vapor lock

[USSMOPAR]

I will attempt to help with "vapor lock".
electric pump does not solve the real problem
worn pushrod? a possibility but wait - The op has not checked the underhood temperature esp where the fuel line comes up along the frame rail. Other places too like the base of the carb. How about a stuck manifold heat control valve, crappy tune up, not enough timing etc?

There has to be enough temperature {BTU's} to vaporize the liquid and there is.

So start with that newfangled device called an infra red temperature gun - sold on amazon - and start checking temps including a heat soak.

 

[Sixpactogo]

We can all speculate on the "whys, hows and what fors" of vapor lock. Myself, I really couldn't care less. I am just glad Mopar got exposed to it and found a fix for it long before we even knew it was a problem. I had never heard of it until my brother's 383 4 speed Charger started doing it. My Charger R/T never vapor locked. After a little sleuthing we found that my car had the 3/8" line with separator and return and his did not. We found a wrecked Hemi Charger in a junk yard and swapped the sender, separator and lines in his car and never had the problem again. Thank you Mopar engineers!

 

[70bigblockdodge]

There is a reason for it. Adding a unreliable, not readily available crutch to patch the problem is no good. Have to find the problem. While I would not rule out the fuel pump push rod. The premature pump fail is a indicator that it is working too hard. I believe all behind the license plate fuel filler are non vented caps to prevent fuel spillage upon acceleration. Vented caps used on higher fuel filler A body and E body, high up on quarter panel.
Non vented needs a separate vent to atmosphere. It will go "no flow" rather quickly when near full tank. Sucking air in fuel line is another way to get no fuel in filter (it's now full of air), you say sending unit good but what about lines, how old? Lastly the ignition system? These new ECU boxes are not as heat tolerant as the old big transistor ones (new ones have fake transistor on the front at heat sink) it's all inside the box with no air. Still on points? New condensers, well they just suck, period. I don't think you have a ignition problem because fuel filter is empty. I'm betting vent is clogged or wrong cap. Start with easy first
Correct cap?
Plugged vent?
Fuel line sucking air?

 

[ynst]

Fuel pump push-rods are an inexpensive remedy but check the camshaft as well while you have it apart. You can easily do that by removing the distributor and looking through the distributor hole at the fuel pump cam lobe. If it's worn (it'll have a groove in it), you're looking at a camshaft replacement as well. Been there, done that.

Most of the time, though, the push-rod is the problem but remember to lube it well when you install it.

 

[69monaco]

I made a base carb gasket myself from teflon ( about 3/8 ) and the problem was solved...........

 

[67 ragtop]

still working on it. I still am unsure of Vented or non vented cap. All of the parts books are showing a non vented cap. but every body is saying vented. I replaced all the rubber lines between the fuel tank and the fuel pump/ but it is back down in the 30,s and 40's today it is 65.
I have a pump pushrod on order. It won't hurt to replace it. I also found that the choke is sometimes sticking open or closed/ it was caused by the spring sticking in the well. I cleaned the rust off of it and lightly lubricated it. I know that you should not lubricate the linkages but it was the way I got it to free up. I found it because the car wouldn't start again cold. pulled the air cleaner to spray some starter fluid and saw that the choke was stuck wide open tapped the linkage ands it closed then the car started.
I don't totally understand it/ My 68 Ranchero with a comp 292 cam 245/245 deg at /050 and Holley 750 cfm double pumper carb and no choke with 22 deg initial timing will start in sub zero weather with no problems. 2 pumps then foot to the floor feather the throttle after it pops.

 

[67 ragtop]

There is a reason for it. Adding a unreliable, not readily available crutch to patch the problem is no good. Have to find the problem. While I would not rule out the fuel pump push rod. The premature pump fail is a indicator that it is working too hard. I believe all behind the license plate fuel filler are non vented caps to prevent fuel spillage upon acceleration. Vented caps used on higher fuel filler A body and E body, high up on quarter panel.
Non vented needs a separate vent to atmosphere. It will go "no flow" rather quickly when near full tank. Sucking air in fuel line is another way to get no fuel in filter (it's now full of air), you say sending unit good but what about lines, how old? Lastly the ignition system? These new ECU boxes are not as heat tolerant as the old big transistor ones (new ones have fake transistor on the front at heat sink) it's all inside the box with no air. Still on points? New condensers, well they just suck, period. I don't think you have a ignition problem because fuel filter is empty. I'm betting vent is clogged or wrong cap. Start with easy first
Correct cap?
Plugged vent?
Fuel line sucking air?

I have a Pertronix replacement for the points and by-passed the ballast resistor per Pertronix requiring full 12v as I could not find a decent set of points. The tank has 2 vent lines to it which I have blown out with compressed air. I also blew air through the fuel line. I may try closing off the line at the tank and pulling a vacuum on i to see if it will hold. I have found an issue with the choke sticking either fully open or fully closed sometimes. It is the spring in the choke well. I had to clean the rust off of it . Above the manifold it looked perfect

 

[67 ragtop]

I will attempt to help with "vapor lock".
electric pump does not solve the real problem
worn pushrod? a possibility but wait - The op has not checked the underhood temperature esp where the fuel line comes up along the frame rail. Other places too like the base of the carb. How about a stuck manifold heat control valve, crappy tune up, not enough timing etc?

There has to be enough temperature {BTU's} to vaporize the liquid and there is.

So start with that newfangled device called an infra red temperature gun - sold on amazon - and start checking temps including a heat soak.

I hjave an infrared temp gun I haven't used it yet on this. I use it on my trailer bearings when towing my boat or RV. I will check it when it happens again. I will check the timing again I set it at the factory setting but will double check it. The manifold heat control valve is wired open and will not move any way. I am trying to loosen it up to make sure it is not wired closed LOL.
This is the first 1960's car I have had that still had stock exhaust manifolds. Even my 60 Falcon and 64 Valiant that I had in the 60's and early 70's had headers. This is the first play car I have had that I didn't soup up. My wife wouldn't let me play with the family cars after I souped up my 71 dodge Colt in 72 with headers 11/2 inch turbo thrush exhaust system and different advance curve. That one GOT ME A TICKET FOR DOING IN EXCESS OF 110mph IN A 55 MPH zone the day the national speed limit dropped to 55 mph.

 

[Scoopy G]

I think if the fuel pump push rod is significantly worn, you would hear a knocking sound, as I did with my '65 NYer. I could hear the knocking from 30 feet away, I thought it was a rod knock.

So, I located an electronic pump under the passenger floor, where the steel line connects to rubber. That solved the knocking sound problem. Now the NYer runs fine, except in hot stop-and-go traffic (Tampa!).

My '67 Newport was having a significant problem re-starting on warm days (Tampa!), so I followed Cbarge's suggestion of fabricating a 1/2" plywood spacer between the carb and the manifold, and VOILA! the re-starting issue is solved. Thank you Cbarge as usual. Now I gotta make a plywood spacer for the NYer and the C-bodies will be good-to-go.

Did anyone mention.........don't use gas with ethanol in it? That stuff boils easily and contributes to the vapor lock problem.

 

[detmatt]

I think if the fuel pump push rod is significantly worn, you would hear a knocking sound, as I did with my '65 NYer. I could hear the knocking from 30 feet away, I thought it was a rod knock.

So, I located an electronic pump under the passenger floor, where the steel line connects to rubber. That solved the knocking sound problem. Now the NYer runs fine, except in hot stop-and-go traffic (Tampa!).

My '67 Newport was having a significant problem re-starting on warm days (Tampa!), so I followed Cbarge's suggestion of fabricating a 1/2" plywood spacer between the carb and the manifold, and VOILA! the re-starting issue is solved. Thank you Cbarge as usual. Now I gotta make a plywood spacer for the NYer and the C-bodies will be good-to-go.

Did anyone mention.........don't use gas with ethanol in it? That stuff boils easily and contributes to the vapor lock problem.

Wait a minute…what exactly did you do to stop the knocking??
And what kind of plywood??

 

[Big_John]

I think if the fuel pump push rod is significantly worn, you would hear a knocking sound, as I did with my '65 NYer. I could hear the knocking from 30 feet away, I thought it was a rod knock.

So, I located an electronic pump under the passenger floor, where the steel line connects to rubber. That solved the knocking sound problem. Now the NYer runs fine, except in hot stop-and-go traffic (Tampa!).

My '67 Newport was having a significant problem re-starting on warm days (Tampa!), so I followed Cbarge's suggestion of fabricating a 1/2" plywood spacer between the carb and the manifold, and VOILA! the re-starting issue is solved. Thank you Cbarge as usual. Now I gotta make a plywood spacer for the NYer and the C-bodies will be good-to-go.

Did anyone mention.........don't use gas with ethanol in it? That stuff boils easily and contributes to the vapor lock problem.

While I'm not saying it doesn't happen, this is the first I've ever heard of a worn fuel pump push rod making a knocking sound in a Mopar. I have heard many times about worn fuel pumps making a knocking noise, and since you've added an electric pump, you've made the mechanical pump so it isn't making pressure, so no noise. If it was a pump push rod, I'm about 99% sure you'd still hear the noise.

That said, wouldn't it have been a lot easier to change the push rod and/or pump? I mean it's a couple bolts and fittings...

One thing I don't like about a lot of electric fuel pump installations is a lot of guys don't install some sort of low oil pressure or "crash" switch. If you crash, that pump could be happily pumping gas while you are upside down or trapped in the car. Even just if the car is idling, and it stalls... It's still pumping gas... By under the passenger floor, I hope that it's forward of the firewall and not the lowest hanging thing on the car.

I'm sorry, I don't mean to pick on you about this... But fire is fire and it's not at all forgiving.

 

[Boydsdodge]

What I have found on a couple of push rod fails was that there was a noise like a knock that had me thinking the new engine had a rod knock starting. Then the fuel pressure went away. Relieved I swapped in a new push rod that only lasted a couple of months with lots of summer road trips. Like wiping a cam lobe and lifter, I don't think I would do a new push rod once wiped. I have run an electric pump in my wagon below tank level on frame rail.

 

[Big_John]

What I have found on a couple of push rod fails was that there was a noise like a knock that had me thinking the new engine had a rod knock starting. Then the fuel pressure went away. Relieved I swapped in a new push rod that only lasted a couple of months with lots of summer road trips. Like wiping a cam lobe and lifter, I don't think I would do a new push rod once wiped. I have run an electric pump in my wagon below tank level on frame rail.

This is only the second time I've heard of being able to hear a knock from the pushrod, first being in this thread, although I'll admit if makes some sense.

IMHO, swapping the pump push rod isn't quite the same as a lifter.

You have a lot less spring pressure on the pump compared to the valve springs.

The replacement pushrods seem to be of varying quality, meaning some aren't hardened as well as others, so a failure of a replacement pushrod seems to happen more often than it should. There does seem to be better quality pushrods out there.

If you think about it, how many of us have even given a thought about replacing that pushrod when we put in a new cam? A lot of guys here have swapped the pushrod without any problems too.