Cause of weak spark

[gunbunny]

I'm having trouble starting my bike, when I checked the spark it was weak and yellow, The battery seems fine when I checked it, I have electronic ignition and a new Bosch coil. I replaced the spark plug but it's still weak. could it be the spark plug cap or lead? Any ideas?

[AgentX]

Check and clean ring terminals at the coil?  Check/clean any other wiring connectors in line with the ignition?

Check rectifier output?

Check alternator output?

Anything else electrical acting funny?

[RGT]

it could be the lead and cap, some caps have resistance built in, usually the ignition manufacturer will specify what to run, also I understand you don't want to run  a resistor plug and cap...

[gunbunny]

Everything else seems fine with the electrics. When she eventually starts she runs fine and once warmed up she will start first kick.

[ace.cafe]

Battery voltage should be at least 12.8v at rest.
After running, it should be around 13.2v.
If it is 12.5v or less at rest, the battery has problems.

[Vince]

     If you can see the spark, it is good enough. In my experience in the shop, customers complain about spark but it is virtually always something else causing the starting issue. 99% of the time it turns out to be a tight valve or carburetion. .99% it is an engine issue. Check valve adjustment. If the bike is used infrequently or is coming off a winter layover clean the carb and change the gas.

[AgentX]

Vince, good points...personally I'd check points too...condition, gap, advance.

[Blltrdr]

Your battery health is important when running EI. I would take Ace's advise and check that your battery is up to snuff. I would check all connections. Check grounding. Check that your HT wire is fully seated in coil. Make sure your wire connection at points is correct with insulator. Ohm out your HT lead and points lead. Wiggle the leads and look for change. Swap out coil if you still have the original. Swap out condenser with a new or known good one. I am sure it is something simple. Like Vince pointed out, could be mechanical issue and not the spark at all. If your compression seems weak and the bike's been sitting for awhile you might try removing the spark plug and give one or two squirts of oil into the cylinder and then kick it a bit using an old plug to raise it up.  Replace with good plug and try to start again.

Good Luck

[gunbunny]

checked the valves, they were tight so I adjusted them. still hard to start have to check everything else. think it might be a carb problem.