Replacement Exhaust Baffle?

Hey all, been lurking and learning for a little while now since I bought this project bike and hopefully the wise and all knowing can drop a little knowledge.

I have a 1982 GPZ 550 with what I'm guessing is the kerker or some similar exhaust, 4-1 header, clamp on muffler (3.25'' diameter at the tip) that mounts to the rear foot peg hole.

Problem is the exhaust is completely straight through right now, no baffle, no nothing. It's not that it's terribly loud it's juts that I want to get some of that factory back pressure back in there.

I've been searching the internet and apparently I'm doing something wrong or 3.25'' baffles aren't that common. I can only find a few extremely expensive ones for $170+ or a few cheaper ones on Amazon that don't seem like they'd work. The majority of the baffles I'm seeing are for 1 3/4'' pipes which I'm guessing are fore dual exhaust setups.

I'll take some pictures of my setup tomorrow if I have time but is this what I should be looking at? At $42 I'd be stoked if this worked.

shop.macperformance.com/MAC-4-into-1-Can...82B55.m1plqscsfapp06

That Mac muffler is useable, but doesn't sound the greatest, sort of like a bunch of BB's bouncing in a coffee can.. The one I had required a lot of jetting beyond stock, but if you are already wide open, then someone should have jetted already.

The Mac baffle has two pipes internally, side by side. One pipe goes to the inlet (in the inlet plate), and exits inside the canister near the end plate. The other pipe goes to the outlet (in the end plate) and is open near the inlet plate. The exhaust gases basically zig zag through the canister. Not a great design since it does not flow straight through (like a Kerker type design). It tends to be kinda loud at idle, and does not flow great at WOT.

Kerkers are generally pretty mellow at idle, while still providing straight-through exhaust flow at WOT.

Kerker mufflers are expensive, but are real easy to make if you can do a little mig welding. I'll see if I can dig up some photos.

EDIT: Here's a link to the one I made. I made several different ones, actually. Go to the last page and see the Supertrapp version. It's simpler and is what should work well inside the Mac canister. (But you want slightly larger holes than the Supertrapp perforation.)
www.kzrider.com/forum/2-engine/313649-i-...l=component&type=raw

You can get the raw perforated baffle tube here: (it comes with packing material too.) 1-5/8" is just about perfect for the street on a Gpz550. And there is enough there to make a couple or three, so you can sell the remainder.
www.denniskirk.com/la-choppers/24-in-uni...6863.prd/4406863.sku

If you don't want to make one, if you search on Dennis Kirk, there are hundreds of replacement, generic baffles, that are straight-through. There is a chance that one will have the correct measurements for your canister.

BTW, gotta love those Scarabs. Had a couple 260's wth 280 motors, but never went all out SBC.

Thanks for all the help man, I doubt anyone has done any jetting to this thing. I bought it from a guy that bought it from another guy as a semi=project. I have a feeling the baffle got lost along the way along with some other things that I'm starting to wish I had like the factory air box instead the pod filters that came on it.

Now I'm just hoping to put some back pressure in the exhaust and hopefully build some restrictor plates to get these carbs working a little better. I've kind of given up trying to piece together a factory air box.

Well, if the jetting is stock, it won't run right. You should try to identify if you have the stock jetting and needles. With a Dynojet kit, you should be able to get it running pretty good with pods. The Dynojet kit comes with new needles and jets.

The guys on the Gpz550 forum might have better info on what you need to identify what you have.

Yeah I'm pretty sure the jetting is stock, the needles aren't adjustable and had no shims/washers underneath but I'm pretty sure that the main jet had 112 stamped on it. That can't be right though because after some research the only 112 applies to the 84-85 model.

After doing some research it seems you're the go to guy for jetting. Is the dynojet kit the only way or can I buy individual jets and just shim the needle as required?

I'm not trying to be cheap but this is a 30 y/o $300 bike, if I can't get jets individually then I'll just buy the kit.

Sometimes people put the 84-85 (TK27 cv) carbs on the 82-83 gpz. They fit on with almost no modification. So you want to make sure which carbs you have. The 84-85 has a remote idle speed knob on the side of the carb bank. The 82-83 (TK26 cv) has the idle speed knob in the center of the rack, near the bottom.

If the needle is not adjustable, then it is likely stock regardless of which type of carbs you have.

I don't have much experience jetting the TK26 or TK27 carbs. Guys on the 550 forum do. I think the Dynojet kit (probably around $125) is the only way to get the proper shaped needle. The kit is likely the easiest way to do it, but if you have plenty of time on your hands, you could probably play with the jets and do some shimming of the stock needle to get it to run ok. I'm not sure of the pilot jet's availability on both of those carbs, but I usually drill them to what I need.

Or, like you said, the easiest thing would be to get the airbox and restore the carbs to stock, but you will have to get a decent muffler on the exhaust. A relatively quiet Kerker-type muffler can usually get away with the stock jetting, or you could bump the main up a little for that.