Unable to restart Daily Driven '79 620 l20b

[banzai510(hainz)]

Wish people would UPDATE so we know what the fix is/was so we can learn and pass info on

[Mitchell]

Not resolved yet, I will once i've figured it out

[Mitchell]

Sorry for no updates, I've had a few things come up all at once and couldn't work on it. Today, checked valve lash and found number 4, exhaust was too tight, but all others measured fine as well as all rockers, all look normal. Went ahead and put a fresh set of plugs in and tried it and had the best result so far, it fired 2-3 cylinders and not again. Definitely getting gas into the carb and to the plugs. Checked the spark again and it still looks weak, more orangish and never bluish as I think it should be and fires spark that to me appears unevenly meaning one firing fatter than other weaker smaller firings that follow, then randomly another fatter firing and repeats inconsistently. I had also added an extra ground from the matchbox distributor body to the cylinder head, with no change. So I purchased a points dizzy remanufactured from rock auto and I'm going to try the ignitor II setup since I've got a new flamethrower 0.6 coil spare on hand that I'll use with it.

Edited May 3 by Mitchell

[banzai510(hainz)]

the L20B point distributors have a ring boss above the point lobe. the magnet ring in Pertronix dont fit over this. You have to pull the dist shaft out then mill that down to get the magnet ring over that to fit over the lobe to lock down.

 

I guess just try with the points but youll have to figure it out How to hook up as your 79 wasnt wired like a point set up. as a 79 dont have a hotstart wire

 

It shows you have multiple cars just take a set up from there I guess but take photos before you remove in case you have to put back.

 

I would have try to find a 79 distributor. But I think you just missing something. as I always found the spark from the EI models always weaker that on the points or pertronix set up.

[wayno]

On 4/20/2026 at 9:42 AM, Mitchell said:

Hey Guys,

 

Need another set of eyes and thoughts about this...

I have a '79 620 l20b with factory matchbox and a genuine weber 32/36 dgev (electric choke) that I've daily driven for more than 30 years and have an issue I can't figure out. Initially I started the truck right up cold (but warm outside temp here in Florida) as normal but after about 20 seconds it shut down by sputtering and not able to build revs before stalling out. It wouldn't restart. I tried the following:

I checked the spark plugs and they were wet with fuel.

I checked the float chamber inside the weber no dirt or rust particles whatsoever, blew on the inlet of the carb to check the float to see if the needle would shut the gas flow and it does. The float is the black plastic type and doesn't appear to have leakage.

I double checked the static timing at 0 and is pointing at number 1 in the distributor and looks good.

I've owned this truck for many years and have many spares...

I have spark to the plugs. The Cap Rotor Wires NGK / NGK plugs are in excellent condition. 1,3,4,2 verified.

I added an additional ground to the distributor which has a spade terminal, no difference. I've swapped Distributors, no difference.

The carb is about 15 years old, considering getting a new one as previously the carb sometimes floods when hot starting causing extended cranking, but always starts... Possibly some tube is clogged or accelerator pump rubber is age cracked...

The color of the spark might not be as bluish as I remember so I've tried several coils including a .6 ohm igniter II, several matchboxes OEM E12-80's as well as new aftermarket

Valves were adjusted about a year + ago. Truck isn't driven hard.

I appreciate anyone's thoughts.

 

Thank you!

 

 

You said you verified the firing order, 1, 3, 4, 2, counter clockwise, correct?

 

[Mitchell]

Thanks for the heads up on the Pertronix needing the shaft collar machined to retrofit, didn't know that. I've used them on 240's and the magnetic ring just slides easily right onto the shaft.

Yes I can absolutely confirm 1 3 4 2 counterclockwise using NGK numbered wires.

In the meanwhile I am going to try one of the hot spark electronic distributors while I am waiting for 2 matchbox distributors to be rebuilt. Considering using https://www.advanceddistributors.com/ has anyone had experience with them or can recommend another company?

[banzai510(hainz)]

I have a feeling your going to induce more of a proplem. If dist is sparking it should work

did you change a coil or anything. Maybe a wrong one like a point coil in there.?

 

let us know what you figure out.

I gave my input. I persoanlly alwasy have a exact spare dist just for trouble shooting and a spare weber.(but never had a weber go totally bad.

[Mitchell]

Good morning, well it started today! Here is what changed. I was in the process of double checking number 1 was at TDC at 0 timing mark and saw the rotor was pointing at number 4 not number 1. I rotated the wires 180 degrees. So tried it and It started, But timing was definitely off. So I retarded and then advanced the distributor while it was running (barely) and It improved while at maximum advance adjustment. I loosened the base plate to allow it to advance further and it ran better, best so far but will not rev more than 2500 rpm. I'll put a timing light on it to see where it is and if it's even close enough before adjusting the distributor base a tooth. Almost there... later this morning, was able to check the timing with timing light and it looks great. Starts well, but not revving past 2500, when given too much throttle and it will pop not raise rpm, checked carb throat and not seeing any spray into the carb, So back to the accelerator pump as Mike said (Thanks) originally way back when to check, now waiting for a new genuine weber replacement carburetor from Pierce. I'll update in about a week...

On 5/3/2026 at 7:24 PM, wayno said:

firing order, 1, 3, 4, 2

Thank you wayno for your idea to look at the firing order...

Edited May 5 by Mitchell

[iceman510]

On 5/3/2026 at 7:39 PM, Mitchell said:

Considering using https://www.advanceddistributors.com/ has anyone had experience with them or can recommend another company?

 

He is a member of this forum and knows his stuff.

 

Edited May 5 by iceman510

[Mitchell]

Thanks icemans510, I was able to speak with Jeff yesterday, he is definitely knowledgeable and familiar with L20b distributors and optimizing curves way beyond what most of us need, he owns a couple of 620's has even taken his 620 to Bonneville salt flats. I am sending one to him today, lucky for us such a rare distributor resource still exists!

Edited May 5 by Mitchell

[wayno]

9 hours ago, Mitchell said:

Good morning, well it started today! Here is what changed. I was in the process of double checking number 1 was at TDC at 0 timing mark and saw the rotor was pointing at number 4 not number 1. I rotated the wires 180 degrees. So tried it and It started, But timing was definitely off. So I retarded and then advanced the distributor while it was running (barely) and It improved while at maximum advance adjustment. I loosened the base plate to allow it to advance further and it ran better, best so far but will not rev more than 2500 rpm. I'll put a timing light on it to see where it is and if it's even close enough before adjusting the distributor base a tooth. Almost there... later this morning, was able to check the timing with timing light and it looks great. Starts well, but not revving past 2500, when given too much throttle and it will pop not raise rpm, checked carb throat and not seeing any spray into the carb, So back to the accelerator pump as Mike said (Thanks) originally way back when to check, now waiting for a new genuine weber replacement carburetor from Pierce. I'll update in about a week...

Thank you wayno for your idea to look at the firing order...

So you had the wires off the cap at some point?

[Mitchell]

3 minutes ago, wayno said:

So you had the wires off the cap at some point?

Yes, replaced the coil, cap, rotor, wires and plugs, I'm wondering if the rotor wasn't the correct one even though it fit but at 180 degrees....?

[wayno]

16 minutes ago, Mitchell said:

Yes, replaced the coil, cap, rotor, wires and plugs, I'm wondering if the rotor wasn't the correct one even though it fit but at 180 degrees....?

 

I only brought this up because I messed up myself, somehow I took the wires off the cap and put it back together installing the wires clockwise, I checked all the wires and they were all hitting according to the timing light, but 2 spark plugs were wet, it idled and ran but backfired when revved, when I figured it out it ran fine, but I cleaned the plugs and lit off both the wet cylinders with a lighter before trying to start it, they both wooshed, it ran fine after that, it did not sound right when running, it revved slow and idled rough, this was on a MG distributor in a 1963 Datsun 320 truck, the distributor is sideways and low on the block, it took me days to figure it out.

[Mitchell]

It's interesting that clockwise wiring order and 180 off clocking creates the same symptoms. Since I'm not seeing any fuel squirting into the primaries, pretty sure that's the problem with not revving above 2500 here, seems like it's not missing, just not revving up, but I'll have a look and see if the plugs are wet just in case, thanks again for your reply

[banzai510(hainz)]

I broght this up a while ago. I asked if when youcycle the linkage is gas squirtng in the carb. This would be the accel pump diaprame.  Most weber really dont go bad. most times its the needle valve or the accell pump. otherwise webers last 20years minimum.

 

now you mention clock wise?

you changed soemthing and not told us.?????????????

I always pop the cap and leave the wires on there and place over to the side.

 

if  is 180 out meanes you took the whole dist off with the mount and put it back on 180 off from the timing cover which will do this . the rotor will lock pointing in the same direction but the housing is off 180 then the plug wires will  be off.

 

your getting there. bu this is a simple fix.

[Mitchell]

Thanks Hainz, I was replying to wayno, never clockwise on my truck, 180 degrees counterclockwise matched the symptoms he mentioned about clockwise. Yes you did mention early on to check for squirt into the primary, it wasn't cranking good enough to be sure if I was able to check for squirts. I definitely had the distributor on an off many times while swapping ignitors and the rotor, not sure the distributor went in at 180 but if it can go in that way, then that would probably be what happened. At this point it idles decent and am able to use the timing light and it looks good, but won't squirt into the primary or rev up so I ordered a new genuine carb from Pierce. The major Weber rebuild kit was fairly expensive and since I have had this Weber on the truck over 20 years, I decided to replace it with a new one and rebuild the existing Weber in the future.

Edited Wednesday at 08:08 PM by Mitchell

[banzai510(hainz)]

24 minutes ago, Mitchell said:

it wasn't cranking good enough to be sure if I was able to check for squirts

crank it just enought to fill the bowl and you can just watch the carb and cycle by hand to see if gas squirts in there.

 

25 minutes ago, Mitchell said:

not sure the distributor went in at 180 but if it can go in that way,

well if the vac advance is on the other side is the obvious conclussion. best to take photo before removing.

 

27 minutes ago, Mitchell said:

won't squirt into the primary

you can remove the 4 screws and look at the accel pump diaphram if torn but usually the gas will leak from that location. Look at the linkage. Sometimes if not truck not driven alot it will get stuck in the IN mode and not release the arm or mechanism or whatever you call it. Please ck that out.

[banzai510(hainz)]

30 minutes ago, Mitchell said:

it wasn't cranking good enough to be sure if I was able to check for squirts

crank it just enought to fill the bowl and you can just watch the carb and cycle by hand to see if gas squirts in there.

 

30 minutes ago, Mitchell said:

not sure the distributor went in at 180 but if it can go in that way,

well if the vac advance is on the other side is the obvious conclussion. best to take photo before removing.

 

30 minutes ago, Mitchell said:

won't squirt into the primary

you can remove the 4 screws and look at the accel pump diaphram if torn but usually the gas will leak from that location. Look at the linkage. Sometimes if not truck not driven alot it will get stuck in the IN mode and not release the arm or mechanism or whatever you call it. Please ck that out.

[banzai510(hainz)]

your ideling. your half way there

[Mitchell]

Good morning,

 

The carburetor linkage is operating correctly, primary butterfly opens for the first half of applying throttle and at about 3/4 throttle the secondary butterfly engages and opens gradually.

 

I cranked the engine about a dozen times and then checked for the squirt of fuel into the primary and could only see fuel dribble into the primary and almost nothing, only an occasional drip of fuel into the secondary at full throttle position.

 

After testing for squirt, checked if it still runs and it started right up on only a half crank. Stills idles okay, smoothly at about 1000 rpm for as long as needed, but will not rev past 2100 rpm if I hold down the throttle too far the engine won't stall but will pop, possibly from too much air and not enough fuel? Tried pumping the pedal while it's running to see if I could get some more fuel to gain rpm but won't pass 2100.

 

After the 5 minutes of 1000 rpm running I checked for squirt again and no change other than the electric choke operates as it should and remained open with the engine warmed up.

 

The new carb is supposed to get here Monday...

Edited Thursday at 01:18 PM by Mitchell

[banzai510(hainz)]

6 hours ago, Mitchell said:

The carburetor linkage is operating correctly, primary butterfly opens for the first half of applying throttle and at about 3/4 throttle the secondary butterfly engages and opens gradually.

 

this is normal

 

6 hours ago, Mitchell said:

checked for the squirt of fuel into the primary and could only see fuel dribble

Its should squirt/SHOOT a steam of gas when the linkage is cycled(like giving it gas). read carefully. IF NO gas squirting then this is a proplem. whchi should have been caust on 1 st page.. LOOK at the accell pump diaphrame. r look at the level and you can see it push the diaphrame. you can remove the diaphrame and check or check for lever movement which you did not anwser back if you check this

 

6 hours ago, Mitchell said:

not rev past 2100 rpm if I hold down the throttle too far the engine won't stall but will pop, possibly from too much air and not enough fuel?

make sure the 2nd barrel doesnt open. there is a spring that keeps this shut untill the mechanism open it. there is a spring that make sure its closed untill the mechinism opens it. If spring is gone it wont rev up and bogs it down with too much air cause not sucking gas thru the jets

 

 

Now I willl repaeat did you see if the accel pump arm inside the accel pump diaphram is stuck or not???????

 

 

since im not a MIND READER. I told know if this the orginal distributor then put in 180 off and or another dist with mount with a different matchbos with the 15 offset mount. Make sure the motor when timed can go from 0- 25 deg BTDC.    IF this is hard cranked one way to get the timing to say 7-10 then maybe this can be a issue you running out of time. I usually see this if the oil pump is off a tooth. it will run but run out of time

 

This is a EZ . and dont think you need a NEW carb. just fix the accel pump issue.  maybe as last resort could be clogged main jet at bottom of bowl. But you can ck the fuel filter if its bad.

Edited Thursday at 07:55 PM by banzai510(hainz)

[banzai510(hainz)]

look at number 34. you see a slot in the accel pump. this can get stuck in the push in mode.

 

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[datzenmike]

The squirt from the accelerator pump is only there to help transition from idle circuit to primary circuit. If you drive off slow enough you don't even need it. It does not stop you from revving up.  

[Mitchell]

Good Afternoon Hainz and Mike,

 

Thanks to both of you for the patience and help with this. The distributor that is currently running in the truck is the original one as well as the pedestal being the original. I did swap with another identical type spare matchbox distributor to test if there would be any difference. That distributor is now being rebuilt by Jeff at Advanced Distributors in MN in case the advance isn't working correctly.

 

The fuel filter is new as well as I checked the inlet strainer on the carb and it was clean, also there are normal fuel pump pulses of fuel from the carb inlet. With this having been daily driven the fuel has always been fresh 93. I checked the accelerator pump arm and it seems to function normally, not stuck, there's definitely been some leakage not dripping but some seepage. Sounds like a mini fuel pump when pumping the accelerator pump arm. I started it again and tried accelerating the throttle very, very slowly but just not able to build revs, and starts popping when approaching 2100 or pushing it any harder.

 

So back to possibly being off a tooth? However, the timing light showed a range of adjustment, but I did clock it almost all the way. Would running the distributor 180 degrees off, limit the revs to 2100? Can the oil pump drive skip a tooth? Or clogged inlet tube on carb?

 

 

Edited Friday at 05:37 PM by Mitchell

[banzai510(hainz)]

5 minutes ago, Mitchell said:

So back to possibly being off a tooth? However, the timing light showed a range of adjustment, but I did clock it almost all the way. Would running the distributor 180 degrees off, limit the revs to 2100? Can the oil pump drive skip a tooth? Or clogged inlet tube on carb?

If this was running before this whole fiasco then NO.  180 off will not make it a tooth off.

 

persoanlly I think it a waist to send that dist in. either the vac adv work or it dont. just grab the plate by hand and push it toward the vac canister and should flex back. Im sure hell say the springs are worn or something but if you swapped 2 in there it isnt it.. But this happen to me My dist plate the e clip or c clip that push pull the adv palce broke and plate would move throwing the timing off. But since 2 dist was swapped in I say it isnt the proplem.

 

 you still didnt mension the accel pump arm to see if STUCK in the IN mode.

 

 

as mike said the accell pump. the motor will rev higher if one gently opens the trottle. and increase the motor speed. The accell pump increases the fuel dump as the plate lets more in . For the sudden influx or air. it will need fuel.

 

Just make sure the choke plate is warm and opened up when you make these tests.

 

only other thought is maybe the float bowl is low but I dont know. I hate taking a carb aprt. its fucking with the choke I hate to get the top off.  so dont do this yet.

 

the key is THE ACCELL PUMP DONT WORK!!!!!!!!!!!!!!!!!!!!!!!!!!  UNTILL YOU ADDRESS THIS DONT MENTION ANYTHING ELESE.