Topic: Cool Pipe/Weak Spark on the 'ol 'Urban Scrambler'

[beveldrive]

Hi All,
I'm busy getting the 'ol Urban Scrambler ready for the road and have noticed No2 pipe is running cool.



The plug is sparking when held against the head but it looks feeble. I've cut off the end of the plug lead for No2 and fitted a new plug cap, but the problem persists. All the other plugs are sparking fine and other 3 pipes are all eaqually (very) hot.

Carbs are new and set up as recommended. It starts instantly and idles steady. I'm gonna measure some voltages and check connections etc, as recommended on the other posts I've found on the subject.

I figure it can't be much, as all other 3 plugs are sparking well. What do you guys think?

Thanks
beveldrive

[Kevin400F]

First step: Try a new plug in #2.

Switch plug wires between cyls 2 and 3 (if the length of the wires allows), and see if the problem moves to #3

Kevin

[wingman1946]

That is a sharp looking bike !!

[beveldrive]

Thanks Kevin, I'll try the wire switch. Plugs are all new (zero miles) so should be fine.
Hey Wingman, thanks. Yes I'm pleased with the way it's turning out. Paid a lot of attention to 'the look', but perhaps not enough to the ignition parts!!

In tha last hour I decided to remove the coils and take a closer look at them. It looks like the PO has been at them. Question is will they tolerate another 'restoration'. And, what did he do to them anyhow? Maybe just put some epoxy round the entry holes to seal them? There's no evidense of the coil moldings been ground out around the wires. Also, is that blue wire always solderd on as in the pic, or is that more PO work



Cheers
Steve

[Silverback]

The leads tend to come loose at that point do to a crack in the insulation. He was just probably making sure they didn't arc. They might have re-soldered the blue wire, but it is certainly in the right spot. Did you cut it? This is the input from the points. They are not beyond a rebuild. What the PO did was just a quick fix.
When I see one cylinder not firing, I immediately think it is the idle jet, especially if there is fuel in the float bowl. It does not take much to clog it up. Does the No2 pipe warm up when you rev the motor?

[beveldrive]

Thanks silverback, yes the pipe stays cooler than the rest, even up the rev range.
Anyhow, the plan was to fit new plug leads and blue/yellow/black-white feeds. But when I removed the epoxy I found saw cuts and after cutting back with a slit saw could see the leads had been replaced sometime by PO.

Not sure it's a great idea to restore them again so I'm seriously considering some new ones. So then I get to wondering, as long as they're 5 ohm, and will fit under the tank, does it matter what coils they are. I mean, a coil's a coil, right? - only there's some real bargains on ebay.

[RickB]

Beveldrive,

I'm not sure if this will be appropriate to your situation, but I recently had a weak spark issue that I couldn't nail down.

I was running brand new 5ohm Dyna coils, DynaS ignition, plugs, leads, rebuilt engine etc.

After countless tests and hours on the multimeter, it turned out to be the length of my suppression core plug leads. Once I cut them all down to the same length, my spark was thick and everything ran great. You can see my thread on the issue here:

http://forums.sohc4.net/index.php?topic=87505.0

I'm not sure if you're running suppression core leads or copper core. Judging by your stock coils, probably copper core. So I'd make sure your caps are the correct ratings and your leads are in good condition.

Good luck,

Rick.

[beveldrive]

Well, just ordered a new pair of coils with leads. Just hope that will cure the problem.
Rick - thanks for that info. Sounds like you were experiencing very similar problems. I'll def ensure the coil lengths are matched.

Steve