Hi all,

I’m hoping someone here can point me in the right direction, since Biketoberfest is less than a week away, and my ride is not cooperating.
I have an almost completely stock 1975 FLH

The bits that aren’t stock are:
Keihin Butterfly carb (I know, I know get an S&S, but you know this carb has done a nice job for me)

Dual plugged single fire with the Dynatek S ignition system

Different exhaust, I think it’s off a sporty or something, it has the baffles knocked out so that it has a little bark.

Last week, I started having an issue where it would cut out at higher RPMs if I held it there. I first noticed it on the Highway doing about 65mph. Consistent throttle it would die, and pick back up 10 seconds later. I really thought it was starving for fuel. It was consistent no matter the gear, so if I held it at a higher rpm in 3rd I’d get the same result. It would pick back up no matter if I released the throttle, or held it in position about 10 seconds later. I was only able to maintain about 55 or 60 mph. I pulled the gas cap while riding to see if I had a vent issue, but no joy.

So I thought fuel. I drained the tank, pulled and replaced the fuel line and filter. Cleaned the petcock screen, and valve. No issues found, In fact it drained 4 gallons through the fuel filter and line into a can in about 5 or 6 minutes, So I have a good flow rate. In any case it’s all new now. I pulled the carb dropped the bowl, cleaned it, sprayed some carb cleaner through the jets and removed the float and valve and cleaned that. Everything looked good, there was a little sediment in the bowl, but not much. I put it all back together with fresh gas and ran it.

It starts off great, runs good, idles normally, but as soon as it heats up it starts to die, I have to blip the throttle to keep it going and the hotter it gets it eventually won’t stay running. When it started to die I shot some starter fluid in the carb to see if it would run with an alternate fuel source, but no go. It’s totally related to how hot the bike is. So in my mind I’ve eliminated the fuel system. Not to mention I can see the fuel flowing from the jets even when the bike is dying. If I let it cool off for 15 min I can restart and repeat the process.

So I thought, ok, if it’s not fuel it must be fire.
I Replaced the plugs. They were older, but a nice sandy color. My mixture has been good. So new plugs. I measured the voltage at the top of the coil. Nice 12.5 volts. At the bottom of the coil it varies from 2.5ish volts to about 5 volts while running. I’m not sure if this is normal, but it seems right. Start and run, No change. So I started to think, ok, maybe the dynatek is crapping out once it heats back up. I’m running out of ideas. I have the old points plate, so I pull the dynatek and return to the stock points setup using one of the dynatek coils and a dual fire setup (Both plugs firing at the same time) Now granted the points and condenser are old, but they look clean and the bike fired right up, and had no change. When it gets hot it dies.
I read somewhere that the main circuit breaker will start to cut out when it gets old so I put a meter on it and ran the bike, I don’t see where it’s dropping out. Solid voltage. To eliminate it I decided to feed the coil directly from the battery, but it doesn’t make any difference. When it gets hot it dies.

So at this point I have some theories that I want to run past you.
I’m going to go pick up a new set of points and condenser, just because the ones I installed are at least 10 years old, although honestly I don’t think it will make any difference, but they are cheap and I want to eliminate possibilities. Since removing the dynatek and installing the points ignition resulted in no change I think I could reinstall the Dynatek, as in my mind it has been eliminated as the problem, but I’m more familiar with the points, so I’ll leave it in for now.

Possibilities

1. It could be the coil. I ran the points ignition using one of the Dynatek 5 ohm coils (Actually 5.5 ohm). It seems unlikely that both Dyna coils would fail at the same time. I also have the old coil that was on the bike originally. That’s an easy swap. Since I’ve swapped it to points I’ve only tried to run it with one of the dynatek coils. I also have the other dynatek coil I could try.

2. Sparkplug wires. Could be I guess. They look fine. I don’t get zapped when I hold them and run the bike, but maybe. I hate to just throw parts at it, but I’m really running out of ideas.

3. The other thought that occurred to me is that maybe the pushrods are out of adjustment, and not letting the valves close when it gets hot. I have never adjusted them. I think it has hydraulic lifters, but to be honest I’m not sure. It seems to me if this were the case I would have a lot of backfiring out of the pipes, but I don’t, so this might be in the wrong direction.

Beyond these three ideas I have no idea what else to do. Any ideas would be much appreciated!

 

Don't forget to inspect the advance unit, those are notorious for causing misfire, dying and backfire.

 

I did inspect it when I pulled the dynatek, Seemed to be working correctly.

 

I had a very similar issue, though not on a shovel, actually not even a harley. When I bought a used Honda VT1100 about 10 years ago it was displaying a lot of the same symptoms. After weeks of chasing it down, it turned out to be the main fuse off the battery had been replaced with the smaller style blade fuse, as opposed to the larger one it had originally come with. When the bike would get hot, the blades would arc, and cause the legs on the fuse to not make connection

Now of course I don’t think you have the same problem, but I do think you may have an intermittent connection some place. Check your other electronics when this starts happening. Are turn signals working? Headlight going dim? Things like that.

Checking resistence, continuity, etc is fine when cold, but have you tried when the bike is at the temperature it is exhibiting this behavior at?

i would start at the battery and chase every down stream connection to assure proper contact. It doesn’t cost anything, is fairly easy, and doesn’t take much longer than an evening after work.

 

No doubt, certainly it is an older bike and an intermittent connection can cause really weird issues. Most of my testing has been at temperature, but I wasn't really looking at the auxiliary systems. When I work on it tonight I'll check to see if anything else is dying when it starts cutting out. Thanks for the idea.

 

The instructions on my DynaS single fire says to never leave the key on for more than 5 minutes without starting the bike because it will damage the ignition.
Not sure why or if it is true

Anyway... I had an issue on my shovel FXR, it would quit running, usually on the interstate, letting the throttle off would usually fix it but the dynamics continuously changed slightly... it ended up being the wire that powers the coil with 12v was slowly breaking internally.... so the bike would run again if I shuffled the wires around if It happened while riding. Once I found what it was, I replace a section of the wire with new one and all good

 

check the main 30 amp circuit breaker and all the 15 amp breakers. they get weak from corrosion over time and will cause problems like you have.

 

I measured the resistance on all three coils that I have.
All were 5.3 to 5.5 ohms on the primary, 18.28k ohms on the secondary and open between the primary and the secondary.

I resisted the urge to install all new parts at once, since I'd rather know what fixed it. I decided to start with the condenser, using the same coil I have been using.

It fired right up and ran perfect.

Originally I didn't think that swapping in the points had fixed the issue, but now I think that it did, it's just that I had swapped in bad parts for bad parts.

The funny thing is that I've done all of the tests recommended by Dynatek on their system, and I can't find anything wrong with that either.

After Biketoberfest I'll probably swap it back in just to confirm it's actually bad.

Anyway I just wanted to thank you guys for the ideas and help.

 

Could still be bad look inside the housing and on the back of the Dyna plate to see if there's any signs of the being hit or rubbing, also any rust trails. Try to wiggle one of the flyweights , if they jiggle around on the post it's junk. Pick an All ***** or one the higher end units with the bearing and big washer to hold the weights in place, does make a difference.

Have you leak checked the intake while running yet ? Fire it up and give a shot or 2 of brake clean on the intake clamps and the flange to carb area, she stumbles you found the problem.

 

Ignition could be shorting after hot. My buddy's bike did this. Pulled the ignition cover off and kept cool air on it while running and worked fine. Removed air and within a minute dies