1983 carbed 454 RV vapor lock fixes ?

[Jarlaxle]

The best fix is an electric pump with return line. A Q-jet likes, IIRC, 5-8psi.

However, what will probably (85-90%) work is this, and should run you-total-less than a hundred bucks...keep the heat away from the fuel. Get a 1/4-1/2" PLASTIC carb spacer-Mr. Gasket 3406 works, or if you're a woodworker, one cut from 1/2" wood might even work better. If so, just use a carb gasket as a template. If you don't have the height clearance for this (though a motorhome should), a thick foam gasket will usually work at least almost as well.

Either buy (eBay, ~$30, search "Quadrajet heat shield)) or make (sheetmetal and tin snips, test fit and trim as needed) a carb heat shield.

Wrap all the fuel lines anywhere near engine heat with insulation-best is foam pipe insulation (Home Depot, 6' pieces are about two bucks), though heater hose works surprisingly well.

Also, make sure the cooling is up to snuff...especially the fan clutch. In fact...maybe wire the fan clutch so the fan always spins and see if it vapor locks. (If not...you need a fan clutch.)

 

[tiger862]

Call Summit racing. Brother had a Chevelle that did same thing. He is Master Mechanic so he spent tons to fix this issue with everyone telling him go EFI. He asked me and I suggested carburetor spacer about 4 inches thick and he laughed so he called Summit racing which they took his engine size as well as the carburetor size then sold him a spacer. He has since sold car for nice profit and still works on this car but never vapor locked after spacer. No electric pump on his car just mechanical one.

 

[Traction]

Using fuel with no ethanol in it should fix it, if that's what you had in it. That could cause that problem for sure in hot weather. The problem is you can't get alcohol free gas in some areas, so the best long term fix would be fuel injection, and then run any gas you want.

 

[350Rocket]

I think gaskets especially the base gasket being in good shape might affect this issue too. My 350 Olds in my Cutlass has a slightly long crank when it's really hot and sits for about 15 minutes give or take. I recently installed a return line which didn't completely solve it. It already has aluminum intake manifold (which also helps compared to a cast iron one). The gaskets are all oozing from the quadrajet, I have a kit from Cliff Ruggles to install as soon as I get a chance. I also plan to put a pressure regulator on since a lot of the mechanical fuel pumps have to much pressure.

My 83 Caprice with cast iron factory intake and no return line has minimal heat soak even after over an hour of pulling a trailer which works the 305 pretty hard.

 

[leroyd92]

I'm going to stick with my initial plan and add the splitter in front of the carb. This will be a permanent thing even if it doesn't fix things entirely.

When I cut the fuel line, I'll be adding some asphalt coated loom over the remaining steel line.

 

[leroyd92]

As crazy as it sounds, I hope to make a trip up this same grade while it's still 95-100 outside, just to test the rig and see if it is drivable when it's hot.

 

[NYEngineer]

This is the mod I made to the carb'd Pontiac before we switched it to EFI. It ran fine. If the fuel wasn't vented to the atmosphere, it could have stayed this way but his wife wasn't having it smelling up the house of gas.
The return line ran out the back of the fuel log.

 

[leroyd92]

This is the mod I made to the carb'd Pontiac before we switched it to EFI. It ran fine. If the fuel wasn't vented to the atmosphere, it could have stayed this way but his wife wasn't having it smelling up the house of gas.
The return line ran out the back of the fuel log.

That's beautiful

My friend at work is a former GM engineer. He told me to ensure the tanks are properly venting into the charcoal canister. Apparently that is a known thing with those chassis. I looked at mine yesterday when I was moving the RV and it's certainly the original one from 83... One way or another I'll make sure the tanks breathe

 

[ragtoplvr]

You do know about the tiny filter in the inlet of the quadrajet?

Other than that a vapor separator near the carb and insulated with something is a good way to go.

Rod

 

[JeffKeryk]

So last year, my 83 454 decided to crap out on me while driving in 95°f ish weather.

Thankfully we didn't reach the really steep grades yet and we were able to limp the rig back home @ 35mph.................

Carb had no fuel in it when it died. Couldn't hear the electric chaser pump pumping so it either over heated or was fully primed. Waited a few minutes and it started, made it half a mile and died again. Turned around and coasted back home.

In the near future, when it's not 117-120°f outside, I'm going to put a Carter 4070 After the dual tank switch valve

From the looks of things, my return line from the mechanical pump is kinked half way down the frame rail, that will be the first thing replaced. I bought a new mechanical pump as well. Lastly, I'm going to put the fuel pump on its own circuit to know it's getting a true solid 12v. Unless I should run a solid circuit AAANNNDDD put a ballast resistor in there???

The one thing I can't decide on is adding a fuel cooler that sits in front the radiator or add a filter with a bypass outlet right in front of the carb. I'm leaning towards the splitter because it seems most efficient to recycle the fuel than to just hope you cool it down enough. Everyone claims the vapor lock starts in the mechanical pump, so I feel cycling fuel is the best way to remedy this

Anyone have suggestions on anything? I'm open ears to things known to fix these issues.


We got the RV from family who only used it during winter months for camping. They never had vapor issues but they only used it when it was 50°f or cooler outside.

What carb? QuadraJunk? My favorite carb, by the way.
Your mechanical fuel pump with 3 ports (in, out, return) sounds exactly like the pump on my old Vette.
I know some prople in the day used a low pressure Carter electric (7 psi) near the tank, wired with a relay.
Since you have the return line, it should be pretty straightforward to install.

Of course a throttle body EFI would be a modern upgrade with improved mileage to boot, but is a ton of $$ and work.

But before I did that, I would check and fix everything you have, especially if it is stock.
Good luck.

 

[another Todd]

I have an EFI jeep that will boil the fuel in the rail on a warm day of it it is turned off hot and sits a few minutes. Luckily I can get it to run by releasing the fuel rail pressure via schrader valve. That gets it sorted out and it runs normal again

You may have a weak fuel pump. Check the pressures against spec. I have never seen a EFI system vapor lock (or boil the fuel) unless it had a weak fuel pump that supplied low pressure, or a bad regulator. You might not notice it while driving because the EFI system can adjust for lean conditions by widening the pulse width of the injectors when the pressure is low.

Now, on a carbed vehicle that is vapor locking you still need to check fuel pressure, but you can also do things such as insulate the fuel line from the pump to the carb, on motorhomes you can add a booster pump back by the tank as that is a long way for the stock pump to "suck" fuel (it is possible to vapor lock between the tank and pump, not just between the pump and carb). Also, back in the 80's era, GM came out with a retro fit panel that fit I believe on the right side frame rail to block air from exiting the engine compartment to the side rather than flowing back and exiting to the rear of the engine, this was specifically to address overheating and melting of the plug wires but ay have had an effect on fuel temp also (not sure), but make sure that panel is in place.

 

[SwampSurvivor]

Unfortunately it's a common problem. It's not a crossflow head, so the intake and exhaust manifold are right on top of each other. To meet emissions, Chrysler had to put cats on each exhaust manifold (it's an i6 with 2 manifolds). Which happen to be directly under the fuel rail.

 

[OVERKILL]

Unfortunately it's a common problem. It's not a crossflow head, so the intake and exhaust manifold are right on top of each other. To meet emissions, Chrysler had to put cats on each exhaust manifold (it's an i6 with 2 manifolds). Which happen to be directly under the fuel rail.

Ford 300 was the same way.

 

[leroyd92]

Hey guys.
So my problem was 2 things, my mechanical pump 100% failed and the electric pump someone installed way before me was only 20gph.

So I replaced the mechanical pump and it runs better then ever. Haven't road tested it but it acts like a fuel injected motor even when it sits for a month or 2.

I'm going to add a vapor filter and put an electric pump back under there before next summer.

 

[antonmnster]

Have ac? Route some copper line next to the low pressure a/c line and wrap it in insulation tape, and run the fuel through it.

 

[atikovi]

Also check and clean the fuel pressure regulator.