Weak spark problem

Hey guys im still working to fix my old mid maxim and ive been trying a few last things before i call it quits. I got a spark tester from autozone and it seems like it works well as it reads after all with the light bulb in the tester that i am indeed getting small spark on all four plugs even though i cant see the spark at the gap in my garage with them grounded. It came with a large ending though to it at the light end of the tool that plugs into the plug cap that doesnt quite fit inside the cap because it is made for resister spark plugs in cars but i have been just touching it inside to where my plugs lock in and it has been giving me the reading. The light is dim though when cranking its not bright like ive seen demonstrated on working bikes on youtube and such so i assumed my spark was weak on all 4. I just purchased new ngk bp7es plugs and gapped them and my battery is an agm and reading at 11.75 with nothing on and cranking volts were at around 9.1-9.5 with my dmm set to 20 volts. Any more insight is greatly appreciated thanks all.

 

I also have my tank off and vaccuum line disconnected for now i didnt know if that would make a difference starting either maybe? Fuse box is also brand new redone with blades in them. And on one last note i am gonna try with anyones suggestions to boost my battery up with car off later after i get off work tonight with some jumper cables attached to battery on bike.

 

I might suggest your battery voltage is too low. You should have over 12.5 volts and should not drop below 10 volts when starting. XJ4 ever has a chart on battery voltages for proper system operation.

 

Right okay i have my battery on the trickle for now and my jumper pack on the charger as well for testing the new plugs i bought. Would having the gas tanks vaccuum line off make any difference in starting?

 

Plug it. That's a huge vacuum leak to the cylinder it connects to.

 

Okay ill just hook my tank back up after i secure my plug wires in tight with the new plugs and battery and all to try to start it up. Could that have been the culprit possibly wink? Or is that not a significant enough problem to cause a no start situation you think?

 

Remove the ht caps and use your dmm to ohm out the secondary output from the coils. Also click/tap your name, then click/tap signature and type in which model you have.

Gary H.

 

Its a 1983 Xj750MK and okay rocs ive done that previously but would that help since ik the coils are getting spark with my spark tester tool with the light?

 

I just attempted to start it last night with all four new plugs in and wires snipped back 1/4 inch to expose new fresh wire and with tank and all lines plugged in. Battery was at 12.85 to start the test and it just kept cranking no fire still though. Took number 1 plug out after and its still saying its getting a small spark on the spark tester as well.

 

Swap the #1 and #4 caps and see if the spark is stronger. Ohming them out will tell you exactly how weak the spark is. Then we can diagnose why it's weak.

Gary H.

 

They are about the same rocs ive swapped all four caps around a few times previously that didnt work either.

 

They all seem to be getting about the same amount of spark reading wise on the tester.

 

Have you ohmed out the primary input on both coils? We're testing backwards since we know there is spark (process of elimination). Are you sure there's fuel/air mix in the holes?

Gary H.

 

Are you using some external fuel tank or are you just using the bike tank for your fuel source as you try to start the bike?
If you are using the bike tank the petcock has to be set to prime since the vacuum line isn't hooked up.

Ignore the tester. They are nie and all, but not really definitive as a test device.
Pull one plug at at time and ground the threads to the head. Thumb the starter and look at the plug gap. If there is spark, note the size, sound, and color of the spark. Blue and snappy is ideal.

 

Thanks guys and k moe yes i have grounded all four plugs and cant see any spark out of them even in the dark but the bike started up randomly today for a little bit after taking cap 1 off with the tested hooked up and an older plug hooked into the other end just hanging in the air and i pushed the starter and it shocked me because i was holding the tester but it fired right up with the number 1 plug cap not even on

 

Would a loose ignition wire cause these problems perhaps? Mine are all hooked in connected to the metal inside of a snap connector i put on them

 

Sounds like your bike had spark. It didn't have anything to ignite.

Gary H.

 

Yes. Which ignition wires are you speaking of?

 

Could be but plugs sometimes have droplets on them of gas but not all the time. And k moe they are blue brown red and a black one

 

Vaccuum line and fuel line from original tank is on as well should i leave it on prime for awhile or what should be my next course of action regarding that?

 

open bowl drain a crack to see if you have fuel in the bowl.

 

have you tried this chart? also unscrew spark plug caps and test ohms. when you get to the tci part check your voltages at both the primary coil plugs 12 volts and at tci
t

 

New battery@ 12.5 and getting a weak spark. I was trying to get him to test from the plugs back to the pickup to isolate why spark is weak.

Gary H.