jetting

Looking for some help to determine what sizes I should go to .I have An 81 GPZ 550 with Tk 22 as well . Has 94 mains and 32 pilots ( stock I think ). Putting on A header an pods .Ran awesome before when it only had the header.Have carbs apart cleaning them ,so nows the time.Heres another dumb question ,when I put on the pods what do I do with crank case vent. Any help would be greatly appreciated

Start with 98, and try up to 102.
With a Kerker (which is pretty restrictive compared to a Mac or open canister), and Emgo pods, I'm using 99 mains with 34 pilots. I drilled the jets myself.

It's really going to depend on the amount of restriction in the exhaust and restriction in the pods, but 99 mains and 34 pilots are a good starting point and will allow the air screws to be in the normal range of turns which gives best tunability for idle and off-idle.

Also check out this mod for the choke system:
www.geocities.com/loudgpz/GPZchokeScrewMod.html

The crankcase vent can just get a tube to the ground. I use a brass elbow that I threaded into the cover (with a pipe tap). The elbow prevents the vinyl tubing from kinking. Here's a photo of the cover on the motor. Sorry I don't have a closeup.

Here you can kinda see the clear hose where it tucks in just behind the clutch cover and exits under the bike.

Thanks for the info. So mac flows better .I bought this bike in 86 3rd owner26000 km. Put it away when kids came , now it's time for Dad to play again

trougher wrote:

Looking for some help to determine what sizes I should go to .I have An 81 GPZ 550 with Tk 22 as well . Has 94 mains and 32 pilots ( stock I think ). Putting on A header an pods .Ran awesome before when it only had the header.

Gotta ask: if it ran awesome with header and stock airbox, why not keep that setup? The carbs are designed to work with the airbox.

trougher wrote:

Thanks for the info. So mac flows better .

No offense to any posters, but every post I have ever read as well as my own MAC header indicates the opposite is true. My MAC (running now) flows maybe as good as stock did, my Kerker clone jetted up richer and made HP like a bandit.

The cheapo Mac system required much larger main jets on my bike in addition to larger pilot jets. This was confirmed using the Dynojet jetting procedure along with tests on an EGA.

With stock airbox/filter and Kerker I could basically run stock jetting albeit taking a little longer to come off the choke on colder days. Ideally, with stock airbox/filter and Kerker, the bike liked 96 mains and could get by with stock pilots. With a change to the Mac, it would never run without stuttering and the EGA was pinned lean. With the Mac and Airbox I run 99 mains with 37 pilots. This was the only way to get the screws in their normal range and gave the smoothest overall running. You can get by with just 102 mains and stock pilots, but the screws will be in the 1/2 turn range and the bike will take longer to come off choke (stuttering all the while).

Now, I'm not saying the Mac flows "better", it's just less restrictive and/or requires larger jetting. I believe overall, a proper Kerker gives better low end torque which makes launches much easier and more fun especially if you have a passenger. I've been running Macs and Kerkers exclusively (on several 81 GPZ550's) for over 15 years (documenting many carb/exhaust/jetting combinations all the while) and these are just my findings/impressions.

However, I never did run a Mac with pods. I know I wouldn't have liked that combo. Both conspire to kill low-end torque. I find I like the kerker with airbox combo best, and kerker with emgo disposable pods as long it's a solo bike only.

You didn't mention what exhaust or pods you have, but if you are using the Mac, you'll likely have to use 100 mains, at least, and start with 34 pilots, but may have to go 37 pilots. (The numbers correspond with available drill bit sizes because I drill my own. I don't have a source for larger pilots.) The key is don't drill larger until you know for sure, obviously.

I can drill them for you if you feel like sending them to me in a padded envelope etc.