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Misfire only when sustaining speed.

Started by drivingbored, September 13, 2022, 01:45:55 PM

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drivingbored

September 13, 2022, 01:45:55 PM
Hey all. I have A 1993 Fj1200 ABS. I have had the carbs worked on by rpm and for the past 50 miles, it rode great. However, I had let it sit for two weeks while I replaced some parts and checked my valves. Bike idles and runs great for the most part. However, when riding around between 2k and 5k rpm it acts like it has a misfire. However, if I give it throttle it has no hesitation and has plenty of power. I run 91 non-ethinal and I have airpod filtres and a 4-1 exhaust. I get the carbs tuned by rpm for this set up. I don't this its a fuel delivery issue and I don't think I have a vacuum leak. I replaced my carb boots a while ago. What do y'all think?

Pat Conlon

#1
September 13, 2022, 05:00:55 PM
Do you think it's an electrical misfire?
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

drivingbored

#2
September 13, 2022, 07:18:39 PM
I would hope not. Since I've owned it, its never seen rain and was stored in a temp-controlled airplane hangar. I was thinking it might have something to do with the carb vent as I read that might cause something like this and is the only thing I have messed with. And by messed with I just unplugged it and then plugged it back in when checking values. I have checked it twice now and it's secure and does not have a hole or anything. If it is electrical where should I start? Not good with electronics.

Domino

#3
September 14, 2022, 02:10:35 AM
I had a similar issue on my 1992 Kawa. It turned out the positive battery cable was in a very bad state. I had someone make me a new cable and the problem immediately went away.

drivingbored

#4
September 14, 2022, 08:38:50 AM
I'll check my connections then. Might change the sparkplug wires aswell. They are original anyway.

Pat Conlon

#5
September 14, 2022, 10:42:32 AM
The oem FJ spark plug wires are a stranded stainless steel core wire with a silicone insulation and is a *very durable* wire. If there is a problem with the high voltage side of the ignition system it can be in the resistor caps.
Because this is an intermittent problem, it can be very hard to track down the exact cause.

Avoid the temptation of throwing parts at the problem ($$$) until you know where the problem resides.
Ask me how I know...
I had the same mid rpm range electrical misfire. After new coils, plug wires and caps ($$) I found the problem to be in a dirty Run-Stop switch on my handlebar. The 12v power for the ignition box runs thru this switch.
How I found the problem was to run a temporary jumper wire from the + side of my battery to the 12v input side of the ignition box. I went for a ride and voila! The misfire went away. After that, it was just a matter of checking each component of the 12v circuit until I found the culprit.
A simple disassembly and cleaning of that Run-Stop switch would have saved me hundreds of dollars of un-needed electrical parts.....although I do like my Dyna coils...
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

chiz

#6
September 14, 2022, 02:22:50 PM
Quote from: Pat Conlon on September 14, 2022, 10:42:32 AM
The oem FJ spark plug wires are a stranded stainless steel core wire with a silicone insulation and is a *very durable* wire. If there is a problem with the high voltage side of the ignition system it can be in the resistor caps.
Because this is an intermittent problem, it can be very hard to track down the exact cause.

Avoid the temptation of throwing parts at the problem ($$$) until you know where the problem resides.
Ask me how I know...
I had the same mid rpm range electrical misfire. After new coils, plug wires and caps ($$) I found the problem to be in a dirty Run-Stop switch on my handlebar. The 12v power for the ignition box runs thru this switch.
How I found the problem was to run a temporary jumper wire from the + side of my battery to the 12v input side of the ignition box. I went for a ride and voila! The misfire went away. After that, it was just a matter of checking each component of the 12v circuit until I found the culprit.
A simple disassembly and cleaning of that Run-Stop switch would have saved me hundreds of dollars of un-needed electrical parts.....although I do like my Dyna coils...

Parts cannon I look at a lot of car/truck diagnosis on YT  Lordy some people go through several shops and thousands then they find a Pine Hollow or South Main and they slap their diagnostic tools on the thing......= bad ground, blows my mind.

drivingbored

#7
September 15, 2022, 01:10:09 PM
Thanks for the advice y'all.
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