Hard to start after warm. Fires up when floored.

[Mucci]

Just rebuilt the 32/36 on the car. Also put in new plugs, wires, and set the ignition timing to "split the Z ball".

 

Car starts right up when cold but if I take it for a 10 min errand it doesn't want to restart. It cranks and cranks without a hint of firing. I found that if I floor it and crank it will fire up.

 

Any ideas?

[Mike G]

Is the choke stuck on? 

['76mintgrün'02]

I floor mine every time I start it warm.  It has me trained that way.  It lets more air into the mix and can help with flooding, even though it seems backwards.

 

The car originally had a diverter valve in the fuel line, to bleed the pressure off between the pump and carb when the car is shut off and one theory is that flooding can occur if fuel bleeds past the needle to alleviate the pressure.  I use a Jeep fuel filter with two outlets between the pump and carb to serve that purpose, since the valve had been removed from my engine before I got it.

Search [ Jeep filter ] and you'll probably see a dozen posts where I've mentioned it.

( : search [ innova 5568 ] and you'll see two dozen posts where I've mentioned that  : )

Tom 

[Mucci]

1 hour ago, '76mintgrün'02 said:

I floor mine every time I start it warm.  It has me trained that way.  It lets more air into the mix and can help with flooding, even though it seems backwards.

 

The car originally had a diverter valve in the fuel line, to bleed the pressure off between the pump and carb when the car is shut off and one theory is that flooding can occur if fuel bleeds past the needle to alleviate the pressure.  I use a Jeep fuel filter with two outlets between the pump and carb to serve that purpose, since the valve had been removed from my engine before I got it.

Search [ Jeep filter ] and you'll probably see a dozen posts where I've mentioned it.

( : search [ innova 5568 ] and you'll see two dozen posts where I've mentioned that  : )

Tom 

But you still floor it for warm starts? So it didn't fix it?

[Mucci]

1 hour ago, Mike G said:

Is the choke stuck on? 

I don't believe so. However I do give the gas one to-the-floor pump before starting to set the choke if the car isn't warmed up fully yet. Maybe I shouldn't do this after short drives? It sounds like this is a flooding issue... Is that right?

[Mike G]

Seems that way to me. Did you set the float when you rebuilt the carb?

[Mucci]

Yes, I had a chat with Weber and was told to set the floats 2-3 deg lower (into the bowl) than parallel to compensate for the buoyanncy difference of modern fuel vs. what there was in the 70's. 

 

Apparently the ethanol in fuel today causes the floats to be less buoyant and put less pressure on the needle valve. 

Edited March 22, 2020 by Mucci

['76mintgrün'02]

35 minutes ago, Mucci said:

But you still floor it for warm starts? So it didn't fix it?

 

Mine is still slow to start when warm sometimes, so I am just in the habit of flooring it.  You could say that the Jeep filter did not fix it, but I could say that it improved it.  Or not. 

 

I just don't like the idea of fuel pressure sitting there and figure it will either work past the valve in the fuel pump, or past the needle in the carb.  The original bypass valve is often removed during desmogging efforts, but I think they make good sense.  Just my opinion though.  Take it or leave it.

 

 

[Buckeye]

3 hours ago, Mucci said:

Car starts right up when cold but if I take it for a 10 min errand it doesn't want to restart.

 

Did this problem exists before rebuilding the carb?

item 03 will fix the issue once for all

[John76]

1 hour ago, Mucci said:

Apparently the ethanol in fuel today causes the floats to be less buoyant

 

Couple of things to check:

-Float....brass or plastic?  If plastic, consider replacing with brass (pay attention to the float level setting for brass).

-Insulator block under the Weber?  Excess heat will cause the fuel in the bowl to dry-up in a hurry. Pressing the accelerator to the floor helps with a "hot start" by squirting any gas left in the accelerator pump diaphragm...which is less able to evaporate.

 

The problem with carbs is the float bowl is open to the atmosphere. If you have a small air cleaner on your Weber, it will allow more heated air from the engine bay to evaporate the fuel. The stock air cleaner connected to the fresh air nozzle is less susceptible to this.

The Ethanol gas we are now forced to use has a very low Reed Vapor Pressure. This means it evaporates very quickly....not a problem with fuel injection, since those systems are totally closed.

 

3 hours ago, '76mintgrün'02 said:

The car originally had a diverter valve in the fuel line, to bleed the pressure off between the pump and carb

 

The fuel return valve does not relieve pressure in the line. The mechanical fuel pump has a 1-way check valve that prevents gas from returning to the pump. The needle valve in the carb actually releases the fuel pressure as the float gradually (or rapidly) drops due to the fuel evaporation.

The fuel return valve returns fuel to the tank when there is high manifold vacuum (closed throttle or idle). This bleeds off fuel pressure  to the carb when it is not needed. The fuel valve return line is closed (no excess fuel to the tank) when the manifold vacuum is low or zero, such as full throttle or when the engine is off. This is when the extra fuel pressure is needed.

 

Possible solution...although I have not done this (yet), is to fit an electric fuel pump near the tank to fill the float bowl (sending fuel through the "old reliable" mechanical pump). This should only take a few seconds prior to starting.  Just a thought.

[Mucci]

1 hour ago, Buckeye said:

 

Did this problem exists before rebuilding the carb?

item 03 will fix the issue once for all

 

I bought the car in rough shape so this is the first time I'm driving it.

 

Is item 3 the fuel return valve? Is there a way to check if this is working properly?

[Mucci]

So now I'm hearing two opposite theories. Either the engine is flooding after a short ride or the bowl reserve is evaporating.

 

What's the best way to diagnose which one it is?

 

I probably cranked it over 60 times on my last errand run with zero sign of starting. Then tried the floor-it technique and it fired right up. I would think that much cranking would refill a dried up bowl no? I also only left the car for about 10min.

Edited March 22, 2020 by Mucci

[Mucci]

42 minutes ago, John76 said:

 

Couple of things to check:

-Float....brass or plastic?  If plastic, consider replacing with brass (pay attention to the float level setting for brass).

-Insulator block under the Weber?  Excess heat will cause the fuel in the bowl to dry-up in a hurry. Pressing the accelerator to the floor helps with a "hot start" by squirting any gas left in the accelerator pump diaphragm...which is less able to evaporate.

 

Floats are plastic. That info was relayed to the Weber engineer who gave me the above height spec. 

 

I'm not sure about the insulator block. Is this a block of aluminum spacer or more of a heat shield? I don't believe it has either... Pretty sure I mounted it straight to the manifold with a gasket. 

 

Can you explain how the electric pump would help in starting? Is this just because it builds pressure at key-on prior to cranking or does it have something to do with fuel return?

Edited March 22, 2020 by Mucci

[Mike Self]

My '73 has exactly the same problem and has had for many years, about as long as I've had the Weber (1981 or so).  I've noticed that outside temperature is a determining factor in how long I can leave the car before it becomes difficult to start.  The colder the air temp, the longer it can sit--20 or so minutes when the temp is in the 30s, 5-8 when it's in the 80s.  

 

It's not the carburetor either, as I installed a properly jetted new Weber a few years ago and it made no difference.  Both new and old carbs are manual choke models, have the bakelite insulator block between carb and manifold, and a full factory air cleaner.  But I have removed all the emission stuff and properly plugged all the orifices in both manifolds.

 

And like Mucci, flooring the accelerator makes it start faster after sitting.  I've noticed that it will either instantly start, or settle in for a long cranking.  When that happens, I slowly press the accelerator to the floor and by the time it's floored, the engine invariably starts.  

 

Interestingly, my '69 with it's original 51 year old single barrel Solex never exhibits this behavior.  Always starts with only a turn or two of the crankshaft.  

 

I too would like to know what the cause is, and how to cure the problem. 

 

mike

['76mintgrün'02]

4 hours ago, John76 said:

The fuel return valve does not relieve pressure in the line. The mechanical fuel pump has a 1-way check valve that prevents gas from returning to the pump.

 

Thanks for the return valve explanation.  I had posted my misunderstanding of its function several times, so I went back and edited the four that I found (using the search feature).

 

Did you mean to say Tank, as opposed to pump?

 

Fuel draining back to the tank has inspired many people to put a check valve inline between the pump and the tank.  I did it for a bit, but took it back out.  

 

The electric primer pump is a fun idea.

 

I went to start my car the other day for the first time in a while and it cranked and cranked without firing, so I went and got starting fluid and shot some down the carb.  Still nothing.  So   then   I connected the coil wire I'd forgotten to reattach and it fired right up.  I put the battery on the charger overnight.  I wish stupid was that easy to fix, but they say it can't be done.  

Tom