Running issues, & now not running (very well)

[WileyRiley]

Hi Everyone,

I'm new to the forum in the last three years, but haven't posted anything.

In 2019 I purchased a 1986 FJ1200. The bike had 26000kms and was in good running condition. Last year, I noticed the bike had an idle issue around 2700 rpm where it would sound slightly rough, some missing/stuttering/occasional pop, and couldn't be reproduced above that 2700-3000 rpm. The issue seemed different under load/riding - I noticed that the bike would sometimes result in a jerking/serging symptom at speed (50-100 km/h), and the lights would flicker. In an effort to troubleshoot, I immediately went to fuel systems to rule that out: cleaned the tank, changed the plugs, and inspected the top portion of the carbs to see if there were any tears/holes in the CV diaphragms - they were fine. I then test drove the bike and could not seem to reproduce the issue, and assumed I had a fuel-related issue that was subsequently cleaned out. Thanksgiving weekend I put on nearly 1000 kilometres, and the bike seemed to run fine.

I noticed I had some sticking issues (hard to push the starter button inward) with the starter button last year, so I took the start button/kill switch assembly apart and lightly lubricated the detent bearing on the starter button. It seemed to be much better.

This year, the idle issue returned, and was reproduced at 2700-3000. The jerking/serging symptom under load was also present. I received some advice to verify that the carbs are in fact clean, even though my gut instinct is telling me that this is somehow electrical. I reluctantly removed and cleaned the carbs - they really didn't need "cleaning". I verified that the air and fuel circuits were clear with compressed air. I put them back on the bike and the idle problem was still present. I then went into electrical troubleshooting and first looked at the coils. The resistance values were 2.9 ohms (left side - cylinders 1&4) and 3.1 ohms (right side coil - cylinders 2&3). Based on what I've read from the forums - these values seem to be in the range, but perhaps I'm mistaken. All spark plug wires and boots seem to be close to each other (I have it written down in the garage, just can't recall the values). Spark is present at all four boots when turning over. Battery is in good condition with a resting voltage of around 12.6 volts, 14.4 when running.

Latest development: Whatever gremlins are present, the bike now does not want to run. When starting the bike, It sounds like it's running off of 2 cylinders. It does not sound good, and I don't want to keep trying it in this state.

My next steps in troubleshooting are to:
- Check grounds (main ground lead, and all ground terminations as described in the Haynes Manual wiring diagram)
- I had considered ordering new coils, in case there's some kind of degradation going on...still uncertain about that.
- Investigate charging system, and check resistance values. (Based on reading some of these threads - this could be suspect?)

Apologies for the lengthy post. Looking for suggestions/confirmation/thoughts from the FJ experts with this issue. I'm usually pretty good with troubleshooting, but this one has me a little stumped.

[melloncollie]

Have you checked the plugs?  If its misfiring at idle I'd think you'd be able to read the plugs to figure out which cylinders are misfiring and troubleshoot from there.  Or see which exhaust pipes are hot/cold.  What about a compression test?

FWIW I thought I had a coil issue at one point but it turned out to be fuel issue.  Maybe not related to your problem other than offering up the advice of trying to troubleshoot before throwing parts at it that may not fix the problem.  I will say, I'm no FJ expert just tossing some ideas out there.

[WileyRiley]

Have you checked the plugs?  If its misfiring at idle I'd think you'd be able to read the plugs to figure out which cylinders are misfiring and troubleshoot from there.  Or see which exhaust pipes are hot/cold.  What about a compression test?

FWIW I thought I had a coil issue at one point but it turned out to be fuel issue.  Maybe not related to your problem other than offering up the advice of trying to troubleshoot before throwing parts at it that may not fix the problem.  I will say, I'm no FJ expert just tossing some ideas out there.

I replaced the plugs last fall, but doesn't hurt to check again. I will remove and check this week - thanks for the advice.

[melloncollie]

I saw you replaced them recently, I was thinking more that you may be able to tell which cylinders are misfiring by looking at the plugs.  If there are two that are misfiring from the same coil, maybe the coil is bad or something like wiring leading to that coil is bad and worth looking into.  If you can diagnose the cylinders are misfiring from separate coils I'd reckon your coils are good and you've got a separate issue.  I've never done it but its my understanding you can tell if a cylinder is misfiring by the exhaust pipe temp coming from the cylinder, the misfiring cylinder would be cold/colder than one that is running properly.

When you checked resistance did you check primary and secondary values?  I didn't do an exhaustive search but at a glance this seemed relevant to you:
https://fjowners.com/index.php?topic=11001.msg107960#msg107960

[Pat Conlon]

Assuming your fuel hose is routed correctly.....(see my signature line)

Lights flickering? Yea, sounds electrical to me.....
Check your red plug, I'll bet you a jelly donut it's melted.
https://fjowners.com/index.php?topic=19557.0

Then..
I had a similar problem, I traced it back to a dodgy run/stop rocker switch on the right handlebar.
The 12v power to the ignition box runs from the battery through the fuse box and then thru this switch then down to the ignition box.  I bypassed this run/stop switch by running a temporary jumper wire from the + lead of my battery directly to the ignition box.....and the problem went away....so I knew where to look.

Electrical woes can be maddening, so just take your time, step by step.
I'll bet you another jelly donut that your coils are fine and that your problem resides in a switch or faulty connector.
The FJ coils, stainless steel core plug wires and resistor caps are very robust.

Melloncollie has a good point.....find out which cylinders are misbehaving. I have an IR temp gauge I take readings on the header tubes....find out which are cold and who's hot. Prior to that fancy tool, I used a squirt bottle to see which header tube sizzled and which didn't.
The FJ firing order is 1-2-4-3  and uses a wasted spark, so if you have a bad coil it's going to affect both cylinders 1-4 the same (via left coil) or if the problem is with the right coil (as you sit on the bike) it will affect cylinders 2-3 the same.

Hang in there.   Pat

[WileyRiley]

Thanks, Everyone.

I tested the plugs and found that I had a weak spark in cylinders 2-4. Replaced all with new spark plugs and now it runs like it did before. Weird how they fouled up in a short period of time; I suspect from applying too much choking during start up and diagnosis. 

I then went into the stuttering issue and looked at the "red" connector, as suggested. At first glance it appears to be in good condition but upon closer inspection you can see signs of melting. I noticed that the wires from the alternator to that connectors were also getting quite hot. I cut this connector off and installed automotive connectors and it made a difference on wire temperature, and I can't seem to get it to do that "jerking" issue anymore. The bike still stumbles/stutters through the RPM band (approximately 2-3k) but I'm wondering if that's normal.

I need to replace the valve cover gasket, as it is currently leaking, and I will plan to check valve shims at the same time - not that any of this is related. Once I have that completed, I can daily drive it for a while to see if my problem returns or is fixed.

Thanks for all your input and suggestions - it was very helpful.