Topic: '78 CB750K accelerator pump problem

[vistirus]

I have been unable to get the accelerator pump on my carb bank to function.  I have pulled the carbs down completely. Cleaned and cleared all parts and passages. I can spray liquid and air through all jets and passages. I have examined the diaphragm and cannot find any holes or tears. Air and liquid spray will come through the ball check valve in the pump base.
I saw a post on Honda Choppers on removing the plug that holds the spring ball valve in place so that the ball and cavity it sits in can be thoroughly cleaned. The problem is that the instructions are for removing a nylon plug (using a small self tapping screw to provide a handle to pull the plug out) but my carbs seem to have a brass plug. It's very tiny and doesn't allow for easy drilling.  The difference I see between the carbs in the post and mine is the model. The ones in the post are I think 46A and mine are 46B. This bike sat for 20 years without running, but the carbs were not too bad when I pulled them apart. 12,000 original miles, the fuel valve was shut off and the bike kept indoors. I have a test set up on my bench with a fuel source and nothing I have tried so far seems to work. Does any one have a suggestion for how to fix this?  How about a way to remove  the brass plug that holds the ball  and spring check valve? This is keeping me from getting the bike up and running.

Any help would be greatly appreciated.

Thanks very much.

Vistirus
Dripping Springs,  Texas

[lrutt]

I had the same problem. But...the fix was to put the hole in the diaghram where the factory didn't. If you study how it works, there is a second hole in the body of hte carb that takes the pumped gas up to the nozzles. The diaghram acts as a gasket around this hole, except there was no hole for the gas to pass through. I used a hole punch to create one and bingo, I had accelerator pumps working just fine. Pull it back apart and study it a bit, you'll see what I'm talking about.

[scunny]

it's the "mickey mouse" ears, should be 2 holes in that diaphram.

[TommyT]

I had the same problem.  Putting a hole in each ear fixed it and worked great.

[S_Spiff]

I'm in the middle of fixing the accelerator pump (and doing some other carb work) on my 78k.  Perhaps some of this will help. 

My accelerator pump wasn't working at all.  I had at least three problems:

1.  The lower check valve was completely frozen up and wouldn't pass air or carb cleaner at all.  I too have a brass plug instead of nylon.  I never did get the plug out to clean the check valve as per the HondaChoppers tutorial.  I did find that liberal carb cleaner, including soaking overnight, and compressed air got the lower check valve working. 

And working means passing air or fuel only one way.  If fuel can pass both ways, it won't pump.

There is another check valve in the #2 bowl (for a total of two) that must also work.  It is beneath a similar square brass plug near the float bowl gasket surface.  The second check ball on mine wasn't nearly as gummed up, but it was partially obstructed.

2. The pump diaphragm was rotten.  It looked and felt ok initially,  but after I assembled and tested the pump it started cracking.  It was clearly shot though it looked like it was in fair condition at first.  The spring in the pump was strong enough to half tear the rotten diaphragm, though just working it around with my fingers hadn't made it look bad.  It squirted two or three times then gave up.

3. Like the other posters mentioned, mine needed a better hole in one of the mouse ears.  One ear was punched so that it had an actual hole, but the other ear had only been pierced (like a needle poked through but no material removed).  The new part has huge holes (in both ears) by comparison.

Of course, the passages from bowl #2 to the nozzles in each carb need to be clear as well. 

[BobbyR]

You have your answer have a 78 and found all of the above to be absolutely true.

[CycleRanger]

1.  The lower check valve was completely frozen up and wouldn't pass air or carb cleaner at all.  I too have a brass plug instead of nylon.  I never did get the plug out to clean the check valve as per the HondaChoppers tutorial.  I did find that liberal carb cleaner, including soaking overnight, and compressed air got the lower check valve working. 

Ah HA!  Thank you sir, I had seen this before but I couldn't find it again when I needed it!
http://www.hondachopper.com/garage/carb_info/accelpump_valve_repair/page1.html

[Spanner 1]

All very good advise....... Also be sure the o ring is installed between thebowl
And body, otherwise yer just pumping back into the carb bowl..

[Tugboat]

^ +1

That little o-ring is often missing, and is hard to find. I think Spanner gave me his old one when mine was lost!

[bollingball]

Did anyone notice he has the wrong carbs
Quote The ones in the post are I think 46A and mine are 46B.
Or did he type a 6 instead of a 2
                                   Ken

[vistirus]

I did type a "6" instead of a "2".  My carbs are 42B. I am soaking all the parts with check valves for a day or so. I can spray cleaner through the passage and have it come out the nozzle of #2.  Ordered a new diaphragm, spring, boot and O ring.

Thanks to everyone for all the help.

Vistirus

[alacrity]

To those following this thread...  let’s say a friend of yours… Hypothetically... popped one of those square brass plugs out with compressed air, and it shot across the garage, into another dimension, never to be seen again.  After teasing him mercilessly about this.... What would be a fast/ easy-ish way to fabricate a replacement for this teeny little piece? Perhaps a chunk of aluminum? It just needs to keep the check ball from escaping while permitting fluid to pass (which is why it is a square plug in a roun home), right?

[flybox1]

if the brass plug flew out, so did the ball and spring.
Might be easier to find a replacement accel pump bowl than to re-create the missing parts....

[alacrity]

spring?!  omg.  Didn't even see a spring fly...But of course there's a spring in there.  argh.....

[flybox1]

spring?!  omg.  Didn't even see a spring fly...But of course there's a spring in there.  argh.....

I have a spare accel pump bowl.  Blocked, but just needs some time in a U-S bath.  PM me if you need.

[alacrity]

Pic shows skewer pointing at the tiny hole from which the brass plug and spring flew.  I managed to find the steel ball. 

[alacrity]

Pic shows skewer pointing at the tiny hole from which the brass plug and spring flew.  I managed to find the steel ball.

Look what I found... after hours crawling around and sifting like a csi tech.  But still no spring