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Keith
fuel isnt making it to the bowl?
#1
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I cant fill the bowl in my carb, so I did some testing.

Should I be seeing negative pressure on the inlet of the fuel pump on starting crank? Conversely, should I be seeing positive pressure on the outlet?

I have replaced the fuel pump, and on the bench it shows pressure but nothing when installed.

Posted on: 2008/12/8 4:49
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frankthedolphintrainer
Re: fuel isnt making it to the bowl?
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did you get the correct fuel pump as im pretty sure a15 ones wont fit a12 and vice versa. you can also try using a peice of fuel hose sucking fuel from a coke bottle straight into the pump and this will tell if the fuel lines are blocked, then if tahts all good see if fuel is flowing out of the pump. this will show if the pump works, then after that reconnect the lines and disconnect at the carby if fuel comes out i would suggest trying a new carby.

Posted on: 2008/12/8 7:32
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Keith
Re: fuel isnt making it to the bowl?
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I can suck fuel from the tank with my mitivac.
I have the steel supply line in the engine bay connected directly to the inlet of the brand new pump then with the outlet hosed to the carb barrel (disconnected) where I can see it from the ignition, when I crank nothing comes out...

Posted on: 2008/12/8 8:04
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frankthedolphintrainer
Re: fuel isnt making it to the bowl?
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i presume the mitivac is a electric fuel pump?

as i asked earlier what model did the fuel pump come from and what model is it going onto. the reason i ask this is that the crank may not be reaching the fuel pump arm therfor not pump pressure

Posted on: 2008/12/8 9:51
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ddgonzal
Re: fuel isnt making it to the bowl?
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Quote:
Should I be seeing negative pressure on the inlet of the fuel pump on starting crank? Conversely, should I be seeing positive pressure on the outlet?
YES.

keith did you ever get it sorted out?

Posted on: 2008/12/13 10:40
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Dodgeman
Re: fuel isnt making it to the bowl?
#6
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Quote:

frankthedolphintrainer wrote:
did you get the correct fuel pump as im pretty sure a15 ones wont fit a12 and vice versa. you can also try using a peice of fuel hose sucking fuel from a coke bottle straight into the pump and this will tell if the fuel lines are blocked, then if tahts all good see if fuel is flowing out of the pump. this will show if the pump works, then after that reconnect the lines and disconnect at the carby if fuel comes out i would suggest trying a new carby.
The A15 pump is interchangeable onto all A series engines from 1974, including the A12.

It will not work on the A10 & the 1200 engine with the front mounted distributor.
Using a late pump on an early engine will result in a broken pump arm.

If the fuel was leaving the pump OK, but not reaching the bowl, then either the fuel line is blocked, or the needle & seat in the carb is blocked. Replacing the whole carb over a simple needle & seat problem will not be necessary.
Quote:

frankthedolphintrainer wrote:
i presume the mitivac is a electric fuel pump?
as i asked earlier what model did the fuel pump come from and what model is it going onto. the reason i ask this is that the crank may not be reaching the fuel pump arm therfor not pump pressure
The Mitivac is a hand held vacuum pump designed to be used as a testing instrument in the automotive trade.
The crankshaft [crank] does not operate the fuel pump, instead, an eccentric on the camshaft is used to operate the fuel pump arm.

Posted on: 2008/12/13 15:17
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Datsunitus
Re: fuel isnt making it to the bowl?
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Quote:
It will not work on the A10 & the 1200 engine with the front mounted distributor. Using a late pump on an early engine will result in a broken pump arm.


So does a US model 1971 1200 Coupe have a early or late model pump? I am searching for a replacement now. The previous owner had a late model pump on the car but it seems to have died very quickly.

Posted on: 2008/12/13 17:03
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ang94541
Re: fuel isnt making it to the bowl?
#8
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Here's a picture of the long and short arms.
I found an A15 (late) pump replaced the arm with the shorter A12 (early). I had to carefully (carbide) drill out the balls that hold the fulcrum pin and then tapped the hole for set screws. Why? because I couldn't find and early pump. The stiffer spring probably gives me a little more fuel presure too.
Open in new window

Posted on: 2008/12/13 18:29
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Datsunitus
Re: fuel isnt making it to the bowl?
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Great comparison picture thank you

Posted on: 2008/12/13 18:40
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Dodgeman
Re: fuel isnt making it to the bowl?
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Quote:

Datsunitus wrote:
Quote:
It will not work on the A10 & the 1200 engine with the front mounted distributor. Using a late pump on an early engine will result in a broken pump arm.


So does a US model 1971 1200 Coupe have a early or late model pump? I am searching for a replacement now. The previous owner had a late model pump on the car but it seems to have died very quickly.
Well since the 1971 Datsun 1200 engine uses the front distributor, which was made up untill 1973, I would suggest that the early [short arm] pump would be the right one.

Posted on: 2008/12/13 18:49
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