'82 XJ750J (Maxim) crank but no run. Getting real frustrated

Hey everyone! I've been on the forum for a little bit now and it has been INCREDIBLE. This site has been an absolute wealth of knowledge to pull from. THANK YOU ALL!
Unfortunately my issues are not going away and I think I'm starting to need more tailored help so here goes my first post!!

So, as the title reads, I've got a 1982 750 Maxim with 10,xxx kms on it. It had sat for 11 years before I pulled it out of a shop at the end of last summer. Didn't do a ton to it over the winter (-30 degrees C in an unheated garage is tough on the fingers) but as spring came up, I began the resurrection. A little bit of work here, a lot of work there, money, time, sweat and a helluva lot of cursing later... still nada. I should also add that I am a first time bike mechanic to this machine. I've got some pretty decent mechanical know-how, but have never applied it to a bike before this. So let me give you a bit of a baseline of what I've done so far and the issues I'm having.

Already done to it:
-Carb cleaning and rebuild (based off the "in the name of clean" post on this forum)
-valves clearances checked and adjusted
-brand new battery (acid levels correct, only ever charged at 0.75 amps)
-new spark plug caps (trimmed old plug wires back 1/8th inch for new caps)
-checked coils as per instructions on this forum, primary and secondary windings test fine
-carb float levels adjusted to spec
-got rid of old fuse box and replaced with new blade style box (my fuse box uses a single common ground though, so looking at the wiring diagram, I wired the "ignition" "signal" and "head" to the common ground and then ran an inline 30 amp fuse for the "main", not sure if this is okay...? but bike still didn't run before this change)
-compression levels similar across all cylinders. little low, but have only been able to check on a cold engine
- check for spark on 3 and 4, got scared after a smoky puff in the air box while testing cyl. 1

Observations:
- before float fuel level adjustment, lots of gas in oil
-cranks but does not catch. no coughing, spluttering, belching. zilch.
-as mentioned above, spark for sure to 3 and 4, pretty sure from previous tests that 1 and 2 should also have spark but could not re-verify
- exhaust backfires
- while testing for spark (spark plug out on cyl 1), got a white smoke, puffy pop come from the airbox. this is where I got scared and stopped further testing
- starter clanks intermittently when cranking, i think the "can of rocks" sound that I've read about (an oil issue..? I had been running 10w-40 synthetic that met JASO standards. ran 3 oil changes through it with that oil to flush out fuel from system. read that these bikes often don't like synthetic so I changed to 10w40 conventional, no flush, just drain of the old, in with the new, still clanks)


If anybody can lead me in the right direction, I would be soo appreciative. I don't know what to check, test, replace, redo, adjust anymore. And the whole smoky puffs and backfiring dilemma keeps me from wanting to just keep cranking with my fingers crossed.

Cheers,
Cole, a frustrated and sad XJ owner.

 

Here is where you went wrong. The factory harness does not have any of the fuses wired to ground at all. Every one of the fuses is on the hot side of the circuit.
You must use a pass-through buss fuse block, or rewire the whole bike.

how-to-install-an-aftermarket-fuse-box.6350

If something else is amiss, we won't be able to do a proper diagnosis without the correct type of fuse box being installed.

 

k-moe

okay, sorry, I guess I just assumed one side of the fuses was to ground. in that case I did not ground them all, but instead wired one side of each of the 3 10 amp fuses to its separate terminal and then joined all the other ends to a common post coming off of it. (not ideal wiring techniques here, just enough for testing is all i did).
Still no good?

 

Entirely no good. While the circuits will be powered, you have no way of ensuring that the fuses will blow and actually cut power to an individual circuit should something go wrong. That's a fire waiting to happen.

 

It couldn't be simpler, at least on my maxim, the colours are linked, across each fuse, from memory anyway?

 

Well a fire is certainly something i dont want! I will get to switching that around today and seeing how she goes.
Would i be expecting any changes in starting from that do you think or just a fire hazard reduction?

 

We'll find out once the change is made. I think everything should have power the way it is now, but since the circuits were not meant to be tied together in that way it might be causing problems.

 

I think you can run with that fuse box, it is just not idea since you have to separate the main fuse, which you have already done. The separate circuits (Ignition, Head, Signal) are still protected through the fuses and should not create any kind of hazard unless the input to output was reversed.

So did you pay particular attention to the enrichment wells in the float bowls to verify they were clear when cleaning the carbs? Have you verified the fuel bowls are filling once setting the petcock to prime? You can wet check the carbs on the bike to verify proper fuel level height. A proper bench sync to the carbs was done?

Even new batteries can cause issues with weak spark. Do a load test and verify the battery voltage stays above 10V when the bike is cranking. A voltage lower than this and there will be a poor spark condition caused by the reduced voltage to the ignition coils.

What kind of numbers were you getting?

That's a long time to sit and the rings could be stuck producing low compression. It would have been idea to add about a tablespoon of oil initially before turning the engine over. Since that is water under the bridge you still might add a teaspoon of oil or so to each cylinder to improve compression and see if it will fire up. Check the battery and carbs first as suggested.

 

Thanks for the awesome replies folks. Work ended up pulling me away from the bike suddenly (as it always seems to do), so I'll have to give those suggestions a go once i get back in about a week.
The bit about the enrichment wells i actually didn't even touch now that i think back to it. So that will be high up there onimy list as soon as i get back, as well as the few other ideas youve put out there.
Looking forward to getting back wrenching again with some new found hope!

 

So, If he were to check the plugs with a plug tester would the color of the spark in the window change as the voltage increases ? What color would the poorest spark be ? A good spark ?

 

With properly gapped spark plugs a bluish white would be a good color. Yellowish orange would indicate a weaker spark. Since the XJ series tends to be on the weaker side a nice blue spark would be encouraging. As for the spark plug tester since gap matters the results based on color may be a bit ambiguous.

 

Thanks, I've never seen any color but orange in the window of the plug tester. Would one get a more accurate color by pulling a plug and shorting the ground electrode to
the side of the engine ?

 

I would try it that way, just remember the XJ ignition system is weak to begin with. And also when cranking the battery voltage will drop considerably even with a good battery, so that orange spark could turn blue once the starter is released and the battery voltage returns to normal voltage.

 

Split the circuits, otherwise you will have problems.

 

would you explain "split the circuits" ?

 

It's really simple, the original fuses were on seperate feeds, depending on what they were and what's on the switch positions. One wire in, one out of each fuse. That's how they need to be.

 

I'm back in town today and I'll be yet AGAIN taking the carbs out. Love that job...
I will be attending to the enrichment wells as per the above suggestions. Is there anything else you folks might suggest I do while they are off the bike? I'd love to minimize the amount of times I gotta pull the carbs.

 

I found a small fuse box with blade fuses that fit perfectly into my bike... here are the pictures. It had the exact number of slots I needed, and was on a turn rack in my local auto parts store.

 

I tried looking for something like that originally but this single-ground block was all they had unfortunately. It a bit tricky to get parts up where I am...
Turns out that's no good! So for the time.being i think I'm gunna have to just wore in some in line fuses on each of the wires. Ugly and messy, but functional.

Also, just to verify, these are the areas that were suggested to try cleaning out better eh?

 

The box you have will work since you separated the main from the other 3. Just make sure the 3 wires you have tied together are truly the output of the ignition switch, which are already tied together in the harness. Pull the 3 fuses and turn the key on, make sure only 12V is present on the 3 wires that are tied together - the input side to the fuse box, the output side of the ignition switch. On the output side of the fuse box, the other 3 wires should be zero volts with the fuses pulled.