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Fuel Pump Ticking

mylesw

Jedi Hopeful
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Hello

The SU fuel pump on my BT7 never stops ticking when the engine is switched off. My understanding of these pumps is that when the engine is not running and the ignition is on that the pump will build up pressure in the system and then stop (until the engine is turned on of course). Therefore I suspect I have a small fuel leak somewhere, the question is, how to I find out where it is? I have already pretty much tightened up everything I can.

Thanks

Myles
 

Patrick67BJ8

Darth Vader
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Hello

The SU fuel pump on my BT7 never stops ticking when the engine is switched off. My understanding of these pumps is that when the engine is not running and the ignition is on that the pump will build up pressure in the system and then stop (until the engine is turned on of course). Therefore I suspect I have a small fuel leak somewhere, the question is, how to I find out where it is? I have already pretty much tightened up everything I can.

Thanks

Myles
Not all pumps stop clicking when pressure is built up with the engine not running but will nearly stop their clicking.

Smell fuel anywhere? Is your overflow tubes working properly and not plugged? Fuel can come out of the carb float bowl tops(this is the black vinyl tubing) and also the intake manifolds copper drain tubes. Somethimes people clamp off the copper drain pipes because they think the engine is running rough due to airleaks from the copper drain tubes. Fuel coming out of these is from leaky jets.
 
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Most pumps will cycle every 5-10 seconds with the engine turned off (they bleed down internally). If the pump cycles more often than that with the engine off it's often caused by an air leak on the intake side.
 
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57_BN4

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Check that it is in fact an SU pump not a similar looking replacement one which are meant to tick all the time. Constant even ticking from an SU is most likely a stuck or dirty valve. Random clattering noise is more likely to be air leaking in. They are pretty easy to get at by removing a rear seat. Andy.
 

RAC68

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Hi Myles,

I am a little confused. As I understand, power to the fuel pump is cut when the key is turned off and the pump should not tick. As I read your question, are you indicating that the engine is not running but the key is in the “ON” position? If this is true, you may not have a problem unless the ticking frequency is rapid as well as continuous.

The SU fuel pump’s check valve will never be sufficient to completely stop flow-back when the “ON” switch is put to the “OFF” position. As a result, fuel pressure will be gradually lost after power is not delivered to the pump and, when the key is turned to the “ON” position, a re-pressurization of the fuel system (with rapid ticking) will take place.

You may, however, have a real problem if the pump is ticking because power is being delivered to the pump without the key in the “ON” position. If this is true, I would be looking for a short.

Hope this helps,
Ray (64BJ8P1)
 

Healey 100

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If the needle and seat in either one of the carbs has a slow leak, the fuel will simply flow above the main jet and drip into the engine. So no leak will be detected and the SU will keep clicking away. Only symptom will be a flooded engine if you leave the key on with the engine stopped for a while. Same effect can happen if the float levels are set too high so the fuel overflows the main jet. Most SU's spec the float level so the fuel level is a quarter inch below the top of the main jet. If all is set right, the clicking really should stop unless that check valve is leaky in the pump.
 

Patrick67BJ8

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If the needle and seat in either one of the carbs has a slow leak, the fuel will simply flow above the main jet and drip into the engine. So no leak will be detected and the SU will keep clicking away. Only symptom will be a flooded engine if you leave the key on with the engine stopped for a while. Same effect can happen if the float levels are set too high so the fuel overflows the main jet. Most SU's spec the float level so the fuel level is a quarter inch below the top of the main jet. If all is set right, the clicking really should stop unless that check valve is leaky in the pump.
If the fuel is seeping above the main jet it will get into the intake manifold and find its way to the ends of the intake manifold where it will drip out of the copper tubing/pipes...at least that's the way it works on my BJ8 which I've owned since '72.
 
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