Topic: 78 cb750 accelorator pump SOLVED

[78whiteorbs]

Not pumping- Have read for over an hour trying to figure this out.
I pulled the lines between the bowls that have the little brass restrictors in them and replaced them with clear yellow tygon and made sure to put the restrictors back in them. The tygon was just slightly bigger than the stock ones but not much at all, would this be a problem?

I can spray compressed in the inlets where the lines go to verify that they squirter jets are not clogs and they blow air through there fine so they aren't plugged.
Took the pump apart and the diaphragm looks good. cleaned the spring and notice one of the mickey mouse ears wasn't punched. This was the one that lined up with the hole in the carb float bowl. I punched a hole exactly like the other so now both mickey's ears are pierced.
The throttle is actuating the rod but there is no fuel in the lines. From my reading I am guessing I need to pull the brass plugs out of the retainers to check the little balls in the check valves. I don't think air is flowing either way out of these but I might not be testing this correctly.

How do you remove the brass plug?  I saw a how to on Honda Chopper about how to remove a nylon plug to clean things up in there but haven't seen anywhere yet how to remove this though I did find a post that showed a photo of the brass plug removed so someone has done it .  Sorry for the long post. This dang accelerator pump is all that is keeping me off the road...

[flybox1]

I went through all of this.  Here's my suggestion
Remove the accel pump bowl and spray carb cleaner in the hole on its lip that goes to the check valve in its center.  If no spray comes through, soak the accel pump bowl in simple green overnight.  Better if you can ultrasonic simple green it. It's gotta spray really well.

Spray carb cleaner into the hole in the bottom of #2 carb bowl to ensure the check valve at the rim of the bowl is working.  (See picture a few posts down)
The little oring at the top of this bowl....replace it if it's old, and if you tighten the bowl screws down too much, this ring overcompresses and will block the bowl lip check valve, blocking the whole system.
Put the bowl on minus the accel pump bowl, and ensure this passage will squirt carb cleaner up and out the squirters...if it doesnt, loosen the screw closest to the tiny oring.  test again.  If it works, then put on the accel pump diaphragm, spring and bowl... it will take some time, and a bunch of compressions of the accel pump to prime the system with fuel.  dont put your airbox back on until you can see spray out the squirters with a twist of your throttle...

Smaller fuel line between carbs will increase flow through the accel pump lines when the diaphragm is actuated.  Go with smaller lines if possible.

[78whiteorbs]

thanks flybox- I will give it a go tomorrow evening. Not sure if I recall seeing a o-ring though.

[seanbarney41]

I just went through a set, yep, you will need that o-ring.  mine would squirt out the joint between the float bowl and the carb without it.  Honda carb kits have that o-ring.  Let me know if you need one.

[flybox1]

$.50 in the metric oring box at your local auto parts store 

78-  I added a few more details to my first post as im no longer typing on a smartphone.  dont worry about removing the brass check valve.  it wont come out easy. my accel pump was so effd up that i sent it to sohcdigger for him to work his magic. his ultrasonic cleaner w simple green did the trick in 5 minutes.  so, if you can do that, you should have it working in no time.  i wish i had thought of it. 

[Tugboat]

If you still don't get a good squirt after cleaning the bowl & pump, you can also remove the squirt nozzles in all of the carb throats - they actually press out! If you look there are brass bungs below each nozzle. Using parallel-jaw pliers if you have 'em (or regular pliers if you don't - both with some tape over the jaws to keep from marring the brass) press the nozzles down. They will contact the bungs from the inside and press the bungs out. Note which way the nozzles are oriented within their slot - you'll want to put them back in the same way. The holes in the nozzles are TINY!! and can get easily clogged, so use that #9 guitar string you use to clean out your slow jets and poke from the bottom and from the side where they squirt. If you have the ultrasonic, drop these in there with some Simple Green. If not, maybe drop 'em in some carb dip. Regardless, make sure they are clean. Reinstall the nozzles - they are press-fit - into their holes, and use a punch to gently tap the bungs back into place, level with the bottom of the carb bodies.

Thanks to Spanner1 for this tip!

[pmurph1x]

Remove the accel pump bowl and spray carb cleaner in the hole on its lip that goes to the check valve in its center.

This seems to be important.
My accelerator pump was working great 2 weeks ago. I took off my bowls to put in new needles (I was having leaks) and noticed a couple of tiny bits of crap in the bottom of the bowl. Being anal I hit them with carb cleaner. While I was at it I decided to squirt the cleaner down the hole to the accelerator - just in case. I put it all back together and suddenly the accelerator pump stopped working.
Taking it apart I found that the diaphragm had two splits (see pics). I'm guessing that the carb cleaner sat in the pump reservoir and caused the diaphragm to weaken or become brittle.
Anyway I wont be allowing carb cleaner to contact the new diaphragm that I just ordered.




FYI - you should be able to check that the pump is working before putting the bowl on. Just put some liquid (other than carb cleaner) in the bowl and manually (gently) pump the diaphragm rod. If it is working you should see it squirt out the side hole at the top of the float bowl. Itll squirt out pretty hard - youll know if its working.

[flybox1]

Yes, it has been documented that carb cleaner is harmful to these diaphragms...

[lucky]

Carb cleaner has trichloretheylene in it and will cause seals to swell up a lot and then they will not fit correctly.

[Tugboat]

Yep - ruined a brand new diaphragm with carb cleaner last time I did my carbs. Lesson learned!!

[lucky]

The diaphram is not usually why the pump fails.
It fails because the check valve in the bottom of the pump gets corrosion from water sitting it.

[78whiteorbs]

Well, back to it . Thanks for the input guys. I am missing that o-ring. Thanks for the picture flybox!
I am gonna try an find an o-ring now. Got the right size lines and installed the restrictors so check there.
I tried the suck blow on the check valves and the one on the pump bowl works fine in one direction. The one on the carb bowl doesn't work either way. Both them bad boys are getting blasted by ultrasonic frequencies now as I type . Hope fully that frees things up . No need to remove the squirters from carb bodies because they aren't clogged.

Will post progress.

[78whiteorbs]

OK, ultrasonic everything and the check valves are working the way they are suppose to now . I can blow air through them one way no problem. I didn't have an o-ring quite that small so I made one from chopping a little piece of tubing that was the perfect diameter inside and out. Put everything back on and still not pumping. I pumped it before installing and it sounded like it was pumping, they there was some sucking and blowing going on in there. Only thing I can think is that the imprevised o-ring is the culprit. That it is blocking the flow . Frustrated but gonna try an find an o-ring tomorrow in town. Hopefully napa or Ace has some that small. I did think at first maybe it wasn't primed but I twisted theh throttle like 30 times and that should have done it ...

[flybox1]

did you make sure it actually pumped before putting your carbs back on?  Save yourself time and energy..don't put them on until they work right.
Get your #2 bowl off and fill it with water WITH the accel pump on it.  Actuate the pump Does it squirt out the top of the bowl?
Fix it if it does not.
If it does, empty the water,and you put the bowl back on, check to see that it pumps...with the carbs OFF the bike....
If it does not, find out where the blockage is..it's in the carb lines as you've just verified the pump works.

[78whiteorbs]

yeah that'd make to much sense for me to do

I have to do something wrong and least twice before I can do it the right way or my altered short term memory will never le me learn the lesson! I just wanted to see that 4-way money shot plus I have become a pro at installing carbs on my cb750 in record time! Now lets give it a go with just the bowl off as you suggested. Hopefully it just that  o-ring . Feelin like I am getting close now.

[flybox1]

Cool. Don't rack'em until you get that '4-way money shot' 

[78whiteorbs]

well pulled it off and manually pumped it and it squirted just fine. The o-ring I made must be obstructing it , blew air through the lines and each post is blowing air just fine. Off to try and find an o-ring now..

[78whiteorbs]

mission complete! squirting just fine now. Hooked everything back up and it's seems to be revving better and all but still off idle stumble pretty bad. I haven't vacuum synced them or adjusted valves though or checked timing for that matter. Still have a ways to go I guess but mark this one solved.

FWIW I found the little O-rings at ace hardware as close as I could to the metric but actually remembered that the guy I bout some cb550 gaskets off ebay included some O-rings I never used and sure enough they were the perfect size.

[flybox1]

Nice work!  glad you found an o-ring that worked.
i battled with that symptom for a solid week until i figured out it was all caused by that tiny d@mn part! 

[Cam]

This thread saved me a huge headache. I just rebuilt my carbs and when I tore them apart that o ring wasn't there so naturally I didn't put one in. Saw this post and had to pull that bowl off again to throw it in there! 

[78whiteorbs]

Awesome!

[lucky]

Thanks for reporting back.

I am sure all concerned appreciate that.