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L16 running very poor. Ideas?


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Ok I need to bounce this off of someone else. I’m sure I’m missing something stupid. 

My current project is a 69 510 goon that I picked up not running. Only reason it didn’t run was the dash was pulled for paint and the gas tank was removed. 

After paint I reinstalled the dash and gas tank (checked to make sure it was clean first) and it started right up but never ran good. It idles fair but when you try to rev it up at all it misfires, backfires through the carb and exhaust and basically falls on its face. 

Its an L16 with an A87 head and a Spanish Weber dgv and a matchbox dizzy. 

180 psi compression across all 4cyl. New ngk plugs, new cap, rotor and wires too. I checked the valve adjustment and they’re at .008 and .010. Timing is at 10 btdc. Dizzy shaft feels tight. 

I pulled the carb and disassembled it looking for debris and it was pretty clean. Vacuum line from dizzy to carb is in great shape and I’ve swapped in 2 new fuel filters. 

Runs exactly the same. 

What am I missing? 



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Since you have eliminated the carb (for now*) I'll suggest a few other things that I have had happen before to me.


Fire it up after dark. It must be extremely dark (like in a garage, but take care) with the hood up. Rev it up so it backfires and look at the coil (negative terminal) all wiring, the nipples on the distributor cap along the length of the wires and as much of the porcelain on the plugs as you can see. Look for a pinkish blue discharge or obvious sparking in the dark. Any aged or damage electrical parts will allow the spark to jump out and to ground... even onto another wire and to ground.  If you have any doubts about the quality of your cap rotor plugs and wires this would be a good time to just replace them.


Inspect most closely, the underside of the cap, the coil tower and the rotor for fine lines that look like a small crack. Yes you can turn the light on for this. ? The white porcelain plugs may also have what looks like a spider web on it. This is carbon tracking and once established, it makes electrical arcing easier the next time. When you throttle up there's more air and gas in the cylinder and it takes more voltage to jump the plug gap. Electricity ALWAYS looks for the shortest and easiest path to ground. What you have to do is make only the spark plug that path buy having good electrical insulation.


* Now if this does not help we must revisit the carburetor...


Look down the carb with the engine and choke off. Pump the gas. What you should see is a strong squirt of fuel into the primary barrel from the accelerator pump. Is it or is it weak or none? There is a transition point where the idle circuit cannot supply enough gas as the engine revs and the opening of the throttle plate drops the intake vacuum and the engine is not moving near enough air to form a vacuum in the venturi to suck fuel in. The engine will go severely lean and bog, fall on it's face. A lean mixture will take so long to burn it's still alight when the intake opens and sets it off causing a backfire through the carb. This is where the accelerator pump squirts raw fuel in to help the transition from idle to primary running.  


The idle and accelerator pump may be working but the primary jet or circuit is plugged. The engine will go lean with the same results.

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33 minutes ago, Stoffregen Motorsports said:

Firing order? Most common L series mistake.


Cam timing.


Distributor phasing.




It's always 2 and 3.... 1 and 4 are the same no matter what way you assume the rotor turns. For the record 1342 counter clockwise.


A87 means the cam sprocket was off for the change. Wouldn't be off enough to backfire though just lack power if anything. A87s are an open chamber head usually and the compression will be 7.72 and even if the rare closed chamber variety, it will be in the low 8s. This is not a good combination as it is.


He says the timing is 10 which is, I think about right for an early L16. It did drop to 7 in the early '70s and for '73 cars it was up to 12. The '73 620 was 5. L20Bs were 12 and the compression was comparable just more displacement. You could try reducing to 5 and prove this is not the cause then put it back. 

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Key is was this running before or is this a diffent install. Motor head ect.....  or just a dash removal?


accel pump on carb squirting gas?


I would look at Cam timming at TDC and then dist timming and make sure the dist isnt cranked to one side.. If dist is cranked to one side  means the oil pump or dist spindal off or a matchbox dizzy install is the offset type dizzy that is soem times installed.


If points make sure the stock coil and ballast .

If a EI coil make sure its a EI coil not a point coil still installed.



ck valve lash but this is a hail mary.


if primary jet is plugged the car might run on thru the second barrel if the choke is  ON

Edited by banzai510(hainz)
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Thanks for the replies. It sounds like a timing/ignition issue to me as well and you all gave me some good ideas to look deeper at. 


Just some one more info, yes I was told it was a good runner before the dash and gas tank were pulled but I have no proof, he could have lied. 

Adjusting timing 5 degrees up or down doesn’t improve. 

The dizzy and base do not match, looks like an L20b dizzy on an l16 base with some creative notching to make it fit. 

I’m going to look closer at that and cam timing. Maybe it jumped a tooth when I first fired it up? 


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Impossible to have enough slack to jump a tooth, and the cam timing has no connection to ignition timing. If you timed it at 10 then it's fine even if the distributor is maxed out to one side. 


1342 counter clockwise wiring


Check the valve lash. A tight intake will not contain the explosive pressures inside the cylinder. It can get past the intake valve and set the air fuel off.


Check accelerator pump is working.


Will it rev up if you go slowly?



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should have looked at the tiimg side of things before ripping the carb apart.


Buty look at dist setting/timming

a L16  dsit mount, really the hole offset is so fare off the abgle its almost useless if using a L20 timmine plate that is atteached to the dist.


I would put motor in TDC. Look at the spindal see if 11.28 and install the dist in anf line up the rorot to #1 PLUG WIRE. 1 3 4 2 ccw FIRE ROTATAION.

now either you hold the dist and have soemone start the car and you gently rotate the dist adv or retard( a timming light might help). . Let it idle soit warms up abit then have the person you you hit the gas and see if it cuts out. and look at the timming plate slots pedastal and it will give you a idea how far the stolts are off.

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Ok I’m going to run down what I have checked in the order that I have done it. 


Installed dash and gas tank and new fuel filter. Ran poorly but started relatively easy. 


Next i I installed new plugs, wires, cap and rotor because old ones were mismatched and worn. Confirmed firing order.  Ran the same. 


Next i checked timing with a light, it was set to 10 btdc. So I tried 5 btdc and 15 btdc and it made almost no difference. 


Next i I cleaned out the carb and installed a new base gasket and checked vacuum line for leaks. No improvement. 


Next i checked valve lash. All were at .008 and .010 respectively. Also checked for missing lash pads because I’ve had them fall out before but all are in place. 


Next i checked compression. It read from 1-4 : 180,180,180,175 


i forgot to check cam timinh when the cover was off so im going to do that next and make sure I didn’t screw up the firing order as well... even tho I confirmed firing order it’s running like the firing order is wrong. 


Even with tring to slowly rev it up I can’t get more that a few thousand rpm. Too much misfiring. 

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Sounds like the return line on you fuel circuit might have gotten clogged in the painting process.   Now your mechanical pump is delivering too much fuel pressure for your carb.  


Does your fuel line have a return to the tank?   If the lines were pulled for paint, they may have eliminated the return as well.  You’ll need a regulator or switch to electric if your fuel pressure is from the mechanical pump direct.  

Edited by tr8er
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You cannot over pressurize if the return is plugged. When the pressure reaches what ever it's designed for it starts returning it to the inlet of the pump and around it goes. The return is almost solidly closed to begin with and the pump easily reaches maximum pressure.


Here's the restriction in the return line of the L20B. Without it fuel would just flow the easy path back to the tank. It's not designed to lower fuel pressure.



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Yes mike it’s not plumbed for a return line under the hood but the car does still have 2 hardlines  running to the tank. I used the larger of the 2 and abandoned the smaller. 


On another note that leads me to still think ignition, it has now quit running altogether. It will try to start, cough and sputter but won’t keep running. 


This is after I pulled the dizzy checked checked to make sure cam, spindle, and timing marks were all at tdc and double confirmed that firing order was correct. Fired it up again and ran like it has but then started acting worse and worse, like running out of gas. Was pretty sure it had gas but I threw in 5 more gallons and now it won’t even start. 

Hainz said to check the coil for heat and it’s cool to the touch but THEN I noticed that the matchbox was wired to the coil backwards. 

B was wired to the negative and C was wired to the positive side of the coil. 3.0 ohm coil by the way with no resistor. 


Could I have been slowly destroying the matchbox with it wired wrong???

Edited by hobbes_the_cat
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One is the fuel line the other is the vent line to the flow guide valve. Big difference. The vent line will run to the driver''s side of the car. The gas cap is sealed to keep vapors from escaping and they are directed to the crankcase for storage when the engine is off. On start up the PCV valve sucks them into the intake to be burned. If you seal off the vent line you must put a vented gas cap on.


The matchbox has a current limiting circuit to protect it. It also automatically powers down if you turn the key on (or stall with it on) and don't restart. 


B and C switched is really no matter. The spark will be backwards and jump from ground to the spark plug center electrode rather than from the electrode to ground.


The correct coil for the higher voltage matchbox output is 0.8 to 1 ohm but you need the proper matchbox coil for this, never a points coil. Order a '79 200sx coil.

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Ok. Both hard lines terminate in the fenderwell on the passenger side on this car so I don’t know which is which, I just went with the bigger of the 2. 


I still don’t think it’s fuel related though because I shot starting fluid into the carb to see if that would get it to fire but it did nothing. 


I’m going to start looking into the ignition side of things by checking for voltage at the coil and try a coil with the proper ohms. 

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After cranking the engine just look at the sight glass window on the front of the carb. Either you have gas in the carb or you don't. When running the gas should be close the the horizontal white line. Later carbs only have a small round glass with a white dot on it for the level mark.



All the matchbox does is open and close a path to ground. This allows current to flow through a coil. Points coils are about 1.5 ohms and paired with a dropping (ballast) resistor total about 3 ohms when running. During start, the ballast is by-passed allowing full voltage to the coil and producing a hotter spark for starting with. When the key returns to run the ballast is re-connected to limit this current or it would over heat the coil and certainly burn the points from arcing. A 3 ohm coil would over all have a slightly weaker spark during start but run about the same. The matchbox module has no points to arc, so higher current can be used and a full 12 volt capable coil used for a much higher output voltage. You may even find opening your plug gap to 0.038-0.042" is beneficial.

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There is not sight glass on a weber.

3 ohm coil?  hard to say on this one as a stock 510 has about 1.6 ohm coil and a 1.6 ohm ballast.  really once running a stock set up should work 3ohms.  you just dont have a as big a sparks.. cause 3.2 once Key is ON is a stock set up. the Matchbox would just be wired up as a Pertronix. starting might be harder as you have a higher ohm coil. that why a bypass was installed but had a lower ohm coil.


this is a simple proplem your just not catching it.


I never have run a return line.a stock manual pump will go limp once the carb is full.


try giving it gas once it strats to die. the accel pump on the carb should keep it runningif you see gas squirt in the carb



should get q good spark at the center of the coil wire if place near chassis(I never have done it with a Matchbox but w/Pertronix and points )


Edited by banzai510(hainz)
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Ok so I have confirmed I have fuel. Fuel pump is strong, accelerator pump is strong. 

Still no start, it’s acting like there is no spark now. Not even sputtering. 


I swapped the coil for a good one I had laying around that I pulled from a 280zx and I bench tested it first to make sure it was within spec for a factory matchbox. It’s good. 

Still nothing, not even a cough or sputter so I stuck a screwdriver into the coil lead that goes to the cap and held it about a 1/4” away from a ground and cranked the engine. No spark jumping to the ground at all. 


It it feels like the matchbox unit is/was the culprit. Can they slowly fail? I know it’s rare for them to die but it does happen. 


I think that’s the direction i’m going to pursue. Is there a way to bench test the matchbox unit? The only test I’ve seen in print involves just eliminating all other ignition components...

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