Timing question L20B

[Str8_69]

OK, my 77 620 Runs great, decent mileage and what not. Timing set at 12 BTC dead nuts on, points dizzy, advance works perfectly, no play, points set perfect. Here's the thing, with #1 piston @ TDC, rotor is pointing at #4 cyl. Is this right? Not computing for me. When I shut The engine off, many times the overrun fires in reverse (as in the truck will clunk and jerk backwards when I drop the clutch to kill it). I'm drawing a complete brain fart on this one...

[Skib]

\ with #1 piston @ TDC, rotor is pointing at #4 cyl.

 

try setting the #4 as the new #1

[Str8_69]

try setting the #4 as the new #1

 

 

Yeah I thought about that, and I'm gonna try it, but how does that solve the reverse bump? That's what got me stumped. I think that's the ONLY way the ign could be 180 out but wtf? Why the reverse bump? Can the cam timing be 180 out on the L series? I've never been in that far on one yet.

[izzo]

Dont know if the timing can be 180 out, however if the oil pump/dizzy shaft is put back in backwards, it can be 180 off. if thats what you mean? I accidentally did this on my goon when i swapped oil pumps.

[hessianben]

you can be 180 out pretty easily, but you can be an entire plug off one way or another if you switch dizzy pedestals.

If you have a couple different pedestals, check out the different angles they all have. sometimes, you can swap them before having to skip a tooth on your oil pump.

[Str8_69]

Dont know if the timing can be 180 out, however if the oil pump/dizzy shaft is put back in backwards, it can be 180 off. if thats what you mean? I accidentally did this on my goon when i swapped oil pumps.

 

 

Engine was rebuilt before I got the truck, so I suppose that could be the case. Thanks for the tip. I'm getting ready to do a matchbox dizzy swap on it soon so maybe I can figure that out when I pull the stocker. Haven't checked the FSM for that but maybe it'll shed some light. Thanks for the tips guys!

[Str8_69]

you can be 180 out pretty easily, but you can be an entire plug off one way or another if you switch dizzy pedestals.

If you have a couple different pedestals, check out the different angles they all have. sometimes, you can swap them before having to skip a tooth on your oil pump.

 

 

Far as I know everything is stock 'cept for being r&r'd for the rebuild, but anything is possible.

[izzo]

Engine was rebuilt before I got the truck, so I suppose that could be the case. Thanks for the tip. I'm getting ready to do a matchbox dizzy swap on it soon so maybe I can figure that out when I pull the stocker. Haven't checked the FSM for that but maybe it'll shed some light. Thanks for the tips guys!

 

 

when you pull the dizzy and pedal off, you can see the shaft sticking out, take a sharpie and mark a line where it rests, makes it easier when installing, then you can tell if you are dead on or a tooth off.

 

If you look closely at the shaft, the tip is slightly off center, and thats how it becomes 180 off.

[Str8_69]

when you pull the dizzy and pedal off, you can see the shaft sticking out, take a sharpie and mark a line where it rests, makes it easier when installing, then you can tell if you are dead on or a tooth off.

 

If you look closely at the shaft, the tip is slightly off center, and thats how it becomes 180 off.

 

 

Is that pulling the dizzy at #1 TDC, or does it matter?

[hessianben]

Yeah, set motor to TDC and then pull the dizzy.

If the shaft is at the '11:28' position, then you may just have a different diz/pedestal combo.

[izzo]

yeah, put in neutral, turn crank pulley till the dimple lines up with 0 on the timing marker. then you're all set.

[banzai510(hainz)]

http://www.guba.com/watch/3000024223/Hainz-Datsun-L-Series-Engine-01-Timing-Tare-down-and-Rebuild

towards the end I install some dizzys. watch this one FAST FWD to it.

 

No way you have it off.

 

 

As for the run on.

L20s with open chamber heads will do this as the stock Hitachis has a antir desieling seliniod. It shuts the gas off when key is turns off. Most webers dont have this. But you can get it its the 32/35 DGEV-IC.

 

to stop the run on I just turn the key off and gas push the pedal in a little and thus will cause a loss of vacuum cause the plate will be open more and should shut off.

 

let me know how it worksthe 180 statemnet

if the motor is TDC the the dizzy rorot is pointing the wrong way just put the #1 pplug wire there and start your 1 3 4 2 ccw. that it.

 

 

No such thing as cam out 180 deg.= broke motor

[dryheat]

There are 2 TDC's on a 4-stroke motor ... You need to have your valve cover off and check the position of the cam to be sure.

 

If you have the motor set at TDC on the exhaust stroke then the rotor will be pointing at #4 ... rotate the crank one more time to TDC on the compression stroke and it will be pointing at #1 ... otherwise your engine would never run at all.

[banzai510(hainz)]

Hes motor is timmed OK

No need to remove the valve cover just open the oil cap and turn motor till the lobe right there is pointing left. Left means its on the comp stoke and its closing. Now just go by the crank positon and dial it up to ZERO.

 

Your timmed fine. If its running good thru the whole rpm range.

 

for the Run ON just hit the gas to open up the carb when the key is turned to OFF

[Str8_69]

http://www.guba.com/watch/3000024223/Hainz-Datsun-L-Series-Engine-01-Timing-Tare-down-and-Rebuild

towards the end I install some dizzys. watch this one FAST FWD to it.

 

No way you have it off.

 

 

As for the run on.

L20s with open chamber heads will do this as the stock Hitachis has a antir desieling seliniod. It shuts the gas off when key is turns off. Most webers dont have this. But you can get it its the 32/35 DGEV-IC.

 

to stop the run on I just turn the key off and gas push the pedal in a little and thus will cause a loss of vacuum cause the plate will be open more and should shut off.

 

let me know how it worksthe 180 statemnet

if the motor is TDC the the dizzy rorot is pointing the wrong way just put the #1 pplug wire there and start your 1 3 4 2 ccw. that it.

 

 

No such thing as cam out 180 deg.= broke motor

 

 

 

Thanks Hainz I'll check it when I get back to town in a couple days. I am already running a Weber, so I'm still confused on the overrun. What's strange is is seems to come and go.

[izzo]

when i first installed my weber on my truck it ran on, i adjusted the idle air/fuel mixture and it never has done it since.

[banzai510(hainz)]

L20s have open chamber heads. This is common with a Weber as most webers dont have the anti desieling seliniod. Just live with it

If motor is cold or maybe run high octane gas its less likely to happen

 

you can try adjusting mixture as h2theizzo said. or maybe try 10deg to 8deg on the dizzy.

[datsunaholic]

Run on is common. Just learn how to kill it. I have a AD solenoid on my Weber. The same weber on an L18 shut off easily, but on an L20B, sometimes gives one last gasp. It's an L20B thing; I had stock Hitachi carbbed cars do it too. Very rarely on an L18 or L16.

[Str8_69]

Run on is common. Just learn how to kill it. I have a AD solenoid on my Weber. The same weber on an L18 shut off easily, but on an L20B, sometimes gives one last gasp. It's an L20B thing; I had stock Hitachi carbbed cars do it too. Very rarely on an L18 or L16.

 

 

It's not the run on that bothers me, I'm used to that, just that the engine jumps backwards when it happens, so I was suspecting some kinda timing issue. I gotta get that matchbox on there and see if that helps. It just sucks when I miss the clutch kill my a millisecond and the truck lurches backwards! I'll have more look-see into it by the end of the weekend. Thanks again to all of you for the tips.

[Str8_69]

when i first installed my weber on my truck it ran on, i adjusted the idle air/fuel mixture and it never has done it since.

 

Good point as well. Now that you say that, it seems I can't get the idle down below 1k rpm without stutter, so I'll try some air/fuel adjust too.. Thanks man!

[banzai510(hainz)]

get the idle down and get the mixture. That should have been first.

 

Like i said B4 when it starts to RUN ON just hit the gas pedal and it should stop. when you turn the key off. They all run backwards at a certain point if it keeps going.

 

time it to 10 or maybe a litlle lower

run Super gas.

 

a matchbox isn going to to anything as the gas is preigniting on byits self. Remeber the key is OFF there is not power to the ignition.

[Str8_69]

get the idle down and get the mixture. That should have been first.

 

Like i said B4 when it starts to RUN ON just hit the gas pedal and it should stop. when you turn the key off. They all run backwards at a certain point if it keeps going.

 

time it to 10 or maybe a litlle lower

run Super gas.

 

a matchbox isn going to to anything as the gas is preigniting on byits self. Remeber the key is OFF there is not power to the ignition.

 

 

Thanks Hainz, you were right about the mixture, I completely brain farted that one. I richened it up a bit, got the idle to cooperate better and dropped the advance back to about 9 BTC and it really smoothed out. I always run plus or super so I wasn't thinkin' shit fuel was the problem. Run-on dropped to nothing or a couple revs now and then. Definately better.