Topic: 1978 CB750K carb rebuild questions

[Mopar_or_no_car]

I just got my 1978 CB750K  that has been sitting for about 10 years running and I thoroughly cleaned carbs which I belive are keihin pd42b so now it will idol nicely with choke off. When I first started cleaning the carbs I did not realize the slow jets could be removed to be cleaned. And turns out they were very cloged and why the bike wouldn’t idol nicely. When I first had the bike running it would spew gas out of the overflow in carbs 1,2, and 4 I cleaned the needle and to the best of my ability where it seats and this solved my problem for carbs 1 and 4 but carb 2 still drips and I’m not sure why else it could be leaking now I should mention I have not touched the float height could that be my problem? Any suggestions are appreciated.

[Burke]

Im going back through a 78' now as well, Im only firing on #4, however I have spark, so I'm thinking I missed something. The slow jets are pressed in correct?

[flybox1]

slow jets are pressed in, and can easily be removed with some gentle persuasion.  dont bend.  twist and pull straight out.
Remove the emulsion tube along with the main jet, and ensure all those holes are clean.
Verify the accel pump circuit (bottom of carb bowl #2) pressurizes, and squirts out all accel jets (brass tubes in carb throats)
ensure fast idle cam works when choke knob is pulled.

IMS should be set at 1 turn out for stock intake and exhaust.
 Check plug caps for resistance.  any past limits should be changed


Get Hondamans book.  itll help guide you thru everything....

[Airborne 82nd]

I just got my 1978 CB750K  that has been sitting for about 10 years running and I thoroughly cleaned carbs which I belive are keihin pd42b so now it will idol nicely with choke off. When I first started cleaning the carbs I did not realize the slow jets could be removed to be cleaned. And turns out they were very cloged and why the bike wouldn’t idol nicely. When I first had the bike running it would spew gas out of the overflow in carbs 1,2, and 4 I cleaned the needle and to the best of my ability where it seats and this solved my problem for carbs 1 and 4 but carb 2 still drips and I’m not sure why else it could be leaking now I should mention I have not touched the float height could that be my problem? Any suggestions are appreciated.

The clear tube test is super easy for our PD carbs Google is your friend. You need to check your float valve or inspect the brass tube inside the bowl some times they split long ways.

[BobbyR]

+1 on all points Airborne

[Mopar_or_no_car]

What is the clear tube test I just googled it and see people using it but I’m not sure what it means regarding float height also i know for a fact that the brass tube is in tact.

[BobbyR]

The clear tube allows you to see the fuel level in the bowls. Too high you get an overflow, too low and you run lean. You adjust the float to get the proper level.

[flybox1]

The clear tube allows you to see the fuel level in the bowls. Too high you get an overflow, too low and you run lean. You adjust the float to get the proper level.

+1
For our PD carbs, you attach the clear tube to the bowl overflow pipe(not the drain screw hole as pictured), and loop it up next to the bowl. Then, turn open the drain screw and see where the fuel level stops.

[BobbyR]

For a CB750 78K, you simply put the tube over the drain tube at the bottom of the bowl and open the drain screw. Very simple. I have a K8 and have done it several times. Easy bike to do this on. Just remember to hold the tube up when you open the drain.

[Airborne 82nd]

I replaced my black overflow hoses with clear fuel line 

[BobbyR]

I replaced my black overflow hoses with clear fuel line 

That is a great idea. You don't need anything fancy since fuel rarely gets to them for very long. Unless something is wrong.