kz550 Big Bore 615cc Yeah or Nay?

Could be jetting, an air leak or the anti smog stuff/reed valves if it's still there. Yes it can be eliminated and should be. R

Lean. Pilots?
jetsrus.com/
Steve

A bit of popping on the overun is no big deal in my opinion, tweaking the pilot airscrews will reduce this but not eliminate it.
Performance motors -which these are, do this when tuned.

I really like the sound actually. If it is good enough for Ferrari and Lotus v8 then I can live with it.

It is the shift pop that is irritating. Don't mind the other stuff, just the shift.

As rrsmsw9999 said, make sure to fully seal off the smog stuff before you play with the jetting. The air suction system will cause backfiring on closing the throttle if it is malfunctioning. You can eliminate it by plugging every hose and port that it connects to.

From member CHANCE :

1. Put vacuum caps on ALL carb holder vacuum ports.
2. Find the two hoses that come off these ports and trace them to your vacuum switch.
3. Remove the vacuum hoses (cap those ports) AND the switch.
4. Remove the BIG hoses from the switch to reed valves and back to where it went into the air box.
5. Put all the stuff in a box and label it and put it in your garage. It will NEVER be reinstalled but it will make you feel better.
6. Then take some BLACK RTV and fill the two snouts atop the reed valves with RTV and let it set till it hardens.
You plug them because when the reed valves flop open there would otherwise be a direct hole down to the port just in front of the exhaust valves outside the combustion chamber. In other words, you don't want flames to come out if the bike backfires as the flames would be right under your gas tank.
7. Some folks will one of the emissions hoses across the two snouts but you will still have that hose awkwardly placed in my opinion

Two comments, Just get caps, RTV will deteriorate over time, vinyl cane end caps work great. Also be sure to plug the air box hole that he hose removal left open. That alone could cause your popping on decel. And if the RTV has shrunk or been blown that would also cause popping on decel. R

For the hole in the airbox, I just use a big vacuum cap as a cork. It fits perfectly.
I wouldn't bother with the RTV. Caps or sealed hose is better, but standard, cheap, parts-store vacuum caps will crack and leak on the manifolds and eventually on the valve cover too. The heat degrades then in just a few months. I use the appropriate size fuel line and plug it with a smooth shank of a stainless screw. On the valve cover I make a plate, or some other metal plug.

You can also buy block-off plates online that look really nice.

Your bike looks and sounds great Kirk.
With such low mileage, I'd be waiting on the big bore kit until I've put some more miles on her.

rstnick wrote: Your bike looks and sounds great Kirk.
With such low mileage, I'd be waiting on the big bore kit until I've put some more miles on her.

Yea with such low mileage I'd find another motor to rebuild and keep the original, original

I have an 83 kz550a4 Sport which I love to death and just bumped the front sprocket to 17T for more top end

The 550's are pretty quick, i've had over 120mph out of a bolt standard 81 gpz, that had about 35k miles on it.

You might likely get a better rpm power swapping to a gpz motor - later unitrack, higher compression and hotter cams. Rather than the midrange tune of your A4 you get more of a cammy rpm power with a GPz.

Your limiting factor here is valve time area : increasing the cc's by 10-15% needs breathing improved to get a similar percentage power gain. Main result of a big bore kit in the absence of any other tuning would be more tourque and the peak tourque rpm going down a bit. Getting the full potential involves further work:

Big bore + high compression + wild cams + cylinder head work+ extractor 4-1 pipe +carbs set up right/upgraded

I just got done looking at the motor and cant find any holes or places to plug. Did the 83 A4 motors have them?