Idle Issues

[feederbb]

  I know some of you guys have helped me in the past and the "cleaner in the tank" has worked the last couple but...  When I moved to North Carolina it seemed like I had idle issues from the start and we went round about as far as altitude, non ethanol fuel, etc. and I looked into having the local idiot fix it with some massive quote so I put it off till now.  If I just pull the choke out a tiny bit I can ride around and pretend it runs right because above idle it's fine.  When I first fire it up with the choke on it stumbles like it's running super rich then will clear up, slight choke and I'm on my way.  Today I pulled the carbs, bowls, jets, etc., and they are spotless.  Shot carb cleaner in all orfices, blew out with air, etc. and she still does the same thing.  One thing I did notice is that the fuel pump seems noisy but this could be that I've never really listened to it with the side cover off.  I'm figuring that it's either working or not, and would be more of an issue at higher rpms, aka, starving for fuel, if it was a pump or filter issue.  Had a fresh set of plugs and threw them in, same-same. If I turn the choke off all the way after I've been riding a while, it seems like it wants to idle but really low and when I give it some gas it sputters coughs and usually dies.  Pipe looks a good color and the plugs I pulled out where a good color as well.  It would seem to me that there was a problem with the pilot jets or circuit but the carbs were super clean inside as well as cleaning them AGAIN.  As I've mentioned in the past it's a pretty much stock 90 that I bought from a guy in Flagstaff (6000 ft) and don't really know if he had jetted it for the altitude and yes of course I forgot to note the jet sizes while the carbs were apart, DUHHH.  When I've had the problem before then it was more of a low rpm issue as well as idle and this just seems like idle only.  Once again I humble myself, put a target on my back and ask for help.  Thanks, Kevin. 

[red]

I know some of you guys have helped me in the past and the "cleaner in the tank" has worked the last couple but...    If I just pull the choke out a tiny bit I can ride around and pretend it runs right because above idle it's fine.  When I first fire it up with the choke on it stumbles like it's running super rich then will clear up, slight choke and I'm on my way. 

Feederbb,

What is the idle RPM setting now?  You need it set to idle at 1000~1100 RPM.  If the idle is set below those numbers now, it will do everything that you describe, and nothing is actually wrong.  Using just the throttle, no choke, what is the slowest RPM that you can hold steadily now?

Cheers,
Red

[feederbb]

With the choke in I can get it down to 1000 (holding the throttle) but it sounds really rough.  I DID figure out why the fuel pump was sounding loud the second start up after replacing the plugs, I forgot to turn fuel back on under the tank, brain fart.  That would why it stopped running completly. I didn't tear down and seperate the carbs all the way because everything looked so spotless but pulled all the jets and sprayed and blew out everything and it all looked great. Didn't mess with any mixture screws or idle screws etc. and didn't really see how they could change by themselves in such a dramtic way basically overnight. 

[Pat Conlon]

Carbs sync'ed?

[markmartin]

...just ruling out some of the more obvious... You've had the carbs of so we can assume the air filter is fairly clean. ?
Have you tried adjusting the main idle screw to increase the idle RPM and if so, what happens when you do? 

[FJ_Hooligan]

Didn't mess with any mixture screws or idle screws etc. and didn't really see how they could change by themselves in such a dramtic way basically overnight.  

Uh, I think I found your problem.  If you didn't remove the idle mixture screws then the idle circuit is not clean.  Your description sounds exactly like dirty/clogged idle circuits.

The idle jet is tiny and dirt can enter the circuit from the air pilot jet.  A grain of sand/dirt can be a significant obstruction at the mixture screw orifice.

[Pat Conlon]

Didn't mess with any mixture screws or idle screws etc. and didn't really see how they could change by themselves in such a dramtic way basically overnight. 

Uh, I think I found your problem.  If you didn't remove the idle mixture screws then the idle circuit is not clean.  Your description sounds exactly like dirty/clogged idle circuits.

Yep^^^ good catch Hooligan! 

[movenon]

Didn't mess with any mixture screws or idle screws etc. and didn't really see how they could change by themselves in such a dramtic way basically overnight.  

Uh, I think I found your problem.  If you didn't remove the idle mixture screws then the idle circuit is not clean.  Your description sounds exactly like dirty/clogged idle circuits.

The idle jet is tiny and dirt can enter the circuit from the air pilot jet.  A grain of sand/dirt can be a significant obstruction at the mixture screw orifice.

I agree with the above.  But before I would pull the carbs apart I would remove the fuel air screws (each screw has a O ring, washer and spring) spray some carb cleaner down each hole. Don't loose any of the O rings or washers.... Re-seat each screw and back each one out 2.5 turns. Start her up and try to get your idle at around 1150 RPM + -.  Now do a blip test. Then sync the carbs and then do another blip test for final adjustment.  Last rest your idle to 1150/1200 RPM and hopefully you are up and running.  If not then I would pull the carbs and do a deep cleaning.

Also as a test you can run your fuel air screws in one at a time. When the screw get toward the bottom you should hear the engine running rough. If you get the screw all the way in and you can't tell any difference then it's dirty inside.

In my experience take your time syncing the carbs, adjust , let the idle RPM settle and touch up as required. When you are close 1/8 of a turn makes a difference.

Your main jets are not a player in your problem as I see it.  0 to 1/4 throttle is mostly the pilot jet, fuel air screw adjustment and syncing.  Something else that can effect it over all is the float level adjustment.  There is a correct way and not so correct way to do the adjusting.  The first time I did that I chose to do it the not so correct way and had the privilege to do it over...    School of hard knocks.
George

[red]

With the choke in I can get it down to 1000 (holding the throttle) but it sounds really rough.  I DID figure out why the fuel pump was sounding loud the second start up after replacing the plugs, I forgot to turn fuel back on under the tank, brain fart.  That would why it stopped running completly. I didn't tear down and seperate the carbs all the way because everything looked so spotless but pulled all the jets and sprayed and blew out everything and it all looked great. Didn't mess with any mixture screws or idle screws etc. and didn't really see how they could change by themselves in such a dramtic way basically overnight. 

Feederbb,

Try removing the fuel filter, and blow some air though it (by mouth) in the direction that the fuel flows.  The fuel filter should flow air freely, with very little pressure.  Then try it reversed, and if air goes through easier that way, the fuel filter was clogged.  Replace the fuel filter, if so.

Cheers,
Red

[fintip]

I used to be an active member at xjbikes.com, and it was taken for granted that with a problem like this, the most likely culprit was you weren't religious enough in your carb cleaning. Definitely sounds like the case. Remove ALL screwable parts, carb cleaner through all of them, pressurized air to test pressure on them all.

fjowners.wikidot.com/carbs

Some good walkthroughs and info on cleaning and tuning the carbs...

[ribbert]

...... you weren't religious enough in your carb cleaning.

I'm sure God is referred to frequently while resolving carby issues.

Noel

[andyb]

I'm sure God is referred to frequently while resolving carby issues.

Noel

Not just in carb stuff. 

Frequently addressed using the long form, too.

[feederbb]

Excuse me while I admit once again my ignorance.  There WAS some gunk in one of the pilot jets when I had them out and I KNOW I should have pulled out the idle screws but was trying to get the bike to run that day with it being such good weather for a ride.  My friend with the carb sync tool wasn't available so YES I was trying to get off the easy way.  Where I was befangled was when I put it back together it actually ran worse!  It was the old "don't change too many things at once" issue.  I figured as long as I had the tank off, and the plugs out checking the color, I'd go ahead and put "new" plugs in.  Aparently one of the plugs was banged around in my move somehow or whatever but one of the plugs was bad.  Put the old plugs back in, fired her up and bingo.  I've gone on a couple of rides since and she does everything like she used to (prior to idle problems).  Good stuff.  It's getting to be excelent riding time of year here in North Carolina and I'm a happy FJ rider once more.  Thanks for all the help.  Kevin

[movenon]

Glad you are making headway.  Also glad you were able to work through it yourself.  Hope the weather continues to get better.
George

[andyb]

Excuse me while I admit once again my ignorance.  There WAS some gunk in one of the pilot jets when I had them out and I KNOW I should have pulled out the idle screws but was trying to get the bike to run that day with it being such good weather for a ride.  My friend with the carb sync tool wasn't available so YES I was trying to get off the easy way.  Where I was befangled was when I put it back together it actually ran worse! 

Doing it right once takes less time than doing it twice.