'72 T Hesitation & lack of top end

[sfh3l]

Hi Chaps and I wonder if I might tap into the font of wisdom again please.

I have a '72T, running on Webers. I had a miserable drive back from Le Mans on Monday, mainly on account of horrible weather in France and then the appalling state of play at the Eurotunnel, where it took them almost 5 hours to get me from the entry to their site and onto a train that actually moved - not good at all.

When I got out into the relative freedom of the M20, it was immediately clear that not all was well with the car. The top end had all but disappeared and 60 mph was pretty much all that we could muster. Backing off seemed to clear the car's throat somewhat, but with 140 miles ahead of me it wasn't looking good. I filled up with petrol, as I suspected that it might be the fact that the car was unhappy on the French unleaded and its higher ethanol. This gave me the opportunity to put in half a tank and some more Millers additive. It was better, but not quite right still. We made it home, since when I have changed the engine bay fuel filter and it is running OK now, but I suspect that there is more trouble up front.

I've had the sender unit out of the tank and it looks OK - not pristine, but not rust haven either. I am not sure what kind of electric fuel pump my car has, but it is hidden by the shield at the underside of the rear of the fuel tank, which I have yet to remove. Does anyone know if there is a pre-filter there (or indeed in the pump itself, as in my contemporary BMW) that might be worth changing? I was working on the basis that I clean/change whatever is there and blow the front-to-rear line out while I am at it, and then see how I get on, but open to any suggestions.

Given the fact that there is a filter in the engine bay and that the Webers were rebuilt units, fitted to the car only 6 years ago (just before I got it), I am hoping that no debris of any kind has found its way into them, but I suppose that would be the next place to check.

Any thoughts guys? Am I barking up the right shrub at least?

Thanks in advance for any help.

[KS]

At less than about 1/2 to 2/3 throttle, Webers rely a lot on the idle jets, with fine tuning courtesy of the emulsion tubes. As you open the throttle wider, fuel is drawn through the main jets. Fine tuning is done via the air correctors. To me it sounds like the main jets may be blocked, or some of them. That would account for it running better when you back off the throttle. It could be you've picked up some crap fuel abroad (petrol stations aren't very good at cleaning out their tanks...). If I remember rightly when you remove the air filters, you'll expose the tops of the emulsion tubes (actually what you see are the air correctors) - unscrew them. At the bottom of the emulsion tube is the main jet. Use an airline to clean out all the passageways. Don't be tempted to use a piece if wire... Oh, also check there's no water sitting in the bottom of the float chambers – water's heavier than petrol – which can get their courtesy of, again, poor fuel/poorly-maintained tanks.

[Dingbat]

What he said, and if it was missing down pull the tank sender out and take a careful look for water in the bottom of the fuel tank, you can get a fair bit in there and it may not be that obvious , if you find some in there pull the tops off the carbs and take a look in there. A s for how it gets in , badly routed breather, blocked drain on the fuel filler well, something like that, as for getting it out drain it out and blow it out with compressed air and change all the filters AND try and figure how it got in there..

[fetuhoe]

Did you add fuel in France ?

If you filled up on E85 it may be breaking down the fuel hoses.

Modern Fabric covered Cohline hose is not really up to the job.

In the UK it lasts between 9 and 12 months before needing replacement but E85 has an almost immediate impact and can cause problems.

The only Ethanol resistant fabric covered hose we have discovered is Aeroquip Startlite but this is around £35.00/metre.

[greggearhead]

At less than about 1/2 to 2/3 throttle, Webers rely a lot on the idle jets, with fine tuning courtesy of the emulsion tubes. As you open the throttle wider, fuel is drawn through the main jets. Fine tuning is done via the air correctors. To me it sounds like the main jets may be blocked, or some of them. That would account for it running better when you back off the throttle. It could be you've picked up some crap fuel abroad (petrol stations aren't very good at cleaning out their tanks...). If I remember rightly when you remove the air filters, you'll expose the tops of the emulsion tubes (actually what you see are the air correctors) - unscrew them. At the bottom of the emulsion tube is the main jet. Use an airline to clean out all the passageways. Don't be tempted to use a piece if wire... Oh, also check there's no water sitting in the bottom of the float chambers – water's heavier than petrol – which can get their courtesy of, again, poor fuel/poorly-maintained tanks.

Exactly what Keith said.

My first question was - "was it running perfectly before?" I assume so, but it isn't stated. If so, then yes, it sounds like a lean condition due to a fuel issue likely, and at higher speeds/rpms, likely the mains or fuel pump starting to give way. Easy to take a glance at the plugs and under the distributor cap as well.

Didn't just do an oil change and overfill it, did you? Would cause reduced power and lots of oil smoke, which you didn't mention.

[sfh3l]

Hey Guys,

That is really helpful, thanks. We had added fuel in France, but it was a good half way down the latest of probably 4 tanks before it started farting around. It was indeed running very well beforehand, though has always had a very slight hesitation if you back off at around 70mph and then reapply the throttle.

I always used Millers anti-ethanol additive, even here in the UK, but especially in France, where I know they have higher ethanol content.

I shall have a look at the top of the carbs. I don't actually have a proper compressor, but hope I can do it with the tyre compressor that I have. We'll see anyway.

Thanks again for all of the common suggestions.

[Nick Moss]

Check your rubber fuel lines for collapsed sections.

[haasad]

All good advice but take care blowing compressed air into the carbs, crushed floats maybe an unexpected and unwelcome result. Much better and simpler to remove the carbs to clean them properly once you are sure the supply is clean and clear.
Andy

[squirejo]

Coil breaking down?

[KS]

All good advice but take care blowing compressed air into the carbs, crushed floats maybe an unexpected and unwelcome result. Much better and simpler to remove the carbs to clean them properly once you are sure the supply is clean and clear.
Andy

No, I meant only using it to blow through emulsion tubes and jets once removed from the carbs. You wouldn't achieve anything otherwise.

[Dingbat]

Hi
I did mean to say pissing down as in heavy rain but corrective text got in the way, and yes if water is found in the fuel tank, remove the tops of the carbs and check the float chambers for water and crap , I once got over a litre of water out of a 911 tank, and the only proper answer is to dismantle and clean out, that's if you do have water in there.

[sfh3l]

Thanks chaps. To be fair, I don't even have a compressor of the kind that might damage things, but I do see the issue, so thanks for the warning.

The coil is new, so no worries there. The fuel lines in the engine compartment are also new, so I am fairly comfortable with them. I need to get down and dirty with what lurks at the back of the fuel tank, as the lines there may well be less pristine, so I think that is where I shall go before troubling the carbs. My thinking is that it is less likely to be the carbs as the fuel filter has always been there to protect them, while what sits at the back of the tank, goodness only knows.

I shall look there first and see what we find. I feel inclined to be prepared to replace the flexible lines there, clean out the fuel pump if it proves possible to dismantle and perhaps also install an in-line filter there if there isn't already one (replace if there is). Only then would I progress to carbs, if I found nothing suspect while doing all of that.

My worry re the carbs is that I don't have the expertise to set them up subsequent to messing around with them. If I could remove them without disturbing the balancing and any adjustments and do all of this on the bench then I certainly would be up for it, but not sure of the chances of that...... If I did so, I would take the opportunity to get the Pelican larger insulating blocks in the hope of reducing the heat-sink to the carbs after a long run, as they appear to boil off the petrol nicely, which is very smelly, not too safe and also hardly environmentally friendly!

I'm going to start with the grubby stuff first though, and see what I find. That will have to wait for a while though, as I am working most of the weekend on trying to keep everyone happy after Brexit and there is also the small matter of getting the CSL ready for the jaunt down to Le Mans on Thursday Only hitch there is if the Eurotunnel is as bad as it was for the 24 hours, the old car will boil itself dry long before I do! Should be air-cooled!

Thanks again.

[Ian 2.2S]

The coil is new, so no worries there.

Don't assume because it is new, it is good. Many tales of new coils failing, even supposed 'proper' Bosch can be Brazilian made shite. Hope you find the cause sooner rather than later. Ian

[fetuhoe]

My worry re the carbs is that I don't have the expertise to set them up subsequent to messing around with them. If I could remove them without disturbing the balancing and any adjustments and do all of this on the bench then I certainly would be up for it, but not sure of the chances of that...... If I did so, I would take the opportunity to get the Pelican larger insulating blocks in the hope of reducing the heat-sink to the carbs after a long run, as they appear to boil off the petrol nicely, which is very smelly, not too safe and also hardly environmentally friendly!

There is little or no chance of balancing carbs on a bench. The need to balance is due to minor variations that occur form cylinder to cylinder of the engine.

These variations are caused by differences in compression ratio, valve timing due cam variation and tappet clearance, slight pitch variation on the crank etc, etc.

Porsche engines are quite good in this respect but even so the system will always need to adjusted on a cylinder to cylinder basis and this need the engine to be running.

Your chances of cleaning out the galleries in the progression circuit without disturbing the baseline settings is slim.

If you have fuel percolation problems the thermal insulators can help.

Porsche never fitted these to cars running on Weber carbs but did fit them for use with the Zenith 40TIN.

They were always fitted between the inlet manifold and the head, which I think is not the ideal position.

Most cars using insulators fit the 'spacer' between the carb and the manifold.

This has tow advantages the delta T at this interface is lower than the delta T between the head and the manifold and this means the insulator has an easier job and has more impact for a given thickness.

It also means that only one size is needed rather than a number of different sizes to suit port diameters.

The basic insulator being sold by Pelican is supplied by Porsche and is available from any Porsche Centre. There is only one size.

PMO make a thicker insulator - again between the head and the intake manifold but this is shaped to suit the SC Style port.


These new insulators appear to be made from Tufnol which isn't ideal as its max operating temperature is around 125 degC.

We decided to make our own insulators which are Epoxy Glassfibre with a max operating temperature of 180 degC.

They fit between the carb and the manifold and are 2.5mm thick.

We tested them in the following manner.

Drive for approx. 30 miles - turn off engine and wait for 20 minutes - Intake Manifold Temp 69.5 deg C- Carb Temp 69degC

We then fitted the insulators.

Repeat exactly the same driving route 30 miles - turn off engine wait 20 minutes - Intake manifold temp 71 degC - Carb Temp 44 degC - 25 deg C reduction.

[911hillclimber]

I run PMO carbs with their manifolds, gaskets and insulators on my 3.2.

Had some acute running issues and only when I stripped all the carbs and manifold down off the engine did I find two gaskets had dissolved in 24 months on a hill climb engine barely used compared to a road engine.
Changed the gaskets for new PMO and all suddenly came right.
Tuned them all with a humble Halfords Colour Tune and balancing meter.