Topic: '78 CB750K accelerator pump

[CharlieT]

Tuning up the boys bike last nite. Removed all the float bowls, jets cleaned everything. #2 carb has the accelerator pump on it. One reason I was taking it all apart was that it seemed to have an excessive hesitation if you cracked the throttle. ROlling it on it was fine, so I did want to check the accelerator pump. In taking it apart, the diaphragm looks fine, no tears or pinholes, etc. However in looking at it, the two "dog ears" that extend out from the body of the diaphragm...one has a openhole but the other dog-ear is solid...no opening, even though it looks like it should have one. All the pics in the manual and online parts sites are too small to tell if both of these dog ears should have openings in them.

Any help here would be appreciated!

Thanks.

[eldar]

I think the is normal. I am pretty sure it is actually. I have not had to open my carbs this year at all so I cant quite remember but I am sure the 1 hole is normal.

[liaudio]

there should be an opening in both holes.  fuel passes through them.

[lrutt]

I don't recall for sure but I know my K8 had a problem in that there was no hole in that diapram that would allow fuel into the accel pump. the pump was dry. I had to cut a hole in there and wow, what a difference once you could get gas. I just don't remember if there were 2 holes or one.

Did you check the accel pump before taking the carbs apart? did you get squirtage?? Just analyze the fuel flow and you can tell if you need a hole in there or not. I've heard of a couple other people that had the same problem so it must have been a common occurance on those old bikes.

[pddpimp]

There should be 2 open holes. I had that same problem with my carbs. As a matter of fact, the brass plug in the number 2 body didn't even have the hole drilled in it to allow the squirter to get fuel. One hole lets fuel in, the other hole goes to the squirter tubes.

[Triker1/auto]

found the same problem with my 76, but i have 2 750's and the 78 had 2 holes soooo I cut a second in the 76 diaphragm bigggg difference in performance...

[CharlieT]

Well.....ya know, sometimes ya can't see the forrest thru the trees!

This is a bike my son just bought. Have plated it yet, haven't really ridden it at all. Was running real rough, missing, backfiring when we got it. Cleaned all the carbs, jets, etc. Starts right up but still had this poor trhtottle response. So I was checking the accelerator pump. Following general concensus, punched another hole in the diaphragm. No real change. SO as I was looking at the thing to see if there was any adjustmetn on the pump arm, I noticed it had a fair amount of tension on it with the throttle closed. Like I said, I have never personally ridden this bike, have only fired it in the garage after cleaning things up.  Well, I happened to notice that there was no free play n the throttle, absolutely none! So I decided to take care of that and adjusted the cable to give about 10deg free play. Then checked the pump arm and now there was no tension on it at closed throttle!!! Had a few thou clearance. So I fired it up and whoa!!! SMooth rapid revs cracking the throttle open and it even is idleing better and smoother.

The tight throttle cable had so much tension on the pump arm form the get go that cracking the throttle basically got no further response from teh pump! Instead of tearing the carbs apart again and taking the pump apart, all I had to have done was adjust the throttle play! Oh well, at least now I know the pump is good and that it also has two holes n the diaphragm.