Broken bobber ignition.

[Verbal]

So I'm working on my buddies '75 xs650.
He has no spark, yep I know another one.

So I sanded the points clean with 1200 grit. Pulled the plugs and no spark. Removed the plugs from the boot and put in a screwdriver, no arc to jugs.

Voltage on battery with charger is 12.5. tested kill switch it has 0 ohms resistance. Push button starter was a doorbell, removed that and put in a generic pushbutton horn button from advanced auto. It attempts to kick over, so those were just cursery checks.

I'm down to the coils and the condenser. So the points have an orange and gray wire coming from them. Shouldn't I be able to test the wires coming of the points for spark? The condenser I know is a . 22mfd cap, and I rest them at work but mine are 2 and 3 post. How can I test a 1 wire for it's charge. Lastly how would I even go about testing a coil?

Thanks in advance for reading that wall of text. Any HP would be appreciated.

 

[Jan_P]

Do you have 12 V in to the Points ?
On the coil in ? R/W

 

[Verbal]

I have 12vdc to ground on brown at each coil. At the points I have tested 1,2,3,4 to a bare metal ground and have 0vdc.

 

[Verbal]

So on the backside of the points arm opposite the touch pads I have 12.4 vdc to ground on one, and fluctuating voltage on the other point arm. It's all over the place. And this has a new battery. Missed these before.

 

[Jim]

Points need to be open to read voltage at 1 and 2 in your pic. With the points closed, power goes to ground instead of through the meter. To check the coil primaries, disconnect one wire and measure resistance across the two terminals. Should be about 4Ω's. Secondary is checked from the HT lead to ground.... about 8KΩ's.

 

[Verbal]

Like this?

 

[Verbal]

One coil with the orange disconnected.

 

[Jim]

Like this?

Yep. If you close the points your meter should go to 0v

 

[Jim]

One coil with the orange disconnected.

That's almost double what the book calls for.

 

[Verbal]

Ok, it's too dark out now, I'll check the other coil tomorrow. So we know we have 12vdc and 0 vdc open close on the points, so the should be fine.

And that coil should be good, or is the resistance too high? I'll test the other and if it's within range where would you go next? And thank you for the help, watching videos and reading is way different than hands on.

 

[Jim]

Well, with the resistance doubled at the primary, power is halved. A good coil would use about 36 watts of power. Yours will only use 18 watts. That might be enough to make a spark... but it'd be a weak one.

 

[Verbal]

Got it. I might as well just replace both coils from the start. Throw the condenser in for shits and giggles.

My buddies been off the road for 7 years I'm trying to help him revive someones unfinished project bike. Thank you again, I'll update this once the new coils are on.

 

[Jim]

Creative routing on the speedo cable.
The CV carbs and the pleated K&N style air filter are well known to not play nice with each other. You can save some tuning woes by getting rid of 'em (the filters).

 

[Verbal]

I just ordered the coils and condenser, should be here by the end of the week. If that was all she needed I'll be a happy camper.

I saw different oval style filters on mikesxs for the '75. I'll get some clearance measurements and see if they will fit under there. If not I'll have to get creative and neck them out and over a bit first. Thanks for the heads up on that, that's saved me another headache.

Honestly didn't expect this quick a response from a forum. Thank you.

 

[Jan_P]

Looks like a small leak at the cylinder Head .left side
I would check the cylinder head bolts
and do it again after a heat cycle.
When you install the new parts grind and clean the cable connections and put some grease on
I would be surprised if it starts directly.

I don't know carburetors so good but the impression is that the float bowls needs to be taken off / down ( can be done with the carbs on the machine )
to have a look at the bottom of those before starting attempts perhaps saving a carburetor cleaning

If the bike ran with those air filters I would wait to replace them after I get startup now.

 

[Verbal]

Thank you, supposedly the guy that he bought it off of had it run in the tail in the last season. The carburetors are an issue that I'm dreading getting into later on here but with the custom job like this from somebody's garage, you know we're going to be tearing them apart.

 

[Jim]

Thank you, supposedly the guy that he bought it off of had it run in the tail in the last season. The carburetors are an issue that I'm dreading getting into later on here but with the custom job like this from somebody's garage, you know we're going to be tearing them apart.

Click on the TECH button at the top of the page. There's an excellent carb guide in the carburetor section.

 

[Verbal]

So the coils and condenser have been replaced and still no spark. Points are clean and opening and closing. I have voltage at the points. No spark at either plug or to ground from the wire. Can't think of what else I'm missing.

 

[Jan_P]

So the coils and condenser have been replaced and still no spark. Points are clean and opening and closing. I have voltage at the points. No spark at either plug or to ground from the wire. Can't think of what else I'm missing.

If there is 12 V at upside coil and points ..You got caught in the master of all Ignition Problems
NO GROUND most likely at points

 

[Verbal]

I adjusted on side of the points that seemed like it never opened and cleaned them again. Not sure if that did it, but now I have intermittent crap orange spark. Gonna go grab some plugs. I'll update!