Starting issues (hot)

[FFGO]

I have a persistent but intermittent starting problem.
1984 FJ1100. The bike usually fires up right away when cold. Sometimes on the second crank after the vacuum has allowed fuel into the carbs. I'll run down the hill and do some errands in town, stop and go traffic. On one of the stops it won't fire up right away and it seems like I only get 2-3 tries and then the battery is too low to get a good crank. If I put some cables and a booster battery on it, the bike will flash up immediately.
I bought the battery last year. Plain Jane lead acid. I went through an issue with the alternator last year but that's sorted. Do I need a battery with better CCA? Should I run relays to the coils?
What do I need to fix this unreliability?

[Pat Conlon]

Could it be that your starting problem isn't electrical related, but fuel?
 I suspect your fuel petcock is failing.
Take the petcock vacuum line off at the intake manifold, clean the end of the hose, and suck on it...can you draw air? (You shouldn't) while sucking on the hose put your tongue on the opening of the hose, does it hold a vacuum? (It should)

[FFGO]

Thanks Pat. I'll check it out tomorrow.
It does seem like the battery gets weak, but the next stop/start it will be fine. I should definitively eliminate the possibility of the problem being a vacuum/fuel issue.

[Meltdown480]

I also have a similar issue. Starts cold on choke fine, will drive 15 min to gym in 100 degree weather. Then when I get back on an hour later wont start even with full choke until I give it throttle. Have rebuilt carbs and a new rpm petcock

[Pat Conlon]

For ALL FJ's with vacuum petcocks ('84-87)
Double check to make sure your fuel line is routed correctly.
 The oem fuel lines get soft when hot and can pinch off fuel flow if routed incorrectly.
The correct routing looks counter intuitive...still, follow it.

See my signature line.

[FFGO]

I took the petcock apart, and all seemed good. Fragile little unit, I could see how it could easily get hung up.
Yes, I'm always diligent about the fuel line routing. Yamaha felt a label was necessary so I've always felt it must mean something.
We've had company over the weekend so I haven't tried it out since. See what happens this week. 
Thanks for the help.

[FJmonkey]

On my 86' I found cracking the throttle open just a little when hot cranking helped. A 4 brush starter has fixed this problem for many as well.

[FFGO]

After some more riding I feel I've narrowed down the issue. I think that a lot of the "in town" riding just doesn't spin the alternator enough to keep the battery in a full charge state. Too much idling at stop lights etc. Since realizing this I haven't had a problem until yesterday. There was a bad accident on the highway and traffic was backed up and rerouted. The bike started to get hot and then died. I pulled over and let things cool off. I had just returned from sort ride to the next town ~100kms and I had been using the grip heaters. I forgot the heaters when I got in the traffic jam and they quickly sucked the life out of the battery. I think a good battery with lots of capacity should fix the issue. I'm a cheap ass bastard so I'll probably try and mind the discharge issue and replace the battery when it reaches its end of life. Haha.

[Pat Conlon]

Yep, a weak battery causes all kinds of weird symptoms.
Turn up your idle speed to 1,000 or 1,100 rpm, helps a bit with battery charging.
Speaking about battery charging, check your RED PLUG https://fjowners.com/index.php?topic=19557.0

 If your bike gets hot often realize that the stock FJ carb jetting is on the lean side (lean engines run hotter)
Re-jetting your carbs will richen up the fuel/air mixture and your engine will run cooler.
Suggest increasing your pilot jets from #37.5 to #40 or #42.5...shim your jet needle 1/2 step and bump your mains up to #117.5.

Cheers

Pat