Capped the straight-thru baffle, jetting?

[jknappsax]

I finally pulled apart the (?)Two Brothers can on the 4-into-1 system on my 1979 GS 1000 that I repacked when I was first bringing the bike back to life. The good news was that all of the stainless-steel wool packing that I put in was still there. The bike was still too loud; it had a straight-through baffle, and I fabricated a cap so the baffle isn't so "straight-through" any more. I can feel that the power has moved lower in the rpms. The bike has K&N pods, the 4-into-1, and DJ Stage 3 jetting. I haven't had a chance to really wring out how the carbs feel, but they don't seem too bad. Any thoughts on if I might to need to rejet at least the pilot circuits, or if I can just lean the mixture with the air screws on the VM 26s? I've been planning on shimming the needles as there is a lag when rolling on the throttle below 3k, and I'd like to sharpen that up.

[Agemax]

the needles on the VM26's are adjustable, they dont need shimming. what size DJ mains have you fitted?
adjust mixture with air screws at idle and low end with needles, raise them and see if it makes it better or worse, if worse, then lower them.

its all a bit of trial and error but plug chops should tell you if you are in the ball park

[jknappsax]

Shimming the needles

I realize that the VM 26 needles have grooves that the e-clip can be moved to, and the DJ kit that are installed in place of them also have them; from what I understand, sometimes people remove the plastic spacers from the top of the needles and replace them with stainless steel washers from Radio Shack that equal about half the height of the spacer, in essence a "half" groove adjustment. I have to admit, I might understand the theory of how to adjust the carbs, I'm not too experienced in actually performing the adjustments, and the plug chops. There isn't anyone near me to help, so I'm muddling through as best I can. Maybe you're right about trying to move the needles up a whole groove first, but it's kind of like smaller increments are easier to tell which direction things are going, better or worse. A whole groove might take it past better to worse again, do you know what I mean? I guess I'm just a little adrift with this.

[Agemax]

the shims are used on CV carbs, where the needles do not have grooves and cannot be adjusted like the VM carbs.

you will over complicate matters by trying to shim the VM needles, just raise or lower by 1 notch and you will know if it is right or not.

you can still mess with the air screws at idle to get the air/fuel mixture ratio correct.

what size DJ mains have you fitted?

[jknappsax]

Not sure about the DJ Main size

They're what came with the Stage 3 kit, but I'll have to pull the float bowls to check.

[Agemax]

They're what came with the Stage 3 kit, but I'll have to pull the float bowls to check.

they give you 2 choices, i think its 138's and 142's off the top of my head.

[Steve]

I am curious how you "capped" your baffle.

Most of the baffles in header systems are "straight-through". There is a large disk that blocks the pipe after the collector, at the front of the "muffler" section. That disk has a hole in the center, to which a perforated tube is attached. The other end of the perforated tube is at the back of the "muffler". All of the exhaust gas has to get necked down through that tube to go out the back. The perforations are so sound waves are partially reflected down the tube, but some are allowed into the outer chamber. The packing is just to control the echo.

Some street-oriented pipes might have a tube that is 1 1/4" in diameter, maybe a bit larger. Race-oriented systems might be 2 to 2 1/2" in diameter, which obviously lets more noise get through, along with simply being less restrictive for the exhaust gasses.

Where did you install your "cap" and what size is your baffle tube?

.

[jknappsax]

My baffle had nothing at end near inlet

There was a 10" long, 2" diameter perforated tube that was attached to the outlet, no disc or other impediment. I had made a wire basket that I held in place with a hose clamp to keep the packing from blowing out, them wrapped everything with stainless-steel wool when I originally repacked the can which had NO packing left in it. It was still WAY too loud. I had seen pictures of Yoshimura baffles that had a hemispherical solid end on the perforated tube, so the exhaust didn't go directly into the baffle, but around the half sphere and through the perforations. I found a 2" pipe cap at my local hardware store, drilled holes 120 degrees apart, and used stainless-steel panhead sheet metal screws to attach it to the end of the baffle, then reinstalled the stainless-steel wool. It took the harsh edge off the exhaust note, and the increased back pressure seems to have moved the power lower down in the RPM range. I haven't had a chance to really ring out the carb response yet; too much rain and work!

[Steve]

Thanks, exactly what I was asking for.

Here is more along the line of what we have:



You can see the "disk" at the left that blocks the inside of the can. The perforated tube allows gas to pass down the middle and out the back. The perforations allow some sound waves to escape the center of the tube, but there is no real gas flow there on most baffles.

On my son's 650, that perforated tube goes straight through. We suspect it is a MAC exhaust system. Has a nice little "bark" to it, not overly lound, if you keep it uner 5k. Wind it up over 6k, though, and EVERYBODY knows that you did it.

The system that I will be putting on my 850 came off my other son's 850. We think it's a Jardine, but have no confirmation on that. The baffle looks just like the MAC, except there is a solid disk in the middle of the perforated tube. That forces ALL the exhaust through the front half of the perforations, around the "plug", then back in the second half of the perforations so it can go out the hole at the back. Probably not the most efficient for ultimate power, but it sounds real nice and is not very loud, even with NO packing in it.

You just KNOW it's not very loud if it's going on my bike. Not as quiet as the Wing, but better than the stock rusted-out pipes that were on it.

.