1977 Newport with a vapor lock and/or boiling fuel in carb problem

[Pclancy]

Hi Guys:

It's Peter and his Canadian Newport once again. More questions:

My lean burn system was acting up. So I had my expert mechanic delete the lean burn. See earlier threads where you guys suggested how to do that.

In making the conversion we elected to keep the original TQ carb. The engine is a 400.

After a few adjustments to the carb, we got the engine running well at all speeds.

Now after use in hot weather, the engine won't start if you let it sit for a bit. It starts if you start it again after use right away, but if you wait more than a few moments, it won't start for many hours. Then it starts right away.

Note that the engine runs well in city/highway conditions. Has never stalled. The problem is only after you shut it down after use.

So I suspect this issue is vapor lock, or boiling fuel in the carb, or both.

I guess my question is this: Should I attempt to fix the carb (it's the original lean burn carb) (possible issues include the float level, exhaust heat riser valve, gaskets, flanges etc) or should I find a pre-lean burn TQ (72-74?) and install that? Or an E-brock carb?

What's the best solution here? I attempt to use the Newport as a DD and don't want to get stranded.

Thanks,

Peter

Thanks to everyone for all the responses. I learned a lot. The problem turned out to be ignition related---a slightly corroded wire running between the coil and the ignition. So sometimes the wire would work and sometimes not. We replaced the wire and she fires up every time, in all temperatures. On to the next issue!

 

[WorkerBee]

Good to hear......and I'm glad you kept the T-Q in the initial conversion.

 

[Big_John]

90% of all carb problems are electrical.

 

[polara66hardtop]

My 77' 400 cordoba did the same thing, and I watched a You tube on rebuilding the carb. There are two little rubber O-rings at the bottom of the lower base that allows fuel to bypass the normal operation when the go bad. I Installed a new kit Including the o-rings, and it runs like a million bucks. I found the help line from a guy on FABO. If I can locate the site on my computer, I will be happy to forward it. The Cordoba went from 9 to 13.5 MPG in town after the repair as well.Granted, my lean burn is gone, and I have dual exhaust as well.

 

[Carmine]

This is why you should never, never, never try to solve a problem with a mass parts-swap. Imagine if you had dumped a few hundred bucks into a carb, spacers, fuel line re-routes, etc. You'd still be chasing the issue. Or more likely put the car for sale in disgust!

 

[commando1]

90% of all carb problems are electrical.

 

[Pclancy]

This is why you should never, never, never try to solve a problem with a mass parts-swap. Imagine if you had dumped a few hundred bucks into a carb, spacers, fuel line re-routes, etc. You'd still be chasing the issue. Or more likely put the car for sale in disgust!

Wise words. I tend to jump to a conclusion (vapor lock, for example) before I have correctly diagnosed the problem. That would have led me to buy all kinds of stuff I didn't need, and end up frustrated..and broke! Fixing the wire cost almost nothing.

 

[Polara-Star]

This may sound stupid, but i'm gonna say it anyway... Big-blocks have a valley-pan gasket, and subsequently an airspace between the cam galley and the bottom of the intake. This caused, in the late 60s and early 70s, the common problem of vapor-lock, particularly in police models, which led to the simple 'fix' of a little asbestos 'pillow' installed between the bottom of the manifold and the valley pan. When normal high-mileage repairs are done, sometimes these wee 'pillows' get lost, misplaced, etc. Then the original problem resurfaces... And vapor lock on that scale would disable a car for 'hours', as the original post states. It was a low-budget 'fix' for a major problem, but it worked

 

[Carmine]

Man, nobody is gonna wanna hear this.

The air gap intake design actually keeps the intake (and carb) cooler. That's why Edelbrock offers a full line of them. The "pillows" were not asbestos, they are fiberglass. Their function was to deaden engine noise (amplified by the taught metal "speaker cone", aka intake valley pan gasket).

 

[Polara-Star]

Man, nobody is gonna wanna hear this.

The air gap intake design actually keeps the intake (and carb) cooler. That's why Edelbrock offers a full line of them. The "pillows" were not asbestos, they are fiberglass. Their function was to deaden engine noise (amplified by the taught metal "speaker cone", aka intake valley pan gasket).

i have to respectfully disagree with this. The so-called 'timpani' effect is a theory that evolved in the 80s; my statement is based on what i was told by dealership mechanics in the 70s, as well as actual state police who drove the cars, and wound up stranded for large periods of time. The amount of material on the underside of the hood could deaden a Grand Funk Railroad concert; Now, i may have been mistaken on the material used to make the blocks, but there is a reason the dimensions very closely matched the dimensions of the baseplate of the carb, and were placed directly under it. The intake design actually amplifies the heat, something Chrysler learned the hard way, because there was no way to actually evacuate the heat generated between the valley and the bottom of the intake.

 

[Carmine]

Many cars came without hood pads. Hell they used a nylon t-chain gear for sound purposes and we know that was a piece of crap, lol.

They've been around since the early 60s and most racers ditch them. There are actually two pads and they cover most of the valley pan.

 

[70bigblockdodge]

Different gear but is that what that foam pad is for on a 2004 5.7 Hemi that goes between the intake and lifter valley?

 

[commando1]

The insulation tween the intake manifold and the valley pan was for SOUND suppression. Do your research. Look it up.

Edit: I wrote this before I saw Carmine's reply. Carmine shows the illustration I was referring to when I said, Look it up.

 

[Big_John]

The insulation tween the intake manifold and the valley pan was for SOUND suppression. Do your research. Look it up.

That is correct. It was a wad of fiberglass insulation in a foil pouch.

The real heat comes from the exhaust crossover that flows through the bottom of the manifold.

It all works great until the heat valve fails on the exhaust manifold, and sticks in the closed position, all the exhaust from one side of the engine is sent across the crossover and out the opposite side manifold.

With the modern gas, a lot of people, myself included, think it's pretty prudent to block that crossover. That might cause some delay in the choke pulling off, but that's easily fixed.

 

[Carmine]

That is correct. It was a wad of fiberglass insulation in a foil pouch.

The real heat comes from the exhaust crossover that flows through the bottom of the manifold.

It all works great until the heat valve fails on the exhaust manifold, and sticks in the closed position, all the exhaust from one side of the engine is sent across the crossover and out the opposite side manifold.

With the modern gas, a lot of people, myself included, think it's pretty prudent to block that crossover. That might cause some delay in the choke pulling off, but that's easily fixed.

This.

 

[commando1]

Many cars came without hood pads. Hell they used a nylon t-chain gear for sound purposes and we know that was a piece of crap, lol.

They've been around since the early 60s and most racers ditch them. There are actually two pads and they cover most of the valley pan.

"Tappet chamber silencer".
Exactly the words I was looking for.

 

[polara66hardtop]

The pad was Indeed for noise suppression, but the crossover problem caused an additional problem. I consider the problem a design defect, as The excessive heat buildup in the Intake fries the exhaust valve on the #6 Passenger side, on 383 two barrel engines. Typically they lasted maybe 35-40K miles before a valve job was in order. Back in the day My 66' needed it at 32K, and again at 70k. I presently have a 66' 383 with 24,000 actual miles, and it needs a Valve job right now. Back then I was advised to get a dual exhaust system, or get used to doing valve jobs.