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Jetting 1974 CB750 with 4 into 1 and/or Stacks

poisonivy

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I'm naively trying to create a post that will be part resource for those needing to properly jet the K4 or relative for 4-into-1 and/or stacks. Before my head is ripped off, I'm not pushing for pods although success stories (no dead-zones, tuning nightmares, etc.) with pods + 4-1 are welcome. There's so much confusion out there, myself absolutely included. Apparently, the '74 was factory-rich because of some lawsuit, adding to the confusion. I cannot find any "right" answers and I understand there probably aren't any. But those with success jetting these superbikes are encouraged to help me and other newbies get it right without too much carb benchin'. Thank you all in advance!

I just found a '74 with no-mods and under 4k miles! She's going the direction of the cafe, however I'm keeping the original seat, chopping rear fender, adding drag bars, and 4-into-1 exhaust for her pre-summer mods. Although I've been entertaining the idea of running pods, I've decided to keep the stacks-in-a-box airbox and going with 4-into-1 exhaust. Got a cracked header joint. Essentially, I'd really like to know what to re-jet my mains to for 4-1 with exhaust, airbox, low altitude. For the distant future, I'd also love to know configs for 4-1 + stacks if I dare in this dirty-ass city.
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K4 or relative questions:

4-1 + airbox
Mains?
Pilate turns out?
Needle clip positions?

4-1 + stacks
Mains?
Pilate turns out?
Needle clip positions?

4-1 + pods
Mains?
Pilate turns out?
Needle clip positions?

Other configurations too, like open headers, anti-pods, high altitude, etc as it's all great to know. And if any config requires bigger slows.

Thanks!
– Andrew
 
There is no way to tell you what you need for jetting. Too many things affect jetting, engine condition, how fresh of tune up, altitude, fuel quality, air temperature, how you ride, every mod you do or change will require a change in jetting. You can only jet for how YOUR bike responds to the mods and how you jet it, every bike will be different. Every body asks the same question all the time and there is no set answer. Start with stock jetting see how it runs, make one change, see how it runs, etc till it runs good and the plugs look good.
 
I am not looking for right answers as I mentioned there aren't any. I'm well aware each bike is different. If someone has a good config, sharing it is all I'm asking for.
 
A good configuration just means THAT guy did it, you may do EXACTLY the same to yours and not get that result. I've seen exact same bikes one runs fine, the other spits that jetting out. Brand new off the showroom floor. I remember a bike mag looking close at two GPz550s and wondering why one was a dog and the other was a hot rod. All of it was in the way the engine was put together, one ended up way screwed up on cam timings due to stackup of tolerances and would not run for spit.

As well, the difference in header design alone can massively kill you there. Some headers are worse than stock exhaust (you jet DOWN!) and some are super killer and you better be able to recognize that quick when it goes way lean. Airbox? Which one? If these are like some I've seen there will be running differences through the years as they proceed to baffle or clutter up the airbox looking for sound reduction. There was one long snorkel used on Kaw 500-3 that if simply unsnapped off bike required several more numbers in jet and added like 4 hp. It happens. Stacks? What length? I've seen go one inch too long utterly kill the engine so completely you couldn't jet it at all. Stacks can REALLY screw up an engine if not near the needed lengths. If the cam was not matched to them often you just detuned.

I've modded just the BAFFLE in a 4-1 before to need like 5 numbers more and an incredible pickup in midrange torque.

I NEVER lock into what somebody else uses for mixture screw turns. I set each engine to its' own best setting. If you can't tell that then you cannot tell whether larger overall jetting is right/wrong either, the same thing happens there.

You just gotta get out there and do it, every one is different.
 
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