XJ550 Starting problems

Hi

I picked up a (modified) XJ550 (4V8, '81) last year. I got it with the intention of working on it myself, which is probably a good thing since it has some issues. The biggest one was the engine stalling when downshifting or idling. Got that solved by having the carbs rebuild by someone. I also changed the spark plugs and oil filter (gotta start somewhere).

The second major problem is the bike often won't start - especially when cold or after standing for a while. It cranks but the engine won't fire up. After reading up on some of the threads, I checked the battery voltage. I had it on a loader till yesterday and measured the charge this evening: 12.85 V. When cranking over the voltage dropped to about 10.5 V. I then started the bike and measured again and hit 13.1 V at about 2000 RPM.

I read here the the operating charge should be around 14.5. A slowly draining battery would explain why it won't start after standing or cold. Any recommendations on what to do or check?

I also plan on installing a battery isolator switch, btw.

TIA.

 

Check the chemistry of the battery cells with a hydrometer or a test stick. Surface voltage on the plates may show 12V but the plates may be heavily sulfated causing there to be only surface voltage with no deep charge available.

 

try setting the petcock to prime for 5 seconds before starting.

voltage dropping to 10.5 volts is very close to the no start threshold.
indicative of bad battery or failing starter

your charging system is low as well. ohm the brushes or do a visual inspection for length and clean copper rings the brushes ride on


you will find your charging system specs in this link
The Ultimate Relay, Switch, Sensor, and Diodes Guide

 

Old bike unknown history, starts fine when warm - valve clearances.

 

I may be wrong but if it was a valve clearance issue it would be running like crap even after a carb rebuild. Valve sealing will cause a hard start but I still suspect it's the battery. The charging system puts just enough surface voltage on the plates to let you re-start it within several hours. After that, the voltage dissipates on it's own due to the lead sulfate on the plates. Very indicative of a heavily sulfated wet-cell battery.

 

If you want to eliminate chemistry battery issues consider getting a LiFe replacement battery. They will last 5x longer than these tiny lead acids and will provide a ton more cranking power in the same size case.

Example: 210CCA versus about 100CCA for basic wet-cell and 1/5 the weight
https://www.bikebandit.com/aftermar...-lifepo4-lfx-battery-lfx14a5/p/38889?m=147107

 

Thanks for the feedback, everyone. I guess I'll be picking up a new battery tomorrow and see how it goes.

Checking the Valve clearances is on my to-do list, as soon as I find a decent how-to.

 

I would just put a high-rate charger, or jumper pack, on it to test the starting before you spend more on a new battery just yet. Disconnect the battery if you use a jumper pack.

 

this is what you are looking for
Bigfitz's AIRHEAD VALVE ADJUSTMENT with Pics - parts I & II

 

The battery was connected to a drip charger and that read the battery as full. After trying to start it a couple of times, it indicated the battery was now at level 3 (out of 7). So yeah, it looks like the battery is a goner.
After a lot of fiddling and removing stuff - the PO apparently wasn't to fixated on accessibility - I got it out and I'll be getting a new one tomorrow. I'll see what charge it still has tomorrow at work (I don't have a multimeter yet).

Thank you, friend. I'm sure this will come in very handy when I do this!