l20b engine cuts out

[loudnlow_720]

my 720 cuts out like its not getting enough fuel but only really does it when its warmed up.and will sometimes die while sittin at the stop light then it is hard to start again. my filter looks good and i cant find anything to cause this. anyone have ideas or had this problem? any help would be awesome.

[datzenmike]

Doubt from the description it the filter but it's cheap and easy and never hurts anyway.

 

1/ Look at the round glass on the front of the carb. The fuel level should be at or near the dot. Is it???

 

Need more info. Where are you geographically? Are there any modifications? like a weber carb or any smog equipment altered or removed?

 

Check and set the valve lash. Loose is noisy but will run. Tight is quiet and valves may leak compression and cause poor intake vacuum and idling. Exhaust valves can burn from being too tight. Check them with motor hot. Intake 0.008" and exhaust 0.010"

 

 

Now check your timing 12 BTDC

 

Check rotor and cap for wear and replace plug wires if old and split. Otherwise clean and replace. Clean and gap (or replace) worn plugs NGK only.and check the gap for the '80 model year.

 

Now you can adjust your idle mixture screw. If you don't check the above don't waste your time.

You have to turn idle speed screw up so it will idle, but only enough to barely idle.

 

Turn idle mixture screw in or out to get the fastest smooth idle. If it doesn't then the idle speed is too high turn down or pull the vacuum advance hose off the distributor temporarily.

 

Adjust idle mixture in or out for fastest smooth idle. turn idle speed down

 

Adjust idle mixture in or out for fastest smooth idle. turn idle speed down

 

You'll find there is about a turn of adjustment between too much in and too much out. Just set roughly in the middle.

 

Keep adjusting until you cannot improve the idle quality and the final idle speed is 650- 750/800.

 

If you cannot get the idle down below 1,200RPMs. Check the idle cut solenoid is working. With engine off turn ignition on/off/on/off and you chould hear a clicking sound at the back of the carb. Without the idle cut solenoid working, there is no gas to the idle circuit.

[loudnlow_720]

sorry i forgot to mention it has a weber carb. this is my first carburated rig and i have no idea what im doing.and cannot afford to go to a shop so i am gonna give it a go

[loudnlow_720]

im in western washington if thats what you mean by geographically.

[datzenmike]

Yeah if Alaska and 65 below that could have a bearing.

 

Well forget the carb adjustments, I know little about the weber. The valve lash/timing/distributor/plugs stuff should still be looked at.

[loudnlow_720]

ok thanks

[H5WAGON]

How old are the plugs.....and what kind. I'm not the only one to say, only use NGK. You will be much happier and so will your motor.

 

So does it only die when idling? 

 

So what year 620...?  Some have points and some have matchbox dist.

 

Mixture screw could be all out of adjustment....if timing is also off, you are making all kinds of problems. Once you get timing set/checked like Mike stated.

 

 

Check where yours is at.....with car off slowly turn screw in softly....Don't crush the needle. count half turns so you don't loose count until it bottoms out..

.DONT PUT TO MUCH PRESSURE ON NEEDLE.

If you didn't know that...there is a tapered tip on the end of the screw, allowing adjustment.

 

Read this.... http://www.carburetion.com/Weber/adjust.htm

 

And pics always help.... B)

 

 

[KELMO]

What year 720?  Do you have an electric fuel pump? Some of the 720's have a fuel pump module (relay) on the right side kick panel up by the dash.  It is a black relay about 2 x 3 inches.  The symptoms you describe are similar to what I would hear way back when I was selling Nissan parts.  the jist of the problem I would hear was: The truck would die like it ran out of gas and then was hard to start.  I don't remember any one talking about it cutting out though.

 

my $.02 worth

[loudnlow_720]

yes its electric its a 79 and i can hear my pump kick on.it only dies while idling i turned the idle up a little and will still die.ill pull up to a red light and sit there for a min or two then it dies sometimes. i bought the truck a week ago and the day after i started havin issues. wires and distributor are fairly new plug look ok. it dies like its running out of gas but its real quick one putt then dies.

[datzenmike]

Only the '80 model year has an L20B in it. That's June '79 to June '80 build dates.

 

Only air conditioned '80s had the electric pumps unless someone put one on. Otherwise the mechanical pump is mounted on the front right of the head just forward of the #1 spark plug.

[loudnlow_720]

 yes its the 79-80

[smoke]

This sounds a bit like a slowly dying coil. Get warm and cuts out. Many times they feel like running out of gas.

[datzenmike]

Two things...

 

Ok runs like shit when warm but ok when cold.

 

The difference is the choke is on. The choke forces a rich mixture and a faster idle for better running and performance when cold. (and a faster warm up)

 

1/ I would say that your primary barrel has a partly blocked jet or the wrong one (too lean)

 

2/ The idle cut solenoid shuts off fuel to the idle circuit when the key is turned off. The idle cut solenoid may not be connected (if this weber even has one) The choke on, also forces a fast idle which gets around the idle cut solenoid until warmed up. 

 

[smoke]

One way to check would be when it's warm and running bad, put your hand over the top of the carb to fatten it up. If it clears up and smooths out a bit, you're lacking fuel.

[ggzilla]

Adjust the Weber. It is done exactly the way Datzenmike explained - same as a stock carburetor.

[kgrantkey]

When the diaphram was going bad in my fuel pump it was a logical assumption the gas was not keeping up with the amount needed.  It'd run out very quick at WOT and sometimes be very stubborn about pumping again. I'd pour som gas into the carb for it to crank.  I nursed it for a while then got a new pump.

 

What you describing seems closer to what advice you are recieving above this post.

[ggzilla]

Say what?

[loudnlow_720]

so did my timing and and a few other things. but its running lean and my distributor has a little play and the points are jumpin around. if i switched to elctronic distributor would i need to get a whole conversion kit or just swap and go. i am bein told yes and no so im not sure.  thanks for all the help guys. really appreciate it

[banzai510(hainz)]

a 79 should have electronic ignition already in it.

 

a 79 has alot more emissio stuff on there make sure the vaccum lines are not cracked

 

carb tight? intake tight?

 

hoit soem carb cleaner in the carb

 

then do a mexican tune up.

take aircleaner off rev the motor up then put a rage over tha carb and hopefull the jets get cleaned out.

But at ilde the idle jet is the most likely proplem. if idle jet is clean then adjust the mixture screw in/out till you get it good

[dr.feltersnatch]

If it has been swapped to points its very easy to swap in electronic. Just use the search function for matchbox and lots will come up

[loudnlow_720]

thanks for all the info guys

[loudnlow_720]

thanks for all the help guys.a little fine tuing on the carb she should be runnin smooth :thumbup: