79 Special Intermittent Ignition cut out

[79xs1100s]

Hi All,

I know this is a common occurrence and I've done some research already but all these cases are slightly different and have left me without any conclusive answers.

I have owned the bike for 5 years and have never had any ignition troubles. I can ride it fine for approx. 20 miles, then it will start to bog or run on 2 cyl, occasionally waste spark back fire, and then may regain normal running. The Cabrs have been completely rebuilt, sonic cleaned etc so I'm almost certain i've ruled out fuel.

The bike did have the TCI replaced when I crushed the original one (Long story) But it was fine after the new one was installed. The Coils seem to spec out on the resistance measurements @ 1.7-1.8 Ohms at about 70 degrees (cold)

I have OEM Coils, OEM Wires, and Potentially non resistor NGK Plug caps. I have heard that this may cause the TCI to fail. I have checked the pick up wires and the are still fine after being repaired.

I apologize if the Data is all over the place, If anyone has any input that'd be great. I just can't quite afford new coils and don't want to swap them if I don't have to.

Thanks
-Mark

[IanDMacDonald]

Nope Mark, followed-along just fine. Going with the party line, I'd suspect your pickup-coil wires. Remove your left-side ignition cover, and give each wire a tug to check for a broken wire. If you find nothing obvious, measure your wires for continuity. Pretty common issue with the bikes due to the mechanical advance moving the wires. Easy fix is multi-meter wire leads from your favorite hardware store.

[79xs1100s]

Hi Ian,

I checked the pick up wires and they were broken a few weeks ago. After I fixed them everything seemed fine and dandy. then I went on a longer ride and had the same trouble on the way home. I rechecked the wires and all of the solder joints are still intact, I will measure the continuity just to be safe and try again.

I was leaning toward a heat related electrical fault because it only happens once it gets hot.

[IanDMacDonald]

Well, depending on where you soldered them . . . Solder does not like to be bent very much.

[79xs1100s]

I soldered in a few extensions of wire. After re inspecting the wires I repaired, there is no separation in the wires which had previously been cracked

[motoman]

My wanna unscrew the fuse panel on right side,(should be replaced with blade type panel if not already done) unplug all five connectore back behind there, clean connections with electrical cleaner or deoxit, put a little dielectic grease on connectors and plug back in.

[79xs1100s]

Ok,

Fuse panel has been updated with the kit from here. I will check the fuse connections

[IanDMacDonald]

I know you checked your coils, but is there a possibility that your wires or coils are cracked? I can't state 100% that it's electrical, but I wonder once your coils get hot, they crap-out on you. Kind of like a dealership, trying to replicate the issue will definitely allow you to isolate your issue. Wiggling your wires while the tank is off, etc.

[79xs1100s]

Thanks for all of the help thus far Ian, I feel the same way about trying to replicate the issue, I keep having to try a few things and then retest to try and try to rule out things. I had seen a few similar threads regarding coils and heat that would fail internally once hot. Albeit rare, I haven't ruled out that possibility. I will likely try and splice in a new section of pick wires and check the resistance at the tci to check that off the list

[thumperjsa]

Best way to help diagnose it is when it occurs, find out which cylinders are colder than the others. I had an issue with fuel starvation which caused 2 cylinders to stop getting hot. Easiest way to check is spray water on the headers. All four should be getting nearly equal as hot.

As others have mentioned PU coils could certainly do this as well. But if you lose a pair that don't have common spark lines, you could be chasing a ghost and it be fuel starvation.

[jetmechmarty]

Have you done anything else to the bike? Mine would run on 2 cylinders, then no cylinders after I replaced my fuel cap seal. It was fine for 35 miles before it ran out of gas.

How confident are you in your soldering skills? Joining those wires with solder is challenging at best. Doing a proper job takes a special talent.

[79xs1100s]

Funny you mention the tank seal, because i did change that from another cap I got that had an almost new seal and it was soon after I started have this trouble. Not right away, but within a few weeks. could It be vapor locking? I am pretty confident the solder joints are holding continuity. I will try to get a meter on it tonight.

Thanks again everyone

[jetmechmarty]

Regarding the cap, it's not really vapor lock. There is a filter in the vent of the cap and it is rotten and plugging the vent hole. I cut out a tiny piece of scotchbrite pad to replace mine. Your replacement seal works and air can't fill the void in the tank, so the fuel won't drain into the carburetors.

[79xs1100s]

This seems like something consider eh?

[79xs1100s]

Update from tonight: I road the bike about 3 miles (1 mile on the Hwy at about 85-90mph with no fault replication. Came home I cleaned all of the connections at and around the fuse block, made a "filter element" for the gas cap vent and cut back and re threaded my 2 & 3 plug boots which seemed questionable. If I can ride it again tomorrow I will try to put 30+ miles and see if I can trip the symptoms again.