[sherman_desouza]

My 1979 Bullet with a 500 engine has been running like a champ ever since I fitted the right jets to my Micarb VM28.
I have ridden it about 500 kms with absolutely no issues since I rejetted the carb, installed a power arc CD1 ignition and changed to a modern ignition coil along with a NGK BR8ES plug.

It was really hot yesterday and I rode to my destination for about 40 mins. I turned off the engine, took care of some business for about another 20 mins and returned to the motorcycle and she refused to start. She would fire up but would die instantly when if I opened the throttle even a little bit.
Also I had to wait a couple minutes between kicks for her to fire. If I kept kicking she wouldn't fire.

She finally started like nothing was wrong, after about 20 mins of trying everything. I rode back home with absolutely no issues. She was idling beautifully etc.
Got home, turned her off and couldn't start her again.

I gave up, came back in an hour and the bike is back to being a one kick start.

started no issues this morning, rode her to work, in cooler morning weather. turned her off and she had no issues restarting.

She started easily from cold this afternoon. Rode back home in the afternoon in about 89F weather and once I got home, same issue... she wont start again!!!

let her cool for an hour and she is again a one kick starter!!!

I have no idea where to start looking. I am still a novice at this stuff and dont know how to trouble shoot.

This is not an electrical issue cause she starts when cold.

All the wiring is brand new, battery is brand new and is showing about 12.6V, charging system is fine. Regulator output shows about 14v at 3000 rpm. Ignition coil is made by power arc so is the optically controlled ignition system. Timing has not changed either.

Does anyone know where to start looking?

thanks in advance.

you can see my motorcycle at: https://www.youtube.com/watch?v=9xsPNDiYnp4

[AgentX]

Have had the same issue with a Bosch coil.  Would die when hot.  Apparently it's an issue and the way those coils tend to die.

Obviously you don't have a Bosch, but you shouldn't rule out electrical at this point.  In fact, it'd be my #1 suspect, if you haven't had any issues with fueling or air in the past 500k.  (Nor would I think these things would be so heat-sensitive...)

[sherman_desouza]

Yeah I have contacted power arc if they can shed some light on it.
It does sound like a overheated coil, which would be terrible since I bought it over a year ago but only installed it this year, so warranty is out of the question.

[AgentX]

Well, might be plenty of things other than the coil, but just saying electrical is not to be ruled out.

[High On Octane]

To ME it sounds like classic vapor lock/fuel vaporization.
My old 1958 700 twin would straight boil fuel in the carb on hot Colorado days and would be near impossible to restart if left in the sun more than 20-30 minutes.

What kind of air temps were you experiencing?
And was it parked in direct sunlight on black asphalt?  If so and it was indeed blazing hot, and bike is running flawlessly now, I'm guessing this is what happened.

[sherman_desouza]

Yeah it was about 32C which is 89F I think.
Was parked on aspault....
But today's ride back in the afternoon she was parked in the sun, started just fine... Ran for about 35 mins to get home... Turned her off and tried to restart, nothing. Same issue. Fires if I wait a few mins but won't stay alive.

[High On Octane]

Interesting.  It certainly could be the ignition coil causing problems.  Tho usually when they act up, they will cause misfires when they get hot.  Particularly at higher RPMs.  But, none the less, a hot faulty coil will cause starting problems.

FWIW, the ignition coil for the Thorspark system on my twin failed after about 18 months.

It's easy to test a coil, there are 2 tests: primary and secondary.  Primary you test the ohms between the positive and negative terminals.  Secondary you test between the positive terminal and the spark plug lead.  Not sure what the numbers should be for your coil,  but should be around 3.5 ohms on the secondary reading.

[ERC]

Scottie is right about the coil. It also could be the valves getting to hot not seating properly until it cools off again. Weird but does happen.   ERC

[sherman_desouza]

too many variables
I will start with the coil since it feels like an electrical issue...

[tooseevee]

To ME it sounds like classic vapor lock/fuel vaporization.
My old 1958 700 twin would straight boil fuel in the carb on hot Colorado days and would be near impossible to restart if left in the sun more than 20-30 minutes.

What kind of air temps were you experiencing?
And was it parked in direct sunlight on black asphalt?  If so and it was indeed blazing hot, and bike is running flawlessly now, I'm guessing this is what happened.

     Agree that's a possible. Had a shovelhead once with an S&S and it was built good and the tune was excellent BUT if I tried to go and kick it again after it was shut down really hot, it might not start. If it did not start first kick and I saw that little puff of white vapor, I KNEW it would Never start. I had to walk away for 10 minutes and then it would immediately start one kick.

       I also agree with Sherman about getting the coil out of the equation first.

[sherman_desouza]

I really wonder why the coil would behave that way though... I dont understand the electrical reasons for a coil to perform flawlessly when its cool but then not work when hot, but once started while hot its fine again.
she starts first kick when engine is cold or when the weather is cooler. though i have ridden on hot days this summer and not had any issues.
I am waiting for power arc to get back to me... I want to know if i can use a standard bosch blue coil with their ignition system so I can atleast eliminate if its the coil indeed. dont want to spend more money on their coil if it only lasts such a short time.

[AgentX]

https://www.jalopyjournal.com/forum/threads/can-an-ignition-coil-quit-when-it-gets-hot.824678/

[sherman_desouza]

https://www.jalopyjournal.com/forum/threads/can-an-ignition-coil-quit-when-it-gets-hot.824678/

thanks Alex, but that would mean I have to wait for the coil to cool completely.... the first time this happened it started without me waiting for it to cool completely. and then acted like nothing was wrong even while the environment around the coil was still very hot.

[tooseevee]

https://www.jalopyjournal.com/forum/threads/can-an-ignition-coil-quit-when-it-gets-hot.824678/

         Just to add to the "coils are funny" discussion -

          This is well known throughout the 2CV community also. Most have long ago been replaced by better than stock coils, they being very prone to hot coil problems. I put an epoxy Accel harley coil in mine (along with electronic ignition and a thousand other things).   

         

[sherman_desouza]

         Just to add to the "coils are funny" discussion -

          This is well known throughout the 2CV community also. Most have long ago been replaced by better than stock coils, they being very prone to hot coil problems. I put an epoxy Accel harley coil in mine (along with electronic ignition and a thousand other things).   

         

mine is a brand new modern coil from Power arc. its not a lucas style coil... has a sectioned bobbin and is supposed to be the thing to buy

[cyrusb]

Have you actually checked for spark when this is happening? Wet plug,etc? One easy check can go a long way.

[High On Octane]

Have you actually checked for spark when this is happening? Wet plug,etc? One easy check can go a long way.

+1 Have you done any actual diagnostics yet?

[sherman_desouza]

+1 Have you done any actual diagnostics yet?

checked all wiring, checked for spark, checked for fuel flow, checked battery voltage, checked timing.
the bike runs fine and this has only happened when it is very hot outside.

i took her for a long ride yesterday in about 20 C ambient temp and no issues whatsoever. this is really bizarre.

[sherman_desouza]

Have you actually checked for spark when this is happening? Wet plug,etc? One easy check can go a long way.

yeah i have a nice spark. plug was a bit sooty so might be running a bit rich...

[cyrusb]

O.K, so it has good ignition during the episode. Plug is sooty, but is it wet? Repeated kicks with no starting should leave the plug wet with unburnt fuel. If this is the case you have a lean condition. Is there a MICARB involved here?

[sherman_desouza]

O.K, so it has good ignition during the episode. Plug is sooty, but is it wet? Repeated kicks with no starting should leave the plug wet with unburnt fuel. If this is the case you have a lean condition. Is there a MICARB involved here?

during the episode it would fire if i left it alone for a couple mins but would quickly die as soon as i opened the throttle, and then wouldnt start again till i left her alone for a bit

plug was not wet when i got back home. just sooty.

and yes, its a micarb VM28 with the jets specified by Hitchcock's.

[cyrusb]

It's the carb. What happens next is up to you. I tossed mine in the trash and bought a pwk 30 and have never looked back. You could keep fiddling with jetting etc, but I just bought a better carb (and a cheap one at that). 10000 trouble free miles.

[sherman_desouza]

It's the carb. What happens next is up to you. I tossed mine in the trash and bought a pwk 30 and have never looked back. You could keep fiddling with jetting etc, but I just bought a better carb (and a cheap one at that). 10000 trouble free miles.

yeah it could be the carb because the electrical system looks like it is in good shape.
I was leaning towards the mikuni TM32 anyways so maybe next riding season I will change it to that.

[cyrusb]

One last data point, how is compression during the "no start when hot episode?" A hung up exhaust valve would give a dry plug after many kicks because the cylinder would be breathing through it and not the carb. This would not be  obvious if starting with the comp release as you are never against the compression stroke.

[sherman_desouza]

One last data point, how is compression during the "no start when hot episode?" A hung up exhaust valve would give a dry plug after many kicks because the cylinder would be breathing through it and not the carb. This would not be  obvious if starting with the comp release as you are never against the compression stroke.

Compression is fine and actually very good.

[banjelele]

ERC mentioned the valves. Fortunately that is such an easy thing to check. One bolt and you can remove that little adjustment plate. Give those suckers a spin. If one is too tight it can even be adjusted hot with the pair of wrenches that came with the bike. No need to even burn your fingers. Ask me how I know.