1985 FJ1100 dies around 4500 rpm

[david f]

Hello fellow FJ owners. I bought a neglected 1985 FJ1100 I knew nothing about and it was running poorly when I bought it. I took it to a motorcyle shop (an old Yamaha dealer) and had the carbs cleaned and synced. The bike absolutely dies at 4500 rpm as if there is a governor or rev limiter stopping it. If you are patient you can eventually get it to rev past 4500 but it feels like 2 cylinders drop off.  The ignition module has been replaced. It may be related or not but the tach sometimes drops to zero rpm and also the turn signals won't work and the neutral light comes on almost every time the clutch is pulled in. Any ideas or suggestions? Thanks. Dave F in Virginia.

[Bezmozek]

Hi, there is nothing like that should stop FJ to rev up.

Check battery voltage with engine running, if generator gives enough energy for spark.
Unplug/clean/plug connectors wherever you will find them.
There is vacuum hose to ignition unit, check if is not unplugged/cracked for air leaks.
But my first guess is carb hose routing, there should be sticker on airbox under the seat, or http://www.fjowners.com/index.php?topic=8015.0.
FJ is simple long range anvil, no rocket science if carbs and valves are OK. 

[FJmonkey]

The tach dropping to zero is a clue. The tach is electrical , it reads pulses from the ignition system to show how fast the engine is spinning. If the engine is spinning and the tach reads zero then that part of the system has electrical issues. Normally a bad ground as is common for any vehicle as old as our FJs. Turn signals are not part of the ignition system but still electrical. This should be an easy one to trace and fix. And you might find the fix also resolves other electrical issues. Fix the easy stuff first. Get them off the list and work on the next issue.

[david f]

Thanks for the tips.

[david f]

The tach dropping to zero is a clue. The tach is electrical , it reads pulses from the ignition system to show how fast the engine is spinning. If the engine is spinning and the tach reads zero then that part of the system has electrical issues. Normally a bad ground as is common for any vehicle as old as our FJs. Turn signals are not part of the ignition system but still electrical. This should be an easy one to trace and fix. And you might find the fix also resolves other electrical issues. Fix the easy stuff first. Get them off the list and work on the next issue.

Where do you think the most likely bad ground would be? Is the ignition module grounded to the frame? Maybe the battery ground?

[FJmonkey]

The best option in my opinion is what Randy at RPM advised. Run a separate ground wire from the the dash to the frame. Another from the triple tree to the frame, very bad should voltage pass through any bearings due to a bad ground. Option 2 is trace all the grounds and test for continuity. Moving and wiggling the wires during the test to better detect marginal/intermittent connections.

[mr blackstock]

G'day,
It's interesting you say the neutral light comes on when you engage the clutch.  Did it do this prior to taking it to the dealer?  If it did, then I think there is a big issue there, if not, then wires could have been re-connected incorrectly by the person working on it, causing such an issue.

I reckon start with the fault you know of, electrical.  It could be a simple issue, or one that existed for ages, perhaps the reason the bike might have been parked up originally?

Download a wiring chart in colour, and start your journey into the mystical realm of electrickery...

good luck, Gareth

[david f]

Thanks for all the good tips. I still have some electrical stuff to work through but the engine dying at 4500 rpm was due to 2 carburetor diaphrams not seated properly in the top grooves. Only 2 slides were working when the throttle was opened. Only 2 cylinders were getting fuel. So much for the mechanic who "cleaned and synced" my carbs. Should old diaphrams be replaced? Is it possible or probable that old diaphrams inhibit performance? Mine appeared pliable but seemed a little small and didn't want to lay in their grooves.

[FJmonkey]

Use a light source and check for holes. Small holes can be filled with liquid electrical tape. Big holes, I would replace with new part. If you have to replace one then consider the condition of the other three for possible full replacement. Otherwise they should be good.

[david f]

Thanks again

[mr blackstock]

G'day,
I replaced my diaphragms years ago, they were filled with tiny pin holes.  I couldn't afford the OEM diaphragms, but I bought some after market ones that I have been using for years for $20 each, I even put some in my XJ.  The material is slightly thicker than the OEM, and this may prevent the slides going WOT.  But over the years I have not noticed any difference.

http://jbmindustries.com/Dimensions.html

anyway, research around, new ones will make a big difference.

cheers, Gareth