Fuel delivery problem?

[hopsedge]

I’m not certain I am having a fuel delivery problem, but something is definitely different than it always has been. Driving a ‘67 SV with a mechanical fuel pump with a “standard” inline fuel filter b/t the mech pump and the carbs. For as long as I can remember that filter has typically been half-full of fuel; same on my former ‘73 MGBGT. Recently after a long drive (3 hrs), the filter had no fuel at all, and it has remained that way for a couple weeks since. The car seems to run OK, although on that long drive, I would really lose power on long step inclines, and I swear yesterday that it smelled like gasoline in the cabin. What do y’all think may be happening here?

 

[Gordon Holsinger]

I had that problem once the plastic fuel line had a crack in it and the pump could not produce enough vacuum to fill the float bowls adequately!

 

[Barry]

I’m not certain I am having a fuel delivery problem, but something is definitely different than it always has been. Driving a ‘67 SV with a mechanical fuel pump with a “standard” inline fuel filter b/t the mech pump and the carbs. For as long as I can remember that filter has typically been half-full of fuel; same on my former ‘73 MGBGT. Recently after a long drive (3 hrs), the filter had no fuel at all, and it has remained that way for a couple weeks since. The car seems to run OK, although on that long drive, I would really lose power on long step inclines, and I swear yesterday that it smelled like gasoline in the cabin. What do y’all think may be happening here?

Gasoline has the ability to absorb and release a surprising amount of air, so it is normal for the fuel system to contain some air. If the inlet and outlet of the fuel filter (clear plastic ???) are relatively level, it is also normal for air to accumulate in the upper half of the fuel filter. Air should not accumulate below the fuel filter outlet; any air below the outlet should be pushed out of the filter and through the carb(s) via the carb float valve(s) and the carb vent(s). Mounting the fuel filter with the inlet / outlet at the bottom / top should prevent any air from being accumulated.

Gasoline is very easy to smell (a very small fraction of a PPM), but smelling gasoline in the cabin indicates uncontrolled gasoline vapor coming from somewhere. The obvious suspects are leaking lines / connections / pumps, / "over-flowing" carbs / fuel "percolating" in excessively hot carbs / etc. A sneaky suspect in Series 3 / IV / V Alpines is the "air balance crossover line" running between the tops of the wing tanks that can allow gasoline vapor into the cabin.

Note that liquids and vapors are both fluids and that fluids always move from a region of higher pressure to a region of lower pressure. Depending on the circumstances, the same leak can be either "inward" or "outward".

 

[junkman]

I just went through this last week on my S3. Fuel pump was the culprit, presented the same way, clear filter, no fuel. Bought a rebuild kit from SS and she's good as new. Do yourself a favor and drain the the tanks before starting. Hope this helps.
Jeff

 

[hopsedge]

Great intel, everyone. Thank you. I’ve been contemplating replacing all the fuel lines, b/c I don’t know their age. Also considering changing out the mech pump for an electric one. I guess this will prod those decisions along.

 

[Mike O'D]

I have the same situation with my car. Re-built 2 fuel pumps and see no difference. Sometimes there is some fuel in the clear filter body and sometimes it appears to be virtually empty. Runs great, but I don't know how the fuel is getting to the carb.

 

[Alpine 1789]

If the tanks have never been cleaned and re-lined, I would also check to be sure the fuel line and/or the crossover tube outlet aren’t partially clogged with paint flakes. I had a similar problem before I cleaned and re-coated my tanks. Enough fuel was getting through for the car to run but it would bog down as soon as I tried to accelerate.

 

[Mike O'D]

Tanks were cleaned and sealed during resto. All fuel lines are new along with crossover vent. No bogging - runs great even under hard acceleration. Checked the fuel pressure and it was running near the top of the spec - 3 psi if I'm remembering correctly. I don't know what it looks like when I'm driving down the road, but pop the bonnet when it's idling and sometimes there appears to be almost no fuel in the filter housing. Really odd. I have been tempted to cut one of these filters open to see how it's constructed - maybe that would help explain things.

 

[husky drvr]

hopsedge and Mike,

When you are observing the fuel filter being empty, is that when the engine is idling, or not running?

Does the filter body tend to fill when the engine RPM is increased?

If this issue developed recently, do you have any idea if it started about the same time as your favorite fill-up spot started selling a winter blend fuel?

Do you have any idea as to the size of the ports' ID's into and out of the filter? If they are smaller than the fuel line ID, that could cause a flow restriction and depressurization in the filter body.

Is the vent in the tank fill cap open and functional?

Just curious,

 

[Mike O'D]

In my case - sometimes completely empty when not running. When idling there is a small amount of fuel at the bottom of the housing. Haven't tried revving it up while watching the filter. Filter is new - mid-summer install - didn't have one before. Not a winter blend issue, but speaking of that, I have seen winter blend fuel "boiling" in the glass bowl of the fuel pump on a warm/hot spring day. Ports into and out of the filter are at least the same size as the I.D. of the fuel hose. Fuel tank venting is good - never had a problem with high-speed cruising or hard acceleration.

 

[husky drvr]

Mike,

Your issue might just be an aberration of the engine's fuel requirements aren't able to completely purge the air from the pump to the carb due to filter angle or distance from the carb.

You might try to manually purge the air from the line and filter, but I have doubts about the filter remaining full over time.

Just a thought and probably not very helpful.

Cheers,

 

[Mike O'D]

Thanks for the comments husky. Since I don't have any starting or running issues, I'm not overly concerned about it - more curious about why it behaves that way. I have a spare filter of the same type. I took a piece of wire and bent a short 90 deg. on the end and put it through the outlet end. It feels like there is a tube that goes almost all the way down inside the filter element to just above the inlet. If that's the case, then I can understand why the filter mounted vertically doesn't fill up. I don't know why it would be built like that, and don't want to cut up a new filter to find out if that's how it's actually built. Curiosity may get the better of me one day though!

 

[hopsedge]

I didn’t mean not to reply to Husky Drvr’s questions, so… my filter housing is def empty when the engine is not running, and this is what originally caught my eye and prompted my post (b/c on this car and on my previous LBC the filter housing always had fuel resting in the bottom of it). During idle, I can see some fuel “spitting” into the filter housing, but again, historically the housing has been half-full, and that is no longer the case even at idle. I’m afraid I cannot check the high-rev situation as I have started removing parts off the car (incl the battery) to start some winter projects. I have no idea about the winter-mix issue, but I live in the Deep South where “winter” usually means 40 degrees or so. On the inlet-outlet ports, again I cannot be certain of their size as I type this response, but I have been using the same type of filter for years and never experienced the housing empty of fuel until recently. This particular filter was new this past spring. And finally the gas cap vent; good question that I do not know the answer to. How would I tell if the vent clogged? Would there have been a “sucking” sound when I last opened the cap to fill it up? I did not notice such a sound.