Topic: 1 cylinder running lean?

[wildrum88]

So i recently solved the problem of my number 3 cylinder not running at all when idling, but now it seems to be running lean while the rest are running great (chocolate brown color on plugs), what could this be from? should i adjust my fuel/air screw out more for this cylinder than the others? thanks!

[phil71]

you're talking just at idle?

[ekpent]

Also what was the 'other' problem you had with it not running at all that you solved ??

[wildrum88]

no i mean cylinder #3 is running lean (white plug) after taking it for a ride while the others run fine. I solved the problem of cylinder #3 not running at idle (cold exhaust) and misfiring whilst riding by switching the vent tube and the vacuum tube running to cylinder #3 from the automatic fuel valve. this seemed to solve the problem of the cylinder misfiring/not running but now that cylinder seems to be running lean. here is a photo of the auto fuel valve . i switched hoses labeled #3 and #4 because they were opposite of what they are in this picture on my bike.

[Dammerung]

So i recently solved the problem of my number 3 cylinder not running at all when idling, but now it seems to be running lean while the rest are running great (chocolate brown color on plugs), what could this be from? should i adjust my fuel/air screw out more for this cylinder than the others? thanks!

I  having the same issue. Cyl 4. Parked night, starts up easy but cyl 4 is totally cold. upon riding around, it is sluggish. After riding a bit warmed up nice cyl 4 kicks in and the bike responds as it shud. shud i be looking at the tubes as well?
How do i determine if its lean or rich?

Thanks

[phil71]

ok... so you've got a DOHC 750... there are number of things you will need to go through to solve this problem. You fixed your idle issue quite by accident.. .you don't say that you pulled the carbs , so that may be in your future soon.

the air/fuel screws only effect mixture on idle and part  throttle.
your problem can be one of these things...
1) vacuum leak
2) low fuel level in the float bowl.. meaning stuck, dirty or maladjusted float height.
3) stuck slide (if the bike's been sitting awhile)
4) valve adjustment radically out of spec (super unlikely)

no matter what, you're only going to solve this with more disassembly, I'm sorry to say.

[wildrum88]

actually it is a 1982 cb650. I did rebuild the carbs recently and cleaned them out thoroughly (about a week ago), so that should not be an issue. i adjusted the valves 2 days ago to spec, so that shouldn't be it. the only thing i can think of is the vacuum leak because the auto fuel valve on my bike is actually from a cb650sc instead of the cb650 like it should be. here is the auto fuel valve i should have: [/img]http://www.powersportsplus.com/images/diagrams/honda/042010/14460A/ILLUST/E1446/0A20.png[/img].
the part that i do not have that may be causing the leak is labeled #1 on this image and is called the "joint set". my carb has a replacement plastic part that is a t-joint with the vacuum hose connecting to one part, a cap on one part (may be causing the leak) and the other part into the carb. i should also mention i have pods and open headers, although i would not think this could affect a single cylinder. the bike seems to run great, no lag in acceleration, no problems idling. cannot seem to figure this one out.

[phil71]

spray some carb cleaner around that carb when it's running. If you have a vacuum leak, the engine speed will change . That'll help you hone in on it.
I forgot they put those CVs on the c650, is that a nighthawk?

[wildrum88]

nope just a 650 standard  . i decided to fiddle around and i took the cap off of that t-joint that connects to carb #3 and connected the vent tube to it. so now that t-joint is connected to the vacuum tube as well as the vent tube, and i drove around a bit and now that cylinder seems to be running rich (black plug). i dunno just an experiment. what are the cons of running either rich/lean. i know running rich will cause the oil on the cylinder walls to be depleted quickly but what is the con of running lean?

[phil71]

this doesn't make a lot of sense. gonna need some history... did the bike come to you in  stock form, or with the mods?
did it run when you bought it? did it run better than it does now?
running rich will foul plugs. fouled plug wont fire, raw gas washes cylinder walls, thins out oil, and increases the amount of liquid in the oiling system.. bad stuff.
lean will overheat and start to melt stuff. Aluminum does not like this.

[wildrum88]

sorry I'm being a bit vague, trying to make sense of it myself. The bike did run when i bought it. i am the one that removed the air box and added the pods, but it didn't seem to run any better when i bought it than it does now. the thing i am confused about is why this bike has the 650sc auto fuel valve instead of the plain old 650 auto fuel valve. ill try and explain this as best i can but it appears as though the previous owner modified these carbs in some form or fashion because as seen in this picture there is a hose running from between carb #3 and #4 (parts labeled 10) to a joint in the middle (part labeled 20) as well as a hose running from between carbs #1 and #2 (parts labeled 11) to that same joint. my carbs do not have these hoses, the carbs simply connect to one another where those hoses should be and in the middle is a hose with that joint (20) but it is not connected to anything. i don't know if this has anything to do with the #3 cyl. running lean but the bike seems to run just fine with these modifications to the carb. very confused. ill see if i can upload a picture of the carbs soon so you can get a better idea of what i am explaining.

[phil71]

can't you put it back to stock? From what you're describing, your potential for fuel delivery is diminished by having fewer places to feed the carbs than it's stock trim. Retrace your steps, fuel either can't get into #3, or out... and there are only a very small number of reasons that could happen, especially at higher revs.. the main jets rarely clog, and you have just cleaned them, right? So it stands to reason it's just not able to replenish its fuel supply as fast as it can use it. So, delivery starts at the tank, through the "T"s and then through the needle/seat, into the bowl.
   get in there!