Bike Won't Roll Over... Still

I posted back in October that I couldn't get my bike ('82 XJ750) to turn over. The problem magically went away a few days later and I haven't had an issue till last night. I rolled it a few blocks to a mechanic, the bike turned over in the street but after we pushed it into the shop, nothing. He tried short circuiting the connection over the starter solenoid, bump starting it, and a few other things. We could get it to turn over but no sparks from the plugs.

Any recommendations for things to look at before I start tearing into the wiring harness?

I'll do my best to answer any investigatory questions y'all might have, but I'm really in over my head with this electrical stuff.

 

The first thing to check is the condition of the battery. It needs to be good enough to operate the starter *AND* provide enough juice to create spark at the same time.

It's a drag to start troubleshooting electrical problems only to find out you have a weak battery. Don't ask me how I know.

 

Here's why I'm confused about the battery. We hooked up a jump starting device (don't know the actual name) and still got nothing from it yesterday. Lights came on and dimmed when we tried to start it so its pulling some juice (both with and without the jump starter attached). That's also why we tried the bump start, in case it was the battery. It turned over but very weakly.

 

Maybe some poor/corroded connections?

 

Sometimes this works. Press the starter and wiggle the wires all you can at the connector blocks. Is your fusebox an original Yamaha one? If so change it for blade fuses. Check side stand switch, clutch switch, earth connection at frame, kill switch turn it on and off a few times. Your right switch earth's through the handlebar. Sounds like a bad electrical connection check wires where they pass through the frame anywhere a wire could have damaged insulation.

https://xjbikes.com/forums/threads/xj750-wont-start.4211/

 

Keep the starter button pressed in and then switch the ignition key on a off a few times. See if the bike starts.

 

The first thing you should do is get the factory service Manuel if you do not have one . At least on my 82 XJ550 Manuel they have a great breakdown (electrical schematic) on each electrical section. As Franz says it could be a number of issues with a forty year old bike. You absolutely need these schematics to understand what's going on and how its wired,especially with all the safety relays that they use on these bikes.

 

What exactly happens when you press the starter button with the transmission in neutral?

Has the oil level been checked?

Has the oil filler cap been removed to see if the oil smells like gasoline?

 

Also as per the battery, even if it turns over, the spark system needs to see at least 10volts, so if it drops below that during cranking, youll have issues. Get a multimeter on the battery and see what it does when you crank it. If the bike is cranking over, then all the safety system stuff like the clutch lever being in, and the kickstand switch being in are probably not at fault. However, if you are cranking, but very slow and weak, the battery is where you should check.

 

The headlight dims but that's about it. I did go out on Friday and Saturday (the next two days) and it turned over no problem and even started (choke had to be fully open for it to start). I changed the oil a few months ago and probably need to change it again as its already pretty dark. The bike sat for probably 25 years before I got it so the previous oil was blacker than midnight. I have tried but didn't smell gas in the oil. What would cause that, and why would it keep the engine from even turning over?

 

I do wonder if its a safety switch that has gone bad because it works sometimes and not others. I will check tonight if it starts with the kickstand down. If it does, I'm guessing that's probably the issue?

 

It did indeed start with the kickstand down. Seems like a good place to start my investigation

 

the suggestion might be that fuel tap and float needles have let by petrol/gas which finds it's way via the airbox the CC breather into the oil, also possibly, in to the motor via open intake valves causing 'hydrolock' or in this case 'petrolock'.

 

If there was fuel in the cylinders due to leaky seats and the engine was hydro locked, then there wouldn't be an intermittent problem..... probably something electrical..

 

The kickstand switch is pretty vulnerable to becoming stuck due to road grime. There is a rubber boot on the switch that covers the plunger and the plunger extension. Peel it back from the switch body and use contact cleaner to spray into the switch body as you move the plunger by hand. Follow up with a dry film lubricant. I make that a part of my annual maintenance. If that doesn't solve the problem then you can pull the relay (it has a blue stripe on the connector and is located under the left side-cover under the voltage regulator). If it starts with the relay pulled you either have a bad sidestand switch or a bad relay. Both can be diagnosed with a continuity test.

 

Figured out the problem! There was a corroded connection underneath the tank. Unplugged it and put some grease on and it fired right up. Rode it for the first time last night!

 

Which connection was it, the wire colour?

 

Hang on, this doesn't happen very often. I will just gloat briefly....

 

I can't remember off the top of my head but I believe there were some reds and/or red/whites. Can't remember for sure though.

 

Live feed to the coils.