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Author Topic: '78 750F jet sizing question  (Read 1051 times)

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Offline Dracon

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'78 750F jet sizing question
« on: September 20, 2017, 06:52:34 AM »
Just wanted to be sure I'm thinking about this correctly. I have a 1978 cb750f with stock air box/filter, mac 4-1 header, and 12" cone engineering straight core muffler.

The PO rebuilt the carbs with #118 mains and #38 slow jets(he had pods...).

Stock is 105 and 35, so I'm thinking I should go back to 35 slow and use 110's for the mains - does this sound right to you guys?

Thanks!
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Offline flybox1

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Re: '78 750F jet sizing question
« Reply #1 on: September 20, 2017, 07:02:24 AM »
You'll want 38s...maybe even 40's for pilot jets.  An idle plug chop w the 38s, and IMS adjustments, will tell you if you need to go to 40s
Try the 110s for mains.  Going back to a stock airbox richens the mixture too much to keep the 118s
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'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 Jnel

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Re: '78 750F jet sizing question
« Reply #2 on: September 20, 2017, 03:24:51 PM »
Do you still have the pods?  I would be interested if in good shape.  Good brand like K&N

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Offline seanbarney41

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Re: '78 750F jet sizing question
« Reply #3 on: September 20, 2017, 05:07:02 PM »
Weren't the f's 110 or 115 main stock?  And the K's were 105's?
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Offline Dracon

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Re: '78 750F jet sizing question
« Reply #4 on: September 20, 2017, 06:07:39 PM »
The pods were just no name cheap stuff...

Confirmed from the Honda parts list that the '78 F had 105's and the '78 K had 110's.

I actually have some 110's taken from an old set of '78 K carbs that I can swap out - they look perfect - not having to buy things is nice!
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Offline flybox1

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Re: '78 750F jet sizing question
« Reply #5 on: September 21, 2017, 06:33:55 AM »
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'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 Jnel

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Re: '78 750F jet sizing question
« Reply #6 on: September 23, 2017, 12:37:10 PM »
Ok... thank you.

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