Fuel level mystery

[Datsun fan]

OK, each time I shut my A15 engine off I watch the carb ( stock Hitachi ) & fuel level ( glass magic eye ) will go down slowly , after about 2 hours there isn't almost any fuel there , starting engine after 3-4 days will take about 5 tries to get that pig started !!!!!!! is this normal ??? is it a faulty one-way fuel valve ??? or is it just the fuel ( evaporation ) from ther carb cos engine is warm ??? anyway the fuel tank is LOWER than stock about 20 inches , no gas leak .

Any ideas ................

[ggzilla]

Yes, it is a common problem. But it can be fixed. Most commonly the main jet gaskets are leaking. Just take the nut guard off and tighten them a bit. Probably does not need new gaskets.

 

Here's my own A-series carburetor before and after leaking:

Hitachi DCH-306 leaking fuel at main jet plug gasket

[Datsun fan]

First thank you ggzill for the ultra super fast post . can I extract from your post that descending fuel level I have is abnormal ??? I carried out visual check of that thing and found no leaks . What is the next step ??

[ggzilla]

It is normal on a 30 year old vehicle. But when new it was a new Datsun it would have been considered Abnormal.

 

With my carburetor I could not observe fuel running out or leaking. Just the fact that it was wet and dirty was the indication. After i tightened those plugs it can sit for a couple of weeks before draining completely.

[Datsun fan]

Hmmmmmm , I will tighten these things and test the leak again

What about one-way fuel valve ??? is it integrated in the fuel pump as I think ?? How to test that valve ???? the return line is NOT connected at all to the pump . Anyway, could you pls let me know what the return line is made for ??

[ggzilla]

The fuel pump and fuel line have nothing to do with Carburetor fuel bowl ascending level. Datsun B310 (150Y) has a fuel return line, but whether connected or not has nothing to do with this problem. Most other Datsuns have a fuel tank vent line, not a return line.

 

The fuel level descending is caused by leak internal to the carburetor. Even if you remove fuel pump, the carburetor should still hold fuel in the bowl for a at least a couple of days.

 

But ... perhaps someone from California or Arizona can comment on how high heat (above 100F/38C) affect evaporation. I am pretty sure that it should last longer than 2 hours, as I have driven my Datsun in those temperatures once or twice and not notice any problem.

Edited June 27, 2009 by ggzilla

[hang_510]

But ... perhaps someone from California or Arizona can comment on how high heat (above 100F/38C) affect evaporation. I am pretty sure that it should last longer than 2 hours, as I have driven my Datsun in those temperatures once or twice and not notice any problem.

 

significantly.

in the 3-4 days of not driving, yeah itd be empty.

 

if my 4dr sat (weber) for a week or so, the bowls were empty.

electric fuel pump allowed it to fill faster so i didnt have to crank it until they were filled.

[ggzilla]

Thanks. So this did not happen in winter, when temperature was 80 degrees or lower?

[Datsun fan]

3 or 4 days ??!!! I'm talkin about 2 hours!!!!!

The bottom line ............ is it evaporation or leaking gasket you guys think???

[72240z]

Would take longer then 2 hours to evaporate. I'm voting leak.