Running rich - I am going mad

[Per]

1978 2000 HPE with DATR as described before. Problem is it runs rich no matter what I do. All gaskets and idle screw O-ring replaced. Float and needle valve replaced. Float level checked and rechecked. Jets correct sizes. Idle jet srewed all the way in and checked with rubber hose on jet nozzle, fully closed.

Even so it runs rich, at idle it starts bogging down after a few secs, a blip will bring it back and so on. CO not less than 7%.

Interestingly it will not run if solenoid is disconnected, I thought that only fed the idle jet with fuel?

Any ideas?

[mangocrazy]

Auto-choke on permanently? All I can think of...

[Per]

Choke fully off.

[hutch6610]

Sounds like you have fuel bypassing the idle circuit, very common on carb VX models, they run even when you have screwed the mixture screws fully home!

Not sure exactly which DAT 34 carb your Norwegian Beta has (photo would be nice) as there is an early and a late one here in the UK
This is the earlier one below;
https://c1.staticflickr.com/3/2179/2407191741_a548d73aa6_b.jpg
fitted about  1978 - 1980

Then there is a later version;
https://www.autobelle.it/altre-immagini/immagini_annunci/55/556848/sorgente_556848.d1521913267.jpg
fitted about 1980 - 82

If its the second carb in the pictures look closely and you will see a diaphragm cover with three screws with Weber and a W cast into it. That diaphragm becomes porous and fuel is sucked into the the manifold past it resulting in the symptoms you describe.
You mention you have changed gaskets, float valves and "o" rings which makes me think its the early one as it would be supplied in the repair kit you used?
If your carb is the earlier one without the diaphragm maybe the idle jet holders are not screwing in far enough to seat the idle jets?

I hope this is of some help.

Out of curiosity what are the idle jet numbers?

[peteracs]

Are you running standard mechanical pump or electric replacement?

If the mechanical, is it the return feed to the tank blocked and causing an issue?

If electric is the pressure too high?

Just my 2 penny worth......

Peter

[Per]

The carb is the earlier one, jets 80, 150, 120, 50 starting from the choke. When fully home the two tubes go equally far down as do the two slow running jets.

Looking at fig 3.11 in Haynes the idle solenoid also feeds the two small holes ("jets") just below the fully closed position of the main choke. So once the throttle opening screw is opening a tad there will be fuel supplied via the solenoid cut off valve as evidenced by engine immediately dying if cable pulled from solenoid. Considering the idle speed is set to about 750rpm that way and the final 100rpm is supposed to be set through the idle speed jet it is clear the bulk of the idling fuel comes from the twin "jets". It is also unlikely that the rich running condition comes from these two "jets" unless opened up somewhere through damage by a ham fisted PO. Still puzzled by the lack of influence through opening the idle jet. Maybe there is something there after all?

Mech pump, I will check the return line for blockage tomorrow.

[Per]

Kind of good news I suppose? The short hose from carb to metal return pipe open and very easy to blow through. Connecting a new short hose to the metal return pipe it was impossible to blow through. I connected a pump and sucked some fuel back standing in the pipe, I had to pump very hard and only then would it move slowly. I then pumped back toward the tank very hard several times, ca 3 - 4 litres of air before putting any pressure on the pump. Tried sucking back again and no fuel. So assume the fuel eventually went into the tank. To me this sounds like a partial (nearly total) blockage of the pipe.

Is there any particular point that tends to get blocked, or should I assume it is s combination of rust and sediment from today's crappy fuel? And so replacing the whole pipe is the only viable solution?

[Per]

An alternative is an electric pump (suction type) in the engine compartment. Anybody know what fuel pressure the 34 DATR wants? Normally carbs like 0.4 bar but 0.3 may be the case here. Some Webers seemingly prefer 3psi so approx. 0.2 bar. How sensitive is it really? I can get an off the shelf locally sourced suction pump suitable for patching into the fuel supply line in the engine compartment that gives max 0.3 bar.

[peteracs]

Hi

Sounds like the return may have been causing the issue, how does it run now you have at least partially unblocked it?

On the electric pump, no idea on pressure required, but make sure you have installed with a cutoff in case of an accident. There has been a few threads here which discuss it.

Peter

[mangocrazy]

This thread seems to cover most of the bases:

https://www.betaboyz.myzen.co.uk/forum/index.php?topic=3984.0

The thread also discusses protecting the pump in the event of an accident with an inertia switch. I can fully recommend a Huco pump, fitted in the engine bay. Guy Croft sells blanking plates for the redundant mechanical fuel pump orifice in the block, and it also means you can dispense with the auxiliary cam lobe that drives the fuel pump (and can wreck a 2 litre engine if wrongly timed).

[hutch6610]

Per  may i ask you several more questions?

Is the thick fibre gasket below the carburettor present? If not the fuel can boil and lead to flooding and "bogging down"

When this "bogging down" was occurring did you have the air filter cover off to see what was going on?

The fuel return line is to keep fuel temperature constant to prevent "vapour lock" occurring, you could try clearing it by using an airline with the fuel tank cap off. You may find the pipe has been dented by over enthusiastic jacking up by some clown and will need changing. A good job later cars have the lines inside.

A mechanical pump manages about 3-4psi max and its good enough for a standard road tune Beta.

Pay no heed to the Haynes manual on setting up the mixture/idle - that 750 rpm and the mixture screw to get an extra 100rpm is bogus, just set it up as any other carburettor, warm the engine up until the choke is off and switch it off.
Screw the mixture screw in until it seats (don't force it) and unscrew it 2- 3 turns anti clockwise, start the engine and set the throttle screw for an idle of about 900 rpm +/- 50, you can then adjust the mixture screw by adjusting it in a little at a time until the engine runs worse and then back out to where it just runs the best. You can then bring the idle to where you want it.
Remember the car is no spring chicken,  If you want to use a gas analyser remember the car is some 42 years old and may not give factory CO readings.

Tappets, ignition timing, plugs air filter etc have to be in good condition and set correctly before you can really tune the carb to get the best. 

If it does the bogging thing again take the filter cover off and look, you will probably see fuel dripping down the barrels.



 

[Per]

Thanks guys. Disconnecting the return line at both carb and where the hose between tank and the return line pipe under the car I could easily blow bubbling sounds in the tank. Applying pressure at the pipe unblocked it. I suspect forcing fuel down the line yesterday helped dissolve dried out crud.

Now it does not bog down anymore. Hoorayyyyyy 

Finally I could also tune it so it runs well. I haven't revisited CO measurement yet, not sure I will bother.

I will however run the tank down and then drain it completely hopefully getting most of the crud out. Then new fuel filter.

[Per]

For how long was Adam in paradise?
It is back to bogging down. Looking into the barrel the accel jet drips fuel after stopping and after a 20 min run it will hardly run unless secondary choke is opened. Therefore fuel starvation due to vacuum building in the tank is not the problem.

The tank lid is aftermarket but is vented. Removing the lid the return outlet (with hose removed) stops dripping as does accel jet. On blowing return line with compressed air pressure builds in tank and only bleeds down slowly through tank lid (cap) plus fuel drips into barrel at accel jet. Blowing with tank lid removed the air wooshes through the return line.

I find this odd? Creating suction in the tank as fuel is used I can understand, but overpressurised even though return line is used? If the mechanical pump sucked air and mixed it into the fuel maybe?

As mentioned I run the original mech fuel pump.

[Per]

More testing: Nothing wrong with lines etc.. The carb is shot, goes out of adjustment in 10 mins. A hopefully good used one hopefully here on Tuesday. If that turns out to be bad as well maybe a brand new DMTR and converting to manual choke is the way to go. Either way I will keep posting here until a conclusion is reached and the car runs properly over time.

[Per]

The used carb looked OK and once membranes replaced pressed into service.

Looks like I uncovered another problem once the return line issue was solved. I believe the fuel pump struggles. At idle it falters and eventually dies unless I blip the throttle. At lowish revs it hestitates and even thhough the accel pump works sudden welly gives a short stumble. Only at highish revs it is ok. And once stopped the fuel runs slowly back towards the tank, this can be observed as bubbles in the clear fuel line after the pump. There are no fuel leaks that I can detect but still odd that bubbles should appear at the pump (and move toward carb). Where does the air enter the line? Could it be the pump partially sucks air? Will check tomorrow. Cracked fuel line at the pump inlet maybe?

[WestonE]

Hi Per

Time for a new electric pump. The manual pump rubber membrane fails over time you get drain back and need more engine speed for fuel delivery that will fail under high speed high load. Their capacity was always marginal and smaller pumps were fitted to 1600s making it easy to buy the wrong replacement manual pump.

Good luck

Eric

[mangocrazy]

I agree wholeheartedly with Eric. An electric fuel pump is the way to go. I'd recommend a Huco, fitted in the engine bay. The other benefit of dispensing with a mechanical pump is that the lobe on the auxiliary shaft can be cut off, removing the possibility of catastrophic failure if the shaft is mis-timed when replacing a cam belt.

[Per]

Thanks guys,  you have confirmed my suspicions. Electric pump it is. Which Huco model do you recommend?

[mangocrazy]

This web page gives details of the different Huco pump models available:

http://www.gowerlee.dircon.co.uk/HUCO.html

I suggest that part number 13 3010 is the one you want. I bought mine from Fast Road Cars ( https://fastroadcars.co.uk/ ), and they also have the pump listed in their ebay shop:

https://www.ebay.co.uk/itm/FUEL-PUMP-ELECTRIC-FOR-SUCTION-HUCO-133010-ENGINE-BAY-FITMENT/264031210689

[Per]

Progress of sorts......
Electric pump installed, return plugged, pump stops once carb primed when engine is not running. At idle it clics leasurely.

It runs lean though, very much so.

However, removing and disassembling the carb from a warm engine gives a cool carb and refitting and immediately starting everything runs perfectly (with a bit of choke despite warm engine). So lean condition confirmed. It very quickly deteriorates though.

When properly warm nearly undrivable as there is hardly any power and much hestitation amid popping and crackling. Opening the second choke suddenly gives nearly full power. I will try the chokes from the other carb just in case they have been messed with.

And on it goes........