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Dave Becker
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Joined: October 16, 2003
Posts: 147
Location: Australia
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 Posted: Thu Oct 27, 2016 12:25 am Post subject: Why is carb float bowl empty after sitting? |
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I have noticed my car is hard to start after it sits for a couple of days, I took off the air cleaner and pumped the throttle linkage and there is no fuel coming out of the accelerator pump nozzle, took out the float bowl drain and no fuel came out at all.
It is a 36hp engine with the stock carb, I put a kit through the carb a few weeks ago as it had been sitting for a while, once the engine has started it runs great.
Have I missed something rekitting the carb?
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AndrewCologne
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Joined: September 05, 2015
Posts: 71
Location: Cologne
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| Posted: Thu Oct 27, 2016 7:55 am Post subject: Re: Why is carb float bowl empty after sitting? |
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| Dave Becker wrote: |
I have noticed my car is hard to start after it sits for a couple of days, I took off the air cleaner and pumped the throttle linkage and there is no fuel coming out of the accelerator pump nozzle, took out the float bowl drain and no fuel came out at all.
It is a 36hp engine with the stock carb, I put a kit through the carb a few weeks ago as it had been sitting for a while, once the engine has started it runs great.
Have I missed something rekitting the carb? |
If the float bowl is empty even after letting the starter rotate the engine it could be a fuel pump problem.
1. Disconnect the fuel pipe on the carbs side and insert its end deeply into a plastic bottle.
2. Make the starter let rotate the engine only about 4-5 turns.
3. Go back and check if some fuel came into the bootle, if yes then continue at step 5.
4. If no fuel can bee seen in the bottle, check the fuel pressure, you might have to overhaul your pump using a new diaphragm but be aware that almost all newer fuel pump diaphragms come with a too strong spring! So try to keep the old spring if possible! Means, if the length of the push rod way is ok, just tweak the old spring if needed and reinsert.
5. If fuel pump isn't the guilty one, check you floating valve needle in the float bowl if it clamps. Just knock a bit on the top of the carbs cover at the part where the needle is. If the engine starts now properly, you found the guilty.
6. Next try is removing the carbs cover and check the needle again if it heavy clamps
7. Now, if the needle works flawlessly you should check, why the fuel level lowers that much in the carb as your float bowl is always empty after a while.
Often the guilty is a leakage at the emulsion tube housing or the main jet carrier. See below, i marked the part of where the leakage could be in red.
With the engine running and accelerating by opening the throttle valve by hand, just look from the top into the carb and check if you can see fuel coming out somewhere else then at the proper horizontal ports of the emulsion tube housing.
I just got EXACTLY the same problem but with a 26 VFIS carb.
Let me know if it helps.
Best regards from Cologne
A.
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sjbartnik
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| Posted: Thu Oct 27, 2016 11:41 am Post subject: Re: Why is carb float bowl empty after sitting? |
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The float bowl is vented to the atmosphere. When the car sits, the fuel inside the float bowl will evaporate. This can happen in as little as a few days.
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Dave Becker
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Joined: October 16, 2003
Posts: 147
Location: Australia
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| Posted: Thu Oct 27, 2016 7:40 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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Thanks for the replies.
The fuel pump is working fine, the car does start but takes about 15 seconds of cranking before it will fire, I'd say thats how long it takes for the fuel pump to fill the carb.
The needle and seat are new and float level is correct.
I suspect it is leaking out somewhere inside, I will remove the carb when the float bowl is full and let it sit overnight and see if empties out the float bowl.
I have another car with a 40 hp engine, it fires first kick even after a couple of weeks sitting so I am not convinced evaporation is the problem.
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Bruce
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Joined: May 16, 2003
Posts: 17290
Location: Left coast, Canada
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| Posted: Sat Oct 29, 2016 10:27 am Post subject: Re: Why is carb float bowl empty after sitting? |
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| sjbartnik wrote: |
| The float bowl is vented to the atmosphere. When the car sits, the fuel inside the float bowl will evaporate. This can happen in as little as a few days. |
A few weeks or months maybe. But not a few days.
My car was doing exactly what you describe. Before you try those other things, put a wrench on the drain plug and give it a bit more torque.
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Strato56
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| Posted: Sat Oct 29, 2016 8:50 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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| What Andrew wrote is the problem and the right way to diagnose. I just went through the same thing myself, I had a spare carb, rebuilt it and the problem is solved. I couldn't get the emulsion tube housing in the previous one to seat, or there is a crack somewhere I can't see, or a plug is loose or something. Either way, you can pull the carb, take the carb top off, pour some fuel in the float bowl and keep an eye on it for a day, if it drains, you have a leak in the carb somewhere. |
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Bruce Berman
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Joined: April 13, 2004
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Location: Long Island, NY, USA
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| Posted: Fri Nov 04, 2016 1:20 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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I have had the same issue for a number of years with my 1957 VW.
I think it is related to the blend of gasoline sold nowadays here in the U.S.
Here in New York State, gas is blended with 10% alcohol, and I believe alcohol evaporates at a much faster rate than gasoline. As the alcohol evaporates, it carries the gasoline with it, with the result that the fuel within the carburetor bowl evaporates at a much faster rate than it did when conventional or "real" gas was sold many years ago.
If my car sits for over about 1-1/2 weeks without being started, it will take a few tries of the starter before she finally fires up. If started within that 1-1/2 week period, she starts up immediately and on the first try.
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wayne1230cars
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| Posted: Fri Nov 04, 2016 3:56 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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If my stock '60 bug sits for less than a week, it will start instantly. If it sits for more than a week it might turn over for 5 seconds and then start. After sitting all winter it might take 15-20 seconds of cranking. Starting pattern is very consistent and predictable.
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AndrewCologne
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Joined: September 05, 2015
Posts: 71
Location: Cologne
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| Posted: Sun Nov 06, 2016 9:08 am Post subject: Re: Why is carb float bowl empty after sitting? |
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I think evaporating or octane rating should not be the issue.
Here in germany I also tried Super Plus, means Euro 98 Octane and had/have the same problem even with a full tank when firing up the engine.
A weak starter which could cause a too little negative air pressure in the carbs suction pipe can't also be the problem as in the very early years the engines where fired up being cranked by hand.
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Bruce Berman
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Joined: April 13, 2004
Posts: 148
Location: Long Island, NY, USA
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| Posted: Sun Nov 06, 2016 10:35 am Post subject: Re: Why is carb float bowl empty after sitting? |
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| AndrewCologne wrote: |
I think evaporating or octane rating should not be the issue.
Here in germany I also tried Super Plus, means Euro 98 Octane and had/have the same problem even with a full tank when firing up the engine.
A weak starter which could cause a too little negative air pressure in the carbs suction pipe can't also be the problem as in the very early years the engines where fired up being cranked by hand. |
Hi Andrew,
I don't think it has anything to do with the octane rating of the fuel.
I don't know if in Europe (or in Germany) the government requires the addition of alcohol to gasoline, like they do here in the U.S. I can recall that before alcohol was introduced to gasoline many years ago, my 1957 VW, which I have owned since 1978, could sit for weeks without being started, and then when I went to start the car, I would pull out the choke and she would immediately fire up on the first try!
Other collector car enthusiasts (cars with carburetors only) here in the U.S., including those unrelated to VWs, also complain of the same kind of starting issues, so I must assume it is the fuel evaporation brought about by the addition of the alcohol to the gasoline. Of course, with fuel injection systems, fuel evaporation is not an issue, as there is no bowl with exposure to the atmosphere where gasoline could evaporate.
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Factory original 1957 Type 1 Deluxe Sedan, with 13,000 miles. I purchased her from the estate of the original owner in 1978. Color: L324 Polar Silver, with light beige leatherette interior, dealer-installed Dehne fuel gauge and Motorola Volumatic radio. |
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AndrewCologne
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Location: Cologne
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| Posted: Sun Nov 06, 2016 12:27 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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Ah sorry, I forgot to mention.
Here in Germany they offer the newer "Super E10" (incl. 10% Ethanol) and "Super" 95 Octane and "Super Plus" 98 Octane (both incl. 5% Ethanol).
In case of my Bugs I always choose "Super" 95 Octane incl. 5% Ethanol.
So I still think, the ethanol mixture should not be the guilty when I need to let the starter turn 20-30 seconds or even more till it fires up.
Because ... even if there would be such an evaporation which would result in no more remaining fuel in the carbs float bowl after some days, ... a starting procedure of about 5 Seconds should make the fuel pump directly fill up the carbs floating bowl so the gasoline "level" in the carb would be correctly high enough also in the emulsion tube housing for making the negative air pressure resulting the vaporized gas going down the suction pipe of the carb to the combustion chamber ... and ... the engine starts.
Thats the theory but as we know many things could affect a starting procedure so ... Im still on the hunt.
Yesterday I did a new try on my Split bug and its 26 VFIS.
Only after applying starter spray the engine fired up. But only kept running for 3 seconds. This typically means there was a remaining amount of gaz in the floating bowl which now has been left the carb to the combustion chamber ... but no more gaz is available keeping the bowl fill up, even with a full tank and trying switching the fuel tab from open to reserve. So ... although my pressure measuring testing gave me a correct pressure of about 0,1 Bar from the pump ... it still could be too low. Maybe the testing setup's manometer is flawed and gives unprecise results ... who knows.
EDIT:
This week I will go on with an extended diagnosis:
- disassembling the fuel pump again and check the two little backflow preventing spring valves and bakelite plates of the pumps cover if all has been mounted really really correctly, cause if not this could result in a significant backflow of the fuel level in the fuel pipe trough the pump when the engine is switched off.
- after this rechecking the fuel pressure and trying to rise the pressure a bit from 0,1 to approx 0,12 - 0,13 Bar by pulling a bit the diaphragms spring or using minimal thinner flange seals
- rechecking both fuel filters in the tanks fuel tab and the tab itself
- maybe tighten all nuts of the fuel pipe connections from pump and carb using more torque so no "air" could slowly enter the pipe system which also here would result in a back flow of fuel from the pump to the chassis and tank. So whats the correct torque for fastening the fuel pipe nuts?
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Bruce Berman
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Location: Long Island, NY, USA
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| Posted: Tue Nov 08, 2016 10:55 am Post subject: Re: Why is carb float bowl empty after sitting? |
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The only way to really verify my suggestion that the issue of hard starting these cars after they have been sitting for >1-1/2 weeks or so may be related to fuel evaporation within the carburetor fuel bowl, would be to:
Take two identical and known good Solex 28PCI carburetors with air cleaners installed, fill the bowl of one of them with "real" gas (i.e., with no ethanol additive), and the bowl of the other carburetor with conventional gasoline with Ethanol, and measure the fuel level in each carburetor bowl after say 2 weeks or so. Obviously, the top half of each carburetor must be reinstalled after filling the fuel bowl, for the test to be valid.
If the fuel level in the carburetor with the Ethanol additive is substantially lower, evaporation is the issue.
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wimkever
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Location: Holland (the Netherlands)
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| Posted: Tue Nov 08, 2016 2:11 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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I had the same issue with my stock vw1300 from 1967. After sitting for three or four days it needed crancking during 20 to 30 seconds before it fired up.
I never solved the problem until I had the carb and the fuel pump rebuilt by a pro.
Now even after sitting for a week or more I only have to touch the key and it fires up within a second.
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Bruce
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| Posted: Thu Nov 10, 2016 11:20 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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| wimkever wrote: |
.... I had the carb and the fuel pump rebuilt by a pro.
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The reason the problem went away when the pro rebuilt your carb is because he tightened the drain so it didn't all leak out.
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Bruce
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| Posted: Thu Nov 10, 2016 11:25 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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| Bruce Berman wrote: |
| The only way to really verify my suggestion that the issue of hard starting these cars after they have been sitting for >1-1/2 weeks or so may be related to fuel evaporation within the carburetor fuel bowl, would be to:..... |
The easiest way to disprove your theory is to find one person that is leaving their car for weeks at a time, using ethanol blended fuel, that doesn't have this problem.
Oh, wait! That's me!
My car starts the instant I hit the starter.
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AndrewCologne
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Joined: September 05, 2015
Posts: 71
Location: Cologne
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| Posted: Fri Nov 11, 2016 8:32 am Post subject: Re: Why is carb float bowl empty after sitting? |
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| Bruce wrote: |
| wimkever wrote: |
.... I had the carb and the fuel pump rebuilt by a pro.
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The reason the problem went away when the pro rebuilt your carb is because he tightened the drain so it didn't all leak out. |
Ok so you where sitting next the mechanic when he solved the issue by simply tightning the drain?
Honestly, tightning the drain "could" help in some cases, but as said there can by many reasons for fuel leaking out the carb slowly.
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AndrewCologne
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| Posted: Tue Nov 22, 2016 1:09 am Post subject: Re: Why is carb float bowl empty after sitting? |
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Problem solved.
Quoting my assumption:
| Quote: |
| Because ... even if there would be such an evaporation which would result in no more remaining fuel in the carbs float bowl after some days, ... a starting procedure of about 5 Seconds should make the fuel pump directly fill up the carbs floating bowl so the gasoline "level" in the carb would be correctly high enough also in the emulsion tube housing for making the negative air pressure resulting the vaporized gas going down the suction pipe of the carb to the combustion chamber ... and ... the engine starts. |
So ... in my case I thought "why won't the floating bowl fill up correctly when using the starter".
After a deep re-diagnose I figured out that it was the low pressure of the fuel pump "when starting". I checked the pressure many times before when "the engine was running" between 850 and 3000 rpm and the pressure was about 1.5 psi, means totally correct. So ... with the less amount of rpm the starter produces it showed that the pump wasn't able to deliver enough of fuel to the (maybe empty) carb.
So I removed the pumps cover, preloaded the diaphragm again (as I did a few weeks before) and ... used again new little bakelite plates for the little two valves within the fuel pump cover. The little springs where ok.
After reassembling the fuel pump again a pressure test showed suddenly 5-6 psi.
So I used new flange seals to lower the pressure till 2,5-2,7 psi where archived.
It's a bit above the factory recommendation but float needle valves and fuel line connections in general should stand a pressure up to 2,9 psi without problems.
With that setup and "a few days later" cold sitting, I was able to fire up the engine with just 3-4 turns of the starter. A test drive on the highway showed that all connections of fuel pipes at pump and carb where leakproof and no fuel overflow within the carb occurred.
So in my case ...
a) as the little valves in the fuel pump cover seemed not to be 100% closed at default, I assume that after a few days the fuel won't be kept in the pipe but moves down from the pipe through the pump to maybe the pipe area of the chassis
b) the pump delivered enough pressure when running at 850-3000 rpm but not when starting, that's why the fuel did not rise up fast enough to the carb – maybe cause of a)
Now with this working setup I did an even tougher check and closed the fuel tab while the engine was idling till it stopped so all fuel devices, lines and pipes in the chassis and engine compartment where free from fuel. I waited 2 days, opened the fuel tab and tried to start the engine. Now, even with "no fuel in the lines from the tank" and after these days cold sitting, it took the fuel only about 8 seconds when starting to reach the carb and make the engine firing up.
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jdub63
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| Posted: Wed Nov 23, 2016 9:46 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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Do you have a hard line between the pump and the carb? I do and I'm wondering how to setup the pressure gauge inline. Any description or pictures would be appreciated
Thanks
Jdub |
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EverettB 
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Posts: 69824
Location: Phoenix Metro
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| Posted: Wed Nov 23, 2016 9:51 pm Post subject: Re: Why is carb float bowl empty after sitting? |
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| jdub63 wrote: |
| Do you have a hard line between the pump and the carb? I do and I'm wondering how to setup the pressure gauge inline. Any description or pictures would be appreciated |
I have done this by using some spare junk parts I had around to have metal fittings for each end but rubber lines with a gauge in the center.
Cut original parts
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AndrewCologne
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| Posted: Thu Nov 24, 2016 3:32 am Post subject: Re: Why is carb float bowl empty after sitting? |
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On a 36hp engine it would be the same setup.
Best would be also installing an open/close valve between the t-piece (below the gauge) and the carb which simulates a closed float needle valve.
This setup was built using the following tools:
http://www.ebay.com/itm/Petrol-and-diesel-fuel-pum...1438339963
http://www.ebay.com/itm/Fuel-Pump-Vacuum-Tester-Ga...0680598717
The first one I bought a time ago to check my K-Jetronic on my 911 SC, so I also purchased the gauge of the second link as it comes with the psi range that is needed for measuring a VW mechanical pump pressure.
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