Another diagnose thread

[GNTurbo6]

I've been riding my bro's '97 Katana since I got my license in August and it's never really idled properly. If the idle is set below 2k rpms it'll sputter, drop down to like 100 rpms and almost die out. For the most part it hasn't been a problem other than it using more gas than it should but since it's the off season I figured I should take the time to fix it.

Back in October or so I cleaned out the carbs but I didn't replace anything. I also ran some Seafoam through both the gas tank and through the air box. The plugs over the fuel mixture screws are still there and I'm thinking the next step for me is to probably remove them and adjust the mixture.

My brother told me he changed the spark plugs last year sometime as well, but when I asked him if he gapped them, he said he hadn't. So I'll probably be getting new plugs as well.

Any ideas on how to fix this problem? Or do the ungapped spark plugs seem to be the culprit?

[Cheriff]

Can't say that this will fix your problem, but if a carb synch hasn't been done for awhile it is worth a shot. It is known for improving idling characteristics and overall smoothness.

I would wait for the more experienced guys though for a better answer.

[MECHANICALMASON]

Check your choke linkage. Mine sticks partially on and has the same symptoms you are describing. If you look at the carbs from the left side and operate the choke you will see something moving in and out. Turn the choke all the way off and then take your finger and push in (towards the right side of the bike). If you feel any movement then it is most likely the problem. Warm it up and retest to see if it is repaired. Mine still does it. Eventually I will take mine apart and find out what is causing it to stick but for now I just reach in there and push it in after turning the choke off. Hope this helps.

[GNTurbo6]

Check your choke linkage. Mine sticks partially on and has the same symptoms you are describing. If you look at the carbs from the left side and operate the choke you will see something moving in and out. Turn the choke all the way off and then take your finger and push in (towards the right side of the bike). If you feel any movement then it is most likely the problem. Warm it up and retest to see if it is repaired. Mine still does it. Eventually I will take mine apart and find out what is causing it to stick but for now I just reach in there and push it in after turning the choke off. Hope this helps.

I just checked it, seems to be fine but thanks for the idea.

I guess I'll try to sync the carbs tomorrow but I'll likely be doing it at 2k rpms as oppose to the 1750 recommended in the Haynes manual. If that doesn't work I'll check the plugs and maybe drill out those fuel mixture brass plugs.

[steves]

Vac leak, air leak, plugs, dirty pilot circuit, etc.

Plugs are generally gapped from the factory, although I do check them.

[The CyberPoet]

What air filter is it running, and does it have stock or aftermarket jetting?

Aside from a bad air filter choice (for that particular jetting set-up), everything MD said...

Cheers,
=-= The CyberPoet

[GNTurbo6]

I just replaced the air filter with an OEM one last year. Seems like a little critter must have been living in there since I found some pieces of acorns among other things. I assume it has stock jetting as I doubt the previous owner and my brother knew enough about bikes to change the jetting.

[md86]

Come on guys , you gonna make me say it AGAIN ? Ok , I'll take the long way around ......
When it's running , see if any of the headers feel cooler . Search for the "spit test" so's you don't burn yourself . Hot pipes are HOT , you know . If one pipe is a little cooler , that probably means that cylinder ain't firing right . NOW I'll say :check your plugs" . I would BET that at least one of them is pretty black , possibly to the point of not firing . Yeah , it'll idle with a non-sparking plug , but you usually need to turn the idle up a tad to keep it running .... Just sayin , I been there before MANY times .

[GNTurbo6]

I pulled the spark plugs today, the gaps on them were pretty close to .026" so I don't think they were the culprit. They are dual electrode plugs. Would there be any tell-tale signs on a a cylinder not firing on the plugs?

I doubt it's a plug that isn't firing because I've gotten the bike revved up real high and have even gone 130 mph on it. I think a non-firing plug would certainly cause a substantial loss of power.

The bike wouldn't even get up to proper temperature today for me to try to sync it so I'm gonna strip it down again and clean the carbs out. The bike hasn't been ran for probably a month, so it's not really a surprise.