rich on cyl #4?

[erik]

I'm trying to figure out why my bandit's running poorly, I think it's misfiring. It idles ok, but at higher revs when accelerating it struggles. I discovered #4 cyl. plug cap was dodgy, the clip was worn out and there was some corrosion inside it, so I've replaced the clip and cleaned it, now the resistance across that coil is reading ok. Went for a ride, but there was still the same problem. So I thought it might be the plugs, tried replacing them. Went for a ride (about 40 minutes?) and it seemed better for a while, but then started doing the same thing at the end of the ride. Pulled the plugs out and the number 4 plug electrode was fairly sooty while the others looked almost new.
I've checked the compression, it was between 112 and 117 psi with the engine hot, which is considerably lower than it's supposed to be, but I'm not sure how accurate my gauge is when testing small engines. And the compression hasn't changed since I first tested it ages ago when it was running ok. It starts fine, now that I've replaced the battery.

So I'm thinking there must be something wrong with the #4 carb? I cleaned the carbs before testing the spark plug cap and grit in the carbs shouldn't make one of the cylinders run rich anyway, right? All the float heights seemed the same. I didn't pull the diaphragms out when cleaning them though, so I'll check them and the needles. Do the floats lose their buoyancy as they get old?

I've got some carbs on a spare parts bike that I might try swapping although I don't know what condition they're in.

Any tips?

[PitterB4]

This is obvious but rich would mean too little air, too much gas or weak spark, right?  In addition to what you've done, check for vac leaks - boots, diaphram...  are you sure you replaced that little o-ring on top when you cleaned the carbs last time?  Is your needle or float binding?  Just some thoughts...

[gsxr400 racer]

this is the side that has the most Carb angle when on the kickstand, my guess is the float needle is whore out or that the orings are dried up and shrunk and allowing gas to leak in. thats all the carb info coming from me till 2010 still tired of answering the same carb questions and im sure people are tired of dealing with the same carb problems. one thing i can say is once you got this bikes carbs figured out you are a specialist at none fuel injected bikes.

[interfuse]

Lol. I went from knowing f all about carbs to having an expert understanding... amazing what taking a carb apart 100x will do... :)

[tomacGTi]

Jay, at least you're not as bad as other boards I'm a part of and say: USE THE SEARCH.

Maybe you can get Rob to make a sticky for you so you can stop repeating yourself.

I know I've learned more about carbs with the little bike than I ever thought I would. I have no idea what I'd do if I owned a FI bike. Maybe I'd ride it more versus constantly dicking with it.

[erik]

Thanks for the suggestions at what to look at. I'll report back later...

[gsxr400 racer]

Oh all the info is on here it just takes someone putting it all in one section

[erik]

Problem solved! 

I checked the diaphragm, looked fine, a tiny bit of gunk on the slides which I cleaned off, also cleaned the slides and diaphragms on the other carbs. Checked #4 carb float needle and o-rings, all looked ok.

I thought maybe the spring for the slide in #4 wasn't in there properly (I now think it was fine, I don't think the slide would've moved much if it was in wrong) and since everything else looked ok I put the carbs back on the bike.

It was then I noticed the #4 choke looked a bit wet and realised the choke cable was holding it ever so slightly open. I think the fact #4 choke was open but not the rest is probably due to tolerances or slight bend in the slide bar. I'd replaced the choke cable inner back in November 2006, 36,000km ago, but made it a bit short. It seemed to work ok then but I guess things must've moved a bit or it needed lubing, and so wasn't closing as much as it should.
So I made another choke cable, 10mm longer, made sure it was adjusted right, took it for an hour long ride and it's all good! So smooth and eager to go, compared to how it was before.

So it looks like I can stop worrying about having to pull the engine apart and do some more riding!

(and yeah I'm  a bit for not thinking of/noticing the choke problem earlier  )