Spark trouble

[gareth]

Yesterday, I tried to start the 79SF after leaving it sit indoors for the past four months. The bike started and ran for a few seconds then quit. I continued to crank it for a while and I guess I flooded it. When I hit the the kill switch , there was a massive backfire on the right side. In the confined space of the workshop it about made me jump out of my skin. I let is sit for a while. I turned the key this time to let it sit...and another almighty bang.
At about the same time, fuel started leaking from the airbox. I figured that there was probably a stuck float valve on that side. Today, I pulled the carbs and checked the float valves and reset the float heights. When I put the carbs back, convinced the flooding was the problem, the bike wouldn't start.
There is no spark at any of the four plugs.
I'm just going to assume that the backfires were caused by some high-voltage discharge when I turned off the low-voltage with the key or the kill switch.
My question is... could that same high-voltage pulse have fried the TCI or some other vital component?
There were intermittent problems with the bike dropping cylinders before I put it away a few months ago, but I had assumed this was just fuel problems. Now I am not so sure.
The backfire problem did happen a couple of times in the past, but now I'm wondering..
Has anyone any ideas??

Regards,

Gareth

[TopCatGr58]

Hey Gareth,

The earlier model XS's were prone to damage to the PU coil wires under the timing cover. Check out the tech tips scrolling down from the MAIN FORUM PAGE, and you'll find it under Repairs, Electrical.

The XS uses a wasted spark system, so sparks are sent to both the cylinder that has compression and fuel/air as well as it's paired cylinder that should be on the exhaust cycle. So...with it being flooded, good chance it ignited the unburnt stuff sitting in the exhaust pipes! The coils are energized when the key is on, and turning the key off could cause the power to collapse in the primaries sending a spark to the cylinders! But the spark plugs are insulated from the TCI, so I don't think you fried your TCI!

Check out your PU coil wires, and also the connectors for the TCI while you're at it, clean them as needed.

Fuel sitting in the carbs for 4 months could have developed some varnish, but many folks have commented that they have stored their machines in uncontrolled environments, and have had no problems with running afterwards! But a little Seafoam goes a long way!
T.C.

[wa407mpp]

No spark at the plugs or no spark anywhere on the ign. side of the system? If it's no spark at the plugs work your way back until you find electricity, if no power anywhere start at the fuses and work from there. It sounds like it could be in the kill switch, does the starter turn over? Sometimes a bad kill switch will cause the cylinders to cut in and out.

[gareth]

It's a tribute to this forum that exasperation drove me to ask the questions before reading the tech tips. Really..that and frustrated impatience.
I started working through the diagnostics posted by Paul Streit in the tech tips and can already see that there is a pick-up wire problem based on the resistance of the coils at the TCI. The wires leading from the coils to the harness run very close to the exhaust and are covered in oil and grease. Seems to me they are solid core wire but I haven't checked yet. The colors of the wires change, though, from solid colors at the coils to the mixed colors at the TCI connector. Where does the change happen? Is it deep in the harness somewhere? When a shady-tree mechanic does the pick-up coil fix, is it just a matter of picking an easy place to make the splice and sealing it up?

While I was reading the tech-tips , I already had two replies to this question.

This forum rocks.

Lets take it one filthy connection at a time..


Regards,

Gareth

[TopCatGr58]

Hey Gareth,

In case you didn't find it, here's the PU coil fix tip by Ken Talbot!!

You shouldn't have to be worried about the wires up in the harness area, just the ones under the timing plate. That is where they get crimped and flex alot from the rotation of the timing plate during running, vacuum advance and cent. advance moving it around alot, the wires get broken, but the insulator keeps them in place, so they look okay! Also, where they get crimped before they leave the housing into the harness!

The tip will explain it all!
T.C.

[gareth]

I checked the resistances at the connector on the TCI from the pick-up coils and there was a definite problem. So I did the pick-up fix. Tested the resistances, pushed the starter and had a good spark again at all four plugs. Nice. I reset the gap between the pick-up coils and the sender to .6mm and the spark was definitely beefier across the line, although more pronounced on one pair of plugs. Very excited now. I take fuel tank, which has been off the bike, temporarily turn it round to hook up the fuel lines and still give me room to sych, and hit the starter.

Nothin'. Not a peep.

Check for spark again and there is no spark again at any of the plugs. What the .....?

Turns out that when I had reversed the tank and moved it back to the rear of the bike, that I had just nudged the connector at the TCI enough to break the connection there. Wiggled it around a bit and the bike started on the first spin. This condition was probably the reason why I lost the entire spark in the first place. When I was doing the initial set-up of the bike a few months ago. I had the tank off the bike and just ran long fuel lines from the tank to the carbs. The bike would run roughly because of the intermittent pick-up wire problem, but at least it ran. Trying to run the bike with the tank " reversed" on the frame exposed the poor contact at the TCI and prompted the initial plea for help.
It turned out that the "no spark, no nothin'.." symptom uncovered an intermittent fault that could have left me scratching my head at the side of the road instead of late at night at the shop.

The connection still feels a little lame though. I will probably just remove the plastic and hook up the connectors directly to the spades on the TCI and crimp them down tight.

It does make me wonder about other connector blocks on the bike.

What have other XS-ives done about this?
Is Electrical Contact Cleaner-in-a-Can just snake-oil?
Is a breakdown of the other connectors and resoldering/crimping a worthwhile project or overkill?
Should I just dismantle, clean, spray, dialectic grease and shrink wrap every connection?

Finally Running on all-Fours,

Gareth.

[Ken Talbot]

Originally posted by gareth
Is Electrical Contact Cleaner-in-a-Can just snake-oil?

Is a breakdown of the other connectors and resoldering/crimping a worthwhile project or overkill?

Should I just dismantle, clean, spray, dialectic grease and shrink wrap every connection?

- no, it actually works pretty good for cleaning connectors

- do the fuse block as you upgrade to blade-style fuses, but you should not need to resolder/recrimp everything else

- I wouldn't heat-shrink them, but sooner or later you will need/want to dismantle/clean/spray every connector on the bike

BTDT...