Holy shit! Possibly carb problems?

[grannyknot]

Just took my 84 FJ for my first ride. What a F--king beast! My heart is pumping. No wonder you guys love this bike so much. After riding a BMW for the last few years I can tell you I haven't felt this dirty, powerful and young in a long time.
OK,   Carbs are all rebuilt, I boiled them stripped before the rebuild and the engine is humming along beautifully.
But now, sometimes, the revs will not drop back down to the 1100-1200 rpm of idle but will get hung up at 1900-2200 rpm when I come to a stop. Bliping the throttle won't bring the revs/idle back down but sometimes
just the clutch in when going slow will bring it down. It only seems to do this while it is fully warmed up.
Linkages or cables maybe?

[Smola67]

Just took my 84 FJ for my first ride. What a F--king beast! My heart is pumping. No wonder you guys love this bike so much. After riding a BMW for the last few years I can tell you I haven't felt this dirty, powerful and young in a long time.
OK,   Carbs are all rebuilt, I boiled them stripped before the rebuild and the engine is humming along beautifully.
But now, sometimes, the revs will not drop back down to the 1100-1200 rpm of idle but will get hung up at 1900-2200 rpm when I come to a stop. Bliping the throttle won't bring the revs/idle back down but sometimes
just the clutch in when going slow will bring it down. It only seems to do this while it is fully warmed up.
Linkages or cables maybe?

PILOT JETS MAYBE.

[SkyFive]

Carburetor sync should fix it.

[Pat Conlon]

.....It only seems to do this while it is fully warmed up.

This is the clue...... I suspect that your idle mixture jets are set too fat. Lean them out 1/2 turn (screw in 1/2 turn) and see if that helps.

[FJTillDeath]

.....It only seems to do this while it is fully warmed up.

This is the clue...... I suspect that your idle mixture jets are set too fat. Lean them out 1/2 turn (screw in 1/2 turn) and see if that helps.

Pat is probably right I had the same problem with my 85, it would idle at 1900 and when it was fully warm after i had been riding and came to slow dowm at a stop or robot it would sometimes idle at 3500rpm - let me tell you nothing teaches you clutch control quite like that

But then I found the skrew underneath for the idle mixture and the bike now idles at 1050-1100rpm. I still get a bit of slack when the bike is getting extra hot and it will rev at 1500rpm but releasing the clutch slowly controls that, so I made need to look properly at my carbs as i suspect the dealers who sold it to me didnt do a very thourough job

[ddlewis]

Carburetor sync should fix it.

yep. I'd check this first.  out of synch makes idle weird.

[doright1]

+1 on syncing the carbs first.  I had the exact same problem a couple of years ago, and that fixed it.

[Pat Conlon]

+1 on syncing the carbs first.  I had the exact same problem a couple of years ago, and that fixed it.

I agree, however, I have assumed a sync. job was a given.
For the life of me, I can not imagine someone removing, disassembling and cleaning the carbs then reinstalling them, without a sync job....

[fb747]

Check that the boots from the carbs to the engine have no cracks in them and are sealed properly.

[grannyknot]

Carbs were sync ed but I just did it again , they were a bit out. Using a Morgan Carbtune. After the sync same problem so I turned down the idle mixture screws from 3 turns open to 2.5 turns open and sync ed again,
and the idle was still high but fluctuating a bit. 160 air pilot jet, 112.5 main jet, 40 fuel pilot jet and the circlip on the jet needle is second from the bottom that's one below the middle (My driveway is 200
long and that is what I'm using at the moment, the bike is not street ready and there is a $5000 fine for for driving without insurance, so I'm sticking to the driveway for now. But I'm thinking maybe because I can't get out on the road and open it up that maybe that might be adding to the problems?

[RichBaker]

I'd say you need to go to a 155APJ, and raise the needle clip to the 2nd groove from top.  Stock airbox, filter, and exhaust?  I had a lot of lean surging at part throttle(25-40mph in 5th) with stock AB, filter and exhaust before rejetting. The 155APJ took care of that....
You also need to read up on the "Throttle blip test" procedure.
  Basically, if RPMs drop under, then return to idle it's rich, if RPMs hang above idle then drops to a steady idle, she's lean, on the mixture screws.

[SlowOldGuy]

The 160 air pilot jet basically defeats the 40 idle jet.  A smaller air pilot jet is richer.

DavidR.

[grannyknot]

Okay, I'll order 4  155 APJ from Randy and try the needle adjustment in the mean time.
Air filters are UNI foams, exhaust is 4-1 with a GIXR muffler from a Suzuki, it's probably a bit restrictive.
Thanks guys.

[RichBaker]

The 160 air pilot jet basically defeats the 40 idle jet.  A smaller air pilot jet is richer.

DavidR.

I'm running UNI pods and 40 apj...................  Works great,  mixture screws are ~1 turn out.

[SlowOldGuy]

Rich,
My point was that he installed a richer idle jet (40) but combined that with a leaner air pilot jet (160).  Net effect of these 2 changes is probably not much different than running the leaner stock fuel jet (37.5) with the richer stock apj (155).

I, too, am running the 40 idle jets in both FJs.  With this crap they are selling for fuel, they seem to resist clogging up as easily as the 37.5

DavidR.