Carb issue?? Ignition issue? Bad gas??

[Scoopy G]

Greetings from Tampa. My 67 Newport Custom with 383 and 2bbl Stromberg started shuttering way back in February. This car has been rock-solid since I re-commissioned her in 2019. A smooth runner with no issues whatsoever until February.

I thought it was a vacuum leak, but none could be found. Eventually I did a tune -up on the car, as it had been 5 years and probably 5 or 6 thousand miles. Points, plugs, condenser. Wires were good. but no dice, the car just wasn't running smoothly.

SO, we farted with the carb, rebuilt it, checked the fuel pressure, checked the timing etc., and still the damn thing didn't like to start or idle.

THEN, I just went ahead and got a remanufactured WWC from Rock Auto and bolted that carb on. The 383 still wasn't happy. Hard starting, barely would idle except if my foot was halfway into the pedal.

TODAY we played around some more, and finally got the car to run and idle at about 750rpm (500 is the spec in the book). I took it out for the first time since Feb, and got some non-ethanol gas in it, then took it out on the freeway and blew it out as best I could. In kicked down perfectly and took off like a shot. BUT, if I'm idling at a stop light in gear, it lopes like it has some kind of racing cam.

It seems I've been through everything. The car idles in neutral just perfectly, smooth as can be. When I put it in gear, it lopes. When I press the gas, it hesitates then takes off just fine.

Any help would be appreciated; this is a most vexing problem! Thanks from Tampa!

 

[CBODY67]

I strongly suspect you got a load of "splash blended" gas (the vast majority of gas is final-blended that way, between the terminal and the station, in the tanker sloshing around) that had a too-large dose of ethanol in it. With the new E0 gas, you diluted that.

Back in the 1980s, I was out driving and needed some gas. I was familiar with the private brand and had used their products many times, so I filled the tank with some super unleaded. The farther I drove, the harder it was to keep the car running at idle. When I got home, after an hour or so of freeway driving, the car did not want to idle in gear, so I manually throttled it to keep it from dying. It took longer to start and the exhaust had a different, more hollow sound to it. Flaky gas! So I "drove it out", put new name brand gas in it, and all was well again. It took the second refill that got things completely back to normal. This was BEFORE the times of ethanol'd gas, too!

Just my experiences,
CBODY67

 

[Scoopy G]

Thanks 67. Yes this problem has been a mystery for the last 6 months, but today I feel we (my car buddies and me) made some progress. The car ran great down the freeway at 70, then was fussy at the stoplights and at re-start. Still, it attracted it's share of Florida-man goofballs accosting me at the gas pump today.

Imagine Captain Jack Sparrow with a walker, crossing the parking lot as you are pumping the gas to tell you his uncle had one of these Galaxies. I'm not making this **** up!

 

[halifaxhops]

By chance did you check the dwell with a meter? Can fluctuate at idle if the cam lobe on the distributor is worn.

 

[Grannys67]

... I had a similar issue, replaced the fuel pump and it fixed it,
-I don't have a fuel pressure gauge, but I assume it was the diaphragm was ate up from the ethanol or something, it would run at speed but had enough of a leak so that it wouldn't supply at idle consistently.

 

[MoPar~Man]

Have you done a compression test?

Have you set the idle mixture screws with a vacuum gage hooked up?

What do the plugs look? Clean / white or black / sooty / oily?

Timing chain issue?

What octane gas do you use? What oil do you use? Is it a thick oil, like 20w50?

Is there a heat riser valve in your exhaust manifold, and is it working or stuck?

General question for anyone to answer: How are these original pre-unleaded engines handling unleaded gas?

 

[Scoopy G]

Thanks everyone for the suggestions.

*Dwell is consistent.

*Mixture screws set by my buddy's ear.

*Plugs are new.

*I use mostly 93 octane non-ethanol, but occasionally end up with regular gas.

*There is a heat riser, and it used to work. When I'd shut the car off, a few minutes later the valve would cool and creak shut. I got a kick out of hearing that . It hasn't done that for a long while now, and I can't move the valve by hand. The exhaust does flow from that pipe though.
How can I tell visually if the valve is stuck shut?

 

[Kuz]

What does a vacuum gauge read at idle?

 

[Just Carbs]

What is the vacuum advance doing?

 

[Scoopy G]

Thanks Kuz and Carbs. I'll throw the vacuum gauge on the thing this afternoon. Where would I hook the gauge into? Carbs, the advance seems to be working fine, the power curve was very smooth yesterday, no pinging.

 

[Kuz]

You should have a vacuum fitting coming off the base of the carb. It may be getting used by your distributor vacuum advance. What model Stromberg?

 

[darth_linux]

You should have a vacuum fitting coming off the base of the carb. It may be getting used by your distributor vacuum advance. What model Stromberg?

He mentioned a reman'd WWC from Rock Auto.

 

[darth_linux]

Could the brake booster have a vacuum leak that you don't notice until the engine is under load at idle?

 

[Scoopy G]

Not noticing any issue with the booster, that is no noise/hiss and braking is good. Thanks.

 

[Big_John]

TODAY we played around some more, and finally got the car to run and idle at about 750rpm (500 is the spec in the book). I took it out for the first time since Feb, and got some non-ethanol gas in it, then took it out on the freeway and blew it out as best I could. In kicked down perfectly and took off like a shot. BUT, if I'm idling at a stop light in gear, it lopes like it has some kind of racing cam.

It seems I've been through everything. The car idles in neutral just perfectly, smooth as can be. When I put it in gear, it lopes. When I press the gas, it hesitates then takes off just fine.

Am I reading this correctly that the gas in the car is at least from February (or older) and when you added some fresh gas to the old, the car ran better? How much was in it when you added the new gas?

I'm just thinking the gas is probably old and bad and you've improved it a bit with new, but it still has some old gas.

Possibly siphon off the gas and put more fresh gas in. Add the old stuff to your daily driver a couple gallons at a time to get rid of it.

 

[WissaMan]

Check the voltage at the coil. I'm not sure what the spec is (I think around 8v) but if it's too low you'll get misfires, which could indicate a bad ballast resistor or a poor/corroded connection somewhere.

A surefire way to test it, if it's running bad/missing is to run a (+) wire from the battery and touch the (+) on the coil, giving it full system voltage. If the misfire is caused by low voltage, when you touch the wire to the coil it should start running smoothly. Just don't leave the wire there as full system voltage will overheat the coil.

I just had to figure this out on my New Yorker where a previous owner had removed the lean burn but hooked the new ballast resistor in series with the original ballast resistor, instead of bypassing it. The coil was only getting between 5.5 - 6.5 volts and it was missing badly, fouling plugs, etc. It would get worse as it ran as the resistors heated up, thus increasing their resistance.

 

[Scoopy G]

The issue began in February with rough running. I tuned the car up but the problem persisted. I then rebuilt the carb (power valve was damaged), but that only helped a little bit. got a reman carb from Rock Auto, and installed that. Somewhat better. I will go out into the shop this evening and check the vacuum gauge, and I'll look at the voltage to the coil.

The gas situation in February was fine, fresh gas at that time. since Feb I've been busy building a room addition, so I've had limited time to mess with the Newport. I did throw 5 gallons of fresh gas during the carb rebuild sessions, and yesterday I put about 10 gallons of the non-ethanol stuff in, plus a big can of Berryman's.

 

[Scoopy G]

UPDATE THURSDAY 6:30. I hooked up the vacuum gauge. The car reluctantly started, but when it got warmed up, it seemed to idle OK. AT IDLE in park, the gauge indicated ZERO inches of vacuum. As I throttle it up to say 1500-2000rpm, the thing is pulling steady around 15". Higher throttle get me up to 20", again steady needle. Once again I did the vacuum leak test of spraying carb cleaner around possible leaky areas, and nothing was found.

COIL: with the car at idle, the voltage at the + side of the coil reads around 15-16VDC. What do you make of this? It's weird.

 

[Kuz]

Sound like you plugged your vacuum gauge into a ported vacuum source and not a manifold vacuum source. Ported vacuum works as you described, there's little-to-none at idle, and the vacuum begins to rise as soon as you open the throttle. Manifold vacuum on the other hand will be highest at idle, and drop off as you increase the throttle. You'll need to find a manifold vacuum source to get any useful readings from a vacuum gauge at idle. Ported vacuum sources are generally located above the throttle plates, whereas manifold vacuum sources are located below the throttle plates.

If you can't find one on the carb, you should have a fitting at the rear of the intake manifold with rubber hoses or caps on it, you can remove a cap/hose and plug in there.

Where is your vacuum advance plugged into, ported or manifold? Just Carbs mentioned your vacuum advance in post 9, check to see if the diaphragm in the advance unit is good.



15-16 volts at the coil is high, they normally like 8-9 while running, and 12-13 volts (battery voltage) when starting only. Once you release the key from start to run, the voltage should drop off as it now runs through the ballast resistor.

 

[MoPar~Man]

You don't measure engine vacuum using the tube going to the distributor vacuum advance diaphram. The vacuum in that line is ordinarily zero at idle, it only kicks in later during higher rpm operation when you're driving around.

Most carbs will have other ports that will be capped that will give a good / correct manifold vacuum reading. If you can't find one, then look at your brake booster - if there's a nipple port on it for a small hose (it could be for some interior vacuum operated gizmo) then pull off the small hose and attach your gauge to the port. Be careful, it's going to be a plastic fitting, don't break it. Or - follow the big line from the booster to where it connects to the intake manifold. Sometimes there's a small steel nipple coming off that port.

A really good vacuum at idle (idle being 600 rpm if you can manage that) is 20 inches if you're at sea level. If you're at a higher elevation, drop 1 inch for every 1000 ft. A really good vacuum is 20, an acceptible vacuum reading is 18. Your distributor timing setting will play a huge role in this. Set your idle timing to be 10 degrees BTDC. Make sure your timing marks are clean and readable. Next will be the idle screws mixture setting. Normally you start by screwing them in all the way (not hard! don't tighten them with force!) and then back them out 1.5 full turns. Then when the engine is warm, at idle, back them out another 1/2 turn and see if that improves engine vac reading. If you turn these, and the vacuum goes up and the rpm goes up, then that's the right direction.

Can you do a compression test? It's not hard, gauge isin't too expensive, but there's a process for it. Take out all plugs, put a screw driver down the carb to keep the throttle open, disconnect a wire going to the coil (doesn't matter which wire, could be the - or + wire at the post). Put a battery charger on the battery either for a few hours before the test or keep it on during the test. You'll be cranking the engine a lot and don't want the battery to sag by the time you get to the last cylinder. Crank the engine so you see the needle jump 3 times. Maybe 4 times, but that's all. Write down what the reading was for the 3'rd and 4'th jump for each cylinder. Screw in the adapter line into each cylinder, but just hand-tight (don't use a wrench). You'll need a buddy to crank over the starter while you hold / watch the guage. If engine is warm when you start this, that will give maybe a more useful reading vs a cold engine.