85 GS550es Kerker 4 into 1 Jetting

[Guest]

I have a full kerker 4 into 1 exhaust for my 1985 GS550ES (GSX550ES). I currently have 38 pilot jets installed stock is 35. I went up on the mains a size or 2 and shimmed the needs up using 1 extra washer. Fuel screws are out 2 turns. It seems to run ok but has a flat spot at 1/4-1/2 throttlle.

It is hard to tell because the flat spot doesnt last long. But it feels lean, when choke is on a little it doesnt happen.

My question is has anyone messed with jetting on these bikes with a 4 into 1. It has the 2 carb setup for 4 cylinder.

I get a crackle on deceleration.

I may repair my stock mufflers that are rotted on the bottom and reinstall those to keep the stock look.

[scratch]

First thing I would do is remove the shim... as you might be transitioning into the thinner part of the needle to quick... to fast on a fatter main, it may cause a bit too much air or gas as you probably have that covered with the 2 up jet. That's why it dissapears past 1/2 throttle. if it's good from 1/2 up... the Main is probably good or close.

That's also a pretty easy thing to try as you may be able to test that from the top without pulling the carbs (can't say for sure as I've never had my nose in and '85)...

Also, go back to basics if you haven't already... Valves, vacuum sync, mixtures...

Timimg & compression dictate how & when a carb pulls.
4 different cylinders... each has it's own compression and valve behaviors. Thats 4 air pumps pulling at there own beat, each one pulling therough a carb... that's why carbs must be sync'd and each mixture set.

If you want your bike to run better than ok... Valves, then balance carbs with a vacuun sync and set your mixtures...

[Curtie94]

I will remove the extra shim I installed and see if it helps. I adjusted the valves and synced the carbs about a week ago. I leaned the fuel screws about 1/2 turn each to get the highest smoothest idle. Seems smoother at idle and in town now.

Still has that flat spot though, so I will try the needle.

With this 4 into 1 it definitely feels better top end pull. Hopefully I can get rid of the flat spot to make it more ride able. I may also try to re sync the carbs.