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obscure gas in oil causes?
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oobleck
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PostPosted: Tue Mar 30, 2021 10:27 pm    Post subject: obscure gas in oil causes? Reply with quote

I've had two gas in the crankcase oil instances in the recent months. after the first time, I replaced the cheapo parts store pump with a nice spendy rebuilt dometop. Today I changed the oil again after seeing that the engine made very low oil pressure and discovered a lot of gas that had diluted the oil again. I just this weekend tossed the Chi-com Amazon 30-pict 1 for a brand new empi.

other than carb/float issues or a bad fuel pump is there anything else that could cause the gas? could really worn out valve guides, valves or cylinder heads cause this? I'm about to throw on pump number three or rebuild the Empi carb.

I searched and really couldn't find any other threads that offered anything but the carb or fuel pump as the culprits. My engine is a 1600SP for reference. Doesn't smoke or give any sign of worn rings, but it does leak a lot of oil/gas around one exhaust port in particular.
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scrivyscriv Premium Member
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PostPosted: Wed Mar 31, 2021 3:26 am    Post subject: Re: obscure gas in oil causes? Reply with quote

A brand new Empi is just a name brand China carburetor.. open it up and check your float level. How much driving do you do?
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PostPosted: Wed Mar 31, 2021 4:57 am    Post subject: Re: obscure gas in oil causes? Reply with quote

It is almost never the fuel pump.

Worn valve guides would cause smoking.

Most often it is a stuck needle valve. It doesn't take much to prevent them from closing.
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oobleck
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PostPosted: Wed Mar 31, 2021 6:41 am    Post subject: Re: obscure gas in oil causes? Reply with quote

scrivyscriv wrote:
A brand new Empi is just a name brand China carburetor.. open it up and check your float level. How much driving do you do?




I drive very little and only short trips...I didn't think the float level on a 30 pict-1 was adjustable really, would I add shim under the needle valve to lower the fuel level maybe?
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PostPosted: Wed Mar 31, 2021 8:15 am    Post subject: Re: obscure gas in oil causes? Reply with quote

OP. You do have a fuel filter under the car at the trans. Right?
As stated above. A little grit/dirt can hang up the needle valve and let excess fuel into the carb. Even after you shut the engine off.

I may be wrong on this. If you add a shim under the needle valve. I think that raises the fuel level. At least that's what I'm visualizing when I think about it.

Last time I set the float lever in a 30 pict 1. I set it at 3/4" below the top of the float bowel.
I run dual barbs. So it's been a while since I have worked on a center mount carb.

Also, try to park the car so the gas tank is below the carb elevation. That way gravity will not push fuel in the carb, when the car is parked.

Good Luck.
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PostPosted: Wed Mar 31, 2021 8:38 am    Post subject: Re: obscure gas in oil causes? Reply with quote

Pumping the gas pedal numerous times will cause gas to be forced by the rings and into the crankcase.

Everytime a car came into the shop as a no start, one of my first checks was pulling the oil dipstick and smelling the oil. If gas soaked, it was either a happy foot pumper, poor ignition system or worn out engine (low compression).
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PostPosted: Wed Mar 31, 2021 1:23 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

67rustavenger wrote:
I may be wrong on this. If you add a shim under the needle valve. I think that raises the fuel level. At least that's what I'm visualizing when I think about it.


Wouldn't adding a shim under the carb needle valve LOWER the fuel level, as the valve would shut off sooner?
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67rustavenger Premium Member
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PostPosted: Wed Mar 31, 2021 2:25 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

Cusser wrote:
67rustavenger wrote:
I may be wrong on this. If you add a shim under the needle valve. I think that raises the fuel level. At least that's what I'm visualizing when I think about it.


Wouldn't adding a shim under the carb needle valve LOWER the fuel level, as the valve would shut off sooner?

Like I said above. "I may be wrong on this". It's been a while since I have played with a single carb.

OP go with Cussers comment!
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PostPosted: Wed Mar 31, 2021 2:41 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

You've now know the three most common causes of fuel in the oil...
    1) Fuel flowing thru the carb fuel bowl into the intake as raw gasoline. Check fuel bowl fuel level. Add washers/gaskets between the inlet valve and the top cover will lower the fuel level but does nothing if the inlet valve is sticking or the fuel pressure is so high it will overwhelm the float + valve. You really don't need more than 3psi of fuel pressure.

    2) Failed fuel pump. Fuel flowing from the top side of the pump diaphragm down into the engine case. Pull the pump and take a whiff of the underside. The bottom of the pump should smell of grease or oil. If it smells of fuel, the pump is leaking.

    3) Aggressive accelerator pedal use. Raw fuel being squirted from the accelerator pump nozzle is the same as raw fuel from the bowl (it comes from the bowl). It takes a lot of pumping but I've seen people that pump the pedal 10x before cranking the engine. That's enough to flood the cylinders. That liquid fuel flows past the rings and into the crankcase. It washes the oil off the cylinder walls and will result in premature wear. You should only need to pump the pedal once, maybe twice before you crank the engine. If you need more than that you have a different problem that needs to be addressed.

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PostPosted: Wed Mar 31, 2021 3:47 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

...and rebuilding the carb with a new but crappy-quality float valve doesn't solve cause#1. Clean and reuse your old one.
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PostPosted: Wed Mar 31, 2021 7:58 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

I appreciate everyone's helpful replies here. I typically do not have to pump the pedal before starting, but I had some distributor swapping lately. Maybe the long starting procedures to re-time two distributors could have dumped a bunch of raw fuel into the case.

Also, I feel that the empi accelerator pump is a little lack luster and it seems like i have the mix screw turned way out to richen the mixture enough to help the bogging when I hit the gas after shifting. I have several jets on order to help dial that, but i hope the rich carb mixture isn't contirbuting because it needs it in order to be driveable.

And only driving it short trips across a small town probably doesn't help.

my fuel pump is a fresh Sparxwerks Dometop, So im fairly sure it isn't bad yet. throwing a gauge inline on the fuel line will tell me fuel pressure....

I will also definitely be adding some shim to the needle valve
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PostPosted: Thu Apr 01, 2021 7:23 am    Post subject: Re: obscure gas in oil causes? Reply with quote

oobleck wrote:
I will also definitely be adding some shim to the needle valve

A word of caution here...
There is a specific fuel level that should be maintained in the fuel bowl. 3/4" from the top (I think that works out to 19mm?). This proper fuel level provides enough of a reserve so there is always enough fuel available for the main jets to draw on and for the accelerator pump. But additionally this level of fuel places the fuel at just the right height that the fuel is almost ready to flow out of the main nozzle "the faucet" in the carb throat/venturi. See pic below (I couldn't find a pic of a 30Pict-1 flowing out the main nozzle so this will have to do).
Image may have been reduced in size. Click image to view fullscreen.

Note that the fuel level at the left is just below the level that the air-fuel flows out from the main nozzle in the carb throat. This is a key design need. As the air flow velocity down the carb increases, the pressure at the main nozzle in the venturi (middle of carb throat) decreases (due to Bernoulli's principle). The difference in air pressure between the atmospheric air pressure pushing down on the fuel in the bowl and the lower pressure in the venturi means the fuel is pushed thru the passages and up into the main nozzles so it flows down the carb throat. This adds to the enrichment at higher rpms.

If you drop the fuel level in the bowl too much (even a few mm), it will delay the onset of fuel flow out the main nozzle. You will need more air flow before the pressure diifference can push the lower level of fuel up and out the main nozzle.

My point is to work towards the proper level of fuel in the bowl and not just reduce it. Adding washers to lower the fuel level as a test to see if the carb is flooding is fine. But permanently lowering the fuel level in the bowl will have a negative effect on the way the carb works at higher rpms. And with a lower level of fuel, you could eventually starve the carb of fuel because the reserve of fuel is now too low.
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PostPosted: Thu Apr 01, 2021 3:49 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

ashman40 wrote:
2) Failed fuel pump. Fuel flowing from the top side of the pump diaphragm down into the engine case. Pull the pump and take a whiff of the underside. The bottom of the pump should smell of grease or oil. If it smells of fuel, the pump is leaking.


With the stock VW/Pierburg pumps, this sort of thing is virtually impossible. Any leakage past the diaphragm will run out the big vent opening at the bottom
of the diaphragm chamber before it goes down the center into the operating lever compartment, and down past the push rod into the case.

If the engine oil has a lot of gas in it, then everything that can be reached by gas fumes from the case will be smelling like gas, including the
bottom parts of the fuel pump, so an odor there is not telling you anything new.

A Sparxwerks-rebuilt fuel pump should be pretty much above suspicion. But the dome-tops do not have the cutoff valves that the "square"-tops have,
and one assumes the VW-supplied external cutoff-valve for use with the dome-tops is missing from OP's engine.
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PostPosted: Fri Apr 02, 2021 8:06 am    Post subject: Re: obscure gas in oil causes? Reply with quote

Do you park on a hill...

https://www.thesamba.com/vw/forum/viewtopic.php?t=102775
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PostPosted: Fri Apr 02, 2021 10:03 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

[quote="kreemoweet"]
ashman40 wrote:

A Sparxwerks-rebuilt fuel pump should be pretty much above suspicion. But the dome-tops do not have the cutoff valves that the "square"-tops have,
and one assumes the VW-supplied external cutoff-valve for use with the dome-tops is missing from OP's engine.



Thats what I was thinking...and I pulled the rebuilt pump off this evening. The base gasket is soaked with fuel, the gaps in the spacer block are full of gas and a lot of the grease has washed out. I disassembled the pump and can find NOTHING out of the ordinary or damaged. It looks as perfect as one would expect.

In lieu of the cutoff valve I have a small motorcycle shutoff valve in the engine compartment at the fuel pump that I am religious about shutting when I park.

I have a brand new Facet electric pump left over from another project that I am going to try next.....
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PostPosted: Wed Apr 14, 2021 4:43 pm    Post subject: Re: obscure gas in oil causes? Reply with quote

What an odd situation with you getting fuel into the oil.
I've never had a rebuilt/restored Pierburg fuel pump reported back with a leak internally. I use only new Effbe diaphragms and they can last 50 years. As mentioned, there is a vent hole in the base of the fuel pump that will leak the fuel out if the diaphragms blew or was leaking. That would be really rare since there's two different diaphragms sandwiched together on the main diaphragm assembly. Clearly Pierburg did that for a reason.

Typically, the only way fuel can get into the engine case is by the float needle valve sticking open or partially open. It's a known issue that the quality of the "new" needle valves in the carb rebuild kits sold today are less than great. I reuse the original German Solex valves if they test good when I rebuild my carbs.

The dome tops did have an optional fuel cut off valve. They were designed to shut off the fuel flow to the carb when the engine wasn't running. Most VW's didn't use them though more buses did than bug due to the fuel tank being higher.

Let us know what you find out. BTW, when you go to put that fuel pump back together, make sure you preload the lower diaphragm assembly. Email me at [email protected] for more info.
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PostPosted: Thu Apr 15, 2021 11:18 am    Post subject: Re: obscure gas in oil causes? Reply with quote

Have you pulled spark wires while running to verify ignition is complete on each cylinder. Maybe use a heat temperature gun on each exhaust port while running. if you have a mighty vac hand pump you can use the pressure port instead of the vacuum port and put it on the fuel fitting going into the carb and check if the needle and seat are holding pressure. best to take the carb off to check this.
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