Starts but dies out immediately.

[Pete-speed]

After blowing out fuel line the bike can be kept running by playing the throttle and full choke, but only to 1-1.5k rpm and is back firing constantly. Is this typical of timing issue or maybe faulty coils? Idk, any thoughts. Still haven't changed out gas, will do next but back fire issue unlikely due to old gas.

[Pete-speed]

Not sure how to update profile but details are I have a 1991 FJ1200, have been riding it for 26 years. Had hydraulic clutch go and after replacing that 2 years ago had dead battery. Sat for about 2 years due to other life demands, and I also have a 1987 XLH with a 89 cubic inch engine so I still had a ride, had this 25 years, now at 70 rather ride than wrench but bike not cooperating

[Pete-speed]

Not sure about mixture settings but was running fine before I let it sit during clutch repair over 2 years ago

[red]

Pete,
Backfiring would not surprise me with old gas, because a lot of unburned gas is going out into the exhaust system.  I would doubt that you have timing or equipment problems, with a bike that ran well when it got parked.  It is far more likely that the carbs need a fuel additive, and old gas is a likely suspect, too.
If you have not used fuel additives before, at the gas station, put the carb cleaner into the gas tank -before- filling the gas tank.  Then the gas pump will put a hard stream of gas into the gas tank that insures a good mixing.  Same goes for using that old gas in the car - put the old gas into the car gas tank just before you fill the tank at the pump.

[Pete-speed]

Drained the tank and filled with new high test, reinstalled new fuel pump and blew out fuel lines. Now bike starts and can rev up to 3.5k momentarily but then fades out after few seconds and can be kept running with throttle play but again backfiring and can't get revs up above 1.5k although will idle sometimes. Poured old gas with all the additives in my 14 year old Tacoma, didn't read idea to put in new additives in tank first, get sucked in first in time. Still baffled why she won't rev up higher and why it dies out, and backfires a lot. Maybe new coils and plug wires? Any more ideas I'd appreciate the help

[fj1289]

What condition is the battery in?

And what voltage is the charging system putting out?

[Pete-speed]

brand new battery and kept on trickle charger for all the starting attempts. seems to be putting out charge when reved to 3k+ as headlight gets bright but as it bogs down light dims out also

[Pete-speed]

anybody ever had to replace the digital ignition unit (TDI)?

[Pat Conlon]

Check the fuel level in the carb float bowls. You could be flooding out (high level) or starving (low level)

[red]

Pete,
High-octane gas burns with LESS power than low-octane gas.  Non-ethanol top-tier regular gas would be a good choice for this time.
Give the SeaFoam a day or three to work its' magic.  I'd expect things to improve somewhat each day.
You can tell if each cylinder is firing by (carefully) taking the temperature of each pipe by hand when started cold, or with a temperature app on a modern cellphone when hot.  A remote infrared thermometer (~$ USD 35.00) works best, there.  Try to borrow one, and see if you like it.

[FJTate]

If revving keeps it alive for a second, my first guess would be gummed up pilot jets.

[Pete-speed]

Thank you Red, simple but smart. Checked pipe temps, by hand, left two cool, thought i hadn't warmed it up enough, right two pipes scorching. so it looks like left coil is not working, finally a solid lead. Glad i didn't fully fill tank. pulling that and will test coil assembly. Spark plugs are all new but question, been running NGK DPR7ea-9 plugs, R is resistance version for rfi suppression and only available version, but manual say DP8ea-9, does 7 vs 8 matter and if so which is best. have to travel so will update results when I return.

[Pat Conlon]

Your firing order is 1-2-4-3 meaning cylinders 1 & 4 share a coil and cylinders 2 & 3 share a coil.

If your left 2 cylinders are cold (#1 and #2) it's not your coils.

My money is on gummed up idling and pilot circuits in your carbs.

Cheers

Pat

[red]

Pete,

If you can find non-resistance plugs, you can still have max spark Voltage and radio noise suppression (better than resistance plugs or resistance wires).  Inductance spark plug wires are a continuous wire, spiral-wrapped, no carbon or resistors, feeding into the spark plugs.  Why that works is a long story, but it does.  That is what the hot-rodders use.
Actually, since few music lovers listen to AM radio lately, you may not have any problems using solid-core spark plug wires, although those MAY interfere with your other radio gadgets.  A good auto parts store should have all of these options.
Inductance spark plug wires are the best, IMHO.  They suppress radio noise, there are no resistors to worry about, and the wire does not go bad when you bend it once.
Some spark plug caps have resistors inside.  You will not need (or want) those types of spark plug caps, with inductance spark plug wires.  Resistor wire and resistor caps work to suppress radio noise by reducing the spark plug voltage (bad plan).

[Pat Conlon]

Switch the plug wires.
Pull the #4 plug wire and put it on #1, put #1 on #4
Pull #2 wire and put it on #3, put #3 on #2

Do the left 2 cylinders still stay cold? If so, your wires are fine.

If the problem was in the plug wires, your left 2 cylinders (#1/2) would now wake up and get hot, and your #3 and #4 would now be cold.

The oem FJ silicone plug wires with stainless steel cores are extremely durable.