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post #1 of 4 Old 07-21-2007 Thread Starter
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Smile fuel starvation

Hi All,

I am trying to nail down a fuel starvation issue on my A4. Here is the setup: tank >priming bulb>Racor>fuel pump>in-line filter>carb. I have the manual from MMI and followed the manual's suggestion for spring start-up and unscrewed the main passage plug on the carb and manually operated the fuel pump. Very little if any gas came out when pumping (I don't know what to look for here ... lots of fuel or a little. There was barely a dribble). I then removed the fuel line on the intake side of the carb to see if the in-line filter between the pump and carb was the culprit. Lots of fuel there. Next, pumped 1 litre of fuel into a container - clean gas - no water/etc. Then put things back together and tried the engine.

I primed with the priming bulb and pressurized the system. I didn;t see any leaks (but this was at night using a flashlight). With full choke it cranked 1.5 seconds and started. Let it idle for 15 seconds reduced choke and the idle rpm picked up and smoothed out as per normal. At 25 seconds removed all choke. Then around 30 - 45 seconds or so the idle increased again for a moment (just a subtle increase). Then decreased (again subtle), then went back to normal. Sort of a wavering, but nothing severe (normal I thnk?). Continuing, Around 90 seconds it started to falter, I increased throttle a touch, but to no avail. It sputtered and stalled. As a note - I did have a priming bulb between the tank and Racor, but removed this as the quality was awful and it was a source of air leaks (cheap parts yeild cheap results). I retried the system and again, after 30 - 40 seconds it runs out of fuel. Hence .... I suspect air infiltration. I have a cork gasket on top of the sediment bowl and actually have a spare. I will try that. But I am curious as to the amount of fuel I should expect to see through the passage plug? Any help or suggestions would be appreciated.
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post #2 of 4 Old 07-21-2007
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I'd guess that either your fuel filter is now plugged with sediment form the winter lay-up, or you've got a sticky float in your carb. With a mechanical fuel pump, I don't think your problem is air, I'd guess fuel related either in the carb or at the filter.

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post #3 of 4 Old 07-21-2007
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You've got good flow AT the carb, right? If so, its your float level in the carb, you've got some gunk/junk under the needle valve, and/or the float isn't... floating.

to check fuel pump operation the quick, dirty and dangerous way, remove the line at the carb, spin the motor over (try not to be lighting a lucky strike at the time)
It'll only take a second to tell if fuel is flowing. You only need enough fuel flowing to keep the carb bowl full when running, it really doesn't take a steady stream.

If you do have a fuel pump problem, wander into your local auto supply house and grab a 12 volt electric model. Facet brand, avail. all over the net for about 35.00 (2-4 psi)

Throw away the priming bulb, the A-4 doesn't use one. Its an inboard with a fuel pump, not an outboard.

heres the link to the carb section of moyers catalog


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post #4 of 4 Old 07-24-2007 Thread Starter
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thanks for the tips

Hi all,

Thanks for the input. Muchly appreciated.

Took the carb off, cleaned it (it was pretty icky). Didn't fix it the issue though. So, also replaced the cork gasket in the sediment bowl with a new one. Then checked all the fittings and pressurized the system, No leaks. Fired her up and she purred like an old kitten. As for the priming bulb - a good one will allow the fuel system to be pressurized and any leaks spotted. In addition, when the racor is serviced it yields an easy way to fill it back up. Oh, and rather than turning the motor over there is a priming lever on the mecahnical fuel pump that allows for testing of the fuel flow at the carb. I use it as I am usually working on her by myself and it is too hard (and dangerous I think) to crank the motor over with the line off. The float needle was also probably playing havoc as the carb was pretty gunky form teh layoff. Again, thanks for the tips - appreciate it.
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