Topic: Ignition issues - 2 & 3 fine...1 & 4 much cooler

[CB750 SS]

Guys, I've got a CB750F '76.  Just about everything is new and the bike has been 100% apart. ...not bad results for a first timer.   I'm in the "shake out" period and a little confused.  As background I upgrade the electrical system with virtually all new electrics (key switch, wiring harness....), a dyna ignition (used) and 3 ohm (green) capacitors.

Last week the bike stopped charging correctly, so I got a stator and field coil (ebay) and installed them today.  Now the engine isn't running very well. Seems to be charging well.  1&4 are much cooler compared to 2&3 (laser temp guns are cool).  If I turn the bike off and do a manual inspection of all the wires and connection points and then start the bike it runs well and the engine jumps to 2K rpms....for a bit...then the rpms fall and it shuts down.   It's as if there is some inflection point were the amps created and the resistants of the motor don't allow for a normal idle speed..2k or 0 rpm.  she's sick obviously.

I checked and I'm getting spark at the plugs. I tried to check if 1&4 had the same amps as 2&3 with limited success. It's tricky to make all the connection and hit the starter button. 

Attached are pix of my coils and Dyna Ignition. 

Since 1&4 are almost identical in running temp, I believe the issue is electrical.

Any help is appreciated! thanks!

[Markcb750]

If you are getting spark at all plugs the problem might be fuel.  are the 1&4 plugs wet or dry when you pull them?

Do you have a timing light to check the timing on both 1&4 and 2&3?

[Vinhead1957]

Try running your old points

[CB750 SS]

I put my old point back on and have the same issue. 2&3 are coming up to Temp, and 1&4 are not.  Could it be the capacitors?  Does anyone know how to test them?

[Markcb750]

Have you swapped the coils & the the 1&4 and 2&3 wires from the points?

[xtravbx]

I'd swap the coils see if the temp issue follows. I doubt it will.

Cooler = richer. I'd be more worried about the pipes that are hotter/leaner..

[Markcb750]

Hey CB 750 SS

where in the world are you, maybe someone close could help...

[Black 750K8]

I put my old point back on and have the same issue. 2&3 are coming up to Temp, and 1&4 are not.  Could it be the capacitors?  Does anyone know how to test them?

Trade them and see if the problem follows

[CB750 SS]

Hey guys, great ideas. I swapped the point and dyna and created a new confusion.  I didn't see the marking on the cam lube and put the thing in 180% off. So it did run at all. After numerous starts and stops the dyna system is working.  Now back to my original issue. Te bike will start and run...within a few minutes @4-5 it dies. The problem is the same.  Not all the pistons are up to temp. Now 2 is down WTF. and 1,3 & 4 seem ok.  So I went for a ride around the block in my hilly hood. After about 1 mile I started losing power. I limped to my front down on 5% power. Then got neighbors to push it up my driveway.  The depreciation in power is odd and delayed. Ay ideas on why it would start strong and then go lame?

[TwoTired]

Spark plug carbon deposits?  The white bit of the spark plug is an electrical insulator.  The black soot is an electrical conductor.  Coat the insulator with a conductive material and you get no spark energy jumping the spark gap.

Look at the spark plug deposits.  Black carbon means there is too much fuel for the air being ingested.  Will it run ok with new plugs for a while?


FYI. Condensers can be tested with a capacitance meter, or by substitution with a known good condenser.