Center spark stops sparking

[rc]

In the past three weeks my bike starts sputtering and stops , it has done it twice. The engine literally quits when it goes. I remove the plugs to check for spark and the center one is dead. I replace it and its off to the races again. The bike is a 74 S3 400 , It had resistor caps and plugs in originally but I have change both to non resistor. The bike runs great for a while then does the quitting thing , change the plug and I'm off to the races again. What could cause such a thing ? All I want is a little consistent spark in my life.

[mraxl]

You could have carb problems that are fouling the plug.... swap carbs to see.

Points might be contaminated, poor connection at plug cap or coil, leaking condenser when hot...

[rc]

Thanks I will give it a go
Another question ? If the center cylinder stops the bike stops, but if the center keeps firing and you lose either outside cylinder it keeps running is that normal for a triple ?

[mraxl]

No, that is not normal. I suspect you have carb issues.

[zambia]

Just out of curiosity, when the plug fouls..is it dead? ie. no amount of cleaning will fire it? I had this on my S3, cleaned the carbs like crazy, but always a cylinder would die, and a new plug would fix it. Turned out to be a very poor battery ground, weakening the system. I think it's fixed by putting a new battery ground wire on (I say think because the tank is off for paint, and I haven't run it much).

It's worth a look, most of these bikes have rust and corrosion at the connectors... All this only after you're sure you've followed MRAXL's advice about the carbs. I knew mine were spotless after cleaning thoroughly several times. A new battery ground wire gave much brighter spark at the plug.

[givr]

+1. I cleaned all of the bullet connectors with switch and contact cleaner. Some of the connectors wouldn't stay together anymore, so a slight pinch of the female connector makes the male connector stay put (translates to everyday life). When I got stranded in Port Perry, the ground wire for the ignition boxes broke and fell off, new wire, new bike feel.

[pipe welder]

"Stranded in Port Perry"
Sounds like a blues tune to me.
Who wrote that song anyhow?

[rc]

The plug just goes dead with no spark at all.
My first plan of attack was to check out the carb, took it all apart cleaned it and adjusted the float bowel ( gas occasionally comes out the overflow). Using the info in Glens repair book for KAWIES set the level using vernier. Then tried to syn the three carbs since one of the slides wouldn't go to the bottom. found out that it would only go to the bottom if placed in a specific carb Yes all the slack was taken out of the cables. So after all the work turned the gas on and it pissed out the overflow . So I guess its back to carb adjusting. Sure wish I had the float bowel special tool.
Lucky I love the smell of gas and I am a none smoker, May the force be with me.

[mraxl]

You have either got a leaking float or bad/contaminated float valve.

[givr]

Sept 3, 2008 23:22:48 GMT -5 mraxl said:

You have either got a leaking float or bad/contaminated float valve.

+1, I have a modifed float bowl that features a hole in the bottom, tapped for a small 1/4" fitting with a clear tube attached for checking fuel level. This is invaluable when setting float height as you can see the fuel level as it is in the bowl, then it's just small adjustments of the tab that's on the float which contacts the float valve to set the height. This involves a couple of sessions removing the bowl, adjusting the float and refilling, but I never need more than 3 tries to get it right. For you, new float and float valve and properly set height should kill this problem.