Hesitation ('pause') under load; going up hills; 3rd & 4thh gear

[henry]

OK Mike, thanks

      Weird thing is that I always thought that the engine would run faster when spraying  the base that had a leak.

          No big problem removing carburetor.

        Henry

[datzenmike]

I theory the leaking gasket is letting in too much air for the fuel being supplied by the carburetor. When carb cleaner is added it's basically more fuel to burn with the extra air and the engine should rev slightly.

[banzai510(hainz)]

one needs to be careful with starter fluid.

 

I spray anywhere near a carb it changes, but and  my motor is fine

[henry]

Hey Hainz,

    Well when I spray behind the carburetor the engine stumbles & feels like it wants to die.

    Henry

[henry]

Sorry, I think I made a mistake posting the first time. Here it goes again...

 

        

 

       I think i found the cause of the vacuum leak. I had installed the bottom gasket upside down. That cutout notch was extending past the intake carburetor base ; there was a clear air passage. My unit does not have a power valve.

    What is your opinion on reusing the same gasket. It sill looks pretty fresh. I could always cut a new one.

   Alright, thank you.

     Henry

[datzenmike]

All Hitachi carburetors have a power valve. On the under side of the carburetor at the front middle is a hollow screw. It's often mistakenly swapped with the one on the rear of the carburetor. This hollow screw allows intake vacuum up into the carburetor under the float chamber. At the bottom back of the float chamber is the power valve.

 

Yes reuse the gasket.

 

 

[henry]

Hi Mike,

      Wanted to let you know that everything is running good. I flipped that bottom gasket so that the air passage was sealed, ( ...got to take those vacuum leaks seriously ).

     Readjusted the carburetor where it idles & shuts off normally. It also fixed that hesitation that I wrote about in the beginning of this thread.

      As far as the power valve goes I don't think that there is one in my carburetor. (Hitachi 2 Barrel 328); no mention of a  hollow bolt or a power valve in the parts list of the repair sheet. I guess I lose out on that feature.

    OK, well thanks for all the help,

       Henry

      

     

 

[datzenmike]

 

See that little notch in the gasket and the spacer??? That is to allow the intake vacuum to get at the hollow mounting bolt. Why else would it be this way???

 

Just took this. It's not a 328 but like I said all Hitachi have this hollow screw at the front. It needs the spacer and gasket with the notch to work. 

 

 

The rebuild kit may very well not have included the 'power valve' in it. The middle screw on the rear of the carburetor is identical but without a hole and easily swapped by mistake. The power valve sits at the rear of the float chamber and is held closed by a spring loaded plunger hanging down from the very top of the carburetor. The plunger is held up by manifold vacuum but pulled down by a spring as the vacuum drops.

 

 

[henry]

Hi Mike,

    Still trying to get to the bottom of this power valve business. Been looking at pictures taken during the rebuild, but don't recognize anything resembling a power valve in the fuel bowl. Would you have picture that you could post of the power valve inside the fuel bowl?

   Thanks again,

      Henry

[datzenmike]

Post yours, maybe I can point it out.

 

I don't have anything at the moment. Here's another carburetor that's similar for location. It's the brass thing in the middle.

 

 http://datsun1200.com/uploads/newbb/174_4e07f441e33c5.jpg

[henry]

Mike,

   I hope this went through. Sorry its sideways. I don't think that I see a power valve.

 Thanks,

 Henry

[datzenmike]

It should be in the center at the back in the bottom of that 'tube'. Can you post the top cover of the carburetor??? as well?

[henry]

Keep in mind that all this is in the past. The carb. has been rebuild & installed.

[datzenmike]

Right. That hole right center of the two barrels is for it. Maybe there were some without.

[henry]

Interesting. On my set up there is no hollow bolt either. 

   Just out of curiosity, would it be possible to add a power valve to that carburetor in the future

   Henry

[datzenmike]

Probably easier to get a different carburetor.

 

It's function is to add extra fuel under extreme load such as passing or any time full throttle is needed. Even though the perfect mixture is 14.7 to one the combustion chamber quickly heats up and pre ignition is a real possibility. Lowering the ratio to say 12:1 by adding more fuel (unburned) absorbs heat to vaporize and lowers the temperature allowing the engine to work harder.

[henry]

OK, I guess  I have an early model 328. Well the engine is running well now. I'm glad for that.

  Thanks for all the good advice everyone has given me.  Until the next project...

       Henry