While trying diagnose an odd loss/lack of power at high end that seems to "surge", I noticed that there are bubbles entering my clear fuel filter that's about 6" after the fuel pump. My thought is that somehow bubbles are getting introduced at the fuel pump.

Now, the fuel pump isn't one I've seen before, having multiple aluminum castings, saying "made in canada" around the outer rim, which is screwed together with multiple screws and having a top that is also screwed on. Most likely yet another hack from my caring, but odd previous owner.

So...the question is, bubbles coming through the fuel line, entering the filter, then traveling to the SUs would certainly be a cause for worry?

Meanwhile, a new pump is on the way, just in case that is wrong.

Per

Bubbles not horribly uncommon when pressure drops in a fuel line. Subsequent compression by pump may not be enough to collapse the bubbles. A very small leak can occur at a barb fitting resulting in a "valve" effect drawing in air but not letting fuel out (not very common, usually you get a messy leak!).

SU's can handle a lot of air in the line but get enough air and your top end will suffer.

Mike!

Per:

I recently had a problem with my '63 544 with oily bubbles in the glass fuel filter just downstream of the fuel pump. My first thought was damaged diaphrgam in the fuel pump. Replacing the pump had no effect on the bubbles. Someone on the board suggested that water in the gas tank can cause oily bubbles in the fuel.

After a half dozen filter replacements and a can of dry gas the bubbles and hesitation seem to be gone.

Good luck,

Joe M

I got a "made in Canada" fuel pump like you describe to put on my big bore
engine when I built it up for my 122 wagon in Panama. It lasted less than
3 weeks before something broke inside, I believe the actuating trigger.
I was about 3 miles from home so I had to blow in the gas tank to fill the
carbs, start it and drive it till it ran out and then do it again. Good thing
I wasn't any further! Have you noticed where the gas cap is on a 122 wagon?
Mighy LOOOooooooow! And since the tank was full it belched about a quart of
gas on me each time I stopped blowing.

I'll stick with a new Pierburg pump from now on! If it is good enough for a
good-breathing 164 it'll certainly handle any B20!

In response to your question, though, you certainly have a leak on the suction
side, but whether it is in the pump, the line or the pickup in the tank is
hard to say. Could be any of the above.

I went to my local pushrod Volvo guru (there actually is one here!) and he took one look at the pump and said, "Penta pump" then saw the bubbles and said "yep, shouldn't be doing that, it's drawing air from somewhere...most likely that boat pump"

so...hopefully the new pump will solve the issue.

Per

Well...got the new pump in, but there's still odd bubbles that I see coming through the line to the clear filter (seen as bubbles percolating out the black fuel line into the clear tube section of the fuel filter, through the filter and then out the other clear tube section to the carbs)

This still doesn't seem right. Where else could I be getting air in the lines?

Or is the fuel boiling in the fuel pump?

blowing backwards through the fuel line..there's some resistance, but you can certainly blow backwards and here some "bubbling" in the gas tank, so I know the lines are at least somewhat clear.

Per

My experience has been that if there's *any* air leak between the tank and the pump, the pump just flat quits. I've seen this various times with various specific failures. I don't think you're drawing air into the pump.

I've also seen lots of bubbling in clear fuel filters, which hasn't hurt a thing. I don't know what causes it, but I say it's not contributing to your problem.

If fuel flow is inadequate with SU carbs, the symptom is a complete loss of power on two or four cylinders as one or both float bowls run dry. A momentary drop in fuel level, short of the amount that kills combustion entirely, has very little affect. I've run such problems at great length (bad pumps, line blockages, needle valve problems) and have never experienced lean surging as a result -- it's more an on-off thing.

My guess is you've either got an ignition problem under high-rpm load, or carbs going unbalanced under those conditions. Neither is particularly uncommon.

Hmmm...high rpm ignition problem under load....you're saying coil, eh? the different distributor didn't help.

thanks for your help.

Per

Per, *possibly* the coil. Possibly it is an A/F problem. I'm really just saying that the bubbles are a red herring -- don't make yourself nuts chasing that.

Ok, I'll check the needles with Joe C. and meanwhile, I picked up a new coil at my local VW shop (mit resistor) as well as new plugs.

Per

What about vaporlock is the gas line near some heat?

I think that might be causing the bubbles...some sort of heating inside the pump that is mostly inconsequential.

Phil had the answer though (all hail Phil!) the underlying consistent problem was with the SU needles. I've got late HS6s with spring loaded needles...the spring keeps them so that the shoulder of the needle is past flush with the piston, acting as a leaner needle than they should be. I replaced them with old school pistons and KD needles...problem solved, revs out well.

thanks for the suggestions!

Per