Did I buy a duff fuel pump...?

[itchyfeet]

My fuel pump spends 99.99% if it's time pumping against a closed valve, I sometimes feel sorry for it but it still seems to work when I do try the fools gold.

[kevtherev]

My fuel pump spends 99.99% if it's time pumping against a closed valve, I sometimes feel sorry for it but it still seems to work when I do try the fools gold.

Ditto.
Tried it yesterday after a 6 month dead end stint and it coughed up the good stuff.
I think the carb was a bit surprised as it spluttered in response the the flood.

[itchyfeet]

I run about 20 quid a year through it, I keep a quarter tank mainly as a reserve and it needs burning off or it goes stale, also carb splutters if you don't run on petrol every month or so for a few miles.
Fuel costs still pale into insignificance compared to the other running costs.

[kevtherev]

Yep but with lpg at such a low price these days, I cant resist.
I used up all the old fuel anyways.

[Santa79]

Lpg will be the way to go for me... As soon as I can muster up the £1000 or so to get it done!

...House upgrades and impending fatherhood is putting that on the back burner though!

[Santa79]

So...
After a bit more fault investigation (and buying a new dizzy cap, rotor arm, leadds and plugs), I removed the spark plugs to check them over.
This is what I found....


I think the van is running a bit rich!
So, with my limited knowledge of internal combustion engines, this relates to my problem thusly:

If it is running rich, at low revs/speed it will run fine as fuel demand is minimal anyway.
When I speed up quickly (as possible in a T25!), fuel demand increases, fuel flow increases, since there is more fuel than required... the engine floods and loses power. Then it cuts out if I put my foot on the clutch.

To back this up; when it does begin to lose power (at about 50mph for example), if I take my foot off the accelerator and let it wind down, it drives normally again. Until I speed up....
Does this sound like sensible reasoning?

[marlinowner]

When was the air filter last changed? Take the trunking off the carb and check that the choke is opening when the engine warms up, you could try driving with the trunking off to eliminate air filter from equation.

[kevtherev]

Plug colour should only really be looked at after a high speed run.
Imho.
Mixture should be checked using a gas analyser.

[Santa79]

The van is in the garage now, they are checking the mixture etc. for me.

The choke is a newly fitted one. It has only done about 40 miles since fitting, and that was on test runs for this problems.

[CJH]

We did, facet low pressure electric pump, tachometric relay, blanking plate. Low cost, reliable and no chance of fuel leaking from mechanical pump diaphragm into the sump oil.

Is this wiki'd somewhere that I can't find? How does this tachometric relay work? I'm assuming it's to kill the pump if the engine stops turning, but what powers the pump during (or even slightly before) starting? I guess I should do as instructed and dig out Bigherb's posts, but I was hoping the 'best practice' was wiki'd somewhere.

[bigherb]

We did, facet low pressure electric pump, tachometric relay, blanking plate. Low cost, reliable and no chance of fuel leaking from mechanical pump diaphragm into the sump oil.

Is this wiki'd somewhere that I can't find? How does this tachometric relay work? I'm assuming it's to kill the pump if the engine stops turning, but what powers the pump during (or even slightly before) starting? I guess I should do as instructed and dig out Bigherb's posts, but I was hoping the 'best practice' was wiki'd somewhere.

Some of the tachometric relays switch on when the ignition is first switched on to prime the system, if the engine is not started immediately they will switch off again after a second or so, they where fitted to the K jetronic injection systems as they had high fuel pressure and cut down the delay in building up fuel pressure. Otherwise they just start working as soon as the engine is cranked and the relay receives the pulsed ignition signal from the coil.

[CJH]

Thanks Bigherb. So I guess it's a case of checking the exact function of any relay that I'm considering buying. That initial priming function seems useful, and seems safe if it turns off after a few seconds. It sounds like it's marginally more complex to wire up, having the pulsed feed from the coil as well as an ignition controlled live. Or does the coil live serve both functions? Coil live is not on the X circuit I believe (which would kill the pump during cranking), but is this the pulsed signal also?

[bigherb]

Both types are wired the same the prime is controlled inside the relay with a timer circuit. The prime type relays are difficult to get hold of and very expensive the standard relay will work fine the electric pump fills the carbs up much quicker than a mechanical pump as it is pumping constantly not relying on slow engine cranking revolutions.

[CJH]

Perfect - thank you.

[CJH]

I've bought a clone of the Lucas FDB502, which has a short priming function when ignition power is applied to the coil. Having now tested it, the duration of the priming timer is so short (closer to 0.5s than 1s) as to be of limited use I'd have thought, but maybe that's all it takes.

I have (or had) no immediate plans to fit an electric pump, but the comment above about it removing the risk of fuel leaking into the engine oil caught my eye.