Unstable and Hanging RPM's

[Warp84]

have you ridden it like this or is all the tuning based on the bike in the garage?  I rehabbed my FJ from PO who let it sit 15 years, I was only able to get it about 90-95% dialed in on the center stand the rest came from riding it and then coming back and making minor adjustments. I can honestly say it took me like 300 miles of riding before I found the sweet spot for my set up. Have you tired fuel mixture screws in between 2.25 and 2.5? Are you using adjustable slide needs or are they the ones with the little plastic donut on them? I'm curious how your slide needles are set.

Also if tuning while idling be sure to put a big fan on that engine to help cool it and even then don't let it idle too long as even a big fan wont cool that engine the way air flow would cool it at even a low speed of 15mph.

We did one test ride when it had the 37.5 jets after the carb stack was put back together with undamaged carb bodies. That ride is when we uncovered the oil pickup screen gasket was cut, when oil started pouring out from the bolt hole just above the exhaust collector, after passing 55mph. That ride had the RPM ticking up and down the 1k rpm, several times a second, instead of the current slow fluctuation it has.

Like you said, it's nearly impossible to get a perfect tune on the centerstand, Since it's running so much better I'm prepping to check a few more things and set out on a test ride in a day or two. Wanted to make sure I dotted my I's and crossed the T's so I don't have another incident like on the first test ride.

-edit- The Slides for both kinds that I have are the fixed type with no clip for adjusting it.

[86FJNJ]

I know you said you have stock intake/air filter, is your exhaust stock too or is it more free flowing aftermarket?

Seems like you have it tuned really close, if it were me I'd put the fuel mixture screws between 2.25 and 2.5 and fill it up with fresh gas and dump half a bottle of seafoam in there and go for a ride and see how it behaves through the rpm range and see how it is when you stop at stop lights and stop signs, what does the idle do then after it's warmed up, what does it do when you ask for some throttle off idle or ask for more throttle at 3k rpm in 2nd gear...make some mental notes and adjust from there.

If your intake and exhaust are stock I don't think you should need to shim your slide needles the stock position should be ok. If putting some miles on it doesn't allow you to dial it in I would probably try the other emulsion tubes and slides you have from the later FJ's maybe that helps smooth things out.

Are the rubber diaphragms in your carbs OEM or aftermarket? Did you inspect them for any pin holes or tears? Do your slides all go up and down at the same rate or are any of them a bit "sticky" and slow to lift or return?