Author Topic: Plug gurus, rate my plugs!  (Read 685 times)

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Offline OneWheelDrive

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Plug gurus, rate my plugs!
« on: April 19, 2016, 08:37:59 PM »
1974 K0 CB550 bored to 605, 650 cam, Uni pods, delkevic 4-into-1 with small baffle, hondaman trimmed advance spring, timing 2 degrees advanced, 38 pilot jets, 110 main jets, needle clip 3 from the top. Bike runs great from idle to redline, but there's some stumbling and popping when cruising in the mid-range. I'm thinking up to 40 on the pilots is in order.

« Last Edit: April 19, 2016, 08:44:27 PM by OneWheelDrive »
1975 CB550 cafe
1971 CB500 stocker
2008 Ducati Hypermotard 1100S *sold*
1973 CB350F *sold*
1975 CB550K Project "Keeper" *sold*
2010 Ducati Monster S4RS *sold*
1976 CB360T *sold*
1974 CB550K *sold*
1973 CB750K *sold*
1978 CB550K *sold*
2007 Vespa LX150 *sold*

Offline CB650CPastor

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Re: Plug gurus, rate my plugs!
« Reply #1 on: April 19, 2016, 09:59:12 PM »
Those plugs look good to me. I would try moving the needles one groove richer.
Tim
Current:1980 Honda CB650C Custom, 1969 Toyota Corona Deluxe Sedan
Past: '07 Honda Rebel 250, '80 Yamaha XS1100 Special, '69 Honda CB160, '67 K15 Suzuki Hillbilly, 1971 VW Super Beetle...

Offline mrfish2

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Re: Plug gurus, rate my plugs!
« Reply #2 on: April 20, 2016, 02:14:34 AM »
Is that a plug chop or did you just pull those out after riding around in multiple throttle ranges?

If it's the latter then you'll need to go back and do the proper plug chops to get an idea of what is happening in each throttle range. Overall they look decent if not a tad lean.
1976 CB550K            1979 XS1100
1980 CB650C - Sold

It's a little motor and likes having the tits revved off it.

Offline OneWheelDrive

  • A journey of 1000 miles starts with your first carb overhaul.
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Re: Plug gurus, rate my plugs!
« Reply #3 on: April 20, 2016, 06:25:09 AM »
Is that a plug chop or did you just pull those out after riding around in multiple throttle ranges?

If it's the latter then you'll need to go back and do the proper plug chops to get an idea of what is happening in each throttle range. Overall they look decent if not a tad lean.

That's a plug chop while experiencing the popping.
1975 CB550 cafe
1971 CB500 stocker
2008 Ducati Hypermotard 1100S *sold*
1973 CB350F *sold*
1975 CB550K Project "Keeper" *sold*
2010 Ducati Monster S4RS *sold*
1976 CB360T *sold*
1974 CB550K *sold*
1973 CB750K *sold*
1978 CB550K *sold*
2007 Vespa LX150 *sold*

Offline flybox1

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Re: Plug gurus, rate my plugs!
« Reply #4 on: April 20, 2016, 06:27:21 AM »
at what throttle position?
RPM, speed...they are irrelevant in a plug chop. 
...and what are your mixture screws set at?
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline OneWheelDrive

  • A journey of 1000 miles starts with your first carb overhaul.
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Re: Plug gurus, rate my plugs!
« Reply #5 on: April 20, 2016, 09:20:10 AM »
at what throttle position?
RPM, speed...they are irrelevant in a plug chop. 
...and what are your mixture screws set at?

Between 3-4k rpm, maintaining approximately 1/4 throttle, mixture screws are 3/4 turn out.
1975 CB550 cafe
1971 CB500 stocker
2008 Ducati Hypermotard 1100S *sold*
1973 CB350F *sold*
1975 CB550K Project "Keeper" *sold*
2010 Ducati Monster S4RS *sold*
1976 CB360T *sold*
1974 CB550K *sold*
1973 CB750K *sold*
1978 CB550K *sold*
2007 Vespa LX150 *sold*

Offline flybox1

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Re: Plug gurus, rate my plugs!
« Reply #6 on: April 20, 2016, 09:24:28 AM »
once you get to 1/2 throttle position, does the symptom go away?

how are you measuring 1/4 throttle position? 
do you have indicator marks on your control & throttle, or is it a guess?
« Last Edit: April 20, 2016, 09:30:19 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline flybox1

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Re: Plug gurus, rate my plugs!
« Reply #7 on: April 20, 2016, 09:28:20 AM »
if truly at 1/4 throttle pos, your slide needles are barely supplying fuel to make a difference.
you're right in the mixture screw/pilot jet wheelhouse, so, go 1/2 turn RICHER on all mixture screws, ride test at 1/4 throttle pos, and if that doesnt get you the result you want, go to 40pilots and back to 3/4 turn on the mixture screws, and retest.
be sure to use OEM Keihin jets  ;)
« Last Edit: April 20, 2016, 09:30:57 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"