99 600 running rough.

[muffinman]

I'll try to make this as short as possible give all the important info so that someone can lead me in the right direction to solve this issue.

Recently purchased a 99 gsx600. The PO had it sitting for quite some time. When I went to pick it up it hesitated and would barely get to 3.5-4k. He told me that he had replaced a carb with a used one and replaced the custom pipe the was installed by the PO for a used stock that was quieter. When i lifted the tank I noticed that the inline filter had the flow arrow in the wrong direction. Once I corrected that the bike would rev to about 7k but still hesitate. I reinstalled the D&D pipe thinking that the carbs must have been jetted for it. After the install of the pipe the bike came to life but i'm still having some issues.

I did a carb sync and 3&4 were all over the place. After the sync the acceleration got much better. Now up to about 4k it's smooth but the mid range in the revs starts to sputter before clearing up. If I go wide open it falls flat till I ease the throttle back and it will eventually catch. If I slowly (really slow) open the throttle to full it will take off like it's shot out of a cannon. I just finished reading the "carbs 102" and I plan on going through those steps in hopes of finding something out of place. I also plan on adjusting the A/F screws cause when I let off after going wot it backfires a lot.

What would cause the mid range to sputter (seems like it's overly rich)?



I apologize for the length of the post but hopefully I gave enough info that someone can help me out.

Thanks

[arsenic]

Well, were to start. First what are the A/F screws set to? Second it's not a backfire, it's an after fire. Third it's not rich, it's lean. An after fire occurs when unburnt fuel hits the hot header pipes and ignites. Start by setting the A/F screws to 2.5 turns out and report back.

[muffinman]

Got home too late to take the carbs off but I tried the spraying water test from the write up and the #3 exhaust is barely warm compared to the others.

[muffinman]

Took the carbs off and drilled out the caps. The screws were #1-3.25, #2-3.5, #3-3.5, #4-3.25. I set them all at 2.25 and nothing much has changed so I guess I'll continue to adjust them in hopes that something changes.

Do they sell a carb rebuild kit that contains all the necessary seals?

Thanks

[scottynoface]

Carb number three is dirty. Clean thoroughly.

Also check your plugs, they will tell you how your bike is running.

[arsenic]

A/F screws from the factory are NEVER at 3.25-3.5 turns out. Nice counting job

[muffinman]

I learned to count very early in life and trust me that's what they were at. Now wether or not a po changed them and stuck the plugs back in, that I can't say. They were all over 3 FULL turns. I read another thread on here recently where they were similar #'s and even one was 4 turns yet no one tried to tell him that he was counting it wrong. I would appreciate if someone could help instead of questioning my counting abilities.

[arsenic]

I already did tell you what to do. But since you added the the #3 header pipe is cold. Let me add that your pilot jets are clogged. At least that one. Clean them.

[muffinman]

Thank I'll try that.

[RedKat91]

Yea... I had the same problem... 3&4 on mine were clogged and the pipes were not hot at all.... cleaned them all out and adjusted properly and we're back to firing on all 4 properly.

That's probably your issue.

[muffinman]

Thanks redkat.

[muffinman]

Update: I pulled the a/f screws out and made sure everything was clean and still no difference there. I put all new plugs in and noticed that my #3 plug doesn"t look anything like the others. It doesn't show any indications of heat. The other three have obvious signs of heat and #3 is just sooty and looks otherwise new. I took a quick spin and it was as if everything corrected itself. Sprayed water on the #3 pipe and it was the same as the others and the hesitation was gone but after it sat for a while it went right back to how it was before.

I think it might be a bad coil. When I checked the spark by grounding the plug it looked very weak. Could my mid-range hesitation be coil related?

[arsenic]

Doubt it. A coil doesn't usually go half bad.

[Kreylyn]

But a bad wire/boot or poor connection there could cause the issue.

Krey

[muffinman]

Can the boot or wire be repaired without coil replacement?