Carb Idle Issue

[ozzstar]

I posted this in the yahoo forum also.

I thoroughly cleaned the carbs on my '86 FJ and have installed them back into
the bike. The bike has 12K miles and sat for about 16 years in a garage unused.
I used Carb Dr. David Rathforth's kit with the new float valve seat o-rings and
stainless allen screws.

I got the engine idle stable and synced the carbs. There is a K&N filter, jet kit
installed and a 4 into 1 V&H pipes. Idle/air screws are 4 turns out.

The problem i am experiencing is a high idle situation. I can get the bike to
idle smoothly around 1100 RPM in the driveway by adjusting the idle screw BUT as
soon as i get down to the corner of my street, the tach reads a steady 2,000
RPM. Blipping the throttle does not bring the RPMS down. I have tried
readusting the idle down to 800 RPM, idles fine in the driveway, take it down
the street and same prob 1900-2100 RPM steady.

I took the bike out on a main road and it pulls strong with no stumbling or
misfiring, jumped right to 75 MPH in a hurry!

Any good advice would be greatly appreciated with this prob. I did notice a
tiny amount of fuel seep out of the the number 2 carb choke circuit hose. I took
the carbs out and made sure the float needle valve was closing before the float
hits the top of the carb body. It seems to be adjusted properly, but there
still is a couple of drips coming out of the hose.

The bike fires right up without any hard starting problems.

Thanks

Ozz
(Glen)

[ozzstar]

UPDATE* 
I went to put the bike on the center stand this morning after letting it sit in the garage all night.   Fuel started to flow out of the #2 carb black choke circuit tube pretty heavily for a few seconds.  I am assuming now that the float/needle are sticking or leaking? 

Ozz
(Glen)

[Dan Filetti]

Have you checked the Float LEVEL?  Apparently the floats sometimes need to have thier tangs bet some to ensure the correct level.  Also, I've heard where smaking the offending carb with a screw driver can, occasionally dislodge a stuck float.

Just a though,

Dan

[Mark Olson]

Glen,

sometimes ya  gotta rough up the needle and seat a little bit with some 800 grit sandpaper  and then it will seat properly.

4 turns sounds too far on the mix screws. most of us start at 3 turns and go up or down from there.

[ozzstar]

4 turns sounds too far on the mix screws. most of us start at 3 turns and go up or down from there.

Yes you are right Mark, i adusted that to about 3 turns out right now and i think they can go in a little bit more.  When i blip the throttle the tach shows the RPM's coming down slower than I'd like to see.  Seems anytime I take the thing past 3K rpms, it takes a while for things to come down to the 1K rpm. Sort of like the throttle is stuck open, but its not.

I also disconnected and plugged the vacumn line going to the spark advance box, thanks to a suggestion an FJ Yahoo group member gave me.   That seemed to help big time.  What exactly does that box do???  On the test drive the bike seems to run perfectly normal, I never really took it over 4500 RPM without a problem occurring.

This morning I changed out the float/valve and seat on carb #2, and the leak looks like it has stopped.  I did not see any overflow out of the carb choke circuit tube while tuning the carbs today. That was a plus.  I have bent up the tabs on the other floats which seem to be okay.  I checked the amount of gas that was in each bowl and it appears to be about 50-55cc each.

Rechecked the sync and that is pretty much on the money.

Appreciate any further advice.

Thanks

Ozz
(Glen)

[ozzstar]

Today I pulled the tank and backed the idle/air screws out to around 2.5 turns.  I was able to get the bike to idle but anytime i went to blip the throttle the engine would shut down.  So i increases the idle screw a little bit and set the I/A screws out to 2.75 turns.  Bike idled okay and I synced the carbs. 

Then i decided to spray some brake cleaner around the intake boots and noticed the RPM's jump way up when #3 cylinder was sprayed.  Turns out the clamp wasn't on tight enough.  So i snugged up all the clamps and double checked everything.  Checked the sync again, all is good.  At this point the bike is idling around 1200 rpms.  When i rev it up to 3K RPM and let off it seems to drop steady till about 1600 rpm, then takes it time to settle back down to 1200rpm.

I took the bike for a very small ride down the block.  It seemed that when I accelerated (3-4K rpm) and let off the throttle or pulled in the clutch to coast to a stop the engine wasn't "racing" as high like in the past around the 2K rpm mark.  Tomorrow i will do a more thorough road test and report what results i get.

Take care

Ozz
(Glen)

[ozzstar]

Another update:

Well today i started the bike and i thought it seemed to run fine.  Idle dropped down pretty smoothly from above 3K RPM. The tach still slowly drops down from 1600 to 1200 rpm. Then it idles okay for about a minute at 1100-1200 and then suddenly drops to about 900-1000 for about another minute.  If i dont blip the throttle at that point and bring the rpm's back up, then the engine will just shut off on it's own. 

If i hit the starter button the motor fires right back up no problem. Then we start the whole cycle over again. 

SO this made me think the idle was to low.  I adjusted the idle screw and it idled nice and steady at 1200 RPM.  Well.......... then I went for the test ride and i'm back to a high reving engine that wants to stay in the 2,000 RPM range for awhile until slowly coming down to around 1500rpm!!!  Ouch, this problem is driving me nuts! Then it wouldnt come down below 1500, so i turned the adjustment screw back.  Now it will idle at about 1100-1200 but eventually stalls out on its own if i dont goose the throttle after a minute or so.  Idle/air screws are still out about 2.75 turns each. Should i turn them in and raise the idle screw??

Any new ideas?  George i did not run wire through those 3 or 4 little holes above the butterfly plate in the carb body...its about the only thing i haven't tried but i'm considering it if no other easier solutions come about.

Thanks

Ozz

[Ratchet_72]

How did you sync the carb? Are you sure you did that correctly?

[ozzstar]

Yes, cylinder 1 to 2 , then 3 to 4 , then 2 to 3. I use a mercury sync tool. 

[SlowOldGuy]

If it's reving up then air is somehow sneaking into the intake.  You won't fix it with the idle mixture screws.  Jacking the idle mixture screws should not cause this kind of behavior, there's just not enough air volume involved.

How do the rubber tips on the choke plungers look?  Is the choke cable and plunger rod allowing the plungers to fully seat?  It would be very easy for air to get in through the choke circuit if the plungers are leaking. 

That is sometimes why the choke air intake hoses leak fuel.  A sticking choke rod can allow enough airflow to pick fuel up from the float bowl, but the vacuum is not enough to deliver it all the way to the intake.  Therefore it will fall back down and find its way out the hose.

Either that or you've got a sticking throttle cable.

DavidR.

[Ratchet_72]

Correct me if I'm wrong David R.

Carb #3 is static, the only way to adjust #3 is with the idle screw. This is why idle should be roughly correct before you start.
Sync #4 to #3. The right bank is now correct.
Sync #1 to #2. The left bank is now correct.
The screw between #2 and #3 balances the left bank to the right bank.

Everything goes off of #3.
When your idle changes after all of this bring it back to about 1k rpm.
Repeat until all is good.

This all needs to be done with the bike warm i.e. operating temp.

I do my sync'ing with the rpms around 1200-1250 rpm because that is where I get the best sync on my carbs.

[SlowOldGuy]

Jason,
You are correct!

DavidR.

[andyb]

Synch can cause these symptoms of a hanging high idle as you describe.

I synch at 3k, from some old guru's advice (at a third of redline, half of peak torque, or near the revs you normally ride at if there's a nasty vibe spot there).

If you take the bike down the block and it hangs the idle high when you're coming to a stop, try this:  Put the bike back into gear (1st) at the stop, hand off the gas, and gently feed clutch until you pull the motor down to the regular idle.  Pull clutch back in.  If the idle stays low, your synch/air is bad.  If it revs back up, you have a fuel leaking added fuel someplace (check the orings around the needle seat assembly and the needles/seats themselves).

Also make ABSOLUTELY sure that the motor is fully hot when you're doing the sync.  As it heats up, valve tolerances change among other things, and it's rough to get things right.


Worked for me in the past (my sync was bad and it drove me NUTS until I figured it out).  Gluck!

[ozzstar]

Synch can cause these symptoms of a hanging high idle as you describe.



If you take the bike down the block and it hangs the idle high when you're coming to a stop, try this:  Put the bike back into gear (1st) at the stop, hand off the gas, and gently feed clutch until you pull the motor down to the regular idle.  Pull clutch back in.  If the idle stays low, your synch/air is bad.  If it revs back up, you have a fuel leaking added fuel someplace (check the orings around the needle seat assembly and the needles/seats themselves).

YES!  That is exactly what happens, i can bring the idle down by doing the first gear 'trick'.  It will not rev up on its own.  So good chance my sync sucks.  Hmmmm, thought i was doing it right.  I need to figure out how to get the sync correct.  Suggestions?

I have been warming up the bike before syncing, and having it idle around 1200 rpm. 

[ozzstar]

If it's reving up then air is somehow sneaking into the intake.  You won't fix it with the idle mixture screws.  Jacking the idle mixture screws should not cause this kind of behavior, there's just not enough air volume involved.

How do the rubber tips on the choke plungers look?  Is the choke cable and plunger rod allowing the plungers to fully seat?  It would be very easy for air to get in through the choke circuit if the plungers are leaking. 

That is sometimes why the choke air intake hoses leak fuel.  A sticking choke rod can allow enough airflow to pick fuel up from the float bowl, but the vacuum is not enough to deliver it all the way to the intake.  Therefore it will fall back down and find its way out the hose.

Either that or you've got a sticking throttle cable.

DavidR.

The throttle cable is definetly not hanging up..that works fine.  The choke plungers look good and seat closed.  I don't think any air is getting in there.  The bike won't tac up on its own,  it just doesnt like to come down off of high idle after taking it down the street.  I am certain now that all the carb intake boots are sealed properly by spraying brake clean around them and not noting any RPM fluctuation.