73 240 carb questions

[foolthrottle]

at some time the previous owner disconnected the mechanical fuel pump and had it running on the electric pump only and it ran fine like that. Although there is fuel pressure it seems weak. The car will not start except with starting fluid and will not continue to run on its own. I have repalced the electric fuel pump with no solution. There is fuel to the carbs but it doesen't seem to get beyond that point. any ideas?

[Nissanman]

I assume you checked for adequate fuel flow at the supply pipe to the carbs?

Sounds like you may need to check the fuel level in the float bowls.

The bowls should be full of fuel at any time.

If they are dry or low, then the inlet connection, float valve or atmospheric vent may be faulty/blocked.

I would advise you to remove the bowls, inspect them for residue clean everything up and replace the valve and seat in each.

Also check and clean if necessary the flexible pipe between the float bowl and the carb.

It is relatively simple to set the float valve correctly to ensure the fuel level in the bowl is correct.

[beandip]

Are you using SUs or Flat top Carbs? I have a '73 also and have been running a electric only for 8 years with out any trouble like what you describe. All SUs need for pressure is 3 to 5 psi. One thing , filters, change the filter in the engine bay and the one at the tank ahead of the pump. If this doesn't cure the problem then , on the SUs ware the gas line connects to the carb , there is a round fitting. This fitting has a vary fine screen. If you still are having flow trouble try blowing air back through the supply line back to the tank . If the line is blocked in the tank this might unplug it. If this clears the problem, you need to pull the tank and take it to a radiator shop. If you have flat tops I cannot help with those.

[foolthrottle]

I assume you checked for adequate fuel flow at the supply pipe to the carbs?

Sounds like you may need to check the fuel level in the float bowls.

The bowls should be full of fuel at any time.

If they are dry or low, then the inlet connection, float valve or atmospheric vent may be faulty/blocked.

I would advise you to remove the bowls, inspect them for residue clean everything up and replace the valve and seat in each.

Also check and clean if necessary the flexible pipe between the float bowl and the carb.

It is relatively simple to set the float valve correctly to ensure the fuel level in the bowl is correct.

Nissanman

Thanks for the help. I removed the carbs and gave them a good scrubbing with carb cleaner and that seems to have worked. I admit I was intimidated by the Hitachis, there was a bit of crystaline goo in the float chambers and inlet screen and a small amount of rust on the float rods. I don't believe these carbs have ever been off. thanks man!

[foolthrottle]

Are you using SUs or Flat top Carbs? I have a '73 also and have been running a electric only for 8 years with out any trouble like what you describe. All SUs need for pressure is 3 to 5 psi. One thing , filters, change the filter in the engine bay and the one at the tank ahead of the pump. If this doesn't cure the problem then , on the SUs ware the gas line connects to the carb , there is a round fitting. This fitting has a vary fine screen. If you still are having flow trouble try blowing air back through the supply line back to the tank . If the line is blocked in the tank this might unplug it. If this clears the problem, you need to pull the tank and take it to a radiator shop. If you have flat tops I cannot help with those.

I replaced the old mechanical pump, removed the carbs and gave them a good cleaning, there was cristalline goo in the float chambers and inlet screen, after reassembling and installation it ran fine, now the problem is the front 3 cylinders (plugs) appear to be running rich, the rear three look perfect, where did I go wrong?

[Z Good 1]

Fool....I have the same flattop carbs and the same problem with one side running rich (mine is the rear side though). In reading the FSM, I came across some info on the accelerator/power pump as a possible cause. If the diaphram in the pump has deteriorated fuel can be leaking into the carb causing the rich running. I plan on checking this tonight. I will let you know.

[foolthrottle]

Fool....I have the same flattop carbs and the same problem with one side running rich (mine is the rear side though). In reading the FSM, I came across some info on the accelerator/power pump as a possible cause. If the diaphram in the pump has deteriorated fuel can be leaking into the carb causing the rich running. I plan on checking this tonight. I will let you know.

You are correct sir. I replaced both power valves needle and seat and bingo, problem solved. Because of the difficulty and time involved I would recommend doing both at the same time, if one went bad the other can't be far behind.

[beandip]

I recommend that you change to SUs . You will find them to be simple and far better , both for ease of adjusting and performance. The Flat top carbs were installed because of emission standards . There performance was one of the reasons that Nissan went to fuel injection. This brought back the performance the Round tops gave , but they could achieve the emission standards.

I am running SUs on a '82 ZX engine in my 240 and recently I took the Z into the Testing station, this car is exempted , I passed and I have zero emissions equipment installed. I was on the ragged edge mind you, especially at idle. Gary