Nikki Carb Mystery

[22350]

Hello,  

 

I rebuilt my nikki carb and finally got all the circuits working, but no matter what I do I can't get the accelerator pump working

 

I modified the orignial with a rubber boot, which didn't quite fit.

 

I then located a NOS plunger unit from a later model, which I swapped out the original shaft and spring from.  It was as correct as anything gets.... still doesn't work.

 

Nothing is clogged and if i pull the top and plunge more, it sprays. 

 

Not sure what is going on

[banzai510(hainz)]

is is possibke to put the diaphram in reversed?

[22350]

Just now, banzai510(hainz) said:

is is possibke to put the diaphram in reversed?

There is no diaphram in this carb.  only leather plunger boot

 

[datzenmike]

Video not working and no sound. At least it isn't working for me.

 

Is the arm that holds the plunger adjustable? Try longer or shorter stroke.

[difrangia]

If the mechanical part is operating as it should and the piston fits the bore, the pump part of the circuit should be OK. Locate the one way valve downstream of the accelerator pump. Should be a little steel ball with a spring. Be sure the ball is freely moving and not hindered from seating or clogged by debris.

[22350]

5 hours ago, difrangia said:

If the mechanical part is operating as it should and the piston fits the bore, the pump part of the circuit should be OK. Locate the one way valve downstream of the accelerator pump. Should be a little steel ball with a spring. Be sure the ball is freely moving and not hindered from seating or clogged by debris.

I think we found the issue.  The check valve in the float bowl was stuck.  

 

Another issue we discovered was that the new accerator pump had a inset end, meaning that it wouldn't depress the power jet.   I am going to have to modify  it.

 

I think that It will be fine now.  tested it after we freed the check valve and everything seemed fine.

 

 

 

 

[Stoffregen Motorsports]

I was gonna say.

 

Luckily you found the stuck check valve.

[22350]

12 hours ago, Stoffregen Motorsports said:

I was gonna say.

 

Luckily you found the stuck check valve.

So now it still doesn’t work. 
 

I pulled the check valve again and it seems to work. Not sure if there are “levels” of working. 
 

It appears that the pump works with a greater stroke, but the minimal stroke doesn’t seem to do what it needs to do. 
 

 

Edited October 27, 2022 by 22350

[difrangia]

Couldn't tell much from the short vid. I'm assuming that you are getting a sluggish/delayed acceleration. When you look down in the carb throat, are you getting a squirt or spray from the accelerator pump ? If so, have you checked the vacumn advance on the distributor to insure that it is working ?

[22350]

10 minutes ago, difrangia said:

Couldn't tell much from the short vid. I'm assuming that you are getting a sluggish/delayed acceleration. When you look down in the carb throat, are you getting a squirt or spray from the accelerator pump ? If so, have you checked the vacumn advance on the distributor to insure that it is working ?

The squirt is a dribble

[datzenmike]

There are two check ball valves. One on the inlet from the fuel bowl that closes on the down stroke to prevent gas being pushed back into the bowl and one on the discharge to prevent air being sucked back in on the up stroke. Basically one way valves that only allow gas to move from fuel bowl to pump and from pump to the discharge.

 

I don't know about the Nikki carburetor but the L series Hitachi has a designed leak back into the fuel bowl. At driving speeds where throttle input is slower and shorter, the pump pushes it back into the bowl as it's not needed by the engine at speed and is wasteful of gas. Any sudden or full stroke of the pump overcomes this 'leak' and the excess pressure goes out the discharge nozzle. 

[Stoffregen Motorsports]

Stroke is important. Even a slight variation in stroke can cause a problem with an accelerator pump.

[Stoffregen Motorsports]

Try putting the original rod and diaphragm in there to see if it does anything at all.

[pishta]

that doesnt look like my glass bowl Nikki pump Mine has 2 spring over the cup also so when it pushes hard the spring compresses and allows the pump to keep pumping. The check ball under the mesh screen prevents pushing pump shot back into the bowl where it fed from on up stroke and the spring ball checks the pump circuit from draining after a shot. Both can become stuck using ethanol gas sitting over time. Who sells my dial spring pump (82 Nikki on a Mazda) by itself? 

[ggzilla]

The original poster has a 1960s Nikki carburetor, from the 1963-1965 model 320 "Datsun 1200". Nikki being a large company, made many different models of carburetors over the years

 

What is a dial spring pump? Do you mean the spring for the accelerator pump? The spring above the plunger cup or the spring inside the cup? They were usually supplied in the rebuild kit