossover, hence the middle cylinders are adjusted a little lower according to the factory service manual):




If you can't get them adjusted exactly right, don't worry about it. This is plenty close enough. I had to loosen the choke cable assembly on the top of the carbs so that my adjustment tool would fit on the middle jam nut. This picture is the right-side adjustment:





Thank you for your indulgence,

BassCliff

[chuckycheese]

No Ceeeeegar

Hi,

If you can't get them adjusted exactly right, don't worry about it. This is plenty close enough.BassCliff

Yeah, I totally agree with that. It's kind of frustrating to feel like you have to get it absolutely, positively, totally perfect. I, too, feel certain that close is good enough!

[nutsandbolts]

Where did you guys place your gas tank during all this?

[crapwacker]

Where did you guys place your gas tank during all this?

I remove mine and use a remote tank, from a lawn mower, that I ziptie to my handlebars. Some guys will strap their tank to their seat

[spyug]

Thanks for the info folks. I tried mine out on the 400 twin and it went easy enough. Not exactly smack on but close enough for government work.
The only problems I had were a) forgetting to plug off the vacuum line to the tank ( I was using a remote tank) b) tightening the locknut without changing the position of the screw.

I don't have the special tool so it was tricky getting the locknut loose then tightening back up. Standard wrenches don't want to fit in the tight space the screw occupies. I did get a 1/4" drive socket in enough to loosen it off but to tighten up I used a flat bladed screw driver while holding the screw with another flat blade. Not the best solution so I'll need to buck up for the tool.

It certainly makes balancing easier and I was suprised to see how far off the carbs actually were prior to doing it. One side was pulling like a banshee and the other barely moved a stick yet the bike felt fine both idling and under throttle. I didn't get a chance to test ride tonight but I'll give her a whirl tomorrow.

I'll be doing the Kat project next and after riding the 750 on Saturday I think I'll need to do a clean and rebuild on those carbs too as I couldn't get any acceleration in 5th gear.

I guess I better get that adjuster tool first.

Cheers all,
Spyug

[fgrable@sbcglobal.net]

Not to try to hi-jack the thread but I noticed the comment about the muffler system having a crossover between cyl 2 and 3. What impact does this have on balance of the carbs?

I am soon to change the 80 GS550L stock megaphone exhaust (with crossover pipe) to a 77 exhaust from a GS550 that does not have a crossover. Thoughts on carb balance for cylindrs 2 and 3?

Thx

[TheCafeKid]

According to the GS manuals (shop and clymer) you should be balancing your inner two carbs a half meter point less than the outer, due to the balance tube. Frankly, I dont. And, its never seemed to make a bit of noticeable difference.

[BassCliff]

I'm just guessing here...

Not to try to hi-jack the thread but I noticed the comment about the muffler system having a crossover between cyl 2 and 3. What impact does this have on balance of the carbs?

I am soon to change the 80 GS550L stock megaphone exhaust (with crossover pipe) to a 77 exhaust from a GS550 that does not have a crossover. Thoughts on carb balance for cylindrs 2 and 3?

Thx

Hi,

As I understand it, once you remove the pre-muffler/crossover you can also balance the carbs straight across.

I'm just reading my manual for all of this. It doesn't really explain it but my theory is; because they are the inside cylinders, 2 and 3 tend to run a little hotter, especially if they have a little more backpressure from the crossover. It seems that you want a little less air in cylinders 2 and 3 to make them a little richer and therefore cooler. Does that make any sense?

For exhausts without the crossover (1979 GS850G):



For exhausts with the crossover (1980+ GS850G):



Here's my temporary tank.



With a barb connector to plug right into the fuel line.



Thank you for your indulgence,

BassCliff

[fgrable@sbcglobal.net]

I was also thinking that it really doesn't make any difference at tuning whether the exhaust crossover existed or not. And yes, i understand about the 2 and 3 being set slightly richer (cooler) to compensate for having less heat dissipation. As someone stated earlier, it probably doesn't make any discernable operating difference but chances are under hard operation, it might make a difference in valve temps and in the end longevity.

But we're probably getting anal on this...run it like you stole it....