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71 Cutlass Sport 350, Runs BAD when warm

Old March 10th, 2019, 01:40 PM
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71 Cutlass Sport 350, Runs BAD when warm

I've been driving this car for 4 years now with no major problems. Now, when the car heats up it starts bogging down bad bad . Takes 20-25 minutes then it will act up and runs like junk.

The following has since been replaced and same problem persists. New edelbrock carb , new coil , new plugs and wires, new cap & rotor . New fuel filter.

I got even compression of 120 Psi across all 8 cylinders , did compression test at operating temp once it starts running really bad.

Running a volt meter over the coil + and - I get 5 volts. Running I get 4 volt , holding the volt meter and having a buddy rev it , drops down to about 3.5-3.7 volts.

With the coil + unhooked , key forward I get 11.9 - 12 volts .

I thought I was only supposed to get 9v with key forward from ballast resistor to + wire . The second wire is supposed to run to the "R" terminal on starter. It seems both wires go down to the starter area, after doing research I was under the impression one wire went to "R" on starter, the other went to the bulk head / ballast .
The 12 volt + wire from "R" is only supposed to feed the coil full power during cranking , then letting off the key it switches back to the resistor wire .

Could the points and condenser be burning up at operating temps ??

All the spark plugs look a dry even burn , maybe a little white but all even .

I'm totally stumped but I know there has got to be a way to figure this out !!!!! Any help greatly appreciated .
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Old March 10th, 2019, 01:59 PM
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Did you throw all those new parts at it to correct the problem? Did you replace the points and condenser? Have you checked your dwell and timing?
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Old March 10th, 2019, 02:29 PM
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Yes I changed all those parts to try and fix the problem. No I havn't changed the points and condenser. It seems there is one condenser in the distributor and also another one on the coil itself going to the + coil... is that a RF cap ??
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Old March 10th, 2019, 02:34 PM
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^^^x2^^^ on what the (other) Eric asked.

In addition, when you say it bogs down and runs like junk - you have the full range of the English language to describe what junk refers to.

Does the vehicle start immediately upon hitting the IGN SW?
Does the vehicle run correctly when at idle after first starting the vehicle?
Does the vehicle run correctly at idle - ever? Even after it starts to bog down and run like junk, does it idle correctly? Or, is this ONLY during the period when driving the vehicle?
Are you running a choke on this vehicle? If so, is it an electric choke or manual choke?
Have you examined all of your vacuum hoses for leaks? Have you tested the vacuum?
Does it appear to bog down and run like junk when under a 'load', as opposed to cruising when not under load?
Does the vehicle hesitate under acceleration?
After you've run the vehicle & turned it OFF - does the engine stop immediately or have any tendency to diesel (continue to run) when shutting down?
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Old March 10th, 2019, 02:54 PM
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Yes it start immediately and runs amazing . idles perfect, full power , will burnout through second gear, really runs perfect .
vehicle has electric choke with switched 12v
I have examined all vacuum hoses , vacuum is at -21 cold and warm.
The vehicle takes 40 minutes to start running bad. It has low end break up and sounds like its running on 6 cylinders when the demon raises his head .
Once it starts bogging / stumbling it will do it all the time but mainly with a load , if you wait long enough it will even stumble all over in park .

The vehicle does not diesel and shuts right down when turning off the key .
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Old March 10th, 2019, 03:01 PM
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Originally Posted by 71sport View Post
... runs amazing . idles perfect, full power , will burnout through second gear, really runs perfect .
If the above were true, why are you asking for help?

No sense in embellishing how your car runs when it 'runs', let's stick with diagnosing an engine which runs like 'junk' - your above statement doesn't add any help,

How can it idle perfect if you said "it will even stumble all over in park"? We're trying to assist you.
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Old March 10th, 2019, 03:02 PM
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When was the last time you cleaned all the gunk out of your gas tank or replaced the bag filter in there?
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Old March 10th, 2019, 03:03 PM
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It runs perfect as described UNTIL reached full operating temp ,then runs like I said.
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Old March 10th, 2019, 03:04 PM
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Originally Posted by Vintage Chief View Post
If the above were true, why are you asking for help?

No sense in embellishing how your car runs when it 'runs', let's stick with diagnosing an engine which runs like 'junk' - your above statement doesn't add any help,

How can it idle perfect if you said "it will even stumble all over in park"? We're trying to assist you.
I don't think you read my posts correctly .
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Old March 10th, 2019, 03:05 PM
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Kind of agree w/ Bsiegpaint - up to this point - without knowing how your points and condenser look. You might even be experiencing a vapor lock in your fuel system.
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Old March 10th, 2019, 03:10 PM
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I had a very similar event with my old '68, which is why I ask about the gas tank. About the time you get the car warmed up, that's when there's been enough time and suction to pull up rust and debris from the bottom of the tank and fully clog your gas filter - keeping the car from getting enough gas no matter what gear it's in. Go for the simple stuff first.
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Old March 10th, 2019, 03:14 PM
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When you changed your fuel filter, did you notice any deposits and/or heavy discoloration of the filter filament? Curious if you change out the filter again, what you might encounter. They're certainly inexpensive enough and easy enough to swap out in a jiffy.
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Old March 10th, 2019, 03:16 PM
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thanks for the suggestions. I have a clear fuel filter by the carb , the gas looks very clean in this car and is clear. The filter is full at the carb.

I have never dropped the tank or checked the bag filter inside.
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Old March 10th, 2019, 03:18 PM
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The condenser on the coil is strictly RF.
Yes the wire from the starter R terminals is the resistance bypass but the voltage you may see cranking may read lower because of the starter load. The reason you may be seeing a lower voltage on the coil when running is your meter is not fast enough to catch the switching when the points open and close.
Inspect your points, make sure they are good
Run a jumper to the coil+ from the battery to eliminate a low power issue.
When it starts acting up look down into the carb and see if fuel is dribbling big drops.
If there is, check float and fuel pressure.
Cap all vacuum ports at the carb and intake manifold including the power booster to see if the issue goes away. Connect them 1 by 1 and see if the issue comes back when you connect a line.
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Old March 10th, 2019, 03:21 PM
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As a follow-up.

Engine starts fine when cold, car runs well - for 40 minutes; then, car bogs down, runs rough - so rough, to the point if you stop and place in Park, the engine is stumbling. Correct?
This continues to occur until you park the car for the evening or after several hours?
Whereupon, the next day (or after an extended period of time). You restart the car and the engine runs fine - but again, after 40 minutes it begins all over again. Sound about right?
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Old March 10th, 2019, 03:31 PM
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Originally Posted by Vintage Chief View Post
As a follow-up.

Engine starts fine when cold, car runs well - for 40 minutes; then, car bogs down, runs rough - so rough, to the point if you stop and place in Park, the engine is stumbling. Correct?
This continues to occur until you park the car for the evening or after several hours?
Whereupon, the next day (or after an extended period of time). You restart the car and the engine runs fine - but again, after 40 minutes it begins all over again. Sound about right?
Yes
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Old March 10th, 2019, 04:03 PM
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When these conditions occur & you open your engine hood, does your engine bay smell any more heavily of fuel vapors than normal (when the condition does not occur)?
Have you experienced any coolant loss or boil overs from the engine recently?
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Old March 10th, 2019, 04:07 PM
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yes it does smell like more fuel vapor.

coolant loss or boil overs, no not that im aware of .
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Old March 10th, 2019, 04:26 PM
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Originally Posted by 71sport View Post
Running a volt meter over the coil + and - I get 5 volts. Running I get 4 volt , holding the volt meter and having a buddy rev it , drops down to about 3.5-3.7 volts.

With the coil + unhooked , key forward I get 11.9 - 12 volts .

I thought I was only supposed to get 9v with key forward from ballast resistor to + wire .
Have you tried adjusting the timing when it is running like "junk"? Is there a setting where it runs better?

Don't the '71s have a thermo-switch that controls the vacuum to the distributor? If that is kicking in when the engine begins to run like "junk", this may indicate that the timing is off. Check to be sure the dwell stays the same when it is cold / good and hot / bad.

Recommendation: Make sure the points are clean and adjusted properly to 30 deg dwell, Then make sure the vacuum control plumbing to the distributor is correct. Then dial in the timing.

Last edited by JohnnyBs68S; March 10th, 2019 at 04:33 PM.
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Old March 10th, 2019, 04:37 PM
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vacuum goes right to source, no switch in between .

I have not checked the timing , will need to do so .

Last edited by 71sport; March 10th, 2019 at 04:49 PM.
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Old March 10th, 2019, 04:50 PM
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Probably the fastest check & least expensive check is to pull the distributor cap, remove the points, examine the points for excessive where, pitting, burnt spots, etc. It doesn't take too long for an engine which may be running a little too advanced to overheat a set of points and cause premature deterioration of the points and possible fouling of the condenser (if it's been a long time since you changed the condenser). When was the last time you checked the points and/or changed the points. I know you said you did a new coil , new plugs and wires, new cap & rotor. Did you say the car sat over winter, also? Condensation on points doesn't take long for them to wear thin and get burnt.

I'd certainly check the dwell & timing. Any chance you're running a little too advanced? Asking since you said your plugs are a tad on the white side which would indicate you're running lean. If you were running rich you'd expect to see a minimum of 'some' carbon on the electrodes; and, a normal tone/color (as you know) would be a sandstone grayish color w/ white leaning towards a lean state.

I don't know, I'm a huge fan of making certain dwell & timing are spot-on. Yet, if the dwell & timing were way off, you wouldn't be running great for 40 minutes and then go to the crapper.

Points and condenser can overheat as they age; and, they do get much hotter as the vehicle travels from a cold idle state to a hot running state - about the fastest & cheapest thing to do now would probably be points/condenser check.

From the above, it sounds like you have no TVS/DCVS switch (or it's -out of the loop - I removed mine completely).
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Old March 10th, 2019, 04:58 PM
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With regards to a more heavy fuel odor than normal when you open the hood during this condition (coupled with the possibility the plugs show running towards a white color - lean state), you may have a fuel leak, or air is entering the fuel system somewhere and you're not pumping enough fuel into the carburetor. The return fuel line, vent, cracked/worn/chafed hoses can be suspect. I once had a similar condition (but I never really checked the plugs or replaced a bunch of stuff, etc.) when my fuel economy went South, there 'began' (but I fixed it before it got worse) more of a fuel odor in the engine bay. I traced the fuel lines and found a couple rotted fuel lines which were not only producing the smallest of leaks, but the converse is also true - those small cracks allow air into the system starving the carburetor from getting the optimal amount of fuel.
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Old March 10th, 2019, 06:10 PM
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I wpuld do a fuel pressure check while under different throttle conditions. check in when cold and then when running bad. may be fuel pump,pick up filter sock in tank.
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Old March 10th, 2019, 06:23 PM
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Check the ignition coil resistance cold, then check it again hot (when itís running bad). I donít remember what the specs of the coil are suppose to be, maybe you have a coil breaking down under heat? Pretty sure you will need to disconnect the coil wiring for a accurate test.

Next time it starts to run bad, remove the gas cap. Maybe the vent is plugged, preventing the pump from pumping fuel the way it should.

If the fuel filter or tank was full of crap, Iíd expect the car to run like crap pretty much all the time. The fuel filter wonít be plugged up, then clean itself up, just to get plugged up again.

I would inspect the points and condenser, replace if questionable. Make sure the dwell is set correctly, changing the dwell will affect ignition timing. Hopefully that helps, good luck.
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Old March 12th, 2019, 11:39 AM
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Originally Posted by matt69olds View Post
Check the ignition coil resistance cold, then check it again hot (when itís running bad). I donít remember what the specs of the coil are suppose to be, maybe you have a coil breaking down under heat? Pretty sure you will need to disconnect the coil wiring for a accurate test.

Next time it starts to run bad, remove the gas cap. Maybe the vent is plugged, preventing the pump from pumping fuel the way it should.

If the fuel filter or tank was full of crap, Iíd expect the car to run like crap pretty much all the time. The fuel filter wonít be plugged up, then clean itself up, just to get plugged up again.

I would inspect the points and condenser, replace if questionable. Make sure the dwell is set correctly, changing the dwell will affect ignition timing. Hopefully that helps, good luck.
I would also be checking the coil and points if it were my car! Electrical things can act up once they get hot.
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Old March 12th, 2019, 11:49 AM
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I had a similar problem, and it was the coil.

When it got hot, it performed poorly.

I would try a known good (or new) coil.
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Old March 12th, 2019, 02:12 PM
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See Post #1:
The following has since been replaced and same problem persists. New edelbrock carb , new coil , new plugs and wires, new cap & rotor . New fuel filter.

Last edited by Vintage Chief; March 12th, 2019 at 02:29 PM.
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Old March 12th, 2019, 03:07 PM
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New coils (and other electrical components) can be bad out of the box. Esp modern Chinesium.

My money is on the coil or its wiring.
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Old March 12th, 2019, 03:19 PM
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There isn't anything necessarily inherently wrong with Chinese products. Manufacturers purchase the cheapest crap from both the Chinese and the United States manufacturing companies. All mobile devices (telephone, laptop, tablet) & computers contain >90% components made in Southeast Asia - Malaysia, Indonesia, Taiwan & China.
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