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Please confirm (or not): Running Lean?

  • Thread starter Thread starter Jim
  • Start date Start date
J

Jim

Guest
Greetings,

The impression I'm getting from browsing other threads here is an air leak somewhere in the system, but before I go to the mechanics, I thought I'd see if my guess sounds right or if you can suggest any other causes. (My 'parking space' is an alley between two apt buildings and under tenants' windows, so as long as I'm living here, I can't work on the bike myself.)

"Historically" my 1980 GS400ET (I'm the original owner), idles about 1300 rpm. (Manual recommends 11-1300, though it's been quite happy at 1500 some years.) Starting a cold engine has always been a pretty predictable process ? 75-80% choke to get it started, then adjust to idle at 2000 rpm for a few minutes before pulling away.

This summer, it's been almost impossible to find a choke setting that allows me to start the cold engine without also manipulating the throttle (and it can take 8 or 10 tries of choke/throttle combinations to finally get it started). And no matter where the choke is set when it DOES start, taking my hand off the throttle risks an instant stall.

Once it's warmed up, there's no trouble re-starting, but idling becomes the problem. If the idle speed is set anywhere near 1300, as soon as the throttle gets the rpms around 2500/3000 the engine will stay there or race higher despite closing the throttle unless I use the clutch to slow things down. If I adjust the idle low enough that the engine reacts normally after blipping and closing the throttle, it's constantly on the edge of stalling when idling. So essentially, any time I take my hand off the throttle (stop lights, bridge tolls, etc.), I risk stalling.

Thanks in advance for any opinions/suggestions.
 
Good guess on erratic idle- you likely got airleak, maybe carb boot itself or that o-ring that sits between boot and cylinder head. These things don't last forever. new one might fix hard starting also, but when did you last check valve clearances?
 
Although it seems that your bike gets regular use, it's probably at least a few weeks past needing to have the o-rings replaced. :-k

While the carbs are apart for o-ring replacement, go ahead and dip them. Because the bike still sees regular use, you might get away with less than the usually-recommended "overnight" dipping time.

It might also be that the mixture screws need to be turned out a bit, especially if they are still sealed from the factory. Your bike had some early CV-style carbs, and they were set rather lean. Richening up the mixture screws will help a LOT to shorten the warm-up time under your neighbor's window.

You also need to learn proper starting technique. When using the "choke" (it's actually an 'enrichener'), do NOT apply ANY throttle.

.
 
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