You may need to catch us up a bit. Did this occur prior to installing the new ignition, or since?  I’m no expert, but in my simple thinking a mis-fire / cut-out at speed nearly has to be ignition related. The carbs really don’t have the means to do that. My only experience with such a symptom was a faulty module for an Alpha aftermarket ignition, which is very similar to the Wedgetail. 

Coil problems can be tricky.  Hard to discover with static testing.  When I installed fresh coils on my ‘78, I stuck with the current Bosch 6v replacements. I also bought the matching mounting brackets, as the new coils are just a bit larger (I think) than the originals. 

Thoughts....

• Ignition coils need to fall into the Impedance range determined by your EI maker. Have you checked the resistance of the coil's primary winding and made sure they meet Wedgetail's requirements ?

• "Spark plug cables share the same resistance"... which should be Zero since the cables must be metallic wire. 

• Did you try new plug caps ? That's a inexpensive upgrade.

• What plugs are you running and exactly what is the plug number ?

• Did you strobe time the ignition AT HIGH RPM to achieve "full ignition advance" ?

There can be another issue here that should be explored as I have had it happen to me.  Check your electrical connections in all parts of the ignition circuit, from the ignition switch to the coils including the grounds.

I went nuts for a year with at first a hiccup and then miss, then cut out.  Never found the absolute problem but after pulling and cleaning all connections, I am pretty sure it was a ground issue.  Good luck, St.

David, symptoms all have been going on since the wedge tail and carb rebuild. I have priced VW 6 V coils at $40 each as I’ve heard those are an option?

Richard, coil resistance, all acceptable for manufacture with multimeter of course I understand that coils can look differently at speed. Cables are good and the caps are new. I will check plug numbers and yes, timing is at full advance.

Steve, yes, I’ll check all grounds again. Thanks to all of you for great ideas!

Mark

No personal experience, but I’ve heard of iffy kill switches causing faults. They interrupt the 12v circuit to the coils - so kill the ignition. 

Though, since this started with the installation of the ignition, sure makes it suspect. Check all those connections really well. 

Posted by: @mark-creek

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Richard, coil resistance, all acceptable for manufacture with multimeter of course I understand that coils can look differently at speed. Cables are good and the caps are new. I will check plug numbers and yes, timing is at full advance.

The "Devil is in the details" applies here. Early models can have mice nests inside the starter or air filter cover. The cross-over fuel line can get crushed. Needles can get pushed as the slide is offered to the carb body changing the needle position. Needles and needle jets can change jetting due to wear. Are you running a quality grade of "high octane" fuel ? Are you sure there is adequate fuel flow from each petcock ? Air filters can get soaked in oil from breather issues. On and on....

You get the idea !!

Getting back to the connections issue, my friend's shop had a bike come in a while back with similar issues.  The problem was easy to fix, the small wire jumper connection between the coils had corroded and failed.  

LOL, I wish my problem had been so easy to fix, but it is a lesson, old bikes depending upon storage, riding conditions or a number of things age differently.  One bike may have clean as whistle connections, the same model year and make with different history (like my RT, ridden in the salt of winter) may have crud.    

Good luck.  St.

Hi 

I had this problem  and things I went though cured the problem 

check connectors on coils these were loose

Check you have not crimped the wire going from bean can to ignition control unit with front cover  

check gas filters in tank, mine were full of dirt and rust, I also replaced fuel lines mine were 20 years old 

cheers chris 

David

I hadn’t heard of the kill switch issue; I’ll explore.

Richard, has new air filter, lines and cleaned petcoks, needles observed through intake tubes, all ok. Ethanol only!

Steven,

I will definitely double check little wire

Chris, I’ll definitely double check front cover

thanks everyone for helping and staying engaged!

Like any problem, start with the small things and work up.  LOL, I prefer total failure of things versus intermittent or popping and misfiring.  So much easier to diagnose a total failure or at least I find it to be so.  

Yeah, crud could have gotten into the kill switch, give it a shot of contact cleaner just for giggles.  St.

Greetings heads,

I’m going to add my experience regarding a similar issue but on a r75/5 running points.

I chased a similar intermittent stumble/ hesitation/ lose of power for many months. What was causing my problem was a loose condenser mount/ strap that would occasionally ground out against another wire/ connection. Sorry but words are failing me at the moment. If you’re in the front cover it’s worth checking this as well as bending this strap back and away from other connections. Read about this via a Duane Asherman reply to a similar problem on another forum…..

Good luck my friend 

Chappy out

Probably not the issue, but Jeff C. reminded me of another occasion I had when my ‘78 had points. Can’t recall where I purchased the problematic points, but the spring portion of the points would touch the head of the lower point plate mounting screw, temporarily suspending the ignition. That was tough to find. 

David, my friend at his airhead shop had the same thing happen to a customer who had changed his own points.  The bike acted up, the customer got fed up and brought it to the shop to figure out the problem.  Yeah, my friend had a little bit of a time to figure out the problem but found exactly what you did.  St.