Trouble diagnosing ignition issue, 1972 SL350K2

Xylocopa

Xylocopa

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Joined
Jun 13, 2026
Total Posts
6
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Location
San Francisco
Hi everyone,

This ones been tricky for me. I'll put the issue up front and the long story below, for those interested.
Short story:
I'm having a lot of trouble setting the ignition timing after replacing both coils, the condenser, both points, and the points mounting plate. No matter what guide I follow, be it the clymer manual or the those guys in Houston youtube video (or any of the various videos on setting points) I cant seem to reliably set them in a way that causes the test light to flick on and off when it should when I rotate past the F and LF marks.

Long story:
(this is my first real post so please bear with me, if I'm messing up with formatting or this is in the wrong topic area let me know and I will edit and revise as soon as I can)
this is my first motorcycle. I bought this bike off a buddy whod had it taking up space for a year. After replacing the battery, the bike ran mostly ok, I had to figure out the hard way how to use a pidcock valve, and there was some funkiness with backfiring and weird power issues. In hindsight, this bike was probably running mostly on one cylinder, as I realized by being zapped in the legs a few times that the lead from the left coil was cracked and arcing out. I went probably way too overboard and replaced the condenser, both coils, new spark plugs, rebuilt both carbs (thought it was the float bulbs, realized I didnt know how a pidcock worked) , adjusted the cam chain tension, valve spacing, cleaned/sanded off old gaskets and replaced them, and finally threw new points on. after doing all this, ladies and gentlemen the motorcycle no longer starts. I've been tearing my hair out trying to figure out why I cant seem to get the ignition timing correct, there is definitely voltage in the system, the points are getting power, but the plugs are NOT firing. happy to take a video of the situation but I thought I'd start with an explanation. Thanks in advance.
 
One of the challenges here is the sheer number of variables changed in the equation. Could be fuel, could be air, could be spark.

Are you getting any popping or “try to fire” or just cranking?
 
I would start with a few simple questions and let things develop from there
  • You have power to the coils. That should mean the test light will go on and off as you rotate the crank. Is that the case?
  • Have you tried holding a plug to the head so you can witness spark while cranking the motor over?
  • Are you aware of resistor vs. non resistor spark plugs and caps? Original equipment was resistor cap with non resistor plug. Nowadays the non resistor plugs are becoming harder to get so folks are switching to non resistor caps. What do you have?
 
First off we have folks here who can set you up with the Factory Service Manual. They'll be along. Clymer is often wrong. Youtube is great for watching music videos.
If you're not getting spark at all the problem is not the timing. That's where I would start, then one thing at a time.
 
Xylocopa said:
Hi everyone,

This ones been tricky for me. I'll put the issue up front and the long story below, for those interested.
Short story:
I'm having a lot of trouble setting the ignition timing after replacing both coils, the condenser, both points, and the points mounting plate. No matter what guide I follow, be it the clymer manual or the those guys in Houston youtube video (or any of the various videos on setting points) I cant seem to reliably set them in a way that causes the test light to flick on and off when it should when I rotate past the F and LF marks.

Long story:
(this is my first real post so please bear with me, if I'm messing up with formatting or this is in the wrong topic area let me know and I will edit and revise as soon as I can)
this is my first motorcycle. I bought this bike off a buddy whod had it taking up space for a year. After replacing the battery, the bike ran mostly ok, I had to figure out the hard way how to use a pidcock valve, and there was some funkiness with backfiring and weird power issues. In hindsight, this bike was probably running mostly on one cylinder, as I realized by being zapped in the legs a few times that the lead from the left coil was cracked and arcing out. I went probably way too overboard and replaced the condenser, both coils, new spark plugs, rebuilt both carbs (thought it was the float bulbs, realized I didnt know how a pidcock worked) , adjusted the cam chain tension, valve spacing, cleaned/sanded off old gaskets and replaced them, and finally threw new points on. after doing all this, ladies and gentlemen the motorcycle no longer starts. I've been tearing my hair out trying to figure out why I cant seem to get the ignition timing correct, there is definitely voltage in the system, the points are getting power, but the plugs are NOT firing. happy to take a video of the situation but I thought I'd start with an explanation. Thanks in advance.
Click to expand...
Download the Honda FSM here: https://drive.google.com/file/d/0B8...UjA/view?resourcekey=0-g2nSAm99nu0sxecpObZWWQ
 
stl360+450 said:
I would start with a few simple questions and let things develop from there
  • You have power to the coils. That should mean the test light will go on and off as you rotate the crank. Is that the case?
  • Have you tried holding a plug to the head so you can witness spark while cranking the motor over?
  • Are you aware of resistor vs. non resistor spark plugs and caps? Original equipment was resistor cap with non resistor plug. Nowadays the non resistor plugs are becoming harder to get so folks are switching to non resistor caps. What do you have?
Click to expand...
Hey, thanks for your help.
  • Yes, the test light will go on and off as I rotate the crank.
  • I have tried holding a plug to the head while cranking, I get no spark.
  • these are the coils and caps I purchased. I am aware of the resistor vs non resistor spark plugs and caps. I know for sure I have non-resistor plugs, the website does not say if the caps I got are resistor on the page I linked, however it seems that they have the same part number for sale individually and they are indeed resistor caps.
 
EzPete said:
One of the challenges here is the sheer number of variables changed in the equation. Could be fuel, could be air, could be spark.

Are you getting any popping or “try to fire” or just cranking?
Click to expand...
Yeah, I've been muttering fuel air spark to myself over and over like a madman.

When I tried kicking it over with everything buttoned up I just got cranking
 
Xylocopa said:
Hey, thanks for your help.
  • Yes, the test light will go on and off as I rotate the crank.
  • I have tried holding a plug to the head while cranking, I get no spark.
  • these are the coils and caps I purchased. I am aware of the resistor vs non resistor spark plugs and caps. I know for sure I have non-resistor plugs, the website does not say if the caps I got are resistor on the page I linked, however it seems that they have the same part number for sale individually and they are indeed resistor caps.
Click to expand...
Pretty sure those caps from 4into1 with your coils are 5k ohm resistor versions, but you can unscrew them from the coil wires and test them with an ohmmeter (actually wouldn't be a bad idea, some members have bought new resistor caps and found they were well over 5k ohms). Those are good coils, I have a set on my 450 that are 9 years old and working fine.

We need a picture of your points and plate so we can see how you have it set up. Take the picture directly in front of the points plate, 90° to it so we can get a good clear look at the points and the wire connections on them.
 
Xylocopa said:
Yeah, I've been muttering fuel air spark to myself over and over like a madman.

When I tried kicking it over with everything buttoned up I just got cranking
Click to expand...
OK - if you're not getting spark at the plug, then I'd start there. Photos of how you have the points installed and the coils wired would help greatly, but I'd take the following steps first.

Verify for 100% certainty that you have 12V+ at the coil, meaning that ignition switch on, handlebar switch set to Run, a voltmeter shows 12V with one probe on the black/white wire and the other on the negative battery terminal.
Ensure that your engine block is grounded (sounds like it is, but let's check anyway. Take the probe off the black/white wire, set meter to continuity and place the probe on the head near the spark plug hole.
Check continuity between the end of the plug cap and the bullet connector where the wire from the points comes in
 
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