Fuel Ain't Pumpin'

[Matt7c]

A few days ago, I ran out of fuel. Silly me. :blink: Having refuelled and re-filled the carbs, all was well. Until it ran out again today (except that the fuel tank is full).

Here's what I know:
1. the carbs run dry and don't re-fill.
2. the fuel level in the glass dome falls below the level of the gauze filter when engine off.
3. the fuel level then climbs just to the level of the gauze when running - before it was about 5mm over the top, engine on or off.
4. when I start the engine, I get a bubbly spurt of fuel into the carbs, but this stops after a few seconds.
5. I ran the engine with the nut over the carb fuel filter off at 3000rpm and no fuel came in!
6. There are no visible leaks.

So, I'm thinking that the there is some problem with the fuel pump, which I fully refurbed a few months ago and have run for only a few hours since. I'm also thinking that the problem was caused by running out of fuel in the first place.

Is there some sort of priming routine for the fuel pump? I don't recall doing anything special after refurbing the pump and the manual gives no hints.

Any tips or easy things to check first (which don't involve removing the carbs and fuel pump)? And please don't tell me to get an electric pump!!!

Matt

[types26/36]

Matt,
Sounds like you have a leak (air leak) on the suction side of the pump, check the hose/filter/connection to the tank and pump. If its sucking air you would get the bubbly spurt of fuel,I once had a prob like this, the glass dome on the pump had a small chip and would not seal on the rubber gasket no matter how tight I screwed down the nut.
When you overhauled the pump did you replace the valves or just the diaphram ?
Of course you may have pulled some dirt into the pump when you ran out which could stop the valves from sealing?
Brian

[Matt7c]

I didn't renew the valves because they functioned well and getting them out looked tricky! You may be right about one being stuck open though. I wonder if the bubbly delivery to the carbs could be more to do with the fuel not getting above the gauze filter? Instead of a clean supply of fuel going down into the filter, it seems its sending up mostly air. The question is: why is the fuel not rising above the gauze filter? Maybe an inoperative valve is the answer and the fuel is just going backwards and forwards within the pump?

[gjz30075]

I assume you replaced the diaphram when you rebuilt the pump? If so, it could have been sitting around for some time, either on the vendor's shelf or your shelf, before installation and could have dry rotted. Then you'll find fuel going into the sump. Pull the dipstick to see if your level has risen or have a gassy smell.

Greg Z
'72 Sprint

[khamai]

Fuel filter???

or clogged fuel pick-up in the tank...

[steveww]

My 2p worth would be to forget the old mechanical pump and fit an electric one B)

[lotus026]

Though having done an electric pump on my Elan for a while and had problems with it eventually.....I'm back to a mechanical pump and more reliability!
Dave
lotus026

[Matt7c]

I took the carbs off and had a good look at the fuel pump while cranking the engine. I saw air bubbles coming into the glass dome and thougt at first they were coming from the base of the dome, so I took it off and resealed it. On cranking the engine again, I could see the fuel coming into the empty dome - so I know that the fuel line isn't completely blocked. Then when some fuel had built up, I noticed that the air bubbles were actually coming up the same 'spout' as the fuel. So I have tightended all the nuts on the fuel line and the bubbles still come up. I sniffed the dip stick to smell the oil and it doesn't smell great - can't identify the smell but it doesn't seem right. Doesn't smell of petrol, but doesn't smell of oil either. So I am thinking that the diaphragm has gone.

You fellas think I'm heading up the right path?

The fuel pump is coming off as soon as I have straightened out my back and drunk my cuppa, so I'll report back...

Thanks for your help.

Matt

[Matt7c]

Okay, now I'm confused (again). Have now dismantled and inspected the fuel pump and it looks fine. The valves are working well, with no crud stopping them closing and the diaphragm looks to be in similarly good order. The air might be getting in somewhere else, but there are no visible fuel leaks. :huh:

[types26/36]

Try assembling the pump, connecting a pipe to inlet side into a can of fuel and and working pump by hand, check if bowl fills and pumps out of outlet.
If you like the taste of petrol you could suck on the fuel line and see if you can draw the fuel through! or blow through fuel line with the filler cap off and get someone to listen if its bubbling.
Check your tank is vented so it doesn't create a vacuum stoping fuel flow.
Never seen it but I have heard of the cam on the jackshaft been worn so much it would not work the fuelpump.
Brian

[pereirac]

I had a similar problem, took my carbs off and the pump out and checked it.... it was fine. The problem was that the small piece of rubber pipe between the fuel tank and the main fuel pipe had started to split. But you only see this if you pull the pipe tight, otherwise it looked fine. Replaced this and everything works....

Carl

[mikefromengland]

buy a new pump for about 30 pounds save all the hassell.make sure it fits on top of the jack shaft other wise it will be very expensive. :rolleyes:

[khamai]

Repeat post...

Fuel filter??? Has it been checked or replaced?

I've had similar problems, rack my brain for days on the pump & carbs, only to find a block fuel pick-up in the tank or clogged fuel filter.

Try blowing air backwards from the fuel pump to the tank to check for blockage.

[type26owner]

That would be a Two-Phase (fuel & mostly air) )flow problem when only a Single-Phase (fuel) would be correct. Brian most likely pegged the problem correctly on the first reply. It's just sucking in enough air on the suction side of the fuel pump to fuel starve the carbies. You've probably got a tiny crack in the rubber hose that connects the fuel tank to the black plastic fuel line. The surface tension of the fuel is high enough so no fuel will leak out through the same crack. It'll suck lots of air in there though.

BTW, an electic fuel pump will suffer form the same problem if an airleak is present on the suction side.

[Matt7c]

Well you were right - having ruled out most things, I had a stab at trying to find the crack, but didn't need to look too far. It appears that the snag is (as mentioned above) on the little armoured pipe that joins the tank to the main fuel line. The little pipe isn't cracked, but it no longer seals properly on the tank. It might not seal properly on the pipe either, but that is harder to judge.

So, using my finest bodging agent to create a temporary air tight seal, I now have fuel arriving at the pump with only a very occasional bubble. I'll work on a permanent solution slower time.

Thanks all for your assistance: as always it is very much appreciated!

Matt