Topic: Points wearing/failing quickly

[Leanier]

Hey guys, I have been trying to figure out an issue with my CB750 for about a week.  It started having ignition issues, so I sanded and gaped my points and timed the bike, and it ran great, for about 10 miles then went slowly back to missing and backfiring.

I just did a 4 hour ride on it (ended up taking six) and I had to stop and sand the points every 50 miles or so to keep it running.  A few times i had to sand and clean a few connections to the points before it ran correctly.  If I didn't sand the points, it would miss and backfire and get slowly worse until it couldn't maintain even 60mph.  It seems to mostly be cyl 1-4, but 2-3 has had issues a few times as well.

Anyone know why the points would corrode so fast? and maybe connections as well, since I have had to clean those a few times to get it to run as well.  I was wondering if maybe my condensers could be going bad?  they haven't been replaced in a few years..

Anyone with any insight would be of great help, I'm going to tear down and clean the whole ignition system tomorrow I think, all the wires and points etc..  I put a new set of points in the bike and it still did the same thing.  I have another hopefully only 4 hour ride on Monday, so I'd like to figure it out by then...

Let me know what other info is needed, this is kind of a tired ramble after my lengthy and stressful ride.

[01Thomas]

If there are lots of sparks and arcing between the points it's probable that your condensers have failed. One of the functions of condensers is to reduce arcing across the points, exactly because this erodes the point surface.

Fit new condensers, make sure they're earthed properly and you should be good to go.

regards
Thomas

[Leanier]

Oh thanks for saying that I totally forgot to mention that, the 1-4 cyl point sparks a ton, the 2-3 doesn't at all.  1-4 has failed I say 20 times, 2-3 only maybe once, and I think they got wet that time.  New condensers it is!

[flybox1]

new condensers, and invest in TEK points, not the sub-par Daiichi brand found in most build kits.

[Leanier]

Yea I made sure I got TEC points, for some reason didn't think to order condensers at the same time..  Now to try and find some by Monday

[TwoTired]

Hey guys, I have been trying to figure out an issue with my CB750 for about a week.  It started having ignition issues, so I sanded and gaped my points and timed the bike, and it ran great, for about 10 miles then went slowly back to missing and backfiring.

Well, there is the answer to your question.

Anyone know why the points would corrode so fast?

Sandpaper sheds it's grit into the soft metal contacts while doing it's abrasive job.  The grit particles are insulators and harder than the contact metal.  The particles effectively raise the contact resistance and make them heat up and wear more rapidly.  Points files and burnishing tools are the proper way to condition point contacts.

Other than that, condensers can also lead to early points failures, as can using low resistance ignition coils.

[lucky]

If there are lots of sparks and arcing between the points it's probable that your condensers have failed. One of the functions of condensers is to reduce arcing across the points, exactly because this erodes the point surface.

Fit new condensers, make sure they're earthed properly and you should be good to go.

regards
Thomas

Always replace the points and condensers as a set.
Make sure to clean the points cam with acetone and put a light
 coat of disc brake grease on the points cam.

Make SURE you check the DWELL of your points.

[lucky]

You cannot really adjust a set of worn points very well or at all.
I will post a pic.