Topic: CB750 Lucky

[lucky]

Well I fought the pump and the pump won.
Oh yeah....We are talking about the carb accelerator pump. CB750K 1978.

Here is what was going on.
This is how it works.
The float bowl fills up with gas. #2 carb.
And there is a little hole in the bottom of the float bowl and that fills up the
small volume space in the accelerator pump housing below.
When you turn the throttle the rod connected to the rubber diaphram pushes
down on that volume of gas in the accelerator pump housing and the gas should squirt up the tube on the side of the float bowl to the nozzles.
IF  the little steel ball in the bottom of the diaphram is closed and seals. BIG IF. The gas is then forced to go upwards through another check ball in the main float bowl to the nozzles, and it cannot come back down because a check ball in the main float bowl keeps it only going one way. That way the accelerator pump cavity can refill from the main float bowl, and have no airspace going to the nozzles.


So my pump will not pump fuel up to the nozzles because when I actuate the throttle and the diaphram pushes down on that small bowl (accelerator pump), of fuel it just goes past the steel check ball in the bottom of the accelerator pump and goes back to the main float bowl instead of going up through the nozzles.


I have taken it apart several times and cleaned it but it will not seal. So I finally decided to buy a new plate with that check ball for the bottom of the accelerator pump. No way out.

So the check ball in the bottom of the accelerator pump is EXTREMELY important because it has to let gas come in but it has to seal closed when you give it throttle.
The little soft spring has to have the right amount of tension.

CLICK on photo for large version.

BTW...I have no idea why this forum changes JPG's into PNG files because a PNG file is the largest file size. A JPG file is the smallest and only gets rid of non image data. Quality is just as good.

Just my 2cents worth.

[fastbroshi]

   Better way to get pics on here is go to one of the various picture sharing websites out there and create an account.  You can upload your pics there, grab links from the website will create for your pics, and paste the links in your posts and the pics show up nice and big without taking up a bunch of space.    I use Photobucket myself.
   Thanks for explaining all that, first time I've seen someone attempt to do so. 

[lucky]

   Better way to get pics on here is go to one of the various picture sharing websites out there and create an account.  You can upload your pics there, grab links from the website will create for your pics, and paste the links in your posts and the pics show up nice and big without taking up a bunch of space.    I use Photobucket myself.
   Thanks for explaining all that, first time I've seen someone attempt to do so.

You are so right. Many of them will resize the photo for you for internet use.
I use Tinypic.com but resize them myself and use the FILE>Save for web feature of Photoshop. Has to be Photoshop 5.5 or higher. The real full Photoshop version.

[70CB750]

+1  on save for web, I worked with photoeditors long enough to treat my pix somewhat right.

Or you can use ImageReady - hmm, that dates me 

[Greggo]

Nice work on the project so far.  That accelerator pump business makes me glad my '76 has the old style carbs.  Have you gotten the frame back from the powder coater?  Who did you use in Sonoma County?

[Freaky1]

Very ineresting, I had replaced the stock carbs on my '77 F with some eariler model ones and am thinking about going back on my rebuild. You have convinced me to build an engine stand so I can run the motor and work out which I like better along with any other bugs before I wrestle that thing back in.

[lucky]

Very ineresting, I had replaced the stock carbs on my '77 F with some eariler model ones and am thinking about going back on my rebuild. You have convinced me to build an engine stand so I can run the motor and work out which I like better along with any other bugs before I wrestle that thing back in.

Personally I would go with the earlier model carbs. Easier to work on, and simpler less parts. Lets face it Honda put that accelerator pump on the last two years of production of the CB750 SOHC and I do not think they had it worked out very well.
If you do use the 77 carbs make sure that when you advance the throttle that those nozzles will all work. All 4 of them.

If you remove the float bowl from #2 carb and use some carb spray (guard your eyes!),
You should be able to see fluid come out of the tube sticking up in the venturi. The fluid sprays out the side and towards the engine. You will see the tube leading upwards to the network of nozzles.

[lucky]

Nice work on the project so far.  That accelerator pump business makes me glad my '76 has the old style carbs.  Have you gotten the frame back from the powder coater?  Who did you use in Sonoma County?

I received my parts back from the powder coater today and they were beautiful and they covered all of the openings and threaded parts for me also.
They did my frame, gas tank, tank fuel fill lid, and battery box.
Nice people. They finished them ahead of the scheduled time and kept their word on the total price. No add on fees!

I saw lots of other motorcycle and car parts being worked on while I was there.
They also do industrial parts. So they have a wide range of experience.
Miller Powder Coating (MPC) Rohnert Park,California

CLICK on photo to ENLARGE.

[Cheffish]

Is that gold?  Looks very nice

[TommyT]

Looks good.  Question on the accel pump for you.  On my K8 When I give it gas up to 1/4 throttle it sputters pretty good then rev's up almost like normal.  When I hit the gas it squirts gas out the tube for the accel pump.  Is there a way to adjust that, almost seems like it's flooding the engine out when I first hit the gas?  Have you messed with that at all?  I check manual on here and it shows it but wasn't sure if you have any more advice for that.

[lucky]

Looks good.  Question on the accel pump for you.  On my K8 When I give it gas up to 1/4 throttle it sputters pretty good then rev's up almost like normal.  ç.  Is there a way to adjust that, almost seems like it's flooding the engine out when I first hit the gas?  Have you messed with that at all?  I check manual on here and it shows it but wasn't sure if you have any more advice for that.

"When I hit the gas it squirts gas out the tube for the accel pump." Which tube???

 Is it squirting gas out all four nozzles? If not you will have to remove those rubber hoses between the carbs and find out if one is blocked by spraying some carb clean through and making sure all 4 nozzles are open.
(Gaurd your eyes!!)

[lucky]

Today I installed that accelerator pump bottom bowl with that new check valve that I bought new.
$85.00!!! OEM part. But no way around it. Like I said I do not like those carbs.
But if I buy new ones it will be $500.-$800.!!!!
I tried 3 times cleaning that part and cleaning the steel ball. No dice.

But now the accelerator pump works perfect. All 4 nozzles spray fuel with the carbs on the bench hooked to a fuel tube! Hurrah!!! Finally.

[lucky]

Is that gold?  Looks very nice

Yes it is gold, and does not look cheap like spray can gold.

[TommyT]

Looks good.  Question on the accel pump for you.  On my K8 When I give it gas up to 1/4 throttle it sputters pretty good then rev's up almost like normal.  ç.  Is there a way to adjust that, almost seems like it's flooding the engine out when I first hit the gas?  Have you messed with that at all?  I check manual on here and it shows it but wasn't sure if you have any more advice for that.

"When I hit the gas it squirts gas out the tube for the accel pump." Which tube???

 Is it squirting gas out all four nozzles? If not you will have to remove those rubber hoses between the carbs and find out if one is blocked by spraying some carb clean through and making sure all 4 nozzles are open.
(Gaurd your eyes!!)

Yeah nozzles in each carb not tube.  At how much throttle engagement does it start squirting on your carbs.

[lucky]

+1  on save for web, I worked with photoeditors long enough to treat my pix somewhat right.

Or you can use ImageReady - hmm, that dates me 

Image ready has one feature that I liked and that was making sure the photo can be seen by Mac and IBM because the brightness of the screen in IBM is not as bright as a Mac.

[lucky]

Looks good.  Question on the accel pump for you.  On my K8 When I give it gas up to 1/4 throttle it sputters pretty good then rev's up almost like normal.  ç.  Is there a way to adjust that, almost seems like it's flooding the engine out when I first hit the gas?  Have you messed with that at all?  I check manual on here and it shows it but wasn't sure if you have any more advice for that.

"When I hit the gas it squirts gas out the tube for the accel pump." Which tube???

 Is it squirting gas out all four nozzles? If not you will have to remove those rubber hoses between the carbs and find out if one is blocked by spraying some carb clean through and making sure all 4 nozzles are open.
(Gaurd your eyes!!)

Yeah nozzles in each carb not tube.  At how much throttle engagement does it start squirting on your carbs.

The engagement can be adjusted a little bit.
On my 78 carbs the little steel tang is sitting right on the pump rod and the throttle has to move at least 1/3 before it starts pushing on the rod.
The rod total travel is very small like maybe 1/4 inch is all.
The workshop manual shows a gap measurement between the steel tang and the top of the accel pump rod and it is..024-.032 when the throttle is closed, and adjustment is by bending the steel tang.
Well when you see where the tang is, you cannot get to it and I do not think you could bend it with pliers. Just would not work.
I would just leave it alone. Those carbs need a lot of fuel.
When you attach the accelerator pump bowl and diaphram with rod,  the rod comes right up to the tang and stops when the screws on the accelerator pump bowl screws are tightened.

The pump rod is protected from being pushed down too far by a spring that limits the pressure exerted on that steel pump rod. Good thing.

Anyone that owns one of thes bikes should have the workshop manual. I cannot imagine NOT having one. Mine is a Clymer's and has problems but it also has valuable essential information.

[lucky]

Very ineresting, I had replaced the stock carbs on my '77 F with some eariler model ones and am thinking about going back on my rebuild. You have convinced me to build an engine stand so I can run the motor and work out which I like better along with any other bugs before I wrestle that thing back in.

Yes I agree because it is easy to work on in the stand and if you spill something it will not be on your frame and other parts.
Just knowing that it is going to run properly when you put it in the frame makes you feel very confident. Otherwise you have to build up the entire bike before you know what will happen.

By the way check ebay because someone sells a stamped steel engine mount that bolts right onto the engine stand. I will try to post a photo and link...hold on.
http://forums.sohc4.net/index.php?topic=65907.0 From a forum member.

[Freaky1]

Very ineresting, I had replaced the stock carbs on my '77 F with some eariler model ones and am thinking about going back on my rebuild. You have convinced me to build an engine stand so I can run the motor and work out which I like better along with any other bugs before I wrestle that thing back in.

Yes I agree because it is easy to work on in the stand and if you spill something it will not be on your frame and other parts.
Just knowing that it is going to run properly when you put it in the frame makes you feel very confident. Otherwise you have to build up the entire bike before you know what will happen.

By the way check ebay because someone sells a stamped steel engine mount that bolts right onto the engine stand. I will try to post a photo and link...hold on.
http://forums.sohc4.net/index.php?topic=65907.0 From a forum member.

I have a Gordon frame kit in mine so it's not quite as difficult to get the motor in but anything to make it easier to get to is worth it. I totally agree on the mess issue, plus it would be easier and cheaper then buying a lift for the whole bike. I think I look funny on a creaper under a motorcycle.

[lucky]

When I first started working in a motorcycle shop there were no motorcycle lifts.
What is strange is that we had scissors jacks and ironing boards as far as ideas to use but no one built a motorcycle lift.

We had to just sit on a plastic crate to sit on and work on the bike.
There was nothing keeping some mechanic from developing or making a motorcycle lift.

Almost 25 years went by before you could buy a motorcycle lift!

We always wanted to get the bike higher to work on it but no one did anything about it.

[Freaky1]

I have plans to build my own lift but we'll have to see how that comes along. With winter around the corner I just might have the time. Mine has sat on a crate several times but once I put the motor in it looks like the crate is very close to it's weight limit. I scored a manacurist chair and wow that thing is the greatest, the seat is more of a saddle and the swing arm makes a great back rest.

[lucky]

I am moving onto the next step.
I got my engine back from Cycle Exchange. It is rebuilt and looks great.
This is the first motorcycle rebuild that I did not rebuild the engine myself.
I was able to get the engine in the frame but have been a little under the weather the last couple days so progress is a little slow.

CLICK ONE TIME ON PHOTOS TO ENLARGE

[70CB750]

Great looking engine, did they paint it too?  The last picture looks like hammered or maybe metallic paint.

[lucky]

Hi 70CB750,

Yes... Cycle Exchange painted the engine cases.
It is a very beautiful silver metallic that sparkles in the light.
Remember to click on the photos on this forum because they will be presented twice as large. Should be 500 pixels wide.

[lucky]

More small but important parts being added.
Ran into a missing nut on the triple trees. Was not on the original bike.
Also the oil hoses need bolts and I will not use hardware store bolts, so I am waiting on those as well.

[fastbroshi]

Very sharp looking so far.