1984 FJ600 intermittent issues

[indymx]

I recently picked up a 1984 FJ600. When I got it #1 and #4 weren't firing. I swapped the connectors to the harness on the coils and the issue followed. No spark on #2 & #3.  Did continuity tests on all of the wires from the coils to the igniter and relay. All tested good. I pulled the connector from the relay (called a flasher relay), found the connector to be mildly corroded. Cleaned it, applied dielectric grease and got spark on all 4.

Went thru the carbs, complete tear down, soak in Berrymans and a trip thru the ultrasonic. All passages in the carbs were then blown out with compressed air. Diaphragms are new, float valves replaced, floats tested and adjusted for proper height and reassembled. I bench sync'd them and re-installed and set the fuel screws at 3 turns out. Sync'd with a fluid gauge once the bike was fired up. Put 4 new plugs in before syncing carbs. Bike has only run 5 minutes with the new plugs installed. They have also been properly gapped. All cylinders are showing 120psi con the compression tester.

So.. the problem I am seeing that brings me to post is that #1 will not fire, intermittently. With a timing light attached to #1 wire, it fires the light normally.  I can verify that it's not firing by looking at the plug and checking the temps on the pipes with a laser temp gun. after a brief run, about 30 seconds or so #1 is about 125F, #2 and #4 are about 175F and #3 is 275F. 

Before I throw any more parts at this bike, does anyone feel (or know for certain) that a coil can fail on just one of the two wires? I can see how it'd still be enough to fire the timing light but not be a good enough spark for proper combustion, but in my experience if a coil fails, both of the cylinders on that coil will exhibit the same problem.

Also, any ideas why the #3 cylinder would run 100 degrees hotter than the rest? That just seems crazy to me. 25 degrees would be understandable, but not 100. I am measuring the temps of the pipes about an inch below the first bend out of the head.

I really hate to think the igniter would be at fault, those little buggers aren't cheap. Plus it seems that if it was failing it'd fail across all of the cylinders, not just one.

Thanks for reading, hope someone can steer me in the right direction on this.

[Pat Conlon]

Correct, if the coil was at fault, then you would have spark problems on both #1 and #4 (assuming that the FJ600 has the same 1-2-4-3 firing order as the FJ1100).

The oem stranded core FJ wires are very durable so I doubt that is the cause...so that just leaves the resistor plug cap. Get a new NGK resistor cap, trim about 1/4" off your oem wire for the new plug cap to bite into fresh wire...and see if that helps.

Re: hot cylinder...check your valve clearances. You might have a tight exhaust valve.

The oem '84/'85 FJ1100 header tubes are double wall construction, so you have to be careful about using them for temp readings. I'm not sure about the same being true on the FJ600 but if it is...
You may have a leak in the inner wall of the tube, causing that tube to read hotter than the others.

Welcome, when you get a chance, head over to the intro. section and tell us about yourself.

Cheers

[indymx]

Thanks for the reply..

I'll check the valve clearances tomorrow..

I also suspected the plug cap being the culprit, I already did cut off 1/4 inch on that wire just to see if that solved it, I'll test further after I get the valves adjusted properly and put new exhaust gaskets in.

I also have to replace the #4 Nut Ring on the pipe.. From what I can see, the only way to do this is cut the pipe and weld it back together. Unless the collar at the end of the pipe is pressed on??? I'm guessing the cut and weld method is more than likely the ticket.

From what I can see, they aren't dual wall pipes.

[mr blackstock]

I had a similar problem with my FJ quite a few months back, I threw a new set of coils at her, new plug caps, even a digital CDI!  All to no avail.  Turned out, if memory serves correct, that the little grey wire running from the coils to the tacho was faulty.  Not sure if the 600 has similar wiring, but it might be worth checking...

cheers, Gareht

[novaraptor]

And, just throwing it out there, it might just be a defective spark plug. Maybe swap it into another hole and see if the problem follows...

[indymx]

I'll be going thru the wiring a little closer, but I can say for certain that it's not the spark plugs.. This is the second set, they are new.

I'm not 100% convinced that the valves are in spec, but I've yet to find a definitive answer on the spec. I think the intakes should be .11 to .15mm but I'm not certain if the exhaust need to be the same as the intakes.

I have to go thru them again to check, but I am pretty sure my #3 intake valve was almost .30mm

I am going to pick up a new set of feelers tomorrow and have another go at it. .30mm seems to be way too huge of a gap. Wondering if there isn't a buildup of carbon on the valve that's holding it open. I have a crappy boroscope I can have a look at it with, not sure if I can get it down far enough to actually see the top side of the valve though.

Whatever I do find, I'll post.

[momodasaint]

i had exact same problem on my fj1100. The solution was to cut the wire from the dash to the cdi box.  This wire is telling the cdi to shut spark to 1 & 4 because it thinks that the bike is redlining.  Very simple to fix, just cut that wire. 

[momodasaint]

mr blackstock said the same thing basically