What causes a 400 to run rich ?

[digitaldan]

Ok guys I have some questions on the GSF400. I run at 5000 feet above sea level, the mainjets are 87.5 so not too big. The exhaust continues to have lots of black carbon in it. I even removed the air filter completely to test and still had some carbon in the pipe. It uses no oil but black smoke can be seen sometimes after startup from cold. As it warms up it's easy to stall the bike when pulling away, in cooler weather it's much better. So if it's not the air filter and not mj's being too big what else can I try ? Carb rebuild ? Incorrect fuel supply ? My bike is a 1995 GSF400VV with 11 000 miles. It has some minor rust in the tank as well.

Apreciate any info 

[Banditmax]

leaking o rings and worn needle jets are the commonest causes.

[gsxr400 racer]

Take care of the rust in the tank and rebuild the carbs

[Thief400]

Check to see if the cold start plungers are closing all the way when you turn the choke off

[gsxr400 racer]

Check to see if the cold start plungers are closing all the way when you turn the choke off

And another great one and often over looked before removing the carbs

[Forde]

My exhaust has some black in it...

However the bike runs well, doesnt foul plugs, doesnt have any flat spots, and doesnt smoke, so im happy enough!!  With my race pipe on i should be getting flat spots and lean running going by what is said on here...  Maybe the previous owner jetted the bike, i dunno...

[Banditmax]

I get black on my exhaust too. Got another set of carbs im building up at the moment and will see if they help.

[digitaldan]

I really have no experience on these carbs. The other day when I was riding to work the bike went to three cylinders while doing 70 mph ! Can it be running so rich ? No I've been thinking the spark plugs may need replacing. Maybe they are the originals from the mid 90's and they can't deliver the needed spark anymore. I had a VFR 400 that sat for a long time and it's plugs were finished. Also would apreciate more info as to where I will find the cold start plungers. I rarely use the choke, I rather open the throttle slightly when cold.

[gsxr400 racer]

as in the choke plungers? your local dealer

[Vanishing_Point]

Check to see if the cold start plungers are closing all the way when you turn the choke off

And another great one and often over looked before removing the carbs

Hmm, I think mine may not be closing completely too. How would you remedy this? Lube the choke cable or something?

[gsxr400 racer]

yes lube the cable and you can pull the plungers out and polish them up with some metal polish.

[yuckhil]

Check to see if the cold start plungers are closing all the way when you turn the choke off

I think I need to check this too.  Could I possibly get a bit of description on where to locate the plungers?  I've never taken the tank off before, but I figure this is as good a time to start as any, since the local mechanics are really screwing me around.

yes lube the cable and you can pull the plungers out and polish them up with some metal polish.

Once the tank is off, will I see/access them directly by finding the end of the choke cable?

Apologies for the newbie questions and thanks.

[gsxr400 racer]

Check to see if the cold start plungers are closing all the way when you turn the choke off

I think I need to check this too.  Could I possibly get a bit of description on where to locate the plungers?  I've never taken the tank off before, but I figure this is as good a time to start as any, since the local mechanics are really screwing me around.

yes lube the cable and you can pull the plungers out and polish them up with some metal polish.

Once the tank is off, will I see/access them directly by finding the end of the choke cable?

Apologies for the newbie questions and thanks.

once the tank is off you will have to remove the carbs to do the plungers but while the cable is still attached move the lever to see the bracket move that connect all 4 choke plungers.

[yuckhil]

Thanks mate.  Turns out the oil level was too high.  Damn city workshops! 

[andrewsw]

another common cause of richness.. though it's easy to spot because the darn thing won't run hardly at all at low revs... stuck float or bits of debris in the float valve causing the float bowl to overflow into the cylinder. If it's a small enough bit of debris, it will just cause it to idle poorly or bog down and misfire when decelerating. Typical symptoms -- fouled plug in one cylinder, clears up when revved, etc...


I know it doesn't really apply to the problems in this thread, but belongs in any discussion of richness problems for later search results.

A