plugs are black after 8 km

I have the bike running, my only problem is after about 8 km the big starts boggin down sounds like it is only running on a couple of cyclinders... than she dies. Pull the plugs and there BLACK!!!

i took the carbs apart and cant remember the main jet size. I am guessing that is my problem..... too much fuel.

Does any one know the standard jet size to a 84 maxim 750.

Just asking so if some one knows i don't have to rip the whole thing apart just yet.

 

Mains are 120 ' s Nice looking bike ! Also the mains thread into the center emulsion tubes, and one of the books mixes up the position with the next jet over.
Also set the floats with a clear tube from the drain. It's best to see a picture of the procedure.
polish your float pivot pins, and the part of the float they slide into.
Set your pilot jets 2 1/2 turns out to start.
make sure your choke/enrichment circuit shuts completely off !!!
New air filter. Hope this helps you !

 

I've been having the same problem as you are. I am willing to bet that you have a float that is getting stuck, or you have an ignition problem. The float getting stuck open allows too much fuel to spill out of the carb or carbs on the intake side, and it makes all the carbs run extremely rich until it bogs itself down and dies. Or the ignition problem causes the same thing by allowing to much unburned fuel to build up.

You can check for the stuck floats by removing the air filter and looking at the intake side of the carbs while the bike is running. If your float(s) are/is stuck, you will see fuel dribbling out of the intake side of whichever carb(s) has the stuck float(s). For the ignition troubleshooting, you need a good manual and a multimeter.

 

The bike looks very nice so I presume it's had all the internals done as well.

Must be running very very rich if the plugs are black after a short time.

I had the same problem aroundd 12 months ago but in my case it was an old and neglected engine - I replaced the rings, polished up the pistons, honed the cylinder sleeves and put it all back together.

I've had the same plugs (NGK BPR6ES - a little warmer than the recommended standard BPR8ES - in for nearly 12 months (too long I know but she still starts up on these winter mornings). Will be doing a major service this weekend and will replace the plugs with 6's but will change in summer to the cooler 8's.

 

Excellent... thanks all for the replies... i'll see what happens after i try some or your trouble shooting.