Misfire and backfire when hot

OK some more things I tried tonight.
Added one ounce of ATF fluid to about 1/3 tank of fuel, put the old dist cap and rotor back on and ran it with out the gas gap.
Pretty much the same results. opening the GAV more than one turn does help a bit as usual.
Now Jackson111 has a good idea. putting a second condenser on the coil in parallel to the one in the dist.
That gets it away from the heat. I like it. will try it tomorrow.
Thanks,
Al
 
For giggles verify that the gav knob is turning the shaft, some knobs in the past would just spin around the shaft.
 
So did it help..................

Now Jackson111 has a good idea. putting a second condenser on the coil in parallel to the one in the dist.
That gets it away from the heat. I like it. will try it tomorrow.
Thanks,
Al
 
Hi Guys,
Update - Just now tried Jackson's trick with a second condenser hanging off the coil with a pigtail to ground and it did seam to help a bit. The engine had to get a little over the halfway mark on the motometer before it started missing and backfiring. Improvement !
Still It responded well to opening the GAV about a full turn.
The next thing I'll try is to use Ethanol Free fuel. It could be boiling on the carburetor bowl.
Thanks for all your suggestions - I'll let you know what happens.
Al
 
Jim/GA said:
I suspect bad ignition condenser. They are often heat sensitive when bad.

I know you replaced it once.

Original pop-out style ignition switch? If so, try bypassing it temporarily, just to see how it runs. They can sometimes make a poor connection internally and get hot inside, which then gives even less volts to the coil (weak spark).
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Jim, What is the tests for bypassing the popout?
 
here we are. .. hot wire to by-pass pop out ( and junction box if you so wish)... it's best to disconnect the exisiting pop out wires in case there's a short circuit in them
 

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Another step in the right direction - To explain, Just before this all happened the temp was about 1/8 inch showing on the motometer. Then for no reason it began to run about 1/3 the way up the motometer.
So today I took it out and the same, 1/3 the way up.
I filled up with E-Free fuel, (.71 more per gallon) it took 9.34 gallons.
To my amazement the engine temperature went down to about 3/16 up on the motometer.
I wonder if the fuel formulation here in south FL change in the Spring?
So no more backfiring. There is still some missing but it's very quiet.
I had changed to a new set of 3X plugs just before this happened. So next i'll put the old plugs back in and take a ride - lets see what happens.
Johnbuckley - I like that hot wire test circuit you sent. I printed it out - thanks.
Al
 
OK - We got it now.
Changed the new 3X plugs for the old Autolite 3076 plugs with 18,000 miles on them and it runs great. No missing, no popping, just smooth! Well smooth for an "A".
Thank you all for your suggestions.
Al
 
What did you last work on just before it started acting up? I know it has gotten worse but just wondering if some of the history might be a tip off for what direction to look. I had a new condenser from NAPA go bad in just a hundred miles so it could be something new that is screwing up.
 
Next time it acts up, toss about a bottle of water on the carb bowl. That would cool it off. Can’t hurt anything.
 
Al 29Tudor said:
OK - We got it now.
Changed the new 3X plugs for the old Autolite 3076 plugs with 18,000 miles on them and it runs great. No missing, no popping, just smooth! Well smooth for an "A".
Thank you all for your suggestions.
Al
Click to expand...

My A doesn't like to run with 3X plugs either and crap gas! Glad you figured it out, take a nice long ride!
 
Johnbuckley - I like that hot wire test circuit you sent. I printed it out - thanks.
Click to expand...

It wouldn't hurt to put an "on-off" switch in the wire between the coil and the starter switch.
 
Al 29Tudor said:
just sprayed propane around all vacuum connections and no change.
Idle adjust screw is working.
Still searching.
Thanks
Click to expand...
I think that it may be vapor locking. If it backfires, it shows a lack of fuel. Get a 1/4” rubber fuel line and split it down one side and put it over the existing fuel line. The condenser is a good idea to change since the new ones go bad often but opening the Gac would have no change if it was the condenser.
 
Big Hammer - how odd some cars don't like 3X and ethanol fuel. I still wonder if the fuel is more that 10% and it boiles at a lower temperature.
 
All this for plugs..made the assumption you threw a set in along time ago,porcelain insulators do fail. Press assembled plugs like the autolite were designed for a reason, the insulator is protected from expansion.Insulators secured by a nut like the 3X are vulnerable, the insulator nut can loosen over heat cycles,allowing the porcelain to expand beyond limit.
 
Al 29Tudor said:
OK - We got it now.
Changed the new 3X plugs for the old Autolite 3076 plugs with 18,000 miles on them and it runs great. No missing, no popping, just smooth! Well smooth for an "A".
Thank you all for your suggestions.
Al
Click to expand...


Am happy you found the issue. As this string illustrates, for such simple systems as the A has, there are almost endless possibilities for this type of issue. Easy to miss something basic. I leaned quite a few things including Jack Shaft's plug design info.
 
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