Runs great one day, horrible another! Any ideas?

[Lucky]

all great suggestions, but you need to diagnose it in an orderly fashion.
pick a system & start with it, test it all the way thru:
start with electrical.. is the battery fully charged, does it have water, are the cables good, not corroded, etc.  does it charge properly when running, etc, etc.

then maybe go to the fuel system. good fresh fuel? good hose, good fuel level?  any cold start isuues? etc, etc.

then check  switches. are they corroded?, open the relays, are they packed full of rust? check all the connectors, are the wires skinned back at the plugs?

check ignition, are the wires cracked? does the secondary curcit pass the resistance tests? are the plugs fouled, worn out? etc, etc...

work in a logical manner & you'll solve it.  it helps to keep a logbook of tests, inspections & results to refer back to.

--Lucky

[PeteXS/GS/CB/XZ]

My problem, the Vision stumble, and a rear carb that did not respond to tuning (turning the air screw didn't affect the idle), turned out to be a shaft seal creating a vacuum leak. Snipping the rev limiter wire had no effect. So check that. With mechanical systems, there's always a reason. Unlike human ones:)

[2002_wrx]

I'm with you Lucky on checking things in an organized way.  Had a few minutes today and went out and messed with things.  The battery is brand new, filled, and the cables are clean.  It's charging like its supposed to.  I couldn't find any terminals or electrical connections that looked damaged...I might need to dig a bit deeper to get to all of them. 

Fuel system seems good (with the exception of an occasionally sticky rear float).  No kinks in the hose, fuel filter clean, carbs very clean, etc. 

I changed the plugs and checked for spark...looked good just by eyeballing. Old ones seemed fine...no residue or funny colors. 

No vacuum leaks that I'm aware of...I sprayed just about everywhere with starting fluid and there were no fluctuations in idle or anything.   

Of course...this was all today...when it was running beautifully.   :-[

[Hartless]

have  you paid any attention to the weather when it runs bad? maybe  its warmer out and creates vapor lock or something of the sort

[muukow]

I know you've had a million suggestions but check your air box flapper a sticking flapper will cause some very erratic running,they do wear as the flap moves allot. I use a little Slyde Glide plastic lube very lightly to keep the flapper lubed when mine stuck it drove me nuts it acted like water in the carb and avoltasge problem!

[YellowJacket!]

I know you've had a million suggestions but check your air box flapper a sticking flapper will cause some very erratic running,they do wear as the flap moves allot. I use a little Slyde Glide plastic lube very lightly to keep the flapper lubed when mine stuck it drove me nuts it acted like water in the carb and avoltasge problem!

Heh heh... I thought of the same suggestion late last night and couldn't wait to log on this morning to post it.  Looks like you beat me to it.

Agreed, check your airbox flapper as muukow suggested whether it is the springloaded type or vacuum activated.

David

[kwells]

Have you disconnected and plugged up the YICS ports?