Original SU Fuel Pump - Fuel Flow Diagnostic Help

[Andrew1]

It's been a heck of a year so far with fuel flow problems.

The latest chapter has the engine dead at 80mph on Toronto's most congested highway. All electrics seem fine, but no "tick-tick" of the fuel pump.

10 minutes of rest, and the fuel pump comes back on and I'm away! The problem however seems to be rapid ticking of the SU pump now.... at idle 60 beats per minute, at road speed 120 - 140 beats per minute and warm to the touch.

The fuel tank full, new gas tank, float level seems fine and no fuel leaking from top of float chamber overflow pipes. High fuel consumption likely due to rich mixture, but I could be wrong.

Based on your experiences can someone provide a list of things to check in order of likely cause?

Does the fuel pump eventually and naturally lose its pumping ability; requiring a more rapid pumping action as it ages (indicating a need to replace)?

Has anyone tried the solid state SU fuel pump that externally looks like the original?

Thanks for your feedback!!!

- Andrew -

 

[Keoke]

HI Andrew,If the chokes are not shutting off completely the pump may tick constantly. As the demand for fuel increases the pump tick rate will also increase.There is the outside chance that the pump may be sucking a little air on its input side check the gaskets and banjo fittings at the pump.However, If this is an old original pump you can benefit by replacing it with one of the new and more reliable "Solid State" electronic units.---Fwiw---Keoke

 

[Dave Russell]

Re: Original SU Fuel Pump - Fuel Flow Diagnostic H

Hi Andrew,
Two simple checks.
Put your thumb over the open line near the carbs or plug it somehow. Turn the pump on. It should not tick. If it does, there is an air leak somewhere on the intake side of the pump or the pump's valves are leaking.

Put the end of the fuel line in a jar, use an extension hose if necessary. Turn the pump on. It should pump around one pint in 30 seconds which is 15 gallons per hour. If not, there's a problem somewhere. Like plugged filters or screens, or defective pump. There is a screen in the pump, maybe a screen in the tank, maybe a screen in the carb inlet, & maybe a filter that someone has added. Make sure that the tank vent is not plugged.

If it's the pump, it's probably easier to replace it than try to rebuild.
D

 

[DerekJ]

Re: Original SU Fuel Pump - Fuel Flow Diagnostic H

Hi Dave

BTW Just to let you know on a related topic. I fitted the new Walbro bellows pump that has a higher rated pressure than standard (but the same as was put on the car by the PO)

Evrything seems fine, the car is running like a turbine (ok touch wood). I'm never sure on fuel consumption because my sppedo is miles out, but it doesnt seem to be too rich

 

[Barefoot]

[ QUOTE ]
Has anyone tried the solid state SU fuel pump that externally looks like the original?

[/ QUOTE ]I put one in about a year ago. So far So good.

 

[Andrew1]

Keoke... Thank you for your suggestions.

I first disconcected the fuel line to the carbs and observed excellent fuel flow, with NO bubbles in the fuel flow indicating no tank side air leaks.

Next, I tightened the Banjo joints to the fuel pump, with no affect on the steady 40 beat per minute ticking with engine off.

Next, I removed the pump, and disassembled the entire fuel flow side of the unit since the contacts seem to be working, with very slight varnishing noticed, but some liquid caught behind the main diaphram indicating potentially a leak. Cleaned all the valves, put it back together with some silcone to boot. Reinstalled, with same ticking reoccuring, maybe not as fast as before?

Looked at the price of the rebuild kits, and decided to replace the whole thing for the additional cost of a new one!

Thanks again all!

- Andrew1 -

 

[Keoke]

/ubbthreads/images/graemlins/thumbsup.gif Andrew ---Keoke