Transient fuel pressure drop

[john.r.davies]

All,

I'll be most grateful for any ideas on diagnosis.

These are the symptoms:

 

TR6 engine (in my race Vitesse)

New alloy fuel tank (in wheel well - non-standard)

Fuel pathway - Tank, Disposable Fuel filter, Facet lifter pump, swirl pot, to Bosch pressure pump, to PRV , to M/u.

All the fuel returns (Swirl pot, PRV, M/u) go back to the tank.

New breather valve on tank.

 

On acceleration under load, the engine hesitates, due to a transient drop in fuel pressure, from 105psi to about 60psi.

It then picks up, and pulls as normal.

It can also hestitate, and stall, as I draw to a halt - has been most embarassing on roundabouts and traffic lights!

Can't reproduce this when revving the engine.

 

Things I've thought about:

All the electrical connections are firm.

The tank is the new item, but it's clean inside, I've checked.

The Bosch makes some weird noises - I know that a Bosch needs some hydrostatic pressure, but not too much, so the swirl pot is mounted slightly above it. Restrict the return from pot to tank, to increase the supply pressure to the Bosch??

Could the PRV be partly blocked, so can't flow enough fuel when the throttles open? But once the engine overcomes the hesitation, pressure and performance return, so that seems unlikely.

Could that disposable plastic fuel filter between tank and Facet have more resistance to flow than it should? But it's clean as a whistle inside (transparent plastic) and is about the size of a 300mls can of tonic!

Inadequate vacuum to M/u might mean that it doesn't enrich the mixture on acceleration - that might cause the hesitation, but the drop in fuel pressure??

 

Please join my brainstorming!

 

John

[TR NIALL]

All,

I'll be most grateful for any ideas on diagnosis.

These are the symptoms:

 

TR6 engine (in my race Vitesse)

New alloy fuel tank (in wheel well - non-standard)

Fuel pathway - Tank, Disposable Fuel filter, Facet lifter pump, swirl pot, to Bosch pressure pump, to PRV , to M/u.

All the fuel returns (Swirl pot, PRV, M/u) go back to the tank.

New breather valve on tank.

 

On acceleration under load, the engine hesitates, due to a transient drop in fuel pressure, from 105psi to about 60psi.

It then picks up, and pulls as normal.

It can also hestitate, and stall, as I draw to a halt - has been most embarassing on roundabouts and traffic lights!

Can't reproduce this when revving the engine.

 

Things I've thought about:

All the electrical connections are firm.

The tank is the new item, but it's clean inside, I've checked.

The Bosch makes some weird noises - I know that a Bosch needs some hydrostatic pressure, but not too much, so the swirl pot is mounted slightly above it. Restrict the return from pot to tank, to increase the supply pressure to the Bosch??

Could the PRV be partly blocked, so can't flow enough fuel when the throttles open? But once the engine overcomes the hesitation, pressure and performance return, so that seems unlikely.

Could that disposable plastic fuel filter between tank and Facet have more resistance to flow than it should? But it's clean as a whistle inside (transparent plastic) and is about the size of a 300mls can of tonic!

Inadequate vacuum to M/u might mean that it doesn't enrich the mixture on acceleration - that might cause the hesitation, but the drop in fuel pressure??

 

Please join my brainstorming!

 

John

Hi John,can you not bypass lifter pump and swirl pot and see if this helps, i know you know a lot more about this than me but just incase might help.Niall

[Guest ntc]

All,

I'll be most grateful for any ideas on diagnosis.

These are the symptoms:

 

TR6 engine (in my race Vitesse)

New alloy fuel tank (in wheel well - non-standard)

Fuel pathway - Tank, Disposable Fuel filter, Facet lifter pump, swirl pot, to Bosch pressure pump, to PRV , to M/u.

All the fuel returns (Swirl pot, PRV, M/u) go back to the tank.

New breather valve on tank.

 

On acceleration under load, the engine hesitates, due to a transient drop in fuel pressure, from 105psi to about 60psi.

It then picks up, and pulls as normal.

It can also hestitate, and stall, as I draw to a halt - has been most embarassing on roundabouts and traffic lights!

Can't reproduce this when revving the engine.

 

Things I've thought about:

All the electrical connections are firm.

The tank is the new item, but it's clean inside, I've checked.

The Bosch makes some weird noises - I know that a Bosch needs some hydrostatic pressure, but not too much, so the swirl pot is mounted slightly above it. Restrict the return from pot to tank, to increase the supply pressure to the Bosch??

Could the PRV be partly blocked, so can't flow enough fuel when the throttles open? But once the engine overcomes the hesitation, pressure and performance return, so that seems unlikely.

Could that disposable plastic fuel filter between tank and Facet have more resistance to flow than it should? But it's clean as a whistle inside (transparent plastic) and is about the size of a 300mls can of tonic!

Inadequate vacuum to M/u might mean that it doesn't enrich the mixture on acceleration - that might cause the hesitation, but the drop in fuel pressure??

 

Please join my brainstorming!

 

John

 

Hi John

Facet lifter pump ? please explain as fuel pressure is my concern on this setup

[john.r.davies]

niall,

Thanks - good sense as always! This problem may need a process of elimination, taking out complexities.

I'll certainly try that.

 

ntc,

It's an ordinary Facet fuel pump, used to lift fuel from the main tank, which is below the pumps, into a swirl pot, slightly higher than the pumps.

The swirl pot is a small accessory tank, vented in its roof by a return to the fuel tank, so the fuel circulates.

The Facet squirts the fuel in quite fast and tangentially, so that it 'swirls' around the cylindrical tank and any air is forced to the centre vent.

Thus, fuel surge in the main tank is of no matter, as the Bosch takes its feed from the bottom of the swirl pot. If the Facet picks up air, it is returned to the main tank and the Bosch gets only fuel.

At least in theory! But in practice too! I've had fuel surge - that's why I have the pot - and this problem ain't it!

 

Thanks for your thoughts - please keep thinking!

 

John

[Alec Pringle]

Hi John,

 

my comments on another thread might have some relevance, although referring specifically to Lucas and T-J installations . . .

 

http://www.tr-register.co.uk/forums/index....c=15481&hl=

 

The symptoms you describe are almost identical to those I've experienced in the past with K-Jetronic installations, and the symptoms indicate a failing pressure pot downstream of the pump. As you don't mention such an accumulator, the insertion of one may just be the answer you're looking for ?

 

Cheers,

 

Alec

[88V8]

This could be two separate problems.

 

Is the Bosch in the back of the car or the front?

 

Ivor

[Eyetee]

Sounds overly complicated, surely if there is a new ally tank, its baffled and has sump to remove likelyhood of air pick up untill fuel level is very low.

So the sequence need only be Fuel tank - filter - pump - pressure valve - metering unit - Injectors. With a return from the metering unit?

 

I have no idea but am interested, so please carry on...

[john.r.davies]

eyetee,

baffles in the tank would have doubled it's cost, and previous experience with the Silverback (a Herald estate with the wide, flat estate tank, so wide and flat that even with baffles, Triumph fitted an integral pot, like the 2500 - that didn't work - but this set up did work!) made me think the exspence unnecessary. And it is - unnecessary! The swirlpot worked . And this is NOT a fuel surge problem - it occurs on the straight.

 

Ivor,

the pump is in the back, next to all the other bits. Why do you ask? Neither Lucas not Bosch pumps in any application are fitted distant from the tank, are they?

The fuel line to the front is made of 8mm bore copper tube. Can't think that the resistance of that is critical, as the OE was half that, so the resistance of this will be 16 times LESS (Poiseullies' Law)

 

Alec,

Swirl pots/accumulators AFTER the pump??? (And I thought mine was complicated)

How did you maintain the pressure, when the pots would need to be vented back to the tank?

More detail please - esp. if this sorted such a similar problem.

The swirl pot I'm using is at least twice as big as an empty Lucas filter housing.

I'll post a picture of the pump house tomorrow, if that will help.

 

Thanks for the thinking!

John

[Alec Pringle]

Hi John,

 

no, the two filter bowls came before the Lucas pump in the usual way.

 

The Bosch pumps are intended to work with a pressure pot, accumulator, immediately downstream of the pump - which is there primarily to assist momentarily when the pump runs out of puff - as in flat-out acceleration down the straight. The old 5-banger Audis needed the pot, otherwise they'd splutter as the revs rose, pedal to the metal. The much-maligned Lucas unit had a better response, it could fuel a long way over 200bhp before needing any such assistance.

 

Cheers,

 

Alec

[john.r.davies]

Thanks, AL!

 

I was hoping NOT to make it any more complex!

 

This accumulator. It doesn't have a vent return, so it will contain fuel at injector pressure?

It must contain some air, to provide a 'spring' so that extra fuel, over and above what the Bosch can provide, on demand.

Or does it rely on the elasticity of the vessel wall?

Can't see that being very great, for a small pot.

 

And how is that air controlled? Either in volume (there must be a bleed on top, to bleed air out when filling the system) or to prevent it escaping downstream, undoing all the good work upstream to keep air out of the injectors' fuel supply!

 

It's not that I don't believe you! I'D just LIKE more detail!

 

Jhn

[Andy Moltu]

A couple of things spring to mind:

Is the swirl pot functioning properly - perhaps allowing the bosch pump to gulp in air at high demand via the swirl pot breather? - Bipass it temporarily & see if this improves the situation.

Is your PRV sticking? The spring should move the plunger almost instantly to maintain fuel pressure but if it's a bit gummed up it may not be operating as freely as it should and hence be suggish at high fuel demand.

 

Other possibilities:

Is your lift pump up to the job of delivering sufficient fuel suddenly? You could also bipass this & perhaps the prefilter too.

Do you have a short on the wiring to the fuel pump that drops the voltage perhaps only doing so when initially accelerating or when decellerating which might explain your stalling too?

 

The pressure accumulator is interesting I remember looking at them a while back (the fuel injected Fiestas & Escorts had them as I recall but were not rated at the 100psi needed for the Lucas PI - the Bosch system fitted to the injected Fords operated at 50 or so PSI as I recall so presumably the accumulator would need to reflect this. That's why I didn't visit the scrappy for one as it would effectively only function as a fuel filled vessel on the TR and perhaps only help to maintain fuel pressure at 50 psi when the pump couldn't maintain adequate pressure transiently - not enough for a Lucas system).

[john.r.davies]

All excellent suggestions - I will try them and report back.

Meanwhile, here's a pic of the pump house/boot;

[Alec Pringle]

Hi John,

 

To be honest I've never given much thought to the internals of the Bosch pot ! It's a cylinder about the size of the pump, fuel in and out, and that's it. As I understand it, fuel line pressure depresses the plunger allowing it to fill with pressurised fuel, then if pump pressure starts to fall the pot briefly expels pressurised fuel to maintain fuel line supply. According to the books, the accumulator is there purely to facilitate hot re-start. However, our old 80 and 90 Quattros from the mid-80s will splutter under hard acceleration if the accumulator isn't up to scratch . . . as discovered by trial and error, and an Audi technician who knew those engines.

 

Google link below will lead you to lots of Bosch info, I've just had a look - the theory as described doesn't quite fit with my past experience, but I have been told that the old Audi accumulators have a higher holding pressure than most systems.

 

http://www.google.co.uk/search?hl=en&q...ssure&meta=

 

Cheers,

 

Alec

[john.r.davies]

Thanks, Alec!

Just come in from garage to find your reply. Now I see what an accumulator does - it has a "Spring loaded diaphragm" - that'll work!. But the Audi system works at about 6Bar (87psi) and the accumulator keeps it up to 3bar(40psi) so I don't suppose that a scrapyard, or even a new Audi accumulator would do the job in a Lucas Pi system. I think I must try other things first!

 

Thinking that mechanical items are more likely to fail, I looked at the PRV. As I had a spare to hand, and no diagram of how it works, I took the spare apart. Sketch below.

All the internal surfaces were covered in a matt, pale brown deposit, I presume from old petrol. Where appropriate, I cleaned this off with a mild Scotch pad.

The valve part captures a central pin that moves through it, but it was sticky, so I freed it in an "easing the spring" manner until it moved well.

The spring adjusting screw can easily be screwed right into the valve body, off its threads. Should the spring be as compressible as this?

 

I'll fit this spare now and see what happens.

But test drive today? Its pouring with rain, again. I feel like Flanders and Swann, "August, cold and dank and wet, Brings more rain than any yet."

 

John

[88V8]

The flow rate of the Facet presumably exceeds that of the Bosch by a good margin, say 20%, to keep the swirl pot full ?

 

Cleaning the PRV.... can't really imagine it holding back 115psi which is what the pump should be doing, but perhaps....

 

While I think of it, don't know if Malcolm has had any hand in your PIing in the past, but my car has a diaphragm PRV which he was trialing in December last.... might be worth a chat with him, and indeed the subject of the PRV could be a nail on which to hang a conversation about the symptoms and so indirectly pick his brains....

 

Transient pressure collapse.... the 60psi is the residual pressure after the injectors stop firing, so we're talking total pressure collapse.... just an idea: when you open the throttle suddenly the manifold vacuum collapses and the M/U releases all the fuel it has, in expectation of more arriving... now if you imagine you're blowing down a straw into a small balloon, you can build up pressure in the balloon pretty fast.... now if you're blowing up a large balloon, it takes longer. What I'm thinking... the pump has, in effect, to blow up that is to say pressurise, all the volume of pipe from the pump to the M/U. It needs to be at 95psi to fire the M/U and 65psi to fire the injectors.... now your 8mm pipe which you say is twice the size of standard... if you meant literally twice (I don't know the normal pipe dia) that means it has four times the volume of the standard pipe. So that's four times as long for the pump to reinstate the pressure...

 

You see, if the Facet can keep up with the engine at full chat, the Facet must have enough capacity.

And the filter must be big enough.

And the pipe must be big enough.

 

So I wonder if the pipe is too big... so it takes a noticeable time for the pump to repressurise it... try a standard dia pipe from pump to M/U.

 

Now, the stalling. Only at junctions and roundabouts... no fuel surge ...? Well, suppose there is.

Suppose it only uncovers the outlet on braking. Then you'd get fuel starvation every time you slow.... you said the pump makes 'funny noises' - like it was cavitating??

But it only stops the engine at junctions.... because when you brake for a bend the clutch is in so the axle is driving the engine so it can't stop... but when you get to a junction you kick the clutch out so the engine can and does stall... so I think you have surge in the main tank or the swirl pot under braking... my best guess.

 

Ivor

[Andy Moltu]

Looking at your pictures I wonder if there are a few too many filters in the set up?

 

The Facet does as I recall have a strainer element in it which should be enough to prevent damage to it and the main Bosch pump. (I used to have the same pump when I ran a roller vane pump but I found it to me unnecessary with the Bosch.)

 

Looking at the picture the Facet pump is not delivering fuel at pressure to the Bosch pump - merely pumping fuel into the swirl pot which provides a head of fuel to the Bosch pump but once the swirl pot is full the excess returns back to the tank rather than priming the Bosch with the 4 or 5 psi that the Facet can deliver.

 

Whilst the Facet can notionally deliver a greater flow rate than the Bosch it may well not be able to do so sucking through the little plastic filter.

 

The filter you indicate as a Bosch pre filter looks like a Bullet filter. I would get the metal mesh filter element for this (assuming you have got the paper element in it currently) and move it to where you have the small plastic filter. Ths will be more than ample as a pre filter for both the Facet and the Bosch pumps yet provide negligable flow restriction. I would not fit a filter between the swirl pot and the Bosch pump. I would keep the post filter on the high pressure side of the circuit to keep fine debris out of the injectors.

 

I would also try and raise the swirl pot so that it is significantly higher than at present as it is this height that determines the pressure of the fuel being delivered to the inlet of the Bosch pump.

[Goswell]

I run a Lucas pump fed by a Facet through a paper fuel filter.

The setup reduces power consumption, as the Lucas works less due to the pressurised fuel.

Also the small reserve in the filter stops fuel starvation on lefthanded bends, as I have an early tank without baffles.

 

I didn't move to a Bosch pump, as the Lucas is very adequate plus I was told the Bosch is not a pickup pump, it needs pressure to prime it.

 

Are you sure that the height of the Bosch pump, plus filters, is not causing too low a pressure and it is struggling ?

 

The facet pump has a micron filter so further filters does seem like overkill.

[john.r.davies]

Ivor, Andy, Goswell,

Gosh, what good ideas! All I need it time to test them out!

The PRV idea was a bust, as the spare one turns out to be so for a reason - it maintains the fuel pressure at a mgnificent 140psi, and no amount of adjustment makes any difference. Either the valve is still stuck, or my ministrations have made it so. I abandoned it and put the original one back.

I've seen a pic of Malcom Jones' diaphragm valve, but there again the last time I did discuss this system with him (yes, the M/u is his work and the Bosch pump his product) he said the valves almost never go wrong. And yes, the idea of sending the old one to him and picking his brains had occured to me - but why, when I have the Brains Trust here?

Next step is to miss out the swirl pot. managed to do that last night, but sleep overcame me, and work overcame me too today, so no time for a test drive tonight.

 

Ivor,

Great minds think alike, and I had wondered about the vacuum, so fitted a vacuum gauge to the manifold, or rather T-ed it to the line to the M/u. The vacuum sems to act just as it should, maximum on the overrun, but less on tickover, drops progressively (m'fold pressure rises)as you open the throttle. No abrupt changes to coincide with the fuel pressure drops. So unless the M/u is faulty, and until everything else is checked I'll assume it is not, that side is not the problem.

 

I take your point about the wider supply tube, but this is hydraulics, not pneumatics. An 'imcompressible' liquid down a rigid tube can't flow any more fuel, or less, than what is pumped through it. AND, the tube that Malcolm supplies is the same diameter! I can't think it's that, but thanks for making me think of it again.

Which leads to - the Bosch is not getting enough fuel, or is getting air, and Andy's point.

 

Andy,

Yes, yes, yes, there ARE too many filters. Last year at Zandvoort, in the Silverback, I thought the surge problem had returned, but it was an outbreak of rust rash in the steel tank. The Facet's internal filter was full of sand-sized rust, the pre-Bosch filter full of dust-sized rust and the post-filter was stained red. That's why the pre-Facet filter is there! The idea was that if it got stained, I could see the fact, whip it out and fit another. But the new tank is alloy, and clean, so yes, I don't need that pre-filter!

That pre-Bosch filter was supplied and recommended by Malcolm, and the element is paper - I changed it after Zandvoort.

 

Supply pressure - great minds, again. I had this out with Malcom, as he was concerned about the pressure from the installation in the Sb, whe there was no swirl pot. He thought that the Facet would over-pressure the Bosch, but experiments with a coffee can of fuel as the supply, on the floor of the car, above it on bricks, and in the rafters of the garage to vary the pressure (0 to about 2 meters head of pressure, or 2psi when it's fuel not water) , seemed to make no difference.

The top of the swirl pot is about - it's pouring with rain again, I'm not going out to the garage now - about 250mms above the Bosch, so when full, as it should be all the time, the supply pressure to the Bosch should be about 1/2psi. Enough? I don't know, but the relationship was about the same in the Sb.

 

Goswell,

I don't think that the Facet's filter is as fine as "micron"; see the rust sizes that got through it, above.

It's a fine mesh, is all, on this one at least.

But you are clearly part of this 'great minds' gestalt!

 

 

OK, time to do something. I've taken the swirl pot out of crcuit, but no test. Back to basics. I'll also remove ALL the filters and run the Facet straight to the Bosch, and see what that does. Then add the swirl pot, which I think I will need to race, and then some of the filters.

 

I could just fill the tank with open-cell foam as baffle, and use no swirl pot, but that stuff is EXPENSIVE - £100 to fill my tank!

 

Thanks again, guys. Talking with you clears the mind, and opens the box.

I'll report back asap.

 

John

[mickw]

John,

 

Not in anyway a solution to your problems but some thoughts.

 

1. Mount the bosch pump under the car there is room to put a bracket underneath out of harms way and in cooler air.This will lower the level of the pump increasing its efficiency as bosch dont like to suck and looking at your set up there is not much of a head between the swill pt and pump.

 

2. Fill the tank with these foam square to reduce surge, from the photo I assume you have no fuel gauge sender in the tank.

 

http://www.merlinmotorsport.co.uk/p1055/80...oduct-info.html.

 

This should do away with the need for the facet and swirl pot simplifying the plumbing and hopefully reducing potential problems.

 

On an entirely different note how far down into the tank do the return pipes go as hope eventually to convert my gt6 to lucas PI and will need to modify the tank.

 

All the best

 

Mick

[john.r.davies]

Mick,

Good point, but that foam is not cheap! I've got the pot etc, and the system worked before I fitted the tank (is there a clue there???)

So I'll try to make it work now, and keep your advice in my back pocket!

 

The idea of the pump out there in the slipstream, victim of any stray stone or tussock (I have been known to leave the track now and again) fills me with dread. All the piping is tucked up in the chassis out of harms way.

 

The returns only project into the tank by a centimeter or so. I think that I might have specced them to go right down to the floor, to minimise splashing and aeration, but I've watched the swirl pot return through the filler cap, and there isn't any bubble formation, so maybe it doesn't matter.

 

I'm working this evening so no chance of a trial run.

 

John

Edited August 27, 2008 by john.r.davies

[Guest ntc]

Mick,

Good point, but that foam is not cheap! I've got the pot etc, and the system worked before I fitted the tank (is there a clue there???)

So I'll try to make it work now, and keep your advice in my back pocket!

 

The idea of the pump out there in the slipstream, victim of any stray stone or tussock (I have been known to leave the track now and again) fills me with dread. All the piping is tucked up in the chassis out of harms way.

 

The returns only project into the tank by a centimeter or so. I think that I might have specced them to go right down to the floor, to minimise splashing and aeration, but I've watched the swirl pot return through the filler cap, and there isn't any bubble formation, so maybe it doesn't matter.

 

I'm working this evening so no chance of a trial run.

 

John

 

is there a clue there???)

John

There could well be looking at the pics you posted the tank breather looks very small maybe not enough?

Edited August 27, 2008 by ntc

[john.r.davies]

is there a clue there???)

John

There could well be looking at the pics you posted the air vent looks very small maybe not enough?

It's a standard after market one way valve, bought at great expence last year.

And it is the right way around!

But, again, good point, it needs checking.

Thanks!

John

[88V8]

But this is all a red herring if the system will supply the engine at full chat. The filters the vent the pipes the Facet, must all be doing their stuff.

Question is, why the transient drop.

OK it's not the compressible petrol I invented.

 

I don't think the Bosch needs supply pressure as such - it just needs not to be pulling a vacuum. The standard PI installation, like in my boot, has very little head, much less then 10". And it works, as do all standard Bosch installations, without downstream pressure accumulators, due to the surplus pressure in the system. If an accumulator fixed it, it would be masking the real problem

 

So it all worked before you fitted the .... new petrol tank ?? (non-disclosure of material fact ).

So the filters the Facet the pipes, were all there and doing their stuff?

 

So what's different about this tank?

 

The Facet - is it demand-led? Does it pretty well stop when demand falls, then pick up again?

Could it be slow to get going, compared to the Bosch which is always full-on?

 

What did you mean when you said the Bosch makes odd noises? When?

 

Is the hesitation worse after braking, or is it as bad when you've been on a trailing or light throttle and floor it?

 

Hmmmm.

 

Ivor

[Guest ntc]

So it all worked before you fitted the .... new petrol tank ?? (non-disclosure of material fact ).

 

Steady on Ivor, John is only trying to resolve a problem ok he forgot to tell us about the new tank.John for the fuel pumps to work they need a head of air or fuel looking at your pics I think air could be the problem. I had some similar issues on a dry sumped rally car ok oil based a few years ago now It turned out to be the lack of an air vent above the scavage pump . Still thinking though

Regards

[john.r.davies]

Er, "New alloy tank" - fourth line , original post. But I didn't dwell on it, and yes, such a major change is material. As is that it replaced a much smaller (3 gallon) rectangular tank, that only had an outlet and a breather pipe, so that the returns had to be piggy-backed onto the breather. That produced similar much much more severe symptoms, as the breather was choked by the returns. Correcting that meant using a spare connection on the swirl pot for the PRV return - that worked!

The pre-facet filter is also new, as the original glass bodied filter cracked.

 

The Facet goes at full chat, all the time, circulating the fuel through the swirl pot and keeping it full.

 

Ivor, you describe the symptom most succinctly, "when you've been on a trailing or light throttle and floor it", though flooring it is not necessary. The lightest application of throttle precipitates the hesitation, nay, total lack of power for a second or more, as the fuel pressure collapses, then reappears, several times before normal service is resumed. It feels like the 'kangaroo juice' that novice drivers use when learning clurch control, and must strain the transmission a lot. The stalling on slowing is, I think the same thing, but without the clutch in there is no momentum of the car to keep the engine turning to catch and run as soon as fuel returns. I suspect I unconciously apply a little throttle as I prepare to set off again in a lower gear, the fuel presure drops and the engine stalls.

Carbs and I presume the M/u provide a richening effect on acceleration. I did wonder if the Bosch was weakening and wasbarely adequate, so this small demand outstripped it. But as you say, full chat, no problem, and it is well able to sustain 140psi as my faulty PRV experiment proved. But pressure is not the same as flow, and there is either a restriction somewhere, or bubbles are getting through.

 

Bosch noises: It usually starts with a high pitched rumbling, if I may put it that way, the noise ascends to shriek, as the pressure rises and settles at 105. Noise while running is difficult to say, as a stripped-out racer with minimal silencing is a noisy environment. There are similar shrieks as the pressure rises and falls, I think

 

ntc,

I would love to have a glass swirl pot. Fiddling with the connections the other night, and running the Facet with the swirl pot to Bosch outlet blocked, I had a plastic conector in the return line (it was convenient). It seemed to take a long time for the bubbles to clear in the return flow, as if the swirling was not as efficient as I hoped. It would be good to see what is happening in there!

 

Sorry no testing progress, work gets in the way. Perhaps this evo!

 

John