Author Topic: ? Supressor Cap CB 750 ?  (Read 200 times)

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Offline hondacr

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? Supressor Cap CB 750 ?
« on: January 07, 2019, 06:46:39 am »
Apologises for my ignorance on this one, I have a question about the NGK plug suppressor caps, is the rubber on the plug-end of the cap important ? 
The reason I ask is because of the problem I have been having recently with Cylinder 4 plug fowling up after a decent run....
I decide to try NGK 7's instead of 8's & also fitted a new NGK plug Cap, when removing the old Cap[but not that old] I noticed that the old Cap for cylinder 4 did not have the rubber sleeve at the plug end so I wondered then could that have caused an inferior spark on this plug , the other 3 plug caps for cylinders 1.2.3. were in place ?
obviously when fitting the new plug cap to cylinder 4 I made sure the rubber was in place.. ive not had chance to try out yet ..

Prior to all this I set the air/fuel mixture to be as lean as possible, I checked the float bowls for over fuelling & all was good.   

Offline bryanj

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Re: ? Supressor Cap CB 750 ?
« Reply #1 on: January 07, 2019, 06:51:14 am »
Not being there would in no way affect the spark. It is there to try and stop water getting to the connection at the top of plug and shorting out spark. You should not use resistor caps with resistor plugs.
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Offline TwoTired

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Re: ? Supressor Cap CB 750 ?
« Reply #2 on: January 07, 2019, 09:19:42 am »
I agree the rubber end is there primarily to block water ingress.  But, it also blocks dust, dirt, and mud from coating the spark plug insulator.  Any coating of a conductive nature will form a path to shunt away spark energy.

If this is an issue, you should be able to see it arcing in a darkened garage.

Spark issues will often show on the plug internal tips as different deposit patterns, especially on the effected plug.

Anyway, you know it should be there.  Why are you avoiding having the proper equipment?
Electrically, the spark circuit only cares about the total resistance in the circuit loop, and doesn't care where it is distributed.  The coil contributes about 15k ohms.  Adding 10k to 20k, with plugs and caps is rather normal and improves spark.
The spark plugs fire in pairs, so the resistance in two leads and two spark plugs are considered in the calculation.  Resistor spark plugs usually have a 5k resistor to consider.  Most run these with 0 ohm resistor caps.  But, a healthy spark loop can still be acheived with a 5k cap also installed.  Not recomended to use 10k caps along with 5k res plugs for the stock ignition circuit, as that would add 30k ohms to the spark loop circuit, which would limit the spark current considerably.


Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

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Offline hondacr

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Re: ? Supressor Cap CB 750 ?
« Reply #3 on: January 08, 2019, 11:47:38 am »
Thanks for the reply guys, if its not the New Plug or Suppressor Cap it then looks like it could be carb 4 that's causing the fowling problem... :o

Offline Don R

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Re: ? Supressor Cap CB 750 ?
« Reply #4 on: January 08, 2019, 02:56:21 pm »
 I'd say plug fouling is most often a rich fuel mixture which may be caused by float bowl fuel level or oil in the cylinder caused by ring seal or valve seals leaking.  A plug that doesn't fire is usually just wet.
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Offline hondacr

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Re: ? Supressor Cap CB 750 ?
« Reply #5 on: January 09, 2019, 01:19:56 am »
I'd say plug fouling is most often a rich fuel mixture which may be caused by float bowl fuel level or oil in the cylinder caused by ring seal or valve seals leaking.  A plug that doesn't fire is usually just wet.

Yes its definitely a rich mixture, on a run for the 1st 15mile or so it runs spot on but then I get an occasional blip from number 4 plug then after around 40 miles that plug it stops firing on cylinder 4, on inspection the plug its all sutted up [ not wet].... The engine / bike was completely rebuilt 4 years ago...float bowl level is Fine & as said before its set to its leanest on the air/fuel mixture screw... :o
« Last Edit: January 09, 2019, 01:22:43 am by hondacr »

Offline TwoTired

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Re: ? Supressor Cap CB 750 ?
« Reply #6 on: January 10, 2019, 11:33:03 am »
Well, some how you have one carb that is "different".

Have you verified the main jet hasn't unscrewed itself?
Have you verified that the needle jet at the end of the holder wasn't "lost" during the rebuild?
Were any replacement parts used in the carb rebuild?  What brand?

Did you use the clear tube method to verify fuel level height?

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

 

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