Jetting for Pods or stacks 77-78 CB750's

[Lucky 1]

- deleted -

Go to...

http://honda-cb750-s.456789.n3.nabble.com/1977-78-CB750-jetting-for-pods-td3900695.html

[shinyribs]

Thank you Lucky. Real world,hands on info is the best.Cool pic,too! I may be getting a set of these to work on soon so this will be very helpful

[Piute]

                            Great job and no luck to it knowledge,and hits and misses,
                                                                  
                                           NOW ........run it and have fun now

[Re-run]

Be ready to still need to tweak jets though. Different engines, different elevations. Just saying that a starting point is good but be prepared for it to need more tweaking on your set up.

[Lucky 1]

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The author has deleted this message.

[Re-run]

Oh certainly, I just didn't want someone to think this was the silver bullet and then still have issues and get pissed.

[Lucky 1]

I am working towards the silver bullet, and may be a couple of days away.
I really want to have a result that is spot on, and reliable. That
is my goal.


Just hold on for about two more days.

[Lucky 1]

OK...Here is the latest story on my 1978 CB750 jetting.

I went back to the stock air box with stock air filter.

I could not get it to run right with the stock #35mm idle jet.
IT has a 4 into 2 into 1 exhaust with a baffle.

So I put in a #42mm idle jet an now it runs great again.
Good throttle response.
SET UP:

!978 CB750:

stock air box and filter.
4 into 2 into 1 exhaust with baffle.
NO shims on the needle.
#120 main jet. Stock is #110.
mixture screw turned out 7/8 turn.

I also found out something else by accident.
When I had the carbs on the bench and all of the slides were bottomed out with #2 slide
by measuring from the top edge of the bottomed out slide to the top edge of the carb casting
all of the slides set to #2 height.

But when you look into the air cleaner side of the carb opening you will see that when the slides on #3 and #4 are all the way up that carb slides #1 and #2 are like 1/8 still showing!!!

The problem is that the linkages have slop in them.
So since #2 is not adjustable and #1 is the same as #2 what you have to do is adjust carbs #3 and #4 with the sync tool.

[Re-run]

Stock setting for the idle screw is 1.5 turns out. therefore that large of a idle jet would not be needed.
Plus, the linkage has no slop, they are adjustable. 1 side should close almost all the way while the other side is open a bit. #2 IS stationary but 1,3, and 4 are adjustable. You take a 1/8 inch drill bit and use the shank and set all 4 to the same amount, called a bench sync. This is the way they should be.
The only linkage that could have slop is the choke link as 1&2 are separate from 3&4.

I know you have done your testing but I have too. I have learned these carbs inside and out for over 15 years. I can, in virtually all exhaust changes, say that rejetting is not required except in all but the most extreme cases such as drag pipes.

[Lucky 1]

I agree with most of what you say Re-run.
My Clymers manual says that idle setting on a stock 77 and prior is 1 turn.  Page 63.
For the 1978 it says the mixture screw is preset at the factory.

So since the 1977 PD carbs are like the 78's I assume it is about 1 full turn also. Page 69

I guess I will use the sync tool to get those carbs #3 and #4 in the correct height.

Funny though because I thought if all the carb slides are bottomed out then when you turn the throttle,
the slides should all come up together at the same time.