1983 Nissan Sentra - Carburetor problem


#1

I have a 1983 Nissan Sentra with a Hitachi carburetor. The fuel in the float bowl seems to drain completely after sitting for 48 hrs. Is this normal? If not, what is the solution to preventing this fuel loss?


#2
  1. Wow. Just our of curiosity, how many miles on your Sentra?

I don’t think this is normal. The fuel in the float bowl should not drain away. If you’ve owned the car for a while you should be able to tell us whether or not it’s normal.

How long have you owned the car?

You have given us very little information to work with. Can you elaborate on the problem?

Given the limited information, I suggest you need to rebuild the carburetor.


#3

It isn’t normal for the float bowl to drain. Whenever I saw this happen, it was most commonly due to a plug or insert near the bottom of the bowl coming loose. It could be a crack in bowl housing but I don’t recall ever seeing that.

To fix it, you need to at least pull the top off the carb to inspect what’s happening.


#4

My older Chevy Nova (Corolla) did the same thing while in the hands of my son. While we never fixed it, the only solution for him to save money like you it seems, was to drive it daily as the leak was very slow. Otherwise, a cracked bowl, leaking plug etc. (love that ethanol) etc. all point to a carb replacement or rebuild if you are lucky getting parts. It’s not that unusual for them to have these problems, especially in older outboards and cars? Anyone with a carborator anything they aren’t using regularly should start using the appropriate additives for this crappy ethanol problem though this is probably just old age.


#5

It’s not normal and this is going to be caused by one of several things.
Hitachi carburetors use a spring loaded power valve that is located in the float chamber and operated by a vacuum operated plunger. When the engine is not running or running under a light load condition the valve should be closed. If it’s stuck open or not sealing gasoline from the float chamber will seep out and into the intake manifold.

Another is the possibiliy of vapor lock; pretty common with these carbs anyway. When you come home during a hot day wait about 4 or 5 minutes, pop the hood, and look at the sight glass on the carburetor. You may see gasoline percolating just like coffee in a pot. Engine heat, combined with ambient heat, can cause all of the gasoline in the float chamber to boil clean away.

Other far less likely possibilites could be a pinhole or microscopic crack in the float chamber housing which is allowing gas to ooze out and on some models (memory is fuzzy here) there is a gasket between the throttle body and float chamber that may leak due to float chamber distortion.
Basically, the metal is warping and anything other than the boiling gasoline scenario means a carb overhaul or replacement, all depending.


#6

Thank you all for your thorough advice. The leaking float chamber is but one of two problems with this carb. The main problem is fuel starvation. A brief History: 2yrs ago I had the carburetor rebuilt by a mechanic from a kit I provided. Car ran perfectly for a few days then died at the end of the street. I checked the float bowl and there was no fuel in it. I was able to fill the float bowl only by using a syringe and hose attached to the carburetor’s intake. The bowl fills easily and the float bobs in the gas. I do not think the needle is stuck. I reconnected the fuel line but engine only ran until bowl was empty. I replaced the fuel pump, fuel filter and put fresh gas in the empty tank. Same result. I took the carb off and examined the float, needle, and seat. Found debris in the seat filter and cleared it, thinking that this would solve my problem. No luck. I am ordering a new rebuild kit, specifically to change the seat and needle ( this should have been changed 2 yrs ago by the mechanic, but I suspect it wasn’t). I do not know why the float bowl will only accept fuel when I inject it with a syringe and not through the fuel line ( all lines have been cleared, checked new pressure from the new pump and its up to factory specs.). By the way I disconnected the anti-dieseling solenoid but that didn’t help either. What else would prevent fuel from entering float bowl?


#7

If the bowl will fill when gas is squirted in with a syringe in the line connection, than the float and needle valve are working, although the needle valve may not be sealing totally and may be allowing slow drainback over that 48 hour period you mentioned . The problem causing it to stop with an empty bowl while it’s running has to be a bad pump, fuse, relay, clogged filter, or kinked line. Or, perhaps, crud in the tank getting pulled up to and clogging the screen on the end of the pump’s pickup tube.

My money is with the crud. When you changed the pump, did you check for this?


#8

From your description, there is a blockage from the inlet to the needle and seat. You don’t need a new rebuild kit, you just need to remove the needle and take a can of gumout (or any brand) carburetor spray and spray it into the seat. It should blow out the inlet. If it doesn’t, then you need to find the blockage and clear it.

In the event that you can’t clear it, or something else is causing a problem that is not easily fixed, and you don’t live in an area that requires smog checks, then you might want to consider a Redline Weber conversion.