Author Topic: Shorter plugs with ported head?  (Read 1651 times)

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Offline MattFreeman

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Shorter plugs with ported head?
« on: April 23, 2015, 05:31:00 AM »
I've been showing my plugs around to a some folk trying to learn what they are telling me and a friend with a lot of motor, but not sohc experience, pointed out that they look like they may be intruding into the ported head too far.

Here's a couple of pics of my plugs. It would seem that I'm running lean and I'm addressing that but should I look for shorter ones?

Offline 70CB750

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Re: Shorter plugs with ported head?
« Reply #1 on: April 23, 2015, 05:42:14 AM »
What engine and what plugs?

Offline TurboD

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Re: Shorter plugs with ported head?
« Reply #2 on: April 23, 2015, 05:43:18 AM »
Those look to be the correct plugs, ported or not. If the plugs are too long the engine will not turn over.

Offline MattFreeman

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Re: Shorter plugs with ported head?
« Reply #3 on: April 23, 2015, 05:49:43 AM »
What engine and what plugs?


F1 engine, the plugs are marked DR8ES-L

It was pointed out that the first 3 threads are sooty suggesting that the are protruding that far in. And that in a HiPro automotive situation they are shimmed to fit flush in the head...

Offline TurboD

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Re: Shorter plugs with ported head?
« Reply #4 on: April 23, 2015, 06:03:57 AM »
I read your other thread, It appears as though you are fighting a power problem (bike will not go over 65mph). I think in the end you will find a actual problem. If your plugs are all firing and without missing or popping, although they may not be optimal, the bike should run faster than 65mph.

it is completely normal for the first few threads to be colored or sooty, the actual combustion sealing does not occur until the sealing washer.

 
« Last Edit: April 23, 2015, 06:07:16 AM by TurboD »

Offline 70CB750

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Re: Shorter plugs with ported head?
« Reply #5 on: April 23, 2015, 06:17:19 AM »
Everybody and his brother is using these in CB750s, I would not worry about the protrussion. 


Offline TurboD

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Re: Shorter plugs with ported head?
« Reply #6 on: April 23, 2015, 06:23:48 AM »
Generally speaking in any engine. Additional spark plug length, as long as it does not imped intake or exhaust flow, will only add to compression.

I think your time would be better spent looking else where for the problem.

Offline MattFreeman

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Re: Shorter plugs with ported head?
« Reply #7 on: April 23, 2015, 06:40:55 AM »
Cool. I hoped for that answer. :)

I was just throwing it out there out of respect for the person who mentioned it.

Thanks for the imput.

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Shorter plugs with ported head?
« Reply #8 on: April 23, 2015, 10:49:42 AM »
Doesn't the -L stand for long??

Doesn't look like the piston hit it though.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline KickOnly849

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Re: Shorter plugs with ported head?
« Reply #9 on: April 23, 2015, 11:17:53 AM »
Doesn't the -L stand for long??

Doesn't look like the piston hit it though.

-L is a half heat range, 8.5

Offline PeWe

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Re: Shorter plugs with ported head?
« Reply #10 on: April 23, 2015, 11:29:19 AM »
DR8ES-L lenght of the tip ..... http://forums.sohc4.net/index.php/topic,77832.msg869100.html#msg869100
I have used DR8ES-L back in the 80 and last year too.
Important to compare how engine run with color of the plugs. Intermittent function/failure of an ignition wire will foul plug. I have seen that last year until beginning of this month.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline MattFreeman

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Re: Shorter plugs with ported head?
« Reply #11 on: April 24, 2015, 05:27:37 AM »
DR8ES-L lenght of the tip ..... http://forums.sohc4.net/index.php/topic,77832.msg869100.html#msg869100
I have used DR8ES-L back in the 80 and last year too.
Important to compare how engine run with color of the plugs. Intermittent function/failure of an ignition wire will foul plug. I have seen that last year until beginning of this month.

Thanks for the link. If they're good enough for Hondaman....