Off-idle stumble & bleed screws

[Waiex191]

Hey all,
I've not been riding or working on the FJ much, as I've been buried in airplane issues etc. Since I got it back together it's had a bad off-idle stumble, and I've had to rev it a bit to get it going. Sort of like a beginner. A couple years ago I was convinced my stock idle jets were getting plugged up, possibly from kreem degradation in my tank. I've replaced the filter, cut the old one up, seemed fine.

I've been on the forum despite my inactivity and bleed screws have come up a few times. I set mine after synching the carbs, mostly my blipping the throttle while parked on the centerstand. But I suspect the engine was not up to temperature.

So I pulled the tank, screwed them all in - 5 turns!  Set them all to 2.5, and it's much better. But not perfect.

Looking for advice. Do I turn them in or out?  How much per iteration?  Do I test by riding, or is there another more efficient method?

Thanks!

[86FJNJ]

Turning the mixture screws clockwise (in) will reduce fuel, turning the screws counter clockwise (out) will add fuel.

Can we assume that at one point in the past the bike was running fine with this same configuration of pilot jets and air intake filter etc? No changes in set up since it was last running well?

Most in this group will suggest a good carb cleaning and they are probably right. I had some issues with a dirty pilot circuit and ended up increasing the size of my pilot jets...bigger hole, less chance to clog. I have also been running Yamalube RingFree + Stabilizer fuel additive in my fuel and that has actually helped a bit and I've been running it in my fuel ever since. Or some people use Seafoam in the fuel which can also help.

If you have a concern over fuel filtration and your FJ has a fuel pump you can run this Golan 10 micron filter between the pump and your carbs. I've got probably 1,500 miles on my Golan filter and not one issue with fuel starvation. I still run the standard yamaha (40 Micron?) fuel filter between the tank and the fuel pump but like having the 10 micron Golan in there as well to keep the carbs clean. The filter is rated at 6 gallons per minute so I would assume it would be ok for a gravity fed FJ but I've not confirmed. Since the gravity fed FJ carbs have two fuel inlets, if you did have fuel starvation issues by running one filter you could run two filters with one filter dedicated to each of the two fuel inlets on the gravity fed FJ carbs, that would certainly eliminate any fuel starvation issues IMO with one filter only servicing two carbs instead of four.

https://www.amazon.com/Yamaha-Yamalube-ACC-RNGFR-PL-12-Ring-Additive/dp/B002GU4SN2/ref=sr_1_5?crid=3MDHKOC2GLCZJ&dib=eyJ2IjoiMSJ9.9MbbKhISmpLz7J71jhJqAHB2Z9O1DjDCnE3n6R3boAAdBurBSZ-6eTZTyhUrzBlrOK2dc_F5LxGJjLHSEfNcdAT-FNDBWgLNRY3fpkFXUbPbjyjNpynagBYawIG3LVGRZw6QzEQWgJBUru4XdhK63Xo-U_Xr4A8cQI_nuw-E6qppQOcNzSMQi2xlRnkcDHtdYEtSFvKuS_qLwCis3WPF8QhZ1pM2gQ9ra2KUqhq5q4P-WpeMEAkV4FdXO4H-L_pm1no_CyMpHiYMdeKZYH2Bag9T4vM4s76GvxfyyVq4Hno.6ySt1bRY3p54N12-YoY71Rbno64oOZFipN2kDh7syXA&dib_tag=se&keywords=yamaha%2Bring%2Bfree%2Bplus%2Bfuel%2Badditive&qid=1761051006&sprefix=yamaha%2Bring%2Bfree%2Bp%2Caps%2C76&sr=8-5&th=1

https://www.amazon.com/Golan-Inc-Super-Filter-70-250G/dp/B00D3R1WOA/ref=sr_1_3?crid=ICZE3UZL4HFX&dib=eyJ2IjoiMSJ9.DoBHOCOFb6G-tWrNM9XNdZZ_XX4gCyz6qlPwMHUVj6y6CauEaRGrGD0Fu7GsNb4DXznSGWE0D4ytJz5gsaI2wcgoWLIn9XvXk8zQDptjtZEmfhw4tE8GoaELm4Xr7T98v9AgD17Xs22IsXydNmMKrOJganGaZlakolZiChzYwNkDZyubxAeTVy8MG8RLgQF0WvLRONdapdlcCwwerx3Qlw.PVhKC8ipxi_GlT6Pj4WT4YQFaBNAKJJF0x9xfRAuv4o&dib_tag=se&keywords=golan+super+mini+fuel+filter&qid=1761051298&sprefix=golan+super+mini+fuel+filter%2Caps%2C59&sr=8-3

[Waiex191]

I've been through the carbs, and except for these bleed screws I've gained a little experience.
https://fjowners.com/index.php?topic=19343.0
I've had the bike since nearly new, all stock jets and airbox. Problem was it sat for 16 years. If I wrote down my bleed screw settings when I took it apart, I've lost that note. I'm pretty sure it's good except for the bleeds.

[86FJNJ]

If the bike sat for 16 years I would suggest sending the carbs to RPM and have them do a full ultrasonic cleaning. That should fix it. If you're bike is all stock then putting the fuel mixture screws at 2.5 to 3 turns out is probably a good starting point and then you can tune from there. But if you're like me you may want to run some Yamalube Ring Free or Seafoam through the fuel and see if it gets any better first.

[Waiex191]

My project thread I linked is a few years old and long.  But the carb summary is I've had them apart a few times, until I really figured out how to clean everything.  Got a lot of help from the good people here.  After I had it running pretty good, the alcohol in the gas seemed to have corroded the float needles, so I had them apart again and stopped using gas with ethanol.  So I really believe they are clean, and I've had a major improvement going from 5 turns to 2.5.  So next I'm going to try going to 2.25 turns and see what I've got.  If that makes it worse I'll try 2.75 turns.

[Pat Conlon]

Hi Bryan, here's an old post about the "blip test" you may find helpful.

https://fjowners.com/index.php?topic=14789.0

Perhaps it's no coincidence that the OP Tim also had a Kreem coated tank.

Cheers. Pat

[Millietant]

I've just had a Honda Shadow that stumbles as you describe and it has been parked up for many years and the owner had had the carb cleaned.

The issue was that the throttle slide was sticking very slightly in the carb bore and wasn't lifting properly immediately when the throttle was opened. Taking it out, thoroughly cleaning the slide and putting it in with some lubrication (GT85) solved the problem.

And............. probably not coincidentally, my pal Pete was having few problems with his FJ's initial off-idle response and after we'd cleaned the carbs and put the slides in, I noticed 2 of them were a little bit lazy in lifting at the bottom. They were not sliding smoothly, so all 4 came out and they were cleaned with light rubbing with a fine scotchbrite pad and carb cleaner, then lightly lubricate and refitted.

Once everything was back together, the throttle response and low rpm running was back to where it should be. Not sure how much the sticky slides had to do with it, but it can only help to eliminate that as a possibility.

[Waiex191]

Pat, thanks.  I think I set the screws a few years ago with the blip test, but the bike was not warm.  That's probably how I ended up at 5 turns.
Dean, the slides did seem good last time I took them apart.  But something to consider.

I turned the needles to 2.25 turns, and that seemed a little better.  Then I tried 2.0 turns and that was bad.  I'm going to give 2.75 turns a try but my clutch slave needs service - again.  I think it's time for a new slave cylinder.  I see RPM has stock ones, but I am considering that aftermarket one Dean and one other guy here used.  I just have to remember what it was.