Bad gas or something electrical?

[alke46]

Wasn't sure where to post this but I think this is the right place.

Was out riding some gently sweeping curves today and things were going well until the main fuse (15 amp) blew out. Changed it and made my way into town for a bite of lunch and figured I might as well re-fuel since I had less than 60 miles to go until empty.

After refueling and taking off, about 65 miles later and the bike started spitting and sputtering then jerking like it was running out of gas. This went on for several miles before it cleared up and resumed running fine. That didn't last long and it was back to misfiring, to the point of extreme power loss and the nearest town was 15 miles away. The last 12 miles I did not think I was going to make it. WOT and using 4th gear then 3rd gear I was not able to get above 4,000 rpm and barely able to maintain 45 mph.

So I got into town and topped off the tank with premium as that was all I could get without ethanol. The bike then started running like a champ and I was sure that it was just bad gas on previous fill up.

I'm now 75 miles from home and the amount of misfiring is just crazy. Occasionally it will run well then the next several miles it struggles to run the speed limit. I would just pull over to the shoulder to let traffic pass but when I went through some small towns with stop lights or signs, it would run ok as long as I kept the throttle active. When taking off in 1st gear then upshifting to 2nd and 3rd acting like a drag racer, it ran OK, then into 4th and add an incline and it would fall flat on it's face again. That was a long 75 miles trying to get home.

Sorry for the long post but I just wanted to get this out there so I could think of something else to do. Results of any diagnosis will be reported here. Stay tuned.

[Brendan W]

Find why the fuse blew and you most likely have found the problem. Chafing at the steering stem is worth a look. Check what voltage you have at the coil supply.
Check the exhaust headers to see if it's a one coil only thing.
Check the new fuse for a hot end. There is a lot of junk out there with cracked solder under the end caps.
Check the charging output as well.

[steve murdoch]

Agree with Brendan that having blown a fuse it is probably an electrical issue but did the sputtering start after you ran out of gas?
Maybe running it dry the crud in the bottom of the tank has made it into the petcock screen or into the carbs?

[bwringer]

Agreed; could be a two-fer, but your first priority is to track down why that fuse went blooey. Fuses aren't consumables.

Intermittent electrical issues aren't really fun, but there are only a limited number of wires, connectors, and devices that could be involved.

You'll need to put a load on the circuits to properly test them; oftentimes intermittent circuits test fine for continuity, but there's only one strand of corroded wire still hanging on. Under load, they heat up and act as a resistor, causing the components to stop working. By the time you pull over, the bad bit cools off and tests OK, and may work again for a while. I use a headlight or turn signal bulb to load test circuits.

Anyway, these overheated bits then often cause shorts and blow fuses because they melt through the insulation. When the bike goes over a bump or the handlebars move and flex the wiring bundle, they make contact with something else or the frame and pop a fuse. You're looking for something burned or overheated. And of course corrosion as well. A more subtle sign is connectors that aren't tight, where the metal has worn out or gotten loose from overheating, repeated use, corrosion, or damage.

Two "hot spots" for intermittents are deep inside the harness leading to the handlebars where it flexes and in the fusebox.

There are several spots inside the harness where two or more wires are clipped together with a little crimp clip, and I've found that these sometimes fail where the harness flexes, even on modern bikes.

And of course on vintage bikes, pull the fusebox out and take a good hard look; pop the back off and look for corrosion, and check each fuse clip or connector for looseness, overheating, and corrosion. Get a good look at every millimeter of the current path.

[alke46]

Thanks for the replies. It appears I have a lot of work ahead to get to the bottom of this issue.

I have other things to do before I can devote time for checking the problems out but I will post anything as I find it.

[alke46]

Find why the fuse blew and you most likely have found the problem. Chafing at the steering stem is worth a look. Check what voltage you have at the coil supply.
Check the exhaust headers to see if it's a one coil only thing.
Check the new fuse for a hot end. There is a lot of junk out there with cracked solder under the end caps.
Check the charging output as well.

Wouldn't this issue cause the replaced fuse to also blow? Just asking because I usually don't know what I don't know.

[alke46]

Agree with Brendan that having blown a fuse it is probably an electrical issue but did the sputtering start after you ran out of gas?
Maybe running it dry the crud in the bottom of the tank has made it into the petcock screen or into the carbs?

After running out of gas I was as able to go trouble free for nearly 100 miles until the fuse blow out.
After replacement fuse was installed, I went another 15 miles more of less then topped off the tank with the suspect bad gas. Even then I traveled another 65 miles before the trouble appeared.

[Brendan W]

Wouldn't this issue cause the replaced fuse to also blow? Just asking because I usually don't know what I don't know.

As Brian said, harness failures internally are not always binary.They may only show at certain conditions of load and or steering movement.
What R/R have you got? A failing rectifier could provide pathways to ground.
What ignition system have you got? I'm sure someone posted recently about some types not liking high voltages.
Start with a cold battery measurement and do charging tests. Without these as foundation, electrical troubleshooting will be hit and miss.

[alke46]

As Brian said, harness failures internally are not always binary.They may only show at certain conditions of load and or steering movement.
What R/R have you got? A failing rectifier could provide pathways to ground.
What ignition system have you got? I'm sure someone posted recently about some types not liking high voltages.
Start with a cold battery measurement and do charging tests. Without these as foundation, electrical troubleshooting will be hit and miss.

The current R/R is one of the honda units that was being provided by member Duaneage. It has served me well since around 2009. During yesterday's ride the volt meter was reading 14.5 -- 14.65 at sustained rpms of 4-5k Seems ok doesn't it?

I'm running a dyna 3-2 electronic with Accel coils. Been on the bike about 3 years.

Battery is a brand new Motobatt AGM just installed in early May.

[Big T]

The first thing I'd do is to pull the fuse box and look at the back. These fuse boxes are prone to over heating and melting the solder connections.

I had to track down why my main fuse was blowing and found my ignition switch had corroded and I as causing a voltage drop to the other 3 circuits

[bwringer]

[/B][/I]

The current R/R is one of the honda units that was being provided by member Duaneage. It has served me well since around 2009. During yesterday's ride the volt meter was reading 14.5 -- 14.65 at sustained rpms of 4-5k Seems ok doesn't it?

I'm running a dyna 3-2 electronic with Accel coils. Been on the bike about 3 years.

Battery is a brand new Motobatt AGM just installed in early May.

Yep, those all sound good.



Basically, it looks like you're chasing an intermittent electrical fault. In other words, you definitely have an intermittent electrical problem (or problems), but you only suspect a fuel issue.

So the logical thing to do is to track down the electrical issue(s) then see where you are. I don't envy you... intermittent faults, especially when they're infrequent, are a giant pain.

Too bad you're 600 miles away!

[alke46]

Yep, those all sound good.



Basically, it looks like you're chasing an intermittent electrical fault. In other words, you definitely have an intermittent electrical problem (or problems), but you only suspect a fuel issue.

So the logical thing to do is to track down the electrical issue(s) then see where you are. I don't envy you... intermittent faults, especially when they're infrequent, are a giant pain.

Too bad you're 600 miles away!

As you know Brian, I do have a trailer and I can be in Indy tomorrow. What time does your shop open?

[Brendan W]

Those numbers sound reasonable to me as well.
Grabbing fist-fulls of harness and shaking can help find the general area of concern.
Top of my list would be the steering stem the fusebox and it's tail and the plugs for the left and right bar switches.
They may originally have had metal ties to the spine under the tank but have lost them to corrosion and the plugs suffered heat damage.

[Gorminrider]

Blowing the main fuse suggests trouble between battery and key-switch(red wire) and also back to the fuse box (Orange wire). The R/R also connects to the red wire but seems to be functioning- it is anyways protected by semiconductors from a short you are describing...

Your other circuits divide from the orange wire at the fuse box to power light, horn, signals, ignition etc which have their own fuses of a lesser rating. This is so they "blow" before the Main fuse if there is trouble on their particular circuit. The wires that leave the fuse box for the various "circuits" are orange with coloured stripes...if fused correctly at 10 amps, it seems unlikely you will find the short on any of those circuits....

ALSO look closely at the auxiliary circuit if you are using it...this also need be fused at a lower amperage than main...

Look closely at any red wire and the orange too. You might have something flopping around near the battery, solenoid posts or key switch or...? that is causing and intermittent short to the frame /ground of the red or orange wires.

[Rob S.]

Grabbing fist-fulls of harness and shaking can help find the general area of concern.
Top of my list would be the steering stem...

I bought a bracket to move my CB350's key up from atop the engine to the middle of the dash, as was becoming fashionable in the mid '70's. The switch couldn't withstand the steering motion.