Topic: Accelerator Pump Madness - Solved

[stocky]

Hey guys new member here with a project 1977 CB750. I'll start off my first post by apologizing on posting another accelerator pump issue but currently rebuilding the carbs and the only thing that is keeping the carbs from being completed is an issue with the accelerator pump. Ive searched high and low for the past few days and read so many threads but none has solved my problem.

Currently everything works except the fuel is just not getting drawn and/or (gravity fed?) into the accelerator bowl from the float bowl. I have pulled the check valve/spring/ball several times to check and re-check, passages are clear and checked with air, liquid, and wire. The little steel ball has been cleaned and polished, valve seat has been cleaned repeatedly and thoroughly. I believe I narrowed it down to an issue with the check valve/spring/ball since I tested the system WITHOUT the check valve/spring/ball in the accelerator bowl by doing the same test I have done now probably 20+ times by filling up the float bowl with water and hand pumping and water immediately squirted out on the first few pumps through the other hole that goes up to the other check valve on the side of the float bowl.

All that being said, I did multiple tests prior by spraying carb cleaner through a straw in the passage that leads to the check valve in the accelerator bowl and the liquid always came shooting out, so I am stumped, assuming maybe something is up with the spring because with enough pressure liquid will come shooting out...

So the only solution I might have found was in another thread by a user named "lucky" commented on saying he had the same exact issue and his only solution was to buy a new accelerator bowl. At this point if I can find these refurbished or oem new, I'll be more than happy to just replace it, but that's proving difficult. It's driving me mad to say the least. The spring, ball, and plastic stopper all look in pretty good shape, I really don't have any idea why something so simple in design would not be working properly. Is it something blindingly obvious that I am completely overlooking?

Help me get this project on the road, thanks guys! 

edit to add:
-bike is specifically a cb750k with pd41a carbs.
-diaphragm is new and has the two holes in the "mickey mouse" ears

[scunny]

Have you adjusted the tang that depresses the diaphragm to spec ?
I don't know about the 750, but the 650 has 2 different lengths of that rod, 1 for mechanical carbs and the other for cv carbs.

[stocky]

Not yet since the carb is still partly apart and off the bike but I remember the original rod was the right length and the new one I got was the same length. However the tang probably does need to be adjusted before the carbs go back on the bike but unfortunately that doesn't really address the problem since testing the pump by hand off the bike, it should have fluids shooting out the upper hole from what I understand.

[stocky]

Hey guys figured it out. Due to the lack of brain power and common sense late last night after working on the
carbs the whole day, woke up fresh this morning and realized I was testing it without the upper check valve that's attached to the float bowl since I had it taken that out awhile ago to clean. Without this upper check valve in place the check system is obviously useless as it was just drawing free air from that passageway instead of the hole in the float bowl for fuel.

After sticking the check valve back in the pump looks to be operating normally. Back on the carb and time to get er' done!

[scunny]

xcellent.