Fuel bowl empties overnight

[gr_diver]

A few weeks ago I removed the carb's cover to swap a main jet. Upon opening I found the accelerator pump's "pressure relief valve" lying at the bottom of the bowl. I thought, that because the cover was a bit stuck, I might have knocked it with the straw hanging from the cover. Anyway, nothing seemed damaged in any way (the straw, the valve itself, it's seat) so I recovered it, sprayed it internally with carb cleaner, verified that it only "flows" one way and re-installed it by gently tapping it into it's seat. Then I verified that it works as the FSM describes (only discharges with rapid throttle motion), and called it a day. The car drove as it used to, so nothing changed in the operation if the accelerator pump. But...

...since that day, the car became difficult to start in the morning, or if has sat for more than 5-6 hours. After eliminating ignition issues I moved to the carb. I realized that if I crank it for a few seconds, and then re-try it will start as normal. The next morning I removed the carb's cover, and the fuel level was just above the main jets. Oooops!!!!! I had never opened the carb before and found the fuel to be anywhere below full...

I searched for leaks, the more probable places would be gravity fed circuits. The accelerator pump does not leak from it's cover, nor from the small brass screw at the side of the carb's body that holds the metering needle. The valve that I had mentioned earlier, even if it leaks from it's seat it would lead fuel to the chamber behind the accel. pump diaphragm, so this is not it either... Fuel cannot leak from the main jets because they are U shaped tunnels in the casting going above fuel level, and from there also the idle circuit feeds, so out go them both. The enrichment valve on the cover draws fuel up by vacuum so out goes this as well... I cannot think of anything else, the bowl bottom does not seems cracked, and the carb on the outside is clean and dry.

I am a bit stumped!!! Any ideas?

[tekenaar]

Originally Posted by gr_diver A few weeks ago I removed the carb's cover to swap a main jet. Upon opening I found the accelerator pump's "pressure relief valve" lying at the bottom of the bowl. I thought, that because the cover was a bit stuck, I might have knocked it with the straw hanging from the cover. Anyway, nothing seemed damaged in any way (the straw, the valve itself, it's seat) so I recovered it, sprayed it internally with carb cleaner, verified that it only "flows" one way and re-installed it by gently tapping it into it's seat. Then I verified that it works as the FSM describes (only discharges with rapid throttle motion), and called it a day. The car drove as it used to, so nothing changed in the operation if the accelerator pump. But... ...since that day, the car became difficult to start in the morning, or if has sat for more than 5-6 hours. After eliminating ignition issues I moved to the carb. I realized that if I crank it for a few seconds, and then re-try it will start as normal. The next morning I removed the carb's cover, and the fuel level was just above the main jets. Oooops!!!!! I had never opened the carb before and found the fuel to be anywhere below full... I searched for leaks, the more probable places would be gravity fed circuits. The accelerator pump does not leak from it's cover, nor from the small brass screw at the side of the carb's body that holds the metering needle. The valve that I had mentioned earlier, even if it leaks from it's seat it would lead fuel to the chamber behind the accel. pump diaphragm, so this is not it either... Fuel cannot leak from the main jets because they are U shaped tunnels in the casting going above fuel level, and from there also the idle circuit feeds, so out go them both. The enrichment valve on the cover draws fuel up by vacuum so out goes this as well... I cannot think of anything else, the bowl bottom does not seems cracked, and the carb on the outside is clean and dry. I am a bit stumped!!! Any ideas?

Check float travel obstruction and needle and seat at carb inlet . . . I don't think it's draining, I think it's never filling to the correct level!

[GTJIM]

Opel carbs are well known for boiling dry due to heat soaking after the motor has shut down. There is LOTS of stored heat in the exhaust manifold that literally "boils" the fuel in the carb fuel bowl so that it escapes from the carb as a vapour.
Check the fuel level as soon as you shut the motor down to make sure that the situation Otto describes is not the cause as well.

[gr_diver]

The float travels freely, and between posting the previous post and this one, I re-opened the cover. I blew through the fuel inlet and manually closed the valve, it operated normally...

But this time the bowl was full, contrary to my expectation! Though the car was when last driven 5 hours ago it did not warm up fully.

I start to think that it is evaporating while the car sits and the engine is hot... But if it is evaporating now that temps are in the 0 to +10 degrees Celcius, what will happen during the summer that +30 are daily? Then again, underhood temperature does not change much...

[gr_diver]

GTJim you were just 1 minute ahead of me!

But the issue appeared suddenly one day, so something changed, and I can't figure out what!

[tekenaar]

I posted because you said it began to happen after you removed the carb top . . . so clear this up for me, did it just start happening after your fix or was it happening before? Also, what's your normal procedure for cold start? . . . pump the accelerator pedal 2-3 times (to set choke and squirt some gas from the accelerator pump) and then start, or what?

[gr_diver]

Yes, it started occurring after the "fix"...

To start it I needed to pump the pedal 2-5 times depending on the season/temperature (2 times in the summer, up to 5 times in winter), and it would always sound "ra-ta-ta-ta-vroooooom"...

Now, no matter how many times I pump the pedal (I have tried from 2 up to 12 times, each time on a different stone-cold morning start attempt), it will either start after 4-5 seconds of cranking, or I will there let go, and then it will re-start on first try, no-matter if I re-pump the pedal or not...

[gr_diver]

I still can't find out what's wrong.

Multiple times I checked the fuel level in the carb, well contrary to what it seemed a couple of times, it is just fine in the morning.

The accelerator pump works nicely, there are no leaks around the diaphragm, nor around the injector's body (o-ring), and there is a nice stream of fuel starting only after minimal movement of the throttle.

The choke closes down normally, and opens in the usual manner that has not given problems in years...

I managed to start it on first try a couple of mornings, and it was after I pressed the pedal 13 times. It started (and sounded) as it used to start with only pressing the pedal 5 times.

When slowly opening the throttle, there is no fuel coming from the accelearator pump (normal). A little faster motion, and fuel comes out, with minimal discharge from the "pressure relief valve. With fast motion, same amount of fuel comes out, but more is discharged back in the bowl (well, I can't really say it's more in quantity, but the fuel in the bowl swirls more...).

I also tried to see if the accelerator pump's circuit drains internally and the many pumps on the pedal are required to prime the circruit, but it is not, the injector shoots fuel in the morning with the very first motion...

No more ideas coming from my head...

[gr_diver]

Re-read the FSM part that describes the "pressure relief valve" 's operation...

This is where my problem is... There should be a speed of opening the throttle that the injector should give fuel, but the valve should not exhaust... In my carb this does not happen, when the motion is fast enough for the injector to give fuel, the valve also discharges, thus leaking fuel that should go down the intake back in the bowl... Funny thing is that there are no driveability problems as I would expect...

I have to take it out tomorrow (it is night now) disassemble it and see if it is recoverable... If not I am in trouble... They were/are/will not be available as a part...

And to be honest I don't think that it will be anything anything in it to fix, so I go a step ahead and ask:

can anybody steal one from a "parts carb"?

[gr_diver]

Today once again I opened the carb to re-investigate. After fiddling for quite some time with the pressure relief valve I realized that the discharge was not coming from it, but from the supposed feed port of the accelerator pump. I drained the fuel bowl, so as to remove the pump's cover, and the check operation of the check valve inside the feed fuel port (where I supposed it would be according to FSM). At the bottom of the fuel bowl though I found that little plastic ball in the pics below. This when immersed was totally invisible, and found it by total luck. When the bowl was almost empty I tried to clear a "bubble" that was stuck in a corner. Well the bubble moved... I checked the FSM and this was not pictured anywhere, so the brain came in to solve the mystery... The FSM shows the pump's feed check ball to be inaccessible inside the casting. Well this was not correct. That little ball IS the check valve (it uses it's negative buoyancy to operate), and initially it was right under the pressure relief valve, which kept it there. When the pressure valve decided to take a dive in the bowl, the ball followed...

After I cleaned everything (including the pressure valve) and put them back together the accelerator pump squirt was dramatically improved. It is now not at all aerated, and falls like a solid column, instead of a very concentrated spray column it used to be like...

True testing will be tomorrow morning, since today while fiddling there I rotated the throttle many times, in fact when I started the car it was flooded, as I expected it to be...

Thank you VERY much for your replies!

[gr_diver]

After the problem I found and fixed almost two months ago I was not really satisfied with the starting of my car. It was easier, but not as it used to be. During the last weeks it had started to worsen again, most of the times it started on the third attempt. I was a little stumped for a couple of weeks...

Yesterday came the answer by itself. While driving, I stopped for a minute to buy a newspaper, and switched off the engine, but not the CD-Player. During cranking afterwards, the CD-Player switched off momentarily. This would not happen in the past, even in winter morning starts. So I realized that the problem was electric. After lunch I cleaned all 4 ground connections (engine to chassis, and battery to chassis), and positive connections from battery to starter, and bingo, today morning it started on the 1st try, and electrics did not fade during cranking (I had the CD-Player on for testing).

So the bad grounds had become bottlenecks, and the starter was using all available amperage to overcome them, not leaving enough for the ignition...

FINALLY solved...