question on MAC exhaust

I finished the installation of the MAC 4 into 2 exhaust on the old girl. I followed the advise of re-jetting the carbs because she was running lean. The jetting has been a long process because I have been going up one size at a time. The question I have is it normal for MAC exhaust systems to be loud and is it normal to go up so much on the jet sizing. Also I had to go up a lot on the main jets in order for the mixture not to be lean. The carbs are Mikuni BS34. They started out at 117.5 mains and 37.5 pilots. Needles are not adjustable. Currently I am at 142.5 mains and 40 pilots. If I go smaller on the mains I get the copper color on the pipes. The plugs are still somewhat white but the next size jet is 145 which is the largest available from mikuni.
Am I doing something wrong or is this normal. Also forgot to mention I bought the exhaust off of ebay used.

Thanks,
Max

kz750ohio wrote: The question I have is it normal for MAC exhaust systems to be loud and is it normal to go up so much on the jet sizing.

No to both questions. Sounds like somebody screwed with the baffle?

Are you running stock air box or pod filters?

I am running stock air box.

maybe the PO drilled the baffle into a straight pipe?

Seems like you are making totally unnecessary richer main jet swaps based on the fact you still have the stock airbox. I'm thinking you have a fuel flow issue, or possibly and air leak (intake boots). My GS1100 had a nice free flowing custom built by me 4-1 MAC with a D&D muffler (stock airbox) and all's I had to do was bump the pilot jets one size richer, and add a .020" shim under the needles.

The 4-into-1 Mac exhaust (bought new) on my 550 was much louder than stock, and definitely required significant up-jetting.

With stock aribox and filter:
The pilots went up from 32 to 37.
The main went from 94 to 99, but I put in a richer set of needles. Without the richer needles, I would have been near 102 to 106 on the mains probably.

I don't know if the 4-into-2 uses the same muffler baffle as the 4-into-1, but my baffles were just two pipes welded together. I ended up crushing the pipes slightly to give a little more restriction and make it slightly quieter. I still don't care for the sound, so a Kerker canister is probably going on it in the near future.

I will look into the fuel flow and make sure she is not being held back. I have the stock petcock (vacuum type)on the tank. This weekend I will put the tank and look at the petcock and make sure the screens are not being blocked and see what kind of flow I get out of them. I will also change the inline filter to be safe. Its about a year old.
thanks for all the wonderful idea's.

max

MAke sure it's not a paper, inline car filter. Those tend to stop flowing. There is not enough pressure from gravity compared to a fuel pump, so they just sort of seal off after a while.

If you haven't done so, I would do five things. Make sure your carbs don't have a blocked screen above the Needle and seat assy. Then use the Clear Tube Gauge for setting the Fuel level in the bowls.
Check for vacuum leaks around your carb holders/ intake manifolds. Make sure the diaphragms are not leaking, either holes or sealing at the caps. Make sure you Ignition advancer is moving freely with correct timing, and coil voltage is within .5v of battery voltage. I guess thats 6.
A valve adjustment is always a good idea, if you haven't recently. 7

Have a good look with a flashlight inside the tank if your tank is rusted, the rust sediment clogs the internal petcock screen choking fuel flow at upper rpm's. Might want to POR50 or KREEM the tank for future trouble free driving.