gas in oil

[sick620]

My 620 w/l20b is getting fuel in oil.. I was having running rich issues due to sticky choke bad plug wires and miss timed distributer when I got it. Aftet getting fuel in oil the first time I fixed all that and gave it a tune up ...well I had more in there this morning. :( .... could my Weber just be in dire need of a rebuild? The fuel pump is brand new I didn't put it on there but its still shiny and gasket looks like it was just installed... its a gold cheap oreillys one.. the weber drips gas at idle. Down inside when u take the air filter off you can look down inside and see it... truck has good compression runs strongly and dosnt smoke or burn oil... please help me? :+(

[datsunaholic]

Your fuel return line plugged? It's critical that the return line be working, or the pump will overpower the float valve. The smaller L16/L18 pumps generally don't, but the bigger L20B pumps and pretty much all electric ones do.

 

Some folks remove the return line to "clean up the engine bay" which then requires running a pressure regulator, which is worse looking IMO.

[banzai510(hainz)]

learned soemthing new today.

 

The gold fuel pumps are OK.

[sick620]

There isn't a return line because its a weber.. where does the return line go? Its in engine bay but not going anywhere? It just hooks to a metal line on front but dosnt go to Carb or intake...

[wayno]

The only way I know for fuel to get in the crank case is for the fuel pump to spring a leak on the mount side of the diaphragm.

I just can't see it getting by the rings, if it was running that rich, the plugs would foul and the engine would quit, a good example would be to pull the choke on after the engine is warmed up, the engine will not run good at all that way.

[sick620]

Scratch that line IS hooked up and seems to be in working order..

[banzai510(hainz)]

sick, I believe the stock carb had 2 lines

 

I guess you could "T" one side to the carb and the other goes to the return line

 

Datzenmike or Datsunaholic might have photos of these.

 

 

I persoanlly use a 510/521 pumps and never dont use a return line and never have proplems.

 

 

I thought late 620s had electric fuel pumps? Then it couldnt be a bad fuel pump then could maybe belive the overrich issue. But I usually dont believe it. Most webers run fine on a L motor. I ran 38/38 and never had gas in oil.

[datzenmike]

 

The output from the fuel pump goes to a hard line to the carb, turns around and comes back to the pump area. This end has a pin hole restriction or pressure could not build up and the gas would simply return to the tank. A hose connects this return line to the hard line to the tank on the frame.

 

L20Bs will barely run or hot start without it. The return line circulates cool gas from the tank past the carb and prevents vapor lock on hot days.

 

 

.

[sick620]

Just checked pump. Removed it and pumped it with hand and smelled back side and I'm pretty sure its not the pump thats the problem... and when the choke was the problem it was shutting all the way when hottest. But that's been fixed for a while

[sick620]

The return line is there it is split with the other in coming line. I checked it for clogs and its fine it seems. So we can weigh out pump or return.. what else could be wrong?

[datzenmike]

My 620 w/l20b is getting fuel in oil.. I was having running rich issues due to sticky choke bad plug wires and miss timed distributer when I got it. Aftet getting fuel in oil the first time I fixed all that and gave it a tune up ...well I had more in there this morning. :( .... could my Weber just be in dire need of a rebuild? The fuel pump is brand new I didn't put it on there but its still shiny and gasket looks like it was just installed... its a gold cheap oreillys one.. the weber drips gas at idle. Down inside when u take the air filter off you can look down inside and see it... truck has good compression runs strongly and dosnt smoke or burn oil... please help me? :+(

 

Well how much? Some fuel smell is inevitable. Maybe there's no problem. Short runs into town or work where the choke is on more than off will make he oil smelly. If the oil level is actually getting higher every time you check then you DO have a problem.

 

Carb may be flooding when revved up. Look at the plugs... if black dry and sooty then too rich. If clean and tan it's not likely the carb.

[sick620]

The choke is totally turned off now since the first problem with fuel in oil.... the oil was half gas the first time I had to change it... The truck wouldn't start there was so much gas in it... I changed it and truck started. And made it home. I did not change filter that day.... this morning was the same story. Wouldn't start and I changed oil and this time filter too... and I put 10w 40 so I would have something thicker in there this time.... the plugs are perfectly tan... and I put in new ones yesterday... but after putting in new plugs and full tune up its running perfect it used to run rich... maybe it was just running too rich and now it will be good?

[datzenmike]

That would be 2 quarts so you would have to have been low on oil for it to fit in the pan. How can you know how much? A shot glass of gas will thin and make it smelly.

 

Is your PCV connected and working? This would 'air out' the crankcase and evaporate gas fumes.

 

I would say if you has that much gas in the oil the fuel pump is the cause even though you looked at it. All Datsun owners have spares of everything so swap the pump or borrow one and see if that cures the problem.

[wayno]

The choke is totally turned off now since the first problem with fuel in oil.... the oil was half gas the first time I had to change it... The truck wouldn't start there was so much gas in it... I changed it and truck started. And made it home. I did not change filter that day.... this morning was the same story. Wouldn't start and I changed oil and this time filter too... and I put 10w 40 so I would have something thicker in there this time.... the plugs are perfectly tan... and I put in new ones yesterday... but after putting in new plugs and full tune up its running perfect it used to run rich... maybe it was just running too rich and now it will be good?

 

If you changed the oil, and went for a drive and then you have gas in the oil again, the stock type fuel pump is dumping gas into the case threw the timing chain cover, try another fuel pump.

 

Edit

Shit, datzenmike beat me to it.

[sick620]

That would be 2 quarts so you would have to have been low on oil for it to fit in the pan. How can you know how much? A shot glass of gas will thin and make it smelly.

 

Is your PCV connected and working? This would 'air out' the crankcase and evaporate gas fumes.

 

I would say if you has that much gas in the oil the fuel pump is the cause even though you looked at it. All Datsun owners have spares of everything so swap the pump or borrow one and see if that cures the problem.

 

it wasnt low on oil, the dipstick was no longer readable there was so much gas in it.. when I drained it the oil was BRIGHT orange and I had just done an oil change a week before...

when I did the change after the problem I didnt do the filter... was there possibly left over gas in filter that caused me the problems this morning? this morning the oil wasnt high but it was higher than where I had thought i filled it too. It wasnt orange, and it wasnt smelly but on a whim I changed the oil when I knew it was the last possible thing it could be. I needed to get to work. After the oil change it fired with a little coaxing. Made it to work fine and made me home fine tonight.. I put in a carb/injector cleaner and filled the tank tonight before I left for home from work, and I can tell its running smoother and with more power.. it wasnt running BAD before but now its running perfect... Think my weber needs rebuilt? is there anyway that a dirty sticky carb could have caused some of my issues? .... I know the first time my oil got gassed it was due to multiple issues, one day on my way home at night it was only running on 2-3 cylinders off and on and was flooding bad because of it, got home and it was plug wires being XTREMELY corroded on the ends. and I mean BAD! so I replaced those and it was fine... few days later and it was running like POO again, I inspected under the air cleaner and the choke was nearly shut at opperating temp.! so I adjusted it and I was fine again.. Couple days later, same problem it was running crappy, made it home, next morning tried to fire it, and NOTHING... looked under air cleaner and choke was as closed as possible, fixed it and it started and ran fine... that morning I was going to a car show, went to show but when I got there it died a couple times while parking it, I thought nothing of it. on the way from the show to a friends house it wouldnt idle at stops and i had to keep on the gas... when I was ready to leave my friends it wouldnt start, checked oil and walllaaa gas. So i stayed at friends and oil changed it and drove home in the morning....

 

 

Sorry for long story but I wanted you guys to see the whole picture as it was hard to post details earlier from work on my phone.... whats your guys thoughts and opinions after hearing the whole story?

[Boaty]

Try a new fuel pump. Pumping it by hand is nothing compared to running the engine.

 

I went through two fuel pumps. The original one, and the brand new replacement I bought years ago. Both did almost exactly the same thing you're describing here, started filling the crankcase with gasoline. The third fuel pump fixed the issue entirely and hadn't had a single problem with it since.

 

Pumping by hand is nothing compared to the rate that arm is moving while the engine is running. In addition, whatever residual pressure is on the carb-side of the fuel pump is likely going to leak through the diaphragm. If it's a newer style, could be leaking past a seal. Definitely try a new fuel pump to see if it alleviates the crankcase filling issue. FWIW, I've never in my life worked on an L-series engine that didn't have some sort of fuel in the oil. Definitely turned black after 2K miles, even with my brand new fresh rebuilt L20B.

 

Now as far as the choke goes, obviously your fuel pump isn't going to be causing that issue. But it might be distracting you from a entirely different issue with the fuel pump. Using a proper PCV system eliminated a lot of blowby issues I was having (blowing oil vapor out of the breather on the valve cover) and after hooking it up correctly, I never had that problem again. It did clean things out better, but it did not solve my black-oil issue. I learned to live with it, and it hasn't been a problem after thousands of miles. And hey, think of it this way: inside of your engine is likely nice and clean now!

 

In my case, my SU's had such bad throttle shafts that not only would it idle at nothing lower than 1100-1200rpm, I never had to use the chokes (fuel enrichment valves.. .). My experience with chokes is nil, hah. But it's basic troubleshooting here. If your choke keeps sticking closed, maybe it's a bad choke coil. Disconnect it, see if those issues disappear.

 

I'm still adding my vote for a leaking fuel pump.

[wayno]

Unless the fuel tank is higher than the engine/carb, and is siphoning into the block while shut off, my guess is the fuel pump is pumping gas into the case, as I have never heard of another way for it to get there while it is running.

I just thought of something, you haven't got your return line connected to that fitting that goes back to the vapor tank, do you?