The Triumph Dolomite Club - Discussion Forum

I've just fitted a new pattern fuel pump. Old pressure was 1.5 psi and falling. New pressure is 8 psi ! Same length arms on pumps no spacers. Guage is trusted from an expensive kit. Anyone seen this high before ?

Tony

Right after that it gradually reduced to 4psi once fully up to temp so maybe normal ish ?

Tony

Filter on inlet side is now empty so that may account for lowering pressure . Blocked tank or lines then...

Tony

Much more than 2 psi will defeat the float chamber valves.

You need to measure the pressure into a blocked outlet....sure you know this.

I set the regulator on my Stag to 2 psi.

Jonners

I watched for 10 mins at 8 -7 psi expecting the overflow tubes to start leaking but they didnt, which i thought was odd, it was only when the pressure dropped I noticed the inline filter was virtually empty. (i'd noticed the emptying on the old pump too).
Ive blown through the front to rear pipes and blew into the tank from the feed line underneath. Couldnt see any floating bits in the tank with the sender unit out either so either the pipe is corroded and flakes are blocking things up until the engine has been off for a while then on its own the inline filter starts to fill to about half full.
I'll try a mock up front to rear pipe tomorrow and then a different tank (when i get one).

The pressure being so high at the start of tonights test made me think I need a spacer (maybe internal leverage is different in this new pump?)

Who sells the spacers? are they the same as OHV spacers?

Cheers

Tony

Might be worth checking that you are not getting a vacuum in the fuel tank. Try running it with the filler cap loose.

Cap was off for all tests- valid point though

Tony

You need to bear in mind that the pressure developed by a mechanical fuel pump is solely down the the strength of the spring under the diaphragm, when the lever is lifted by the cam-lobe the pump sucks fuel from the tank, when the lever drops the spring pushes the diaphragm up and the fuel to the carb.

If your getting too much pressure you have the wrong or faulty pump.

If the pump is incorrectly fitted it will either work poorly or break, this can't cause excessive pressure.

Gordon

Page 19-8 of the Sprint workshop manual gives the pressure as 2.5 psi.
There is a note that adding extra gaskets will reduce the pressure if its too high.
I have a fuel filter on the inlet side of the pump on my 1850 and that is never more than 1/2 full but it seems to run O.K.
Tony.

So after going through everything I could think of, Ive done the following:
Ran the engine til fuel filter showed next to nothing.
Got underneath quickly and pulled the rubber pipe from the tank outlet to drain into a bucket. Thinking was if the pipe was now clogged due to flow entering the pipe, I would see a reduced or zero flow. It flowed normally so I ruled out the tank.

Next I attached a pipe to the metal pipe that goes under the car and put the other end in the bucket of fuel. No change in the filter fill level.
Im then convinced that the tank and fuel linr (back to front) is not the problem.

Next I pulled the inlet to filter pipe off and connected a new pipe that was submerged in a bucket of petrol, no change in filter level.

Next I pulled the pump OUT pipe off and added another pipe and put this into another bucket to check the flow. Flow started but a bit rubbish in volume. (Engine running on bowl remains)

Next was to add a new pipe on the pump INLET (no filter in line) flow was massively improved and the pipe into the bucket was pumping with vigour.

Hmm I thought. I then added the inline filter into the new pipe and bucket scenario and hey presto.... rubbish flow!

Then removed filter and great flow.. then added filter and rubbish flow, so.....
The filter on the inlet side was causing a restriction and the pump was being starved and resulted in bad pressure and more importantly feed volume.

So I reconnected the pipes to pump and carbs as factory WITHOUT a filter and took it out for a test... No problem and car is fast! No starvation feelings at 80mph on my private road .

Fuel pressure with new pump is still to high so Im going to get a reg/filter setup and see how it goes.

I did consider using the filter on the pressure side but I wanted to try the theory first so I may add the same filter later in the week and see how it behaves.
As a hydraulic engineer always says- pumps are great for pumping but crap at sucking so maybe the restrictive filter was making the pressure drop too much to get enough through.

As a side note yes the inline filter was fitted the correct way .

I know some here have filters on the suction side (which makes sense to me) but somehow with 2 filters tries I had the same result even with the too much pressure coming from the new pattern pump.

I really need to get mileage on this car as its going on holiday to the isle of man on the 24th! and I need confidence lol.

Hope this is laid out to make sense for others.

Tony (pessimistically optimistic )

Was it a plastic filter?

I had a similar problem until I removed the filter.

I've bought a glass one.

Yes just the usual cheapie in line plastic. Never had an issue in 35 years of seeing them on cars. I'll invest in a proper filter king jobbie now, I just didnt want to drill for the bracket mount initially, as its more clutter.

Tony

That's interesting. Well done Tony.
There are 2 types of these plastic filters. One is about 1/2 in in dimeter and the other is about 1.25 inch in diameter.
Were your measurements done using the small version or the large one ?
I always use the larger one as I reasoned the pressure drop across the filter element would be lower as it filled up with rusty bits; there is a larger filter element area.

The larger diameter used. I do have a fancy anodised ali one somewhere with a metal mesh type element so I may try that too.

Another point I noted was when the filter and test guage were fitted, on switch off the pressure held for quite some time, but after removal the pressure died off in about 10 seconds so it even restricted that lol

Tony

Filter king added today and set to 2.8 psi (im expecting it to drop with break in) All good so far. I had to richen the mixture about half a turn once the pressure was correct, as I'd been leaning off with the too high fuel pressure. Going to try a bigger run out tomorrow weather permitting

Tony