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Post by class115 on Jun 3, 2018 19:45:41 GMT -5
Tom, Thank you for your patience, I recorded the voltages and just before I posted them I decided to try a new switch - but only because I had the luxury of having a new one around and NOT because I know what I'm doing. I guess I had the voltage to crank it and the backfires happened when the voltage when the key was in START. I didn't put two and two together.
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Tom
CO-ADMINISTRATOR
Itching to get back to posting!
Posts: 737
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Post by Tom on Jun 3, 2018 21:41:13 GMT -5
Glad you got it figured out.
Reaching back 20+ years to my days at vo-tech.....
I believe the voltage at coil should be battery voltage when cranking (some voltage drop should be expected)
Voltage at coil in run position should be lower as ballast resistor is part of that circuit. How much lower, I don't remember...but I'd guess around 9.5-10 volts.
So, I think your cranking voltage was a bit low...but probably good enough for ignition to work. The run voltage being zero (16-20mv is as good as zero) was the big problem.
How did things look at the steering column/ ignition switch plug? Anything burnt?
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Post by class115 on Jun 5, 2018 19:38:23 GMT -5
Nothing burnt, continuity of the wires checks out. Must be internal to the switch. I guess that's why they sell replacements
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Post by brigond on Jun 6, 2018 0:28:25 GMT -5
Glad you figured it out also. You changed out that switch quick. I did mine last year and it was alot of work. At least to me it was.
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Post by class115 on Jun 10, 2018 21:18:33 GMT -5
Glad you figured it out also. You changed out that switch quick. I did mine last year and it was alot of work. At least to me it was. About 6 hours, but only because as the weeks went on, I made a mental checklist of the entire ignition system and figured the switch may need to be changed. So I read up on how to do it, prepped everything and had all the parts waiting. I was convinced it wasn't going to work, but I thought I would be asked about it sooner or later, so I wanted to be able to say I ruled out the switch
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setauketjeff
Settling In
1971 440 MGM Every stoplight is a staging light!
Posts: 230
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Post by setauketjeff on Jun 14, 2018 15:02:05 GMT -5
While everyone is on vacation this weekend, ha, I'll try to get you started. When there is a backfire my thinking is a valve is open when the plug fires. Not the only reason possible but it's a start. Whenever you're trying to diagnose a problem look at the basics first. You need fuel/air mixture, compression and spark for an engine to work. You've done well basically do a tune up and checking to see if the timing is close. I would do two things next. Perform a compression test and check to see how much slop is in the timing chain by putting the engine at TDC, remove the dist cap and move the crank back and forth looking to see how many degrees you can move it before the rotor starts moving. If I remember right you should only have 6-8 degrees of movement. My car had 13-15* of movement before I replaced the timing chain. It didn't help solve my problem as I had a wiped out cam. Good luck. Gives a couple of things to look at until others chime in. Thank you for helping me. I ran out and got a compression tester and now I among the proud few who can get a tester up and over the power steering housing and down into the #3 spark plug hole on a big-block in a B-body My compression test results are cyl 1=150 psi cyl 2=155 psi cyl 3=135 psi cyl 4=140 psi cyl 5=140 psi cyl 6= 140psi cyl 7= 130psi cyl 8= 140psi 73% humidity& 73 deg F I did not try to start it Cam is a Comp Cams 280H P/N 21-237-4 with about a thousand miles on it, and plenty of zinc (Gibbs High Zinc oil). Stock heads, stock intake, and exhaust manifolds. going to check for the reluctor gap and crankshaft-to-rotor slop right now I did not try to start it afterward Thanks, again Vic Real men don't have power steering, nor power breaks ; ). Might be a bit better to prime the carb with a little gas in the primaries than to use your starter to crank the fuel pump. When I used to race my old 1971 SE back in high school and college, I had an electric fuel pump back at the gas tank outlet. Turned the switch on and waited for the pump to turn off. Two pumps of the pedal and the car started right up. Hid the switch too, so if the car was stolen it would make it a block or two before stalling out. New York City thief prevention. Once my college roommate went out to my car to get his cigs, thought that he was doing me a favor by moving the car from two blocks away to right in front of the bar. Right in the middle of the K turn, the car died across the two lane road. He came running into the bar in a total frenzy. I was laughing my a$$ off!
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Post by 71se3834v on Jun 15, 2018 6:36:48 GMT -5
I'm always dumbfounded when l see on the car shows them cranking away to get the fuel pulled up from the tank. Here's what I've been doing for years. I have an empty 80w/90 quart bottle with a rubber hose stuck on the nozzle. Then a small vinyl hose runs out of the rubber hose and is small enough to stick in the vent of the carb. Easy peezy fill up the carb bowl! The engine WILL start right away with fuel in the bowl! 😀
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DynoDave
CO-ADMINISTRATOR
Motown Mopar-Wizard
Posts: 11,148
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Post by DynoDave on Jun 15, 2018 8:37:51 GMT -5
I'm always dumbfounded when l see on the car shows them cranking away to get the fuel pulled up from the tank. Here's what I've been doing for years. I have an empty 80w/90 quart bottle with a rubber hose stuck on the nozzle. Then a small vinyl hose runs out of the rubber hose and is small enough to stick in the vent of the carb. Easy peezy fill up the carb bowl! The engine WILL start right away with fuel in the bowl! 😀 Totally agree. That, or an electric booster pump will fill those bowls right away.
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Bob
Settling In
Posts: 193
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Post by Bob on Jun 15, 2018 14:06:27 GMT -5
I'm always dumbfounded when l see on the car shows them cranking away to get the fuel pulled up from the tank. Here's what I've been doing for years. I have an empty 80w/90 quart bottle with a rubber hose stuck on the nozzle. Then a small vinyl hose runs out of the rubber hose and is small enough to stick in the vent of the carb. Easy peezy fill up the carb bowl! The engine WILL start right away with fuel in the bowl! 😀 Totally agree. That, or an electric booster pump will fill those bowls right away. Electric fuel pump fixed mine.
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Post by goldrush on Jun 15, 2018 17:54:54 GMT -5
+1
That's an old farm boy trick from WAY BACK !! Glad to hear I'm not the only one...
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