OK, new diagnosis

Did the fuel cap cleaning, ran around normal speeds for about 15 miles, no issues. Came home, let it idle for about another five minutes. Decided to run it out on the highway to check again, same issues. Now it stalled and I tried the open fuel lid, no help. Started it with full choke and it ran at high idle back home. It seems like it may be losing two cylinders as when it was running, it seemed to have some backfire. Now I think it may be a bad coil? It gets hot and stops working? At first start with choke it cranks right up, idles great at about 1200-1500 after a minute or so. Runs around at 40mph no issues, only seems to have this issue at highways speeds, and it starts having that problem within a few minutes of highway speeds. OK guys, help me out here!!!

 

I think it is fuel as described, it is possible the screens for the needle and seat are clogged with crap and not able to pass fuel at the rate required to run at highway speed. Just a thought, you are welcome to ride over and let me take a crack at it.

 

Total generic WAGs: check grounds, check for spark after it acts up, check any micro inline fuel filters or failing petcock, check air intake blockage ... oh and I hate carbs.

 

Could be right with a bad coil, but not sure why running with the choke would help in this situation but these coils are starting to get a bit of age up so anything is possible. You have an old wiring loom, old switchgear, bad contacts in the connectors that heat up and start to fail. All depends on how much time, effort and money you are prepared to throw at it, sometimes there is no quick, easy, straight forward fix, sometimes there is

 

Maybe?

Carbs recently looked over, all checked OK, synched and all. If I rev the engine as it is just sitting, it does not happen. I wish i could "run it over!"

 

I'll check grounds, it seems odd that it happens at certain times though, not sure how the ground could cause the issues I am having but I will try that. Fuel filer is clean, have not looked at air filter, petcock seems OK, checked it with line off and fuel runs well. Yeah, ALSO not a fan of carbs!

 

I'm just guessing, as for the choke, added fuel to the two cylinders that ARE working makes it limp home? I think I'll look for a new coil and see if that helps. Otherwise I am stumped.

 

Spark plugs?

 

What I would try if it were mine, is fit a relay and run nice fresh unmolested power directly to the coils, it is one of the mods the Supersport boys do and anybody that does it is amazed at the starting and how much better the bike runs in general, gets rid of a lot of potential electrical gremlins and then of course they fit CBR coils and that makes a huge difference, can't expect old stuff to perform like new

 

+ 1 for the coil suspicion.
Bad coils play up when hot.
Electrical connection problems are usually when it's cold, not hot.
Do you have a spark check tool?
Very cheap and can narrow down ignition problems quickly.
It doesn't sound like a carb problem to me.

 

Could be CDI problem related to heat or, more likely, pulse generator coil breaking down when hot.

 

Checked spark, all OK, plugs fine and correct ones for the bike. Air filter checks fine, coil wires good connection, plug wires fine, coil connections good, good grounds. Started up today with choke, idles about 1200, revs great. Noticed voltage regulator gets warm, I guess it is supposed to. Maybe that does not send enough voltage out after it gets too hot? Or coil craps out after getting hot?

 

Rick if you keep this running it as 2 topics it is too hard to keep up with what is going on, no different that messing around with spark plugs/ coils/carbs, in the end you have no idea what is going on. Have the carbs been cleaned on this thing?

 

Got it, and yes, carbs have been checked, cleaned, synched etc. I'll get it to a mechanic and get it straightened out.