Gs 550es Carb Jet Question

[reem98]

Can someone tell me I have a 83 GS550ES with an K&N (the stock airbox is open) a 4 into 1 exhaust and I moved the main jets up from 97.5 to 102.5 is this enough of a jump for these mods
Thanks

[Carter Turk]

Only the plugs will tell.

[reem98]

Heres what it does
It has excellent power up to 6k then it has a miss above that.
I can hit full throttle under 6k and it does fine then when it hits about 6k it misses bad.
can anyone give me an idea about this
Also the number 2 piston chrome exhaust pipe has turned blue, and the others have not, does this mean it was runnin lean??
Thanks

[reem98]

if anyone has any idea about my blue exhaust pipe please let me know thanks

[Carter Turk]

So does number 2 plug look bleach white compared to the others? You haven't mentioned plug color yet.

Maybe .5mm washer under the needle may help the flat spot.

[chef1366]

Lean

Blue can mean a lean condition. Pull your spark plugs and post a picture so we can help you. If your running strong on full throttle till a certain point it almost sounds like fuel starvation.

[reem98]

Well I pulled my plugs and my number 2 which was the one with the blue on the exhaust pipe was definatly whiter then the others. I checked out the carb and didn't see any problems. I did the full throttle pull on two different times one spark plug on the #1 cyl and one on the #4 cyl. Brand new plugs full pull then killed the motor.

they have a white blue look on the cathode
No black just kinda white blue
I'm guessing I'm running lean??

[KEITH KRAUSE]

Can someone tell me I have a 83 GS550ES with an K&N (the stock airbox is open) a 4 into 1 exhaust and I moved the main jets up from 97.5 to 102.5 is this enough of a jump for these mods
Thanks

My opinion is these minor air box mods aren't worth the trouble. There's not enough power gain, even if jetted spot on.
I'd install the air box lid and re-test. The one size up on the main may be enough for the pipe only. A 7.5 increase will not be enough for the air box lid removal included.
You're also most likely running lean on the jet needles without the lid. This may be your "6K" problem but it's more about throttle position. Even with the lid, you should still take 1/3 throttle reads and full throttle reads for the main to see how the pipe effects things.
An additional turn out on the mixture screws may be enough for the pilot circuit.

[reem98]

Thanks Keith
I was hopin you would chime in here cause the last advice you gave me was spot on. haha
Thanks man

[reem98]

well I jumped up another size (5 points from 102 to 107) it now has better power up till about 8 or 9k then if flatens out again. I have now gone from a 97main to a 107 main with these changes 4 into 1 full exhaust K&N and open air box. Does this seem right or do I need to go higher. How might I check if I'm starvin for fuel for some reason.
Thanks

[KEITH KRAUSE]

well I jumped up another size (5 points from 102 to 107) it now has better power up till about 8 or 9k then if flatens out again. I have now gone from a 97main to a 107 main with these changes 4 into 1 full exhaust K&N and open air box. Does this seem right or do I need to go higher. How might I check if I'm starvin for fuel for some reason.
Thanks

First, the carbs must be clean, synched, floats levels checked, etc. If all basic tuning has been done, then you're ready to focus on the jetting.
For the main jet, I'd test at full throttle, chop off, and read the plugs. If the plugs porcelain is still fairly "whitish", it generally means you're more than one full size (5) away. It sounds like you're still too lean on the main jet. As I said before, a 7.5 increase isn't nearly enough, so a 107.5 wouldn't be much better. I'd have to know/see the degree of white/color to really guess the right main. Just playing numbers and keeping in mind that air box mod's are not what I have as much jetting experience with, I'd guess a 7.5 increase for the pipe alone, and about 7.5 MINIMUM increase for the open air box. So that's a 15 minimum increase from the stock 97.5 (112.5). In my opinion, that's still probably too lean. I hate to have you buy jets just based on my guesses, but if I was betting money on this, I'd try 117.5.
Like I said, I'd really have to see the plug color after a full run.
Also, in my experience, you're probably running lean on the most used/most important jetting circuit....the jet needle. You need to do solid 1/3 throttle tests to see what the plugs say about the jet needles. Most people spend much more time riding on the jet needles than the mains. If you have non-adjustable needles, you'll need to shim the needles up some.
The pilot circuit may need re-jetting too. Anywhere from simple richer mixture screw adjustments to a larger pilot jet?
Your bluing pipe suggests a lean mixture. Lean problems can result in pre-ignition and holes in the piston and burned valves, besides poor performance.
Jetting is more than just the main jet.

[Nerobro]

*watches this thread carefully...*

You might consider a stage 1 jet kit from dynojet.. I'm more apt to go with keiths advice though. Go stock.