Topic: 1972 CB500 Plug Cap Resistance

[jmelche2]

When measuring the resistance of the OE plug caps, I get the following readings:

#1     7.7k
#2    10.6k
#3    10.7k
#4    12.8k

Should these caps be replaced?  David Silvers has the OE caps ($22) for cylinders 2 and 3 only.  Also has NGK replacements for all four cylinders.  Thanks.

[KeithB]

Other experienced people here have noted that the TOTAL resistance in the high voltage side of the ignition should be about 5000 ohms.
There are resistor caps and resistor plugs. How you get to the 5000 ohms is your choice but it should be EITHER plugs OR caps.
In your case you can replace the caps with new 5K caps and check that your plugs are not "R" rated.
If you have resistor plugs, use non resistor caps.
Either way, all the caps should be the same resistance.
.
D8EA is a non resistor plug
DR8EA is a resistor plug.(5000 ohms)

[jmelche2]

Okay, so I ordered XD05F and  VD05F, NGK caps from Dennis Kirk.  I would also like to replace the wires while I'm at it but don't know what brand/part number wires you guys are using.  Can anybody tell me what and where to order these?  Splice connectors?  All advice appreciated. 

Thanks

[goldarrow]

If using stock coils, replacing wires are not so easy

[Deltarider]

If using stock coils, replacing wires are not so easy

NGK has cable connectors (J-1) you can cut the leads, ad the cable connector and use more supple silicone HT leads further on. 7mm will do and remember: NO carbon core!

[TwoTired]

When measuring the resistance of the OE plug caps, I get the following readings:

#1     7.7k
#2    10.6k
#3    10.7k
#4    12.8k

Should these caps be replaced?  David Silvers has the OE caps ($22) for cylinders 2 and 3 only.  Also has NGK replacements for all four cylinders.  Thanks.

The stock resistance for each output lead is 10K Ω  +/- 10-20% of rating.   Accuracy is not that important.  Is the bike running properly?
If not, I would replace #1 & 4, if I couldn't clean the caps into compliance. Otherwise, you don't have much choice but to replace them.  I can't find new caps in the 10K value anymore.  With today's pervasive use of resistor spark plugs (5KΩ rated), NGK has decided to only offer 5K caps.  To maintain originality of circuit operation, 5K caps would be used with 5K resistor spark plugs.

The bike will run ok with just 5K caps and non-resistor plugs.  The down sides are; slightly higher electrical load on the battery/charging systems, higher coil heating values, short points contact life, and shorter spark plug life due to accelerated spark erosion, all due to increased current flow in the coil's output circuit.

It seems unlikely anyone on this forum would notice a difference in practical terms, though.  If effects can't be noticed (or smack one in the face) within one day to a week, memory retention of root cause is simply lost.