Power to coils, but no spark @ plugs

I have finally started to tinker on my 82 XJ750. After going thru the wiring, and finding the fuse panel rusted, I cleaned and got power thru the fuse box. I am not getting any fire to the plugs, but I am getting good power to the coils. Any ideas???

 

my guess would be the connection from the coil to the plug , they tend to get corroded , check for voltage coming off the coils to the plug wires

 

One of your interlock systems has the TCI box shut down.

Locate and unplug the "safety relay" as a temporary troubleshooting aid.

 

Where would I find the safety relay??

 

if you've got power at the coils you should be able to see if the voltage fluctuates. the voltage has to shut off and on for the coil to produce spark. if it stays on then the coil can't do it's job.

think of the old days when cars and motorcycles had points. when the points were closed. power flowed through the coil and back to ground. when the points opened. power stopped flowing through the coil. when the power stops the voltage created inside the primary windings would collapse into the secondary windings and down through the coil wire and into the plugs.

the pickup located inside the motor is the off/on switch. but like the other posts suggests. the tci or other switches could be your problem. safety kill switch, kickstand switch, neutral switch. whatever the bike has.
you have to have power to the coil and you have to have a ground connection from the coil. AND, a signal that shuts the power supply off and on.

you should be able to supply power by hand to the coil. disconnect the power and touch the power connection by hand. when you break the connection you should see a spark.

 

im havin kinda the same prob. i just bought a 1980 650. the guy i got it from was having electrical problems so he started messin with it and was way over his head. he finally gave up and sold it to me cheap but with spaghetti wires. it had nuthin at the start button. i went round the safety stuff, still nuthin. i finally tracked it down to a bad solenoid. i changed it and got juice to the button but no spark. coils and pickups seem to be ok on the ohm meter. i kinda guessed it was the icu but not 100% sure. i bought a guaranteed used one (for more than i paid for the bike) but i don't want to plug it in only to have it instantly fry. any thought would be appreciated thanks all

 

If the Bike has an Original Fuse Panel ... it's possible that the Fuse Panel is part and parcel of the Electrical Problems.

Guarantee that the Circuits protected by the Fuse Panel are actually being powered by replacing the Fuse Panel with a 4 -to- 6 Circuit Modern Fuse Panel.

Once you're guaranteed that you got juice.
Locate the Safety Relay.
Unplug the Relay ... Put the bike in Neutral ... Test for Spark.

The Odds that you have two bad coils are pretty high.
But, ... it happens.

 

What he needs is somebody with a 750 Maxim to tell him where the safety relay is. I only have 550/650 factory books, and the 650/750 Haynes wasn't any help.

 

Look on pages 235 and 236 of the Haynes. The two pictures there are the same as in the 650 service manual found on the XJCD. (If nothing else, that'll tide one over until a paper manual can be gotten. Plus, the factory manual's got a gorgeous cutaway view of the engine.)

As for the "safety relay", as you call it... The sidestand switch is down (obviously) near the sidestand. The sidestand relay, according to the Haynes, is underneath the tank, if I'm reading this picture right. (Page 241) The ignition cutoff relay is somewhere near the TCI box itself.

 

The 750 Safety Relay is located;

Under the Tank
Under the long, Center Frame Tube
Just ahead of where the Fuel Tank Support bolts to the Frame.
To the rear of the Turn Signal Self canceling Module.

 

Ah, thank you, Rick. Saves me having to go and pull the tank off mine to go look for it.

 

Thanks for the replies guys. Rick, you are right, I do still have the old buzz fuse block and have been looking around town here for a good "sealed" blade fuse block to put in. I will try the safety switch this weekend. If that doesn't work, then on to the pick up coil I suppose.

 

The wire from the Pick-up Coils may be pinched by the Shift Lever Cover.
Look under the "Shield" at the front of the Shift Cover.
If the Shift Cover was ever removed; the Pick-up Coil Wire gets captured and shorted-out.

Get the Fuse Panel updated.
I swear that my bike runs better with the New Fuse Panel.

Other things to consider;
Incorrect Relay used as Safety Relay.
Stuck Clutch, Neutral or Sidestand Switch.

 

I now have spark to the plugs!!!. On the left side of the bike, below where the rectifier and TCI box mount, there is a relay (anyone know which one this is). Not sure which one it is, but when I unplugged it, BINGO!!! the plugs fired, And quite a healthy spark I might add.
Then, as I sat exuberant over the troubleshooting with the help of XJBikes knowledgeable members, I decided, "What the heck, I'll shoot some ether in the pods and see what happens". Much to my surprise, she fired on the first revolution! Spit up a bit of black smoke, cleared up and purred. Then I thought, if it fired so easily on ether, maybe I should put some Petrol in the go tank and see what happens. As I was re-assembling the tank, I broke the $%@# fuel filter. Oh well, needed a new one anyway. Off to the parts store tomorrow for filter and other various items.

So far, $100 bucks for the XJ; $50 bucks for a new battery; $25 bucks for fuses, sandpaper, and a multimeter (and 30 minutes of cleaning with a Dremel), and I have bike that runs. Of course, this is just a start, lots more stuff to check. I am going to completely strip it down and repaint, and restore the bike. I am assuming chacal is the go to guy for part, is that correct?

 

The Safety Circuit Relay ??

Highly likely.

See if the Bike will start IN GEAR with the CLUTCH Lever PULLED.

If the Bike NEEDS to be in NEUTRAL ... you have a Bad Relay.

That Safety Relay ==>> Is Different from a Std. Power Relay.

Replacing the Safety Relay with a Power Relay will cause problems.

 

I was just reading one of the information posts from chacal. Apparently this is the side-stand relay. This matches the description and location he describes. So it seems I need to clean or replace the switch and/or the relay.

I put some fuel in the tank, but it doesn't seem to be pulling fuel into the carbs. I put a new clear inline filter in, and it fills up properly, but it will not run. If I shoot it with ether, it will. So now on to a complete fuel system rebuild. I have good compression across the cylinders, so I am going to put new seals in (ie-valve cover and oil pan are leaking). Then I will adjust the valve train and then sync the rebuilt carbs.

Thanks so much for the help thus far, it has produced great results and I am confident now I have a good bike to build. The info and members in this forum is vastly invaluable.

 

That Relay gets Signals from:

Sidestand
Clutch Lever
Neutral Switch

If any one of the Switches is not working properly; the Relay will prevent the Bike from Starting.

However, IF the Bike is in NEUTRAL it should Start.

 

If I plug the relay in at all, no fire. If I leave it unplugged it will fire, slip it in gear (relay unplugged), will not fire. With it in gear, pull the clutch (with relay unplugged), will fire. Side stand up or down, no difference, so I assume that the side stand switch is the issue...