1983 xj750 Midnight maxim build/project

1983 xj750 Midnight maxim build/project

Hey guys! First post here - not sure if I’m doing it right...

Anyway,

Got this bike as a project, got it running so took it home and dove in. Ride for the first time yesterday - then blew the main fuse and the ignition fuse, replaced those, and started - electrical is back ... good news... kind of.

Problems now,

1. Starter safety relay? Silver relay near starter Solenoid , stays on and vibrates while bike is running? Is that likely wiring problem or need a new relay?

2. Next is blue wire coming out of ignition (one of three) not sure what it’s for but burnt when main fuse blew, could that be the culprit? I spliced it back together and seems to be okay now.

3. battery is newer and should be fine, having it checked tomorrow but trickle says it’s full And my fluke gives good continuity as well 11.7 to 12.4 volts consistently. Dies too fast though, maybe a bad ground somewhere? Suggestions?

4. Getting a chirping sound from right side of engine near intake/boot/carb. Replaced main header seal already so doubtful that’s it. Any ideas?

Sorry to unload so many questions but this is my first build and am loving it, lots to learn....

Thanks in advance!

 

Welcome to the forum, always good to see a new member.

The bike is running well enough to drive and or ride. That is a good thing, normally we have to break down the carbs before they will run right. If this is the issue consider yourself lucky.

As for the electrical system, depending how the bike was stored would be my nest question. I normally go through every connector on the bike to make sure there is no corrosion on the wires. It might look good from the outside but there might be all kinds of the calking looking white and green corrosion in those connectors.

Remove the NEG wire from the battery and then take one connector apart at a time and look at them. Get a small flat tip screw driver or a dental tool and clean any of the corrosion you might see. Putting some dialectic grease on those connectors will help as well. You might just fix your issues that way.

Most of our older bikes also have a fuse box issues, those bus fuse holders normally need to be replaced or have corrosion on them as well. Some of us install a new fuse block and go with the mini fuses that are used now days. That is if you are okay with cutting and soldering a few wires. You have used a multi meter so it sounds like something you should be able to do.

Hope this helps out, more will be along shortly to give even better trouble shooting advice.

 

The starter cutoff (safety) relay should be located under the tank. It should energize and close a set of contacts anytime the bike is in neutral or whenever the clutch is pulled in and the side stand is up. May need some more info on this just to be sure you are identifying the correct relay.

https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

1982-84 XJ750 Maxim and Midnight Maxim models:

Flasher: near the steering headpipe, on right side frame rail, under the right side ignition coil.
Flasher canceller: under the rear of gas tank.
Starter motor solenoid/relay: attached to and behind the battery box.
Starter/Ignition cut-off relay (no color): behind self-canceller, under rear of tank.
Sidestand (kickstand) relay (blue): behind the left frame side cover, on the plastic regulator-rectifier mounting plate.
Headlight relay (yellow): not used.
1982 XJ750 Maxim safety relay single diode: outside the main wiring harness bundle, in the area just behind the fuel tank.
1983-4 XJ750 Maxim Diode block: inside the headlight housing.
Neutral switch: in a hole in the bottom of the crankcase, just "outside" of the oil pan, on the bottom of the engine, up inside a recessed "well".

The burnt blue wire is likely not the culprit unless the wire had chafed to ground. Unfortunately, Yamaha screwed this one up on all the non Atari bikes as they relied on the main fuse to protect the tail / brake circuit, which is what the blue wire does. I would suggest inspecting the tail / brake wires looking for damaged insulation. A good inspection of the actual bulbs and sockets would be good also.

Battery voltage on a charged battery should be at a minimum of 12.6 volts. A DIY load test can be done by measuring the voltage at the battery while the bike is cranking. A good fully charged battery should not drop below 10 volts and preferably is closer to 11 volts.

My recollection on previous post about chirping noises were mostly related to the intake, and specifically the intake manifold boots / gaskets. A bit of caution here though as intake manifold bolts are easily snapped off and can lead down a very undesirable path.

 

Thank you so much TimBox and Rooster 53!

As for relays this bike was CHOPPED before I bought it. So putting everything back where it belongs took some time and maneuvering. I’ve got everything hooked up now aside from tail lights and turn signals. Only thing not working is the neutral light... came on with a new fuse but it’s gone again... kind of strange.

I had the battery tested and it came back totally fine from a local shop in town, so I suspect there’s a ground or something somewhere, it tends to die after about two days (mind you trying to start it and not getting anywhere over and over is likely the culprit. I got it running poorly yesterday, but it slowly dies after about 3-5 minutes of riding, I suspect some cables were pulling since my routing is likely off. Currently working on it so likely have it running again tomorrow at least for a test.

I think I’ve got a vacuum leak in my number 4 cylinder boot - did a carb sync and all the needles were in sync which suggests carb is acting properly, but on top of that the pipe isn’t hot... which makes me wonder if my ignition coil cables are incorrect? Currently I have them at 1-3-2-4... are they supposed to be 1-2-3-4?

Thank you SO much for the advice! It’s helping a lot, also main fuse is now soldered with a standard plastic (car?) fuse.

Anyway I looked at the book but can’t really decipher the correct foreign order. Thoughts?

Cheers!

 

The firing order is 1, 2, 4, 3. The left coil connects to 1 and 4, and the right coil connects to 2 and 3. Since the ignition is a wasted spark sytem the 1 and 4 and 2 and 3 can be swapped without affecting the ignition system.

A large vacuum leak is going to kill that cylinder particularly at idle resulting in a cool pipe for that cylinder.

It's a process to get the bike running where it is a safe and reliable ride and it's best not to trust any information from the previous PO unless they are a trusted source. The following links are lengthy but contain valuable information to get you there.

https://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/

And to identify relays by wire color and markings.

https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

 

Hey Rooster53,

I tried switching them, but plugs 1 and 4 are shallow and plugs 2 and 3 are like deep sockets on the spark plugs. I tried going 1-2-4-3 but cable 3 wont extend to cylinder 4, Furthermore, the engine is deeper where 2 and 3 plug in, which leads me to believe the order is 1-2-3-4 on the engine. Ive got [4-1][3-2] for coil alignment as well. Thoughts?

Thanks again

 

It's not. Rooster gave you correct info. A PO may have cut the plug wires too far back for them to reach, or swapped the coils around on the frame.

 

Im in the process of learning with this bike, iv'e been riding for a little over three years now on an 01 cbr f4i, AKA never have been (or needed to get) too in depth past oil changes and chain tightening. Anyway, that would probably explain why my exhaust pipes coming from the engine get hot on 1 and 2 but 3 and 4 stay cold?

 

From the link provided earlier, which clarifies it a bit more:

https://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

- WHICH COIL IS WHICH?:

"The -82310 part number is the left side ignition coil and is for cylinders #1/4 spark plugs. It has the solid orange (ground) wire and the red-with-white-tracer-stripe (hot) wire input leading to it.

The -82320 part number is the right side coil and is for cylinders #2/3 spark plugs. It has the solid grey (ground) wire and the red-with-white-tracer-stripe (hot) wire input leading to it."

The 1 and 4 plug wires should have the short caps, and the 2 and 3 plug wires should have the long caps. The wires were also originally labeled for the correct cylinder. I am not 100% sure the #1 will reach the #4.

 

Thanks guys!

I think I may have been mixing up firing order and lead order.... I’m attaching a diagram from the book below, is this correct? So in order the leads are 1-2-3-4 aka short cap long cap long cap short cap? Must be a vacuum leak on right side, carb is chirping on right side somewhere as well, likely the culprit

 

#1 will reach to #4 as long as it hasn't been cut back too much.

 

Correct. Firing order is not the same as the lead order, and you have the lead order figured out.

Chirping could be from a loose carb hat (allowing the diaphragm to be a bit loose), a crack in an intake boot (rare for the cracks to go all wht way through though), or a gasket (intake or exhaust).

 

Just took it for a ride, rode through all the gears... I think I like it more than my cbr!

Now the only real issue is when I pull the clutch in, engine revs a ton, as soon as I let it out into gear and get it moving it settles down again. Chirping is faint but still there, it’s almost like it works great when cold but as it warms up the throttle becomes more problematic.