low voltage at coil...

[Stupid_fast]

Hello everyone, my L20b has been running okay for a while, tuning the carb has gotten rid of most of the issues.

 

The car is a 72 510 wagon m/t harness, L20b is rebuild, new carb(32/36), new dizzy(napa reman), new cap/rotor/plugs/wires, fuel pump, fresh fuel filter(less than 100 miles) ect. Has about 3,000 miles on it since I got it running. Plugs have been replaced since then, and I've got a new set waiting to go in.

I've got a 60 amper internally regulated alt, other than that most is stock.

 

 

It still runs rough, but pretty strong and decent power through the midrange(3-4k's) seems to drop off after 5k's and not get much power... ? also got a carb pop/backfire at 6k...(un-burnt gas maybe??) I decided to check over the ignition system, and found the coil + is only getting about 8v with the key to ON, and 6.5v with the car running. Isnt it suppose to get 12v??

Its a pertronix ignitor, with pertronix flamethrower coil. Bosche plug wires, NGK iridium premium(if it matters...).

 

 

I have noticed some weird wiring done by a P/O, and I have to dig in and search through it but I wanted to get some more ideas of what could cause this low voltage.

 

Battery is getting 12.76v(off) and ~14.5v while running. Most of the other wiring is good, most things seem to be working fine. (fan, lights, radio, wipers, ect...)

 

Thanks.

[banzai510(hainz)]

remove the 12volt wire(blk /wht) to the +coil.

Then put key to ON and ck for the 12volts If not 12volts then you have resisitancee in the wires or fuse box.Or just a high resisitve connection.

 

if you get 12volts then wiring is OK and maybe the coil is loading the system down

Or there is another draw on the system with key on.from soemthing else.

 

Do you have a ballast resistor in there or not?

If yes then 6.5v would be close to normal.

But I will ASSUME you have the 3 ohm Flamethrower and the blk/wht wire is at the + coil

[Stupid_fast]

remove the 12volt wire(blk /wht) to the +coil.

Then put key to ON and ck for the 12volts If not 12volts then you have resisitancee in the wires or fuse box.Or just a high resisitve connection.

 

if you get 12volts then wiring is OK and maybe the coil is loading the system down

Or there is another draw on the system with key on.from soemthing else.

 

Do you have a ballast resistor in there or not?

If yes then 6.5v would be close to normal.

But I will ASSUME you have the 3 ohm Flamethrower and the blk/wht wire is at the + coil

 

Last night before I posted I removed all the wires to test them indavidually, the blk/wht was getting low voltage on its own.

 

 

Yeah, no balast. blk/wht, blk/blu, and pertronix red are connected to coil +. I do have the choke and idle cut jumped off the coil also, I removed those and only saw a 0.5v increase in voltage. Didn't run any better with them removed.

I'm pretty sure I found some shitty too high gauge wire in the ignition circuit(blk/wht wire next to fuse block is going in to the tach through some higher gauge wire???), I just printed out a nice wiring diagram and am gonna go check it out.

 

I'm gonna go take a look at it in a minute, see what I can find. I'll post back with more info if I don't find the problem.

 

Thanks!

[banzai510(hainz)]

If your not getting the 12volts from the blk white wire (coil not hooked up) then there is your proplem.

Now if you have other stuff hooked up to to this power source(blk/wht) I would also start disconnection them. As you say you had a Tach ,choke,idle cut off selinoid hooked up also.

 

soemthing is loading down the circut.

reconnect the plug by the key switch maybe a high resistance connection there. Could be the key switch but I havent seen this my self.

 

 

have you ck the other fuses and make sure it isnt low valtage across all the fuse circut? Then maybe there is a high resisitwance by the starter lug or fusable link. If its low volatge across all. But im thinking highly unlikely but just ck.

[Stupid_fast]

If your not getting the 12volts from the blk white wire (coil not hooked up) then there is your proplem.

Now if you have other stuff hooked up to to this power source(blk/wht) I would also start disconnection them. As you say you had a Tach ,choke,idle cut off selinoid hooked up also.

 

soemthing is loading down the circut.

reconnect the plug by the key switch maybe a high resistance connection there. Could be the key switch but I havent seen this my self.

 

 

have you ck the other fuses and make sure it isnt low valtage across all the fuse circut? Then maybe there is a high resisitwance by the starter lug or fusable link. If its low volatge across all. But im thinking highly unlikely but just ck.

 

Thanks.. I found it! There where two high gauge wires from the blk/wht after the fuse block going to the tach... I hooked up the blk/wht wire bypassing that and it now gets about 12v on its own, and about 11v on + side of coil with everything plugged in.

Idle cut/choke take like 0.5v, pertronix takes a little also. There is a 3-pin connector next to the wiper motor one, has 11.4v on one of the pins when ign ON, can I tap off this to get power for the choke/idle cut without effecting anything else?

 

 

Now how do I properly wire up the tach? it does have to be inline with the blk/wht? If so I'll get some new same-gauge wire and hook that up correctly.

 

 

Now its running better, idle has smoothed out. Have not driven it yet, just ran it in my garage(with door open, exhaust facing out!!) I tuned the idle as best I could and its almost smooth at 800rpm(can go lower... but rough, spark plugs need replacement already, I have new ones to go in soon.).

 

There is still a lingering problem, If I revv it, hold it at around 2,000 rpms then drop it suddenly, it will die. When I throttle hard say idle to 25% to 0% it will respond fine, revv right up drop back to idle. This is the same problem I had before, it seems worse after fixing the ignition and tuning the idle? I've been messing with the timing too, it likes around 25 deg to run the smoothest, stalling does not seem to be effected much anywhere from 10-25deg advance. Just spent like 20 minutes fittling with things while it was running to get it better but with no luck.

Before fixing the ignition i had nearly gotten it do go away, tuning the float timing ... It rarely did it anymore, but now it seems to be as bad as it first was?

 

Thanks.

 

 

[banzai510(hainz)]

Idle cut/choke take like 0.5v, pertronix takes a little also. There is a 3-pin connector next to the wiper motor one, has 11.4v on one of the pins when ign ON, can I tap off this to get power for the choke/idle cut without effecting anything else?

 

I think the 72 510 had a eleltric choke carb and there is a wire for this you could splice from near the wiper motor.

Now if you have a Internal reg alternator I think it will drain the battery. So Be honest I would wing it myself if you know its 12volts. Or try unplugging the choke relay and if that wire still has 12volt with Key on then maybe its good.

 

Tach I never hooked up one. Will assume one goes to 12volts ON as like the BLK/WHT wire one goes to ground then the trigger will be - side coil. I dont run one on any of my rigs. Never needed it.

 

I would adjust the dizzy timming and mixture. ck the idle cut off if plugged with dirst or working properly.

CARB CLEANER!!!!!!!

 

Ck the speed screw on carb, Now if you have this crank all the way in there is a proplem

Also hate to find out you got a HUGE door spring used as a return spring on the carb and its just slamming it shut!

 

intake carb tight ?

[Stupid_fast]

Idle cut/choke take like 0.5v, pertronix takes a little also. There is a 3-pin connector next to the wiper motor one, has 11.4v on one of the pins when ign ON, can I tap off this to get power for the choke/idle cut without effecting anything else?

 

I think the 72 510 had a eleltric choke carb and there is a wire for this you could splice from near the wiper motor.

Now if you have a Internal reg alternator I think it will drain the battery. So Be honest I would wing it myself if you know its 12volts. Or try unplugging the choke relay and if that wire still has 12volt with Key on then maybe its good.

 

Tach I never hooked up one. Will assume one goes to 12volts ON as like the BLK/WHT wire one goes to ground then the trigger will be - side coil. I dont run one on any of my rigs. Never needed it.

 

I would adjust the dizzy timming and mixture. ck the idle cut off if plugged with dirst or working properly.

CARB CLEANER!!!!!!!

 

Ck the speed screw on carb, Now if you have this crank all the way in there is a proplem

Also hate to find out you got a HUGE door spring used as a return spring on the carb and its just slamming it shut!

 

intake carb tight ?

 

Yeah I disabled the choke relay, I'll take a look at the circuit again and find a good place to pull power from.

 

Tach is inline with the black/white ... one side goes into tach, other side comes out and goes to coil +... I like tachometers, as I don't want to exceed redline as I'm eventually wanting to autocross it.

 

Timing mixture is like 1-1/4 turns out, tuned and retuned, idle speed screw is barely touching also, in maybe 1/2 - 3/4 turn ... 800rpm

 

I will check the idle cut again, make sure its nice and clean.

 

Timing set to 12 deg is OK, but runs better at like 25 deg.. not much change on the stalling.

 

There is only the stock 32/36 return spring, the only other ones are on the pedal itself, otherwise the throttle will never close fully...

 

Throttle does not slap shut, the springs on the pedal apply very little pressure on the throttle, all my testing was done opening the throttle on the carb itself, not pushing the pedal down.

 

 

 

Gonna get back out messing around with it... thanks.

[banzai510(hainz)]

all sounds good what you just said.

 

 

I believe in most cases thereis a blu air condioner wire under the fuse box one can use for a 12v switchble circut.Its just rolled up under the fuse box. But dont break the fuse box if a stuck screw!!!!!!!

 

But like I said ealier maybe you could use the other wire.

 

 

other basics is ck valve lash, tighen intake/carb loosness of distributor. ect....

 

maybe you got just worn out stuff. I dont know what else to ck.

[Stupid_fast]

all sounds good what you just said.

 

 

I believe in most cases thereis a blu air condioner wire under the fuse box one can use for a 12v switchble circut.Its just rolled up under the fuse box. But dont break the fuse box if a stuck screw!!!!!!!

 

But like I said ealier maybe you could use the other wire.

 

 

other basics is ck valve lash, tighen intake/carb loosness of distributor. ect....

 

maybe you got just worn out stuff. I dont know what else to ck.

 

The blue air cond wire I'm using for the cig lighter/DC jack... I wired it up nice so I can run a power inverter through there if I wanted!!

 

Yeah, the 3 pin connector next to the wiper motor will work fine for the idle cut/choke... seems OK with a test wire on there.

 

 

I found the problem!! It was my error, I screwed in the idle cutoff too far... blocking idle flow. I loosened it a bit, and now the car runs great!! I broke the O-ring though... gonna get a new one at the store.

 

Thanks for the help.

[banzai510(hainz)]

So does it now run perfect? timming good at 12btdc???????

[Stupid_fast]

So does it now run perfect? timming good at 12btdc???????

 

Yeah it runs GOOD now, not perfect. Stall issue is still there but barely noticeable and rarely does it now, still boggs/hesitates also in certain situations if I come on the throttle suddenly, not bad. Definitely runs more smooth, sounds nicer, and more power now that there is full 12v going to the coil.

 

I set timing to 12, runs good. Idle still a bit rough, 800rpm its smoother than it was before though. Improvement is always nice! I'll replace the plugs next time the car is cooled down and check valve lash again.

 

Thanks for the help.