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Topic: 71 no sparky spark

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71 no sparky spark (1/4)
 5/21/20 12:47pm
71 Sting
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Harrodsburg, KY - USA

Vette(s):
1971 Red


Joined: 5/21/2020
Posts: 2

Hello all -

 

I have a 71 that I started running last summer for the first time in over a year of sitting (pretty much). While driving it last summer I noticed it started to stutter (like it was losing fuel or spark). It eventually got bad to where it left me stranded while trying to limp it home.

When it got home I found that it would start idle rough for a moment then die. If I supplied it with fuel externally (I used carb cleaner as I was also checking for vacuum leaks) that it would pick up RPM and run happy for a moment. I deduced it was a fuel issue so I rebuilt the carb, ran the vehicle in the driveway using an external fuel tank and it ran great. I then went and connected it to the fuel tank (replaced all fuel filters) and it had the same issue. I looked into the tank and could see rust, goo, and what appeared to be a liner that had turned into a film and chinks all through the tank. I parked the vehicle as I was busy with other things so I could handle it this summer/fall and start doing a restoration (with an engine upgrade).

As luck would have it my other vehicle was stolen causing me to get the 'vette running before my budget was full enough for the upgrades  I had planned. I went out yesterday and replaced the fuel tank (better job if you have two people I found the hard way) rebuilt the carb again and thought I would be on my merry way. Unfortunately now that I have fuel in abundance I have no spark.

I decided to replace the plugs, wires, points, condensers (both dist and ign), and coil (about everything I could think that would be affecting my spark). I have to admit that points were a thing of the past before my dad even met my mom and all prior vehicle experience has been on HEI systems. That being said the ol' Google's got me the info needed for setting the gap. All installed - still no spark.

 

I measured across the coil and I have 4-6 volts. I have two wires and the condenser on the + and then the wire running to the points from the -. If I unhook all of this from the coil I get 12 volts from the wires to the + to the alt ground. I'm going to go pull 12 v from the battery to the + of the coil and see if it will start. I also was looking through these forums and found one with a 76 that was doing something similar (only he had HEI) and the issue was the tach cable. I have a mechanical tach, but I am going to figure out which wire is the actual 12 v and the one that isn't I am going to leave of and try again.

Other than that I am out of ideas, and could use assistance from you all.

 

Thanks in advance.

 

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Re: 71 no sparky spark (2/4)
 5/21/20 9:21pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19733

Welcome to C3VR !

You should expect to see 6-8 volts on the coil + with the key on, engine off. The coil gets a full 12v(or battery voltage) ONLY while cranking the engine to start. This full battery voltage comes from the "R" wire(outside small terminal) at the starter solenoid. Once the key is released from the "Start" position, the voltage is reduced thru a resistor wire from the ignition switch. Th voltage is reduced to keep from melting the points while the engine is running, but it requires full battery voltage to get it started. I would suggest you jumper 12v to the "+" terminal on the coil temporarily to see if the engine will then start. If it does start, then remove the 12v jumper to protect the points. At that point(no pun intended), you would need to see why you are not getting voltage up from the starter solenoid to the coil while cranking. Might just be a loose/corroded wire, or similar easy fix.

hth



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Joel Adams
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Re: 71 no sparky spark (3/4)
 6/8/20 4:24pm
71 Sting
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Harrodsburg, KY - USA

Vette(s):
1971 Red


Joined: 5/21/2020
Posts: 2

Thanks for the reply. I checked the voltage on the wire from starter to coil +. Read 10 v to ground during cranking. 

I ended up replacing the points and the engine fired right up. Let it idle for awhile then turned it off to swap back to original carb (had taken the Quadra jet from my boat to test with known good). Put on the original carb and the thing wouldn’t start. I had an Edelbrock 1906 I had just purchased along with a new Edelbrock intake so I put those one. 

Once that was done the system wouldn't start. After trying everything I could think of I replaced the points again. Sure enough it fired right up. I was able to tune the carb and take it for some test runs without issue.  

I am currently on my 4th set of points and don’t understand why they are failing. I’m not leaving the key on with the engine off so that shouldn’t be the issue. It has gone from starting right away to needing some gas pedal prompting but still starts. 

Saturday I ran it around town some without an issue, then took it in the freeway and after about 20 minutes it started “hesitating”. This got progressively worse and upon hard acceleration it would sound like it was missing and had no power. As long at I kept it below 2200 rpm and didn’t accelerate quickly there was no problem. I was able to get it home and in the driveway out of gear it revs great and sounds great. It just seems to happen under load. 

I’m not sure if they are related, I am scratching my head and need some assistance from more experienced minds than mine. Thanks in advance for the help. 



|UPDATED|6/8/2020 1:24:40 PM (AZT)|/UPDATED|
Re: 71 no sparky spark (4/4)
 6/8/20 10:01pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19733

If you have more than 6-8 volts on the points while it's running, it will fry them fairly quick. This is why there is a resistor wire from the ignition switch to lower the operating voltage once started. You should have 2 wires on the + side of the coil...one from the ign switch, and the one from the starter. The resistor wire is usually covered in a fabric/cloth-like cover. It's possible someone back in the day ran a new, solid wire to the coil for whatever reason. You can buy ceramic type resistors to use, if your original wire has been removed/modified. Chrysler used a solid resistor in their ignition systems for years.



|UPDATED|6/8/2020 7:01:38 PM (AZT)|/UPDATED|


______________
Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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