TheSamba.com :: View topic - Carburetor runs fuel after engine turned off

Sun Jul 19, 2020 3:48 pm

Hi There. 1972 Type 3 fastback with dual PDSIT 32 carbs. Rebuilt carbs, fixing a concave pump cover in the process.

Now, both carbs are leaking fuel after the engine is stopped. I discovered the leak is coming from the throttle plate linkage - which is a bit old and loose. Turns out when I run the engine for a while (one minute) and stop the car, the two injectors (accelerator pump and power fuel system) at the top of the carb throat continue to drip/flow fuel (left-side pic below). This fuel gathers on top of the throttle plate and then leaks out around the loose linkage.

So, now I know what's happening but I don't know why it's happening.

I was told in a different post that my fuel pump may be a higher PSI than recommended (right side pic below). Would that be an issue-releasing pressure from the bowl via that injector?

Sun Jul 19, 2020 4:21 pm

Based on the tone of what you wrote.... I am assuming you think this behavior is a malfunction. It isn't.

This is something that happens when carburetors get hot.

It's the same way a mr. coffee machine works
Also how a steam tube toy boats work
https://en.wikipedia.org/wiki/Pop_pop_boat

You can add features to the carburetor to prevent it doing that.
You can use insulators to lessen how hot the carbs get
You can add a vapor recovery system to absorb the fuel vapors.
Or just realize that back in the day people didn't park thier cars indoors on clean concrete....sorry this isn't that kind of vehicle :lol:

But, thing is I don't know if you have a problem of if you just alarmed at the reality. Why does my clear fuel filter has a bubble inside? or, why does it idle on two cylinders.... :P Just messin with you.

Maybe the carbs are too hot, or, maybe they aren't. You can check the fuel pressure. You can check how hot the carbs are. Maybe it needs some improvement but maybe not.

Sun Jul 19, 2020 4:54 pm

modok wrote: Based on the tone of what you wrote.... I am assuming you think this behavior is a malfunction. It isn't.

This is something that happens when carburetors get hot.

It's the same way a mr. coffee machine works
Also how a steam tube toy boats work
https://en.wikipedia.org/wiki/Pop_pop_boat

You can add features to the carburetor to prevent it doing that.
You can use insulators to lessen how hot the carbs get
You can add a vapor recovery system to absorb the fuel vapors.
Or just realize that back in the day people didn't park thier cars indoors on clean concrete....sorry this isn't that kind of vehicle :lol:

But, thing is I don't know if you have a problem of if you just alarmed at the reality. Why does my clear fuel filter has a bubble inside? or, why does it idle on two cylinders.... :P Just messin with you.

Maybe the carbs are too hot, or, maybe they aren't. You can check the fuel pressure. You can check how hot the carbs are. Maybe it needs some improvement but maybe not.

Hey Modok, thanks for the response. I'd agree expect for two things: the fuel flow happened on a pretty cold engine this morning. Only ran it for a minute first thing in the morning and had the leak. Second, it's quite a bit of fuel that leaks out - creates a puddle that pretty much fills the indent in the heat shield tin that sits below the carbs. Enough fuel to smell it down the street - that ain't right. :wink:

I thought it was a heat issue prior till this morning. I'm leaning more toward the really loose/worn throttle shaft. If it were tighter, less fuel would leak out and more would leak past the throttle valve. That or the fuel pressure. Probably going to get a fuel pressure gauge to see what's up there.

Sun Jul 19, 2020 5:30 pm

If the throttle shafts were perfectly sealed that gas would just end up in the engine, either way it's a bad deal.

You mention "rebuilt" carbs, did you do it?, or someone else?, did you (or they) install the needle and seat that came in the "kit"?, or re use the originals?

Sun Jul 19, 2020 5:40 pm

busdaddy wrote: If the throttle shafts were perfectly sealed that gas would just end up in the engine, either way it's a bad deal.

You mention "rebuilt" carbs, did you do it?, or someone else?, did you (or they) install the needle and seat that came in the "kit"?, or re use the originals?

I rebuilt the carbs using the Royze carb tune kit from J-Bugs. Installed the needle and seat from the kit. Think I should put the old needles back in? They seem to work the same - pretty loose. I guess if the needle were to stay open the fuel pressure would keep going through the system...

Sun Jul 19, 2020 7:37 pm

I see. In that case the float bowl must be overfilled. So, look for why

Sun Jul 19, 2020 8:05 pm

modok wrote: I see. In that case the float bowl must be overfilled. So, look for why

Yeah, that seems possible. There's a carb diagram I have from VW slide series #20 that shows a "power fuel system" injector going into the carb throat. Maybe it's siphoning off fuel from an overfilled bowl.

Hard to test or adjust the float in that bowl. I guess I could bend the arm a little...

Sun Jul 19, 2020 11:24 pm

There's a plastic piece that fits over the float hinge. It kind of looks right when it's the wrong way up but when it's upside down it stops the floats floating high enough to cut off the fuel. Worth a look as both carbs were apart and both now over filling.

Mon Jul 20, 2020 12:39 am

If you can givea precise id of the carbs/engine, I can tell you exactly what thickness of washer(s) to put on the needle valves, ifit's a stock setup.

Type 3s had a weird thingy in the fuel T. I never really understood what it does, but it probably does sometning.

Mon Jul 20, 2020 8:09 am

MonsterMovie wrote: modok wrote: I see. In that case the float bowl must be overfilled. So, look for why

Yeah, that seems possible. There's a carb diagram I have from VW slide series #20 that shows a "power fuel system" injector going into the carb throat. Maybe it's siphoning off fuel from an overfilled bowl.

Hard to test or adjust the float in that bowl. I guess I could bend the arm a little...

Agreed. something like this is the problem.
You are overflowing your bowels after shut down. Pretty common issue with a leaking inlet valve.
Fix it soon.....

Letting gas run into your motor after shut down is very bad for it.

It will make the motor hard to re-start.
It will wash the oil off the cylinder walls and lead to ring failure.
It will dilute the motor oil.

Either your fuel pressure is too high, or you inlet valves are leaking.
Since they were recently serviced, I would look at them again.
Something isn't right...

Mon Jul 20, 2020 12:33 pm

FreeBug wrote: If you can givea precise id of the carbs/engine, I can tell you exactly what thickness of washer(s) to put on the needle valves, ifit's a stock setup.

Type 3s had a weird thingy in the fuel T. I never really understood what it does, but it probably does sometning.

Hey FreeBug, it's a mexican-made dual-port 1600 that's now a 1776. Carbs are 32PDSIT-2 and -3.

Tue Jul 21, 2020 12:14 am

Add a fuel t before and after the fuel pump. Connect a fuel hose that goes from inlet to outlet of pump with a very tiny restrictor inside. (AmI think I used the smallest weber ict jet I could find.)

When engine is hot fuel pressure builds in the lines. This floods engines. Adding this small restricted "bypass" allows the pressure that builds from pump to carb/s to escape to the line just before the pump.

Cured my flooding while parked issues. Yes bad needle seats do this but when 4 of them do it you start finding alternatives

The fuel pressure loss is almost non existent while running with the restrictor.

Worked for my brazil PDSITs and now with my 34 pict too.

-Frank

Tue Jul 21, 2020 12:42 am

carb gaskets these days are way thicker than the originals, so you have to compensate for that with thicker washers under the needle and seat,which by the way are pretty bad in most rebuild kits too

Tue Jul 21, 2020 1:06 am

MonsterMovie wrote: FreeBug wrote: If you can givea precise id of the carbs/engine, I can tell you exactly what thickness of washer(s) to put on the needle valves, ifit's a stock setup.

Type 3s had a weird thingy in the fuel T. I never really understood what it does, but it probably does sometning.

Hey FreeBug, it's a mexican-made dual-port 1600 that's now a 1776. Carbs are 32PDSIT-2 and -3.

Ok, that's not a stock setup. The carbs should still have an identifying mark. The Info is mostly on a little tag, attached by one of the carb lid screws. Those tabs are most often long-gone.. :cry: .There shoulsd also be a stamp on the carb body, with a code such as "VW 101-1". That would help, but anyway, type 3 carbs come with three needle valve washer thicknesses: 1.0mm, 1.5mm, 0.5mm. So start with a 1.0mm washer. But it could be crucial to know the exact model, for the fuel level to pla well with those power valves. Also, needle valves on PDSITs are 1.2mm, not 1.5mm like on single-carb models.

Mr Bassam may have just explained what the stock thingy did. Thanks!

Tue Jul 21, 2020 3:02 pm

FreeBug wrote: MonsterMovie wrote: FreeBug wrote: If you can givea precise id of the carbs/engine, I can tell you exactly what thickness of washer(s) to put on the needle valves, ifit's a stock setup.

Type 3s had a weird thingy in the fuel T. I never really understood what it does, but it probably does sometning.

Hey FreeBug, it's a mexican-made dual-port 1600 that's now a 1776. Carbs are 32PDSIT-2 and -3.

Ok, that's not a stock setup. The carbs should still have an identifying mark. The Info is mostly on a little tag, attached by one of the carb lid screws. Those tabs are most often long-gone.. :cry: .There shoulsd also be a stamp on the carb body, with a code such as "VW 101-1". That would help, but anyway, type 3 carbs come with three needle valve washer thicknesses: 1.0mm, 1.5mm, 0.5mm. So start with a 1.0mm washer. But it could be crucial to know the exact model, for the fuel level to pla well with those power valves. Also, needle valves on PDSITs are 1.2mm, not 1.5mm like on single-carb models.

Mr Bassam may have just explained what the stock thingy did. Thanks!

Yes! Sorry, NOT stock. This used to be F.I. and was carbed before I bought it.

Sooo, the diagram below came w/ my carb rebuild kit and is a good representation of my carb. There is a needle valve and needle seat gasket (#23 and 24) but there's no needle valve washers included (or in the carbs). The gasket, if I remember (I'll crack the carb tonight to make sure), is just red hard rubber. Needle valve spacer washers are news to me.

Tue Jul 21, 2020 5:54 pm

no washers? Oops.
The solexes do not have an easy way to set the float level, but it still needs to be set right.... as is true with any carburetor.
If there was an easy trick to do it I'd tell you, but I don't know of one.

May have HOLD the float against the lid, balanced on top if the silly plastic spacer thing, and figure out the right thickness of washer to use to get the relationship right.

tho one thing kinda odd about the whole thing is......IF the fuel level is too high.....why is the fuel coming out the acc pump and high speed enrichment nozzle? I would think it would just come out of the main nozzle.

Wed Jul 22, 2020 11:50 pm

Are you talking about a red fiber washer? That's for the float bowl drain/main jet access plug.

Thu Jul 23, 2020 6:09 pm

Updates:

Right Carb ID: VW41-2 6780644
Left Carb ID: VW 98-1 B 6 334

See a video of the carbs leaking here: https://youtu.be/oYbMzHxFn5U

Fuel pressure = 6psi when idling typically.

What's a good pressure regulator for these cars? I see the EMPI is a POS.

Thu Jul 23, 2020 6:16 pm

I would start at 3

Thu Jul 23, 2020 6:16 pm

The fuel pump IS the regulator.
It should be 3-4psi.
If the pressure is too high check the pushrod height.
If that is Ok take it apart and shorten the spring.
https://carterengineered.com/mechanical-fuel-pump-m60175