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Fuel Delivery Brainteaser

2031 Views 2 Replies 2 Participants Last post by  RITTER
Ok I have a disguting problem here.Fuel Supply Not doing it's job.
Problem: Lack of fuel under load( doesn't matter at high or low RPM's)
Diagnosis: Bad fuel pump, Obstruction,Faulty hoses, Dirty Fuel Tank.
Well i narrowed it down to bad fuel pump only getting 2 lbs of pressure at Carb. So buy a new fuel pump right? Tried it doesn't improve fuel delivery! Seems I have @ 9-11 lbs of pressure at filter just before carb but hardly any fuel volume . Is it possible the new pump is bad? could be? has anyone else had this problem before?Replies are welcome I would like to know before I purchase another fuel pump( just so you know i did NOT purchase this pump from OGTS).

Thanks, Clay
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Pressure and volume are not the same thing. If little fuel is being consumed (engine only idling) then 9 PSI is probably too much. A Solex, Weber 32/36, or 38 DGAS only need around 3-4 PSI at the carb. But there should also be 3-4 PSI should no matter what the load or RPM. If a pump (or fuel tank/lines, etc) can't deliver enough volume, then the 3-4 PSI will drop when the engine needs more fuel.

If something is clogged, or a fuel line is collapsed/crushed, then pressure can build up to 9 PSI even if it is going through a pin-hole sized opening. But no volume will get through the pin hole. So, when the engine needs volume, it won't be there.

Another problem could be that the screen filter built into the fuel inlet of the carb could be clogged and simply not letting enough fuel into the float bowl. Same thing for the needle & seat for the float bowl. If the needle doesn't open to let fuel flow freely into the float bowl, you won't have the fuel when your engine needs it. If the problem is with the needle & seat it would be that it is jammed "shut" and is only letting a trickle of fuel in.

The float bowl holds around a cup of fuel. This provides a reservoir of fuel at the carb. Starting from an idle, your float bowl should be full. A full float bowl contains enough fuel for a full throttle blast for at least first gear even if no more fuel enters the float bowl.

If you can't get a short full throttle blast like this either the float setting is bad, needle & seat is bad, … or something else is wrong other than fuel delivery.

So before I go on guessing, a couple of questions:
1. What carb are you using?
2. Are you still using a mechanical pump?
3. Did you at least buy the pump from an Opel specialist… if not shame on you (See my post on Thank you OGTS - Support your Opel specialist!!!)
4. Is this a quiz… I mean, do you already know the answer and want to tease us with something you found that is bizarre?
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Figured it out

I figured it out I believe...
This little episode has been plagueing me for a week now.. mostly due to snow and crappy weather. I ran a pressure test on fuel system ( I am using a 38Dgas Carb from our favorite supplier) tore it apart, cleaned it, checked it, put it back on.(just for GP)got 9-11 PSI before filter. Cleaned breather tubes on gas tank, Checked fuel pressure and volume at fuel tank, disconnected fuel lines and blew them out then pressure tested and volume tested up to fuel pump (by the way volume test came up like 12 GPM) Only know this because it took 56 seconds to drain my tank and i had about 12 gallons in it. I doubted there was a problem there. So i returned my fuel to the tank,tried the pump again ...very little gas about 1 cup per HOUR . Also I thought it might be the eccentric on the distributer but alas no it was fine and dandy( by the way that reminds me did they not stick to any certain way of drilling those buggers , eccentric was in an entirely different place ... guess it doesn't matter it just runs a pump rod)So I am assuming that the Opel Gods are angry at me for not buying the pump from OGTS and therefore have sent me a Headache... So i take the pump off tear it apart (mind you it is like 14 degrees tonight in the shop) saying words that would send the pope into fits of grabbing for the good book. As I tear it apart I realize the out line has a hole in it the size of a pin ( casted that way from AC). So now I know what caused it and to Appease the gods I am ordering a new pump tomorrow morning from Gil . Also to let you know I use a thick wall 1/2 inch clear fuel line. So i am sure it is not collapsing in side. Above in the motor compartment i use steel line. Well I think that says everything and Gary is going to kill me for such a long message.So thanks for the points you made and yes I still run a mechanical pump.

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