Topic: 77-78 CB750 PD42A Carb Rebuild Info

[flybox1]

^^Correct
The washer has to go between the spring and the o-ring
(to protect the o-ring from being chewed up by the spring end when adjustments are made)

[hondacr]

Spring, washer, O ring

+1
I'm also guessing you were over fueling with the 135 jets even with the free flowing K&N pods.

quote +1
No I don't think so, if that was the case it would be fowling up all of the other 3 plugs as well...no K&N's now they are crap even though they were the correct ones for this bike, the polished velocity stacks on are spot one & work very well...ive just got to get this carb 4 sorted

[drdave]

No bottle will clean accel pump system (check valves and jets) debris or clogs....period.
No bottle will scrub or poke emulsion tube and pilot jet holes clean...period.

Get in there and do it right.

Hi there, Just a question. I have a 1978 f2 supersport and in the schematics pic you can see the o ring and washer with the fuel mixture screw #7 on the image. however my bike doesn't have these, and when I try to purchase on the cms website they only offer the spring and screw. Im sure this would make difference? do you know where I could purchase the extra bits?

[AfgLEP]

First all hail to the author of this pictorial Go-By. As I Was researching unsticking a stuck accel pump check valve (which I have) as the nylon one on my 77 K is snafu’d a little. My problem is the one in the bowl. I read the screw into the nylon block one on Honda Choppers site and hoping I can do that as a last resort. So, two questions: Can I poke a slim blunt instrument thru the Mickey ear against the ball from the bottom to dislodge or push the ball, spring and nylon block out? Or, how about compressed air shot into towel to keep from disappearing the spring, etc. ? Any help appreciated too.

[bryanj]

Drdave, bit late to this but the bits you want were never supplied seperate, all you can do is buy 1 set and measure the bits wanted to see if you can get generic ones. Would be nice if you posted thesizes for others.

As an afterthought Siriusonic in Canada may do something but you will have to trawl the website

EDIT
Sirius Consolidated do both washer and O rings in 50 packs but you have to keep trawling Honda carb parts page after page up to about 50 on my dumfone

[ktm136]

Have any of you ever encountered an accelerator pump actuation spring that was took weak actuate the pump? Mine works but only if I pump it by hand. It won't work when I twist the throttle.

[JimsCB750]

My 78 750K has a small brass tube sticking up on the accelerator pump row next to Carb#2 without a rubber hose connected to it.   When I connect a rubber hose to it with the carbs off, I can freely blow air through it and suck air through it.     What is the purpose of that small brass tube on these 77-78 carbs?

[TwoTired]

My 78 750K has a small brass tube sticking up on the accelerator pump row next to Carb#2 without a rubber hose connected to it.   When I connect a rubber hose to it with the carbs off, I can freely blow air through it and suck air through it.     What is the purpose of that small brass tube on these 77-78 carbs?

I think you might be talking about an air vent used to place atmospheric pressure on the fuel in the bowls.  This is the pressure that pushes fuel through the fuel jets, whenever the engine lowers the pressure in the carb throat.  It should have a long tube that routes down near the fuel overflow drains.  The long tube helps keep dust and debris from getting into the carb bowls and contaminating the jets.

[Captain Ron]

I'd like to add:

Spanner1 discovered that the little brass bung underneath the accelerator pump nozzle can be gently pressed out using a pair of pliers (put some tape on 'em to keep from messing up the brass!). I'm referring to the round brass part just above the right float post, to the left of the top screw hole.


Once you press out the bung, the nozzle will come out so that you can fully clean it.When you put it back in, make sure the little grooves line up so that fuel flow is not obstructed.

Does anyone have any further info on getting these out so that I can get the accelerator nozzles out to fully clean? I'm not quite sure what you mean by 'press them out". Thanks

[madmtnmotors]

I am currently working on a set of PD carbs for yet another K8 CB750 and came back to this thread for a little refresher. I am compelled to set the record straight here and confirm that I had provided incorrect information in a previous post:

http://forums.sohc4.net/index.php/topic,48858.msg2023456.html#msg2023456



The diaphragm pulls from the #2 bowl through the check ball in the bottom of the pump bowl, and up through the check ball at the accel fuel pump crossover at the back of the #2 carb. The arrows indicate direction of flow through the accel pump bowl: