Bike wont start after it gets hot.

[Golfwang]

Even if i let the bike run for just 5 minutes i have to wait an hour before she'll start again.
Any suggestions on what to check?
I have a 1980 xs650 with boyer ign, rebuilt engine, perm magnet charging system, new battery, carbs SHOULD be perfect... This shit should work!!

 

[Grinder]

Pretty much have to go back to basics, Is it getting spark,fuel etc. Might want to check the vent in the gas cap to make sure it's open or pop the cap open when it doesn't start.

 

[pumps]

What exactly does it do? Nothing? Or does it crank or what?

 

[Golfwang]

It seems to me like it stops sparking. Starter cranks her just fine, plenty of compression... I don't THINK there's anything wrong with the carbs. I mean damn, she starts like shes anxious to roll when she's cool. She gets that fire in her belly and then she doesn't wanna purr for me. What a cunt! hahaha

 

[gggGary]

Could a poor voltage path to the coils, try a jumper from the battery to the coil hots if that fires it there's your answer. A common fix is a relay that removes all those power robbing wires connectors and switch contacts from the circuit.

 

[Golfwang]

Would the voltage path to the coils "narrow" when the engine warms up? I really don't know I'm a total newbie... as far as I'm concerned the whole electrical system is black magic. I'm wondering if the spark plugs are wrong, or if maybe the boyer ignition unit is somehow the culprit. Any thoughts on those possibilities?

 

[gggGary]

My experience is that a spark that is good enough for a cold engine is often too weak for a warm one. So I tend to agree that you need to go looking for spark. One issue is often poor connections on the 12 volt feed. I notice that boyer is sensitive to low voltage. What do the plugs look like when it won't start?

 

[retiredgentleman]

I agree with gggGary..................you may be losing voltage to the ignition system. If you still have the original fuse panel (glass fuses in clips), it can cause intermittant faults like you are having.Remove it and and replace with automotive blade type fuses, and solder all connections with heat shrink insulation. Even if that is not your problem here, the panel is unreliable.

Along the same line, the kill switch and ignition switch could be high resistance. A bypass as suggested is a good idea.

 

[Golfwang]

Well i already redid the wiring on my bobber and used the blade type fuses. I put a 20amp fuse on the ign unit, and another 20 amp fuse on the coil pack. But I did some digging with the multimeter and found out that im getting 0 volts at the coil pack. But i'm getting 13+ volts to the boyer unit. Think I should order a new unit from mikes?
Though... I can honestly say I FUCKING HATE THIS PIECE OF SHIT BOYER IGNITION!!!
Sorry, but I need to vent... this scooters been pissing me off for weeks now.

 

[Tech7]

The Boyer unit doesn't supply voltage to the coil. Power comes from the ignition switch. Boyer (or any system for that matter) controls the ground side of the coil.

 

[Golfwang]

oh shit... lemme go check that again! lmao
<<<< newbie
(....still hate this boyer pos though! haha)

 

[Tech7]

My Boyer works great. Don't have to deal with mechanical advance stuff. AND, it came on the bike when I bought it!

 

[Golfwang]

OH wait no... I checked it correctly! You confused me with your wiring diagram. I even checked continuity throughout the wires coming off of the unit. There's no connection through hot and ground on the ign box even when I touch the 2 "control" (stator?) wires together. I tried all sorts of voodoo to get that damn multimeter to move! Sound like a fried ign box to anyone smarter then myself?

 

[Golfwang]

Well shit Tech... Send me yours! I wanna ride my scooter already!!

 

[Tech7]

First, do you have 12 volts to the pos side of the coil? Should have 12 volts with ignition on. This has nothing to do with the box. Then, there is a 12 volt source to the Boyer unit, a ground wire to the Boyer unit, and 2 wires to the pickup.

 

[Golfwang]

Yes sir, both the coil and the ign have a good 12v+ feed.
BUT I checked it yet again...
Maybe it's just my imagination but I SWEAR I did this same test earlier...
I took the wires out of the back of the coil and put my multimeter leads in the connectors (the meter is in place of the coil)...
lo and behold, when I turn the key to "on" the needle moves to register some resistance (quite a bit actually) which it did NOT do earlier. I turn the key off and back on again, it registers LESS resistance
hmmm...
I turn it on and off several time and the resistance levels continue to change... whatever!
So I switched the knob from ohms to volts and its reading less then 1 volt. I unconnected the PICKUP wires and touched those ends together... the needle jumps, but is still under 1 volt.
WHY ISN'T THERE 12+?
I have damn near 13 volts on the pos side of BOTH the coil AND the ign unit. By connecting the coil to the blue ign box and I lose 12 volts???

:Edit:
OH and I SWEAR that damn meter wasn't reading anything before. I'm almost certain this ign unit is shorting out from vibration or something.

 

[Tech7]

Your testing this wrong. Leave the coil connected. Set meter to DC volts. Positive lead to backside of the connector on pos side of coil. Start it up and run it till it dies. Is there still 12 volts? What we are trying to do is check the ignition side of the coil. We are not testing the secondary side yet. When troubleshooting, you have to go one step at a time. And, leave your meter OFF of ohms. We don't have any resistance specs anyway. Touching the wires together for the pickup won't do anything either. It's a magnetic pickup, not points. Like I said, we are trying first to see if you are losing power TO the coil FROM the ignition switch.

 

[Tech7]

Another thing I just thought of. What's the battery voltage with the engine running? Boyers don't like to work without a good charging system. Should be at least 13.5 volts.

 

[Golfwang]

Welp, i put a new boyer ign unit in it. She starts every time now! Thanks for the help, you guys.