1979 850 MAC exhaust carb jetting

[Stan Zovko]

I have a 1979 Suzuki 850g and am going to be installing MAC 4 INTO 1 EXHAUST. ANYBODY DO THE SAME AND SUGGEST ANY JETTING CHANGES. THE INTAKE AIR CLEANER IS STOCK
THANKS
STAN ZOVKO:mask:

 

[Big T]

Stan, check your Caps lock key

with a stock air cleaner, you'll probably just need to lift the needles a notch

 

[joe penoso]

Stan, check your Caps lock key

with a stock air cleaner, you'll probably just need to lift the needles a notch

I THOUGHT LESS BACK PRESSURE IS MORE RELATED TO MAIN JET CHANGES......ps CORRECT ME IF WRONG.
JOEPENOSO

 

[Steve]

CAPS LOCK must be a "thing" with newbies from Brampton. :-k

Less back pressure doesn't mean much if you can't suck anything in to replace it. The stock airbox is the biggest restriction in the entire system. As long as it remains in place, you could run just about anything for an exhaust system and not have to change much in the jetting department.

Conversely: if you leave the stock exhaust in place and replace the stock airbox with pods, you will have a LOT of changes necessary in the jetting. If you also change the exhaust, you will likely have to make another minor adjustment.

.

 

[Big T]

I THOUGHT LESS BACK PRESSURE IS MORE RELATED TO MAIN JET CHANGES......ps CORRECT ME IF WRONG.
JOEPENOSO

No

The main jet only works over half throttle, so 80% of the time, it has zero effect. Needles control fuel from off idle to 2/3 throttle, so you adjust them

 

[joe penoso]

So I put a washer under the needle clip or raise


the needle by dropping clip 1 notch .........correct?
thanks
joepenoso

 

[KEITH KRAUSE]

If your stock main jet size is for example, 100, I'd try a 105. I doubt you'd need a larger increase. The main jet takes over completely at 3/4 throttle position.
I'd test before making changes to the jet needle position. Try running a constant 50 mph on level ground/5th gear and then again at speeds up to 75 and see if you notice any surging or lack of power. Then if you can, try doing the same thing but going uphill/placing more load on the engine. You can also run it several miles as suggested and chop off the throttle/turn off the ignition and see what the plugs look like. All though it's about throttle position, at these speeds, especially 60-75 mph, the jet needles are regulating most of the fuel with some overlap from the pilot circuit. You may find no jet needle changes are needed. If you think it's a tad lean, try richer pilot fuel screw adjustments first. Maybe 1/2 turn or less. Keep record of any adjustments and re-test. If you do need to adjust the jet needles, I doubt you'd need to raise the needles more than 1/2 a position. A typical jetting spacer such as used by Dynojet stage 3 kits is approx' .022" thick. If you change the needles, then you must manually bench synch the slides and then synch with a carb vacuum tool.
To raise the jet needle 1/2 position, lower the e-clip one groove or position. Place the jetting spacer directly on top the e-clip. Re-assemble the factory nylon spacer and the thicker nylon "ring" in correct order...thinner spacer under the e-clip and thicker ring on top the jetting spacer.