L20b Engine Dieseling

[motavated]

The engine was not tunned right and dieseled every time I turned her off. So today I went on craigslist and bought me a timing light and timed it at around 8 degs and had her idling at around 700 rpm. BUT THE FUCKER STILL DIESELS!??!??! Ideas? Has a weber 32/36... Maybe to much gas pressure? Thanks!

[motavated]

I read online and found this...

* A carburetor that does not close entirely can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling.

 

Does the weber primary have to absolutely closed at idle? I have it open maybe a hair width.... I might bring the rpms down to 500 or less but might idle like crap. Any ideas?

[motavated]

I also read some where that a weber can only take so much fuel pressure and a fuel pressure regulator is needed? What is the max fuel pressure the Weber 32/36 can take? Thanks!

[motavated]

How much fuel pressure can an l18 fuel pump produce? I read this online wiki 1200

 

"The 32/36 requires a low-pressure fuel feed (2.5 to 3 lbs). This matches the stock Datsun 1200 pump (2.6 lbs)."

 

I will check next time it diesels if spark continues to shoot after the ignition is turned off if there is a fault.... I need help guys... My brain is confused... This has been going on for years!!!!

[hessianben]

i don't know the answer adam, but what i would do is put it in 4th gear before i killed the ignition, and slowly let out the clutch right as i shut it off... fixed. :)

[ariascarlos1990]

i don't know the answer adam, but what i would do is put it in 4th gear before i killed the ignition, and slowly let out the clutch right as i shut it off... fixed. :)

 

I have to do this with both my cars. it gets old.

[datzenmike]

L20B motors are notorious for hot run on. Just the heat and compression will cause the fuel to ignite without the ignition on. This is also known as dieseling.

 

To prevent this Nissan added an idle cut solenoid to the carb. The idle cut does just that... it shuts off fuel to the idle circuit when the key is turned off. Your Weber most likely is an older one and it won't have this important solenoid on it.

 

If idle speed is too high or mixture too rich, this will aggravate it but I doubt it will go away totally even in the winter. As suggested, hold the brake on and lift the clutch slightly while in 4th or 5th so it begins to drag and then shut the ignition off. This will stall the engine quickly. Once it stops release the clutch fully. Takes a little practice to do smoothly and without the truck jumping ahead.

[motavated]

Thanks everyone! Datzen mike would there by away to integrate this idle cut solenoid? I have checked and there is no spark when the engine is turned off. I guess I would have to deal with it... If the pressure regulator does not solve it then I will give up.....

 

But I honestly cant stand it. Well I have been doing the clutch thing but damn it! I want it to turn off proper!

 

I is also using platinum Denso plugs for a 1979 620. I tried to look up the part number on Kragen but they dont stock them anymore? Only NGK? So my question is... Should I use spark plugs from a L18 standard copper or the 1979 l20b ones.

 

I have a l20b with a peanut head.

[motavated]

Maybe an 160 degree thermostat? Will that cause problems if I change it? I have one some weres....

[datzenmike]

I don't think the L20B came with a peanut so you are adding compression which makes dieseling worse. I doubt that the idle cut can be added to a carb that doesn't have it. Running the engine cooler will reduce it's efficiency (mileage/performance) and may not cure it.

 

Datsuns run with NGK so if you are changing them get the ones for the '79?

 

Bottom line is all L20Bs will diesel when hot. A peanut head will make it worse. You'll just have to stall with the clutch or replace the Weber with a stock carb.

[motavated]

Your right I guess... I have a w58 peanut I just bought so maybe some came peanut????

 

I will change the sparks when its time again to the NGK.

 

:(

[motavated]

BTW I bought this carb no more then 3 years ago. Were would a weber have this solenoid if it had one.

 

I found this online... I am willing to buy a new carb to make this go away... This is how pissed off I am...

 

http://www.lceperformance.com/Weber-32-36-Idle-Cut-off-Solenoid-p/1035032.htm

[datzenmike]

I don't think they (L20Bs) came stock with peanuts. I did however fine a W58 in a junk yard with a tag marked 200sx. I have checked the part number for the '78-'79 200sx and they are the same head as the truck and A10 W58s so my theory is it was a dealer replaced head or a JDM import engine head.

[motavated]

Ahhh! Thanks mike! I did more research and i found a smog legal weber for the 22r 20r toyota engines. I am betting these have that solenoid.

 

ALSO! If a person wants a LEGAL weber why not buy the 22r legal weber, buy the appropriate adapter for the l20b engine and run it... It should pass smog right since it has a sticker... Right?

[Charlie69]

Here is the IC sonoid on a 32/36 Weber

[motavated]

Thanks! I will see if my has it plugged. Or new weber time!

[izzo]

motavated....

 

When mine did that, i just re-adjusted the timing as you did, then re-tuned the carb. Never did it again... Tuning the carb was easy too! (weber 32/36)

[yello620]

Bottom line is all L20Bs will diesel when hot. A peanut head will make it worse. You'll just have to stall with the clutch or replace the Weber with a stock carb.

 

Adam,

I have to disagree with this, as i drive a L20b daily with a weber and i NEVER have to deal with any dieseling, NEVER. L20b, U67 head, L16 intake and exhaust manifold. And i do not have a IC solenoid on my weber, Have had three different webers on this motor and none of them have had a solenoid on them.

 

My timing is currently around 15*...need to back it off a little.

[motavated]

I is seriously fucken confused. I will try that fuel pressure regulator and see what is up... Maybe I need someone to tune my car i guess...

:cool:

I wish you were local yello...

[Charlie69]

Here is what I am putting on my L20B.

 

Weber Carburetor for the Datsun L Motor (L16, L18, L20B)

 

Carburetor Model Weber DGEV 32/36–IC

Part # 22680.533B

Electric Choke w/idle cut-off solenoid

 

http://www.webernorthamerica.com/pdffiles/WeberCarbbuyersguide.pdf

[motavated]

I looked at old Datsun.co and it said factory is sorta 12b timing advance and 750 rpm idle speed... I will keep it like that and buy it the pressure regulator. If not then I will buy the carb... :(

[banzai510(hainz)]

not all weber DGVs can be converted to the IC selinoid.

If the idle jet on the main side has the bigger brass screw then yes you can buy the selinoid.

But most weber DGVs esp the 5A series it will have the smaller jet size as in the 2nd barrel.

 

So to make this RETARDED proof. If you have 2 different size idle brass screws then you can convert to a selinoid.

But most like both are the same size.

 

 

Remember later Datsun came stock with the idle cut off selinods.

 

My L18 in my truck with U67 head desiels when Hot.

I have tried the cut off selinoif on another weber and it worked when I ran 92octance but on really hot days it would still soemehow desiel.

 

best way to stop is to when shutting off clutch it and I slightly hit the pedal so to decrease the vacuum. Usually works.

 

I tried running a colder 160 stat also but depends on temp of the day. Youll notice if you run car before it warms up it wont desiel shutting it off.

 

Sooner you accept this the sooner you will be FREE.

 

You can buy a new weber and maybe it works. then on really hot days it might not. But my carbs are all over 20years old. Maybe a new one will be better.

[79D50]

I had the same problem on my L18. It has a shaved peanut head and a few other goodies yada yada. I leaned the carb a bit, dropped the idle a bit, and advanced the timing. It has never diesled since.

 

BTW - Most literature will tell you that the proper fuel pressure for a WEBER 32/36 is 2-4 LBS. For a WEBER 38 the books say 3-5 lbs. A lot of different sources say different things. I run my 38 at 5-6 lbs and don't have a problem. The literature is conservative because it is assuming you are a stock motor and without replacing floats and jets they don't want you to have runability issues. CARB Connection, WEBER Direct, and Top End Performance all recommend a higher fuel pressure for best results. The key is tuning i.e. timing, jetting etc. TEP even mentions the use of a fuel pressure regulator is not needed. I disagree with that but like I said, everyone has thier opinion.

[datsunaholic]

The fuel pressure issue is because the float valve only takes about 7PSI to get forced open when NEW, and gets weaker over time.

 

I NEVER run a regulator. It's just one more thing to go wrong. What I run on an L20B is the stock fuel return line, that keeps the pressure below the level that causes the carb to overflow, AND it keeps the electric pump cool by constantly circulating rather than getting stopped/stalled by the float valve. Keeps the tank cleaner too. I had several trucks where the prior owners had removed the stock L20B fuel rail, either just running a hose straight from the filter or using the L16 type single-line rail. The Weber carbs always overflowed with the stock Datsun electric pump... 3 different trucks. I put the return line back (having had to scour junkyards for a couple of them) and the problem was gone.

 

This of course doesn't work with the 1974 or older trucks that don't have a return line. I was able to adapt the tank vapor line on a '74 to use as a return (this meant needing a vented fuel cap) so I simply went back to using the mechanical pump- it's sufficient to run the 38DGAS on my truck.

[motavated]

Well thanks for all your advice. I went today and see what is up. Timed it to around 12 and it idles are 750 rpm. But when I flog it for a while it starts to idle at 1000rpms once I let go of the gas.

 

Another thing I found is that my carb could probably accept the solenoid. There are two copper/brass screws and on the side were the choke is at. It is bigger!

 

So my question is how can I integrate it into the 1974 620? My truck had this on it. Is it needed for the solenoid?

 

Datsunholic. I had to cut the pipe down since I could not connect the stock fuel line with the weber. So I cut it down and added maybe like half a foot of fuel hose. Look.

 

If my truck has a solenoid stock. Which wire was it so I can hook it up?