My 521 diesels quite badly

[Roger]

It has the L16 and weber carb. It was dieseling when I got it and I checked the timing. 2 degreees off--I corrected it. The idle speed screw I turned all the way out and still I think it idles too fast. No tach. Can't lower idle speed cause the screw is all the way out now. Could it be the carb?

[jefe de jefes]

Is your choke opened up all the way?

[banzai510(hainz)]

If u have a open chamber A87 or a U67 head this is common.

put timming to 7 to 10 and see if this lowers the RPM

[MicroMachinery]

Clutch kill: When you're ready to shut it off, put it in First with your left foot on the Clutch pedal and right foot on the Brake pedal. As you turn the ignition off, quickly remove your left foot from the Clutch pedal. The engine will not be able to run on with the transmission in gear and the truck not able to move(foot on brake, just in case).

 

At first, it took a little while for me to get used to this, but now I do it automatically without thinking.

[izzo]

Clutch kill.

 

^^ lol, it works

 

Past few times i had this issue, i just double checked timing with timing light. And re-adjusted the carb. Cured it... (idle speed, and air/fuel mixture)

[Roger]

choke plate is wide open. Timing is 10 degrees, was 7 or 8. Diesels more now. Don't know what head. It is a stock 1971.

[izzo]

choke plate is wide open. Timing is 10 degrees, was 7 or 8. Diesels more now. Don't know what head. It is a stock 1971.

 

 

Guessing A87 open chamber maybe? Look below #1 spark plug on head, should be a casting number there. grab a rag to wipe the head off if its dirty

[Roger]

Maybe run a very low idle?

[izzo]

dunno, any idea what its currently idling at?

[Rob W.]

If the idle is already adjusted to it's lowest your idle jet could be too large which would make it impossible to slow the motor. Or as mentiones try leaning out the fuel air mixture a bit. What is the gas mileage like does it suck? Could be the carb is too rich.

[banzai510(hainz)]

later model Datsuns have a anti desieling selinoid on the Hitachi carb. so when you shut the key off it plugges the idle jet.This is common with open chamber heads that cam to the USAand later years for emmisions.

Since then most people buy Weber DGVs and 95% of them dont have the Weber DGV with the selinoid.

 

 

closed chamber heads tend not to do this

 

My 521 does it everyday. its a L18 with a U67 head. And when I had a aniti desieling selinoid on my other DGV I had it would still desiel on very hot days

[Arun]

I would check the carb for a air leak

[Arun]

Spray some carb cleaner around the base of the carb to see if it sucking air

[datzenmike]

It has the L16 and weber carb. It was dieseling when I got it and I checked the timing. 2 degreees off--I corrected it. The idle speed screw I turned all the way out and still I think it idles too fast. No tach. Can't lower idle speed cause the screw is all the way out now. Could it be the carb?

 

Check that the linkage is adjusted with some slack in it so the throttle can return to it's rest position.

[wayno]

Hey Roger, you have a stock L16 with a weber on it, correct? Didn't the 1971 L16 have the 210 head on it, look just under the #1 sparkplug as mentioned in an earlier post right where the head rests on the block. If it doesn't say 210, it will be something like U67, or A87. I have a L20b with the W53 head Roger, I have dual SUs, and it has always dieseled, get used to it, the truck is so happy to have a new home that it just wants to keep going, and going like the energizer bunny.:lol: As mentioned before, just put it in gear and turn the key off and let out the clutch at the same time, before you know it, you will be doing it automaticly without even thinking about it.

[Roger]

Right you are Wayno. It is a 210. Woo hoo? Truck wants to keep running because it likes its new home. LOL

Got to deal with that weber. I bet it wouldn't do it with a Stock carb.

 

Like I say, I got this truck second hand and do not know the details of the weber carb. Don't know anything about it. It sounds like an air issue of needs jetting. Is there a wever web site where I can buy those jets? I'll spary the carb w/cleaner and check for excess air.

[banzai510(hainz)]

dont buy Arco gas. try another Gas company in case this might be suspect

 

I have never had a 210 head desiel.

I wont know if you feel good about doing this but ai get the motor going really good and pour a lilttle stream of water in the carb to hopefull clean out(steamclean the valves and pistons)

[datzenmike]

Check that the linkage is adjusted with some slack in it so the throttle can return to it's rest position.

 

Did you check this???? If it is it's an easy fix!!!!!!!

 

 

It could have the wrong jets also. The head carbons up and it detonates. Check your plugs... if they are dry and black with carbon it could be the mixture.

[Roger]

Good points. Wayno, we saw all that carbon in your head.

 

I hear automatic transmission fluid can be used in place of water. Put a syphon straw in it and dhook it up to the intake--rev engine. I will investegate the spark plugs first. Water is a good idea as it is cheap. A bit wont hurt.

[wayno]

Fact is Roger, my 521 has dieseled since the day I bought it and it has not effected it in any way that I know of, it did not wear it out, did not cause it to use more oil, it did not rob me of any power, in the past I have let it diesel to see how long it would, I beleave it almost made it to a minute, but it made all these unnatuaral knocking noises, so I didn't do that anymore. I wouldn't worry about it to much, just let out the clutch and turn the key off at the same time while it's in gear. I have heard of pouring stuff down the carb for somekind of end result, and it may just work, but if it was that reliable of a techniquie, you would know about it as a comman practice, like your neighbor would say something like, I have a fluid injection appointment next thursday to clean out the engine, not one person I know has ever said anything like that. As I said, it may work but I won't be doing it anytime soon, so far that buildup has not effected my engine other than to beat the shit out of the top of my pistons, and I did not know it did, till I pulled the engine apart. Be careful, I can imagine lots of things that could go wrong, like thermal lock.

[datzenmike]

Alcohol will eat carbon. Windshield washer solution should work perfectly for this. Run a hose over to the carb and clip in place. Get the motor nice and hot out on the highway and floor it in third gear and hit the wash button. You'll notice a drop in power because much of the combustion heat is removed and not available to heat and expand the air and push down on the pistons. The carbon cools and shrinks suddenly and begins to crack and flake off. You will likely have to drive along to warm up the interior of the combustion chamber to repeat. I would try 3-5 second squirts and adjust as necessary. Many people have had leaky blown head gaskets, me included, and can attest to the cleaning effects of small amounts of coolant getting into the combustion chamber.

 

Most drivers today have EFI and carbon isn't a problem. If they were convinced of it they would simply run and get a can of 'engine cleaner'. Carbon is more of a problem in carb engines. A friend showed me this trick back in the 60s. He had a 283 4bbl chevy. We opened the headers and revved it up while pouring a coke bottle of water down the open carb. A huge cloud of steam blew out the back and when we moved the car there was black shit all over the ground. He said the trick was the engine should be good and hot. Cost? about $0.25 for a Coke and some tap water.

[Roger]

The dieseling was fixed 521 on da highway for about 500 miles. I think it got carboned up from lots of short, slow trips. I just blew the carbom out by driving the speed limit on the interstate.

[wayno]

You must have some really slow speed limits on the interstates back east, I didn't know a stock 521 would do the speed limit.:lol: :lol: :lol: