Carb clean; accel pump

If it's broken or just needs tweaked

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michael_650
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Carb clean; accel pump

Postby michael_650 » Thu Mar 29, 2018 7:33 pm

I am carb cleaning. Specifically the accelerator pump.
LINK to a great resource: http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
Two questions:

1. should there be a boot or seal around the shaft? there wasn't. The shaft was so badly corroded it was frozen. Mr. Rubber Mallet and I persuaded it loose. I cleaned it and oiled it so it moves.

2. The bowl has a vent with brass diffuser. It is blocked. I have boiled in water and simple green for 3-4 hours and it's still blocked. I can't get a high-e guitar string through it for the life of me. Thoughts?

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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Thu Mar 29, 2018 10:24 pm

Minor progress. With the diaphragm and cover off, i can see the two holes; one that allow gas from the bowl to the diaphragm (thru hole), and one with a brass diffuser pressed in. I i tried spraying brake cleaner through the second and nothing worked. i gently pressed the brass block out from the back with a nail and mallet (EVER so GENTLY) and now i get a nice spray of fluid coming through. Using a dial caliper, the brass diffuser is now 0.005" proud of the gasket surface.

With the diaphragm and cover in place, however, when i fill the bowl and press on the diaphragm rod, nothing happens. I notice the pump cover has some holes and a brass diffuser pressed into place. There is no access from the back to press the diffuser out, and i'm afraid. I'm thinking of buying a new diaphragm on the 'bay, but if the passages in the cover are blocked, what can i do?

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Folsoml
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Re: Carb clean; accel pump

Postby Folsoml » Fri Mar 30, 2018 7:59 am

Sadly, some things just can't be brought back to life. You may have to search for a new cover on the bay as well. Sadly, you will be rolling the dice that you get one in better condition than the one you have. You also might need to get the entire #2 float bowl. You may not be able to find one specifically for the VB44A carburetor bank that is on your cb650, but one from a cb750, cb900, or cb1000 (maybe others) from that same era will work. There are minor differences, but it will get the job done.
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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Fri Mar 30, 2018 1:26 pm

I'm not a huge fan of that response. :(

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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Fri Mar 30, 2018 6:20 pm

If i spray cleaner into the hole on the lip, should it come out the tiny round hole or the hole with the brass diffuser in it, or both??

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Folsoml
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Re: Carb clean; accel pump

Postby Folsoml » Sat Mar 31, 2018 9:30 am

Refer to page 20 of the MacGregor Manual link you provided. It should come out of the brass diffuser. The other hole is to allow it to refill with fuel.

For what it's worth, when the accelerator pump is in actual use, it will happen in reverse of how it is shown in the manual. Fuel will fill the accelerator pump bowl (what we have been calling the cover). When the throttle handle is turned, the diaphragm shaft is pushed down--compressing the area within the bowl. The fuel is then forced through the brass diffuser, out through the hole in the lip, and into the #2 carb via hole with the brass insert on the #2 float bowl.
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tario
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Re: Carb clean; accel pump

Postby tario » Sat Mar 31, 2018 8:00 pm

You can soak in carb cleaner for a few days and hopefully it will eat away everything but the metal. Ultrasonic cleaners are a good option if you can find a restoration place that uses them. You might have some luck with the freeze-out style anti seize sprays. If you can get the cover cold enough it might break free any clogs. Or Just heat the cover up as much as you're willing to... just don't warp it. If she's already f#$% you can't f@#% it any more.
1979 cb650
1980 cb650

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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Sat Mar 31, 2018 9:08 pm

<deleted bad links to photobucket> -michael_650
Last edited by michael_650 on Mon Apr 02, 2018 9:47 am, edited 1 time in total.

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Folsoml
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Re: Carb clean; accel pump

Postby Folsoml » Sun Apr 01, 2018 7:30 pm

Photobucket is the worst now. I need to redo the tutorial with instructions for postimg.org. It's like photobucket, only better.
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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Mon Apr 02, 2018 10:53 am

I just found this PDF about accelerator pump bowls on the 77-78 CB750. Is the diffuser in the middle plastic or brass? I was under the impression it was brass but now I'm left wondering...

http://www.hondachopper.com/garage/carb_info/accelpump_valve_repair/Repairing_77-78_Accelerator_Pump_Valves.pdf


.

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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Mon Apr 02, 2018 12:17 pm

Here's a pic of the accelerator pump diaphragm/shaft from my #2 carb. I assumed it was a fixed and unmovable mystery part until I read up on it. Finally took the accelerator pump bowl off without losing the spring, tapped gently with a mallet, and realized it had been frozen in place with rust. No boot on the shaft: gotta love previous owners and their shenanigans.

Red arrows indicate where the rim of the diaphragm doubles as o-rings for through passages.
Attachments
pumpShaft.jpg
pumpShaft.jpg (58.71 KiB) Viewed 1889 times

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michael_650
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Re: Carb clean; accel pump

Postby michael_650 » Mon Apr 02, 2018 9:01 pm

Impatiently waiting until 10am Tuesday when the dealer opens to find out if I can order one. Until then, looking up aftermarket alternatives just in case.

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GeorgeSweety
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Re: Carb clean; accel pump

Postby GeorgeSweety » Tue Apr 03, 2018 4:26 am

That shaft looks a bit short unless it is the angle of the picture.
https://www.ebay.co.uk/itm/Accelerator- ... Sw3yVZhgCm

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Folsoml
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Re: Carb clean; accel pump

Postby Folsoml » Tue Apr 03, 2018 6:40 am

michael_650 wrote:Impatiently waiting until 10am Tuesday when the dealer opens to find out if I can order one. Until then, looking up aftermarket alternatives just in case.


They stopped making OEM ones a while ago.

https://www.partzilla.com/product/honda ... ec5a2d4f72

Here is an aftermarket one for $20.

https://www.ebay.com/itm/Accelerator-Pu ... Cm&vxp=mtr
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GeorgeSweety
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Re: Carb clean; accel pump

Postby GeorgeSweety » Tue Apr 03, 2018 6:56 am

Michael, be sure to check the length of the shaft before you fit it, I would not cut it the same as the one you already have as that one looks like it has been cut way too short.


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