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Old 09-25-2021, 04:39 PM
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Default Sudden stumbling and erratic timing

I took my ‘67 out today for only the second time this year. Car ran fine and drove it for about an hour. Coming home on highway, at about 60 mph, I felt a stumble, almost like it was out of gas. I knew my gas gauge wasn’t off but I stopped to fill it up anyway. It only took about 8 gallons. Anyway, it progressively got worse from there. It would backfire, and sputter and kick. I limped it home and even in neutral giving it gas, the engine feels like it is misfiring or something. I made sure all the plug wires were attached properly. This engine has about 250 miles on it. I took a look at the timing any it looks like it is set to about 6 or 8 degrees initial. I think that’s correct. My balance has two lines on it and the top one lines up with the 6 degree mark at idle (with vacuum advance plugged). Even as I give it gas, the timing jumps around. Any suggestions?



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Old 09-25-2021, 04:54 PM
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My buddy who owns a speed shop suggested I pull distributor cap to make sure rotor wasn’t loose. It seems like it is fine.



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Old 09-25-2021, 05:03 PM
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Could it be something like a bad fuel pump or a clogged filter? Everything is brand new but i realize that’s no guarantee.


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Old 09-25-2021, 05:06 PM
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I’d post a video of it running if I could


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The frogs take up where they left off.
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Old 09-25-2021, 05:20 PM
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I’ve been doing some reading about others whose cars started running rough and vapor lock seems to pop up a lot. When I turn the car off, you can here what sounds like a hiss or boiling water. It sounds like it’s coming from carb


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Three times the sound peaks, falls back, peaks again. A throttling back to cruising speed, a dwindling grumble of thunder and...gone.
The frogs take up where they left off.
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Old 09-25-2021, 05:43 PM
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Check your point gap and condition of contacts.

Inspect the lead wire that goes from points out to coil(-) terminal.

Clay

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Old 09-25-2021, 05:48 PM
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I thought about swapping on a different carb. Just to rule that out, even though my 7028273 is completely rebuilt. When I disconnected the fuel inlet line, no fuel dribbled out whatsoever. Is that normal? I always thought you got a little bit of fuel leakage there.



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The frogs take up where they left off.
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Old 09-25-2021, 06:36 PM
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That a in-line fuel filter? They'll trap air in the top. (and that's ok).. Things heat up the first few minutes after you cut the engine off. That air expands and will shove air past the needle and seat and also push gas back through the reed valves in the fuel pump. Some pumps worse than others on what gets shoved back down.

So I wouldn't worry about no fuel taking the line off, if it sat a while after shut down. Should be a spoon full of fuel held in by the lower part of the fuel nut though.

With the backfire I'd be looking at the points and the lead wire to them.

Clay

  #9  
Old 09-25-2021, 07:38 PM
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Maybe the condenser. Maybe the fuel pump. Maybe a vacuum problem. Maybe a loose wire, or a ground wire. Something may have come loose. Also may have vapor lock. Good to have a fuel return line to help stop vapor lock problems.

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Old 09-25-2021, 10:17 PM
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Sounds like classic Pertronics symptoms - but it looks like you are running points?

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  #11  
Old 09-25-2021, 10:21 PM
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You have the wrong crankshaft hub on your engine. That is for an earlier engine. The first timing mark is 6 degrees before top dead center. The second mark is Top Dead Center. This won’t cause your problem but you should know what mark to use to set timing.
Check your point dwell and have someone crank engine and check for fuel coming to carb. Two of the easiest things to check first.

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Old 09-26-2021, 04:20 AM
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Quote:
Originally Posted by Goatracer1 View Post
You have the wrong crankshaft hub on your engine. That is for an earlier engine. The first timing mark is 6 degrees before top dead center. The second mark is Top Dead Center. This won’t cause your problem but you should know what mark to use to set timing.
Check your point dwell and have someone crank engine and check for fuel coming to carb. Two of the easiest things to check first.
Correct.
This hub is for 1964-65 with two timing marks used with a timing cover with a pointer, no scale.
Using the first mark (6° BTDC) in rotation direction to 6° on 1966-67 scale will give the engine 12° ignition advance.
6° to much lead at max engine rpm´s may cause damage to the engine, especially if the centrifugal advance stop bushing is missing (VERY common) in distributor.

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Old 09-26-2021, 12:14 PM
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Quote:
Originally Posted by "QUICK-SILVER" View Post
Check your point gap
The pic you posted in the street section looks like the point rubbing block is worn down from lack of grease. That closes the point gap and could very well be your only problem.

Check the gap
Clay

  #14  
Old 09-26-2021, 10:17 PM
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Racerboy, here's a thought... go with a Pontiac HEI distributor. I kept having problems with the points distributor in my 66 GTO and switched. I've not had one problem after switching to the HEI at all. HEI is far better than the points.

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  #15  
Old 09-27-2021, 03:41 AM
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If you can use a screwdriver and an Allen key there is no need for a HEI distributor.
Points distributors were used in the whole perfomance era, and no-one complained on the performance from Tripower, H.O. RamAir or SuperDuty engines.
Millions and millions Pontiacs actually ran quite good with points distributors.

"It is seldom the part itself that is the problem but what you do with it"
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