what does 'running lean' mean?

[Guest]

I have a 1980 GS850. Last time I cleaned the carbs (the whole ball of wax - take apart, dip, new gaskets, etc) was last year when I had an issue with a petcock that I had to replace.

That time and the previous carb cleaning I did, I just bench synched the carbs and the bike ran fine. But I always wanted to do a proper vacuum synch so I finally shelled out the cash and got a Morgan Carbtune. Today, with my new tool, I did a vacuum sync.

But I'm getting a little bit of popping on decel when I first run the bike. Once I got it warmed up after a little riding, the popping stopped, even on decel and downshifting.

Reading over other threads, I'm thinking I'm running lean but I don't really understand what that means. Is it possible to be lean in just one carb? Or when people say the bike's running lean, is that referring to something that's happening with all four?

I read that the Morgan colortune is supposed to help ensure all four carbs are firing properly so I'm thinking of getting one of those, too.

If this is too dumb a question, I imagine someone will come on and tell me to quit being lazy and use the search tool. I did, but most of the strings I saw, people seemed to know at least what running lean meant.

Sorry for the long post - and if this is too dumb a question to ask.

[tkent02]

Lean means not enough fuel for the air you have going in, or to much air for the fuel you have going into the engine. When gasoline burning piston engines run lean the pistons, and the valves can get hot, sometimes too hot doing damage. Blue exhaust pipes are a sure sign that that cylinder is too lean at least some of the time.
it can burn a hole in a piston or burn a valve. Sure one cylinder can be lean, or all of them. This is actually quite common on engines such as ours with separate carburetors on each cylinder. It can also be too lean at some times/conditions and too rich at other times/conditions. Way too much to explain here, but Mikuni has a lot of good info on their website, search for it.

[nikosg]

from the popping on throttle release, id assume your running a bit rich.

isn't "running lean" just mean your air-fuel mixture is a little light on the fuel (too much air)?

and running rich means you have excess fuel (hence would hear that popping, which is unburnt fuel combusting in the exhaust... me thinks... I'm a noob though!! LOL )

[Allie]

You honestly don't know the answer so it's not a dumb question, or even a rhetorical one. Running lean meas that the air/fuel mixture has too much air and not enough fuel. Running rich is the opposite of that. It is very totally extremely possible to be running lean in only one cylinder, or any combination of them. One of the most common causes of this is a vacuum leak, as in cracked intake o-rings, which very well could be what you're experiencing. They have been known to leak badly when cold but seal up and run better as they get hot and expand. You really ought to have a look at them, and check your valve clearances while you're at it. Basscliff's splendid website will be of invaluable help in this.

[tkent02]

Too lean can cause popping too.

Also air leaking into the exhaust will do it.

[oldgsfan]

I replaced the intake o-rings about two years ago when I first got the bike, so I'm fairly confident they're still good.

I did do a valve job, but I can't swear it was a great valve job and it is entirely possible I need to check my valve clearances.

I'll check out the Mikuni site. But all your explanations help quite a bit and I appreciate that.

[old_skool]

Small kernels of corn in hot oil causes excessive popping as well

As Tom mentioned, check for exhaust leaks as well, this will cause popping, inspect your plugs for burn color, to help aid in determining what cylinder is running lean/rich.

[OldVet66]

Since it stops when it is warm, I would suspect it is a slight leak that seals when metal expands. I have four into one pipes and pods with a stage 3 jet kit. It is considered normal for this setup to have a very muted popping on deceleration.

[oldgsfan]

Well I did loosen the bolts on my exhaust pipes just to see if I could do it. I'm getting ready to replace my old pipes for a vance &hines 4 in 1. Maybe I didn't tighten them up well enough. I'll check that too.