Weak spark on my 82 XS400 DOHC

Hi guys, I'm in need of some help, my 82 Maxim refuses to start, there is a weak spark at the plug's. But it seems not enough to start the beast? I'm in the process of checking all the wiring on the ignition circuit, cleaning and checking all connections as I work my way forward!

Any help and advice, will be truely appreciated

Merlin _/\_

Have you tried to see if it will fire on starting fluid? I wouldn't use starting fluid regularly, but to diagnose whether the spark is actually the problem, it works well.

I'll have to find out where to get that starting fluid, here in the UK! and then get some! Thanks for that tip, but I'll continue checking all the connections, kiil switch/starter button, and coils connections? Thanks mate! Merlin _/\_

That's always a good idea. I cleaned every connection with a Q-tip (cotton bud) and mineral spirits. I'm sure it has saved be much time over the years. I suggest trying to get it firing, eliminating the carbs as an issue because I wouldn't want to se anyone rush into changing parts if the spark really isn't the issue.

I can't understand why it won't run, there is fuel mixture getting into the cylinders, as is evident when I try to start it, the plugs, get wet, after spinning the motor over on the electric starter. (No kick starter fitter to my machine, as you will see on my profile photo!) I have sprayed a carb cleaner into all the vent holes in the atmosphere side of the carbs, and seen evidence that there are no blockages in the jets, and transfer tunnels, and yet it still will not fire up!

MerlinDudley said:

I can't understand why it won't run, there is fuel mixture getting into the cylinders, as is evident when I try to start it, the plugs, get wet, after spinning the motor over on the electric starter. (No kick starter fitter to my machine, as you will see on my profile photo!) I have sprayed a carb cleaner into all the vent holes in the atmosphere side of the carbs, and seen evidence that there are no blockages in the jets, and transfer tunnels, and yet it still will not fire up!

Click to expand...

You can always do the redneck test, and stick a screwdriver down in the plug wire, then hold it next to a ground and see if it jumps. Maybe not the best way to figure out if you don't have spark or not but it works.

After finishing the connector check/cleanup, I tried your "Redneck test" unfortunately, the old knackered screwdriver I used had a crack in the insulated handle! And when I grounded it on the engine, and hit the starter button, it threw me against my shed door! So hard it threw me, that the door, was hanging from one hinge, afterwards!
Having recovered a little, I put the plug caps back on, ans attached them to the plugs, the old bitch, started on the second push on the button! It only ran for two seconds, I tuned it off, as the exhaust pipes had been taken off, for an inspection, and a proper cleaning!

Now I just have to find the right sized exhaust gaskets, and two exhaust collets! (My 19 year old grandson, dropped a sledgehammer, on two of them,by accident!)
My local Yam dealer, says that he doesn't stock, spares for models as old as mine (34 years old!) I still have some new spark plugs, older than that in my shed!
Still the old girl is a runner again, and thats the important part,isn't it?
Now I also find that my clutch cable, is badly frayed, and is ready to snap, if I'm not very careful!

My left arm still has a little numbness, from the ignition jolt, I had! but I should be back on the road, by the weekend!

A big thanks to everyone who contributed, with helpful,friendly advice!

Merlin

The slightly less redneck test works too: remove the plug, put the plug cap/wire back on the plug, hold the plug body against the engine with your boot, try the starter, and watch the spark plug spark.

I got it running well, and went to take it for a good run! Being low on fuel, I called at the petrol station, and Yes, you guessed it! The bloody thing wouldn't start! I eventually got it started,(bump started it) and gave it a bit of a thrashing, in taking it a long way round, to home! It seems that now, not only bad starting, but it won't rev, over 5K, no matter how hard I try!
When I got it home, I took the plugs out, and replaced them with new ones. Same problem!
Took the plugs out and tested them for sparks (both set's tested) with the result of an intermittant, weak spark.
Now, I'm thinking that it is possible that the HT Leads, are the problem? As they look to be the original's that were fitted from new! I have been ringing around all the bike shops, and motor factors, in my area, but it seems that no one is stocking Copper Cored, HT leads, anymore?
Would silicon cores, work with such an old electrical system?
What is the difference between the two, apart from the obvious, of one having a metal core, and the other silicon?

Thanks in advance, for any help!

Merlin