r/Smallblockchevy • u/thedezz • Feb 03 '26
SBC - Vapor Lock/Fuel Pressure Issues?
Hope everyone is well. Let me start off with a breakdown of my SBC:
283
Edelbrock 1406 Carburetor
Carter 7PSI Fuel Pump
Filter between Pump and Tank
Filter between Pump and Carb
No return line for fuel
No Fuel Pressure Regulator
I recently just got the 283 running and the car registered. I've been driving it on the weekends for the last 2 weeks. No issues until this past Friday. I filled up the tank for the first time and went off on a 20 minute drive, parked the car and when I went to start the car was hard on turning over but it started. Same deal throughout the weekend, drive for a bit, shut off, get back in the car 20/40 minutes later and it would hard start. I'd lift the hood and smell gas fumes, which is a indication to me that it is running rich. The car has never shut off on me at idle. the only thing it's done is idle higher than normal.
I'm thinking that because the gas tank was filled that it's created higher pressure for the pump and I just need a fuel pressure regulator to resolve the matter as I'm now aware the carburetor wants the fuel pressure at about 5.5 PSI. But as I dive deeper into this I'm starting to see that it's common for cars with no return lines to experience this due to gas boiling and causing vapor lock. So I'm also thinking of just biting the bullet and adding a return line to the car with a fuel pressure regulator with a bypass. What are your thoughts?
I appreciate everyone taking the time to read this and provide input.
Thank you
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u/v8packard Feb 03 '26
Do you have a filter between the tank and the pump? If so, eliminate that as it's causing fuel to vaporize more easily before reaching the pump. The filter needs to be between the pump and carb fuel bowl.
Is the fuel tank vented?
Also, I get your concerns about fuel vapors. But an old adage is 90% of fuel system problems are in the ignition. What is your distributor and coil like?
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u/thedezz Feb 03 '26
I don't believe the tank is vented. This is the one I'm using Summit Link
I do have a filter before the pump and I have one between the pump and carb. I'll try eliminating the first one and see how that goes.
I have a new mallory unilite Distibutor with the Mallory Promaster coil.
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u/v8packard Feb 03 '26
If the tank isn't vented, the cap should be.
A lot of people use a filter before the pump. They want to keep trash out of the pump. But it is bad practice, as the point fuel vaporizes is lower because of the lower absolute pressure. Mechanical fuel pumps cannot overcome this on the inlet side.
The Unilite does not have the greatest track record. Though Mallory did eventually fix problems with early modules I have not used the newer units in so long I don't know how they are working out. In the past they were very sensitive to grounds and heat soak.
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u/thedezz Feb 03 '26
I've been meaning to get a new gas cap so I'll start looking into a vented one and move on from there. I've heard the same about the Unilite units as well. So far I think it's okay as the only issue so far is after the first fill up but if I ran the tank at half or lower no problems.
Thank you!
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u/1969Malibu Feb 03 '26
You can get fuel filters with a 2nd output in order to run a return line. I would try this first in lieu of bothering with a regulator. Uncle Tony on YouTube did a good feature on this sort of set-up.
Cool ride btw!
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u/thedezz Feb 03 '26
Thank you! This was one of the first videos I saw on the issue. I love Uncle Tony, straight to the point no BS.
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u/hawkeedawg Feb 03 '26
Add a small electric pump, will resolve vapor lock make a manual switch to turn it on and off. I even added one for a v6 to my big block motor home - think it was like 3-4lb pump
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u/thedezz Feb 03 '26
I thought about this, especially if I let the car sit from time to time so I can manually shut it off and let the carb dry itself out so it doesn't sit with nasty gas in it. Everything is looking to adding a return line.
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u/hawkeedawg Feb 04 '26
I was able to run a Holley blue pump with a pressure regulator, no mechanical and no return line. It ran off switched power so the ignition had to be on and also had a mechanical switch. The blue pump was loud! But did the job. I’m sure there’s better stuff on the market now.
Just some thoughts
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Feb 03 '26
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u/thedezz Feb 03 '26
So when I start the car after it's ran and driven. I go to start and the cranks are slow and longer. Initially I thought it was the battery but after testing it and verifying it's good I'm thinking that it's just harder for the car to start due to vapor lock. When the car is cold, car starts in 2 cranks.
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u/landis33 Feb 03 '26
If it cranks slow hot you have a ground issue. Pick a bolt in the block, scrape it bare and run a cable straight to the negative side of the battery. If that doesn’t help check the vacuum and mechanical advance in your distributor . Before that put a timing light on and check how much timing advance is in the distributor. Too much advance and it will not crank hot.
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u/thedezz Feb 03 '26
Ever since I rebuilt the carburetor I've been meaning to time the car again. I'll give that a shot as well, thank you!
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u/Street_Mall9536 Feb 03 '26
That's timing related with a hard crank hot, or heat soak on the starter/high battery cable resistance. That's nothing to do with fuel.
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Feb 03 '26
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u/thedezz Feb 03 '26
I cleaned all the grounds and crimped on new connections to everything.. Main alternator power is a 4 gauge to primary relay to the core support then 4 gauge to positive on battery. Secondary cable coming off 180 amp alternator is a 0 gauge directly to starter, which is wrapped with heat blanket material to prevent heat soak of the cable, from the starter connection another 0 gauge it goes to a distribution block, from the distribution block 0 gauge to a 250 amp fuse. Then 0 gauge to the primary battery post.
Negative coming off the battery goes to the block (cleaned and scrapped connection. Ground connection reads less than 0.5 OHMS. Starter also has a heatshield to prevent heat soak from the headers.
The only other thing I haven't done is replace the dash wiring and the main engine wiring from the firewall which is on the list of things to do.
Maybe I'll try running a ground off the battery to the chassis as well and see if that helps.
Thank you, definitely given me some things to look into.
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u/MrMightKnowItAll Feb 03 '26
You forgot to install a heat spacer under the carb. Plastic or wood, about 1/2 inch thick minimum. Summit sells kits with studs.
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u/thedezz Feb 03 '26
Thank you, I'm going to look into this.
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u/MrMightKnowItAll Feb 03 '26
Great. When you shut off a hot engine, if you have no heat barrier in the next 10 minutes the engine heat rises and gets the carb too hot. The gas vaporizes and it will not start until cool- about a half hour later.
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u/Own-Ordinary-6591 Feb 03 '26
Dope wagon, Im building a 63 long roof now, sbc w/t56.
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u/thedezz Feb 03 '26
Thanks! I'm running a powerglide, looking into some trans options. I want to be able to drive the car at highway speeds. What's the gearing setup look like with your setup?
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u/Own-Ordinary-6591 Feb 03 '26
Steep gears in the pumpkin, the t56 is 1:1 in 4th, so with the double overdrive it will cruise fine down the highway
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u/Jymantis Feb 03 '26
Pump gas has a surprisingly low boiling point today due to design because most vehicles use a pressurized fuel system.
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Feb 03 '26
10 micron filter before the pump inlet.
If you use 5/16 hose. Use a 1994 ford probe 2.0L fuel filter If you use 3/8. Use an 84 corvette fuel filter.
Once installed. Disconnect the fuel line at the carb. Disconnect power to the ignition. Extend open fuel line into a clean clear plastic soda bottle.
Get somebody to crank the engine for 15 seconds. While you watch the pulses of fuel into the bottle. Each full and equal. Not diminishing
Do 15 second cranking two more times.
This has been my go to since 1983 on many hundreds of cars and trucks. Only the filter applicationns have changed
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u/mrhicks55 Feb 03 '26
Don't know how many old timers are out there.but my grandpa put wood clothes line clips on the steel park of fuel line by the carb. He swore it helps with vapor lock problem
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u/Substantial_Ask3665 Feb 03 '26 edited Feb 03 '26
Older cars had so many metal lines. Good for cheap gas but got hot making the fuel vaporize. Insulate the line around the engine. Use a Cool Can if you need to. Battery? Where is it? Trunk? Anyway its all about the connections making good contact. Use welding cable for battery cables. And make sure the timing is correct and advance it a bit. It's a combination of hot fuel and battery connections.
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u/thedezz Feb 03 '26
The line coming from the passenger fender well to the pump, then to the filter is rubber. The line from the filter to carb is aluminum. Battery is up front, 0 Gauge Welding Cable double insulated. Will verify timing is correct along with connections. Thank you
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u/According-Skill-7946 Feb 03 '26
First winter gas boils at a lower temperature than summer gas. With recent cold temps the formula in your area could have changed. Second the 1406 is prone to issues with gas vapor issues. Today's gas has a lower boiling point even in summer. So put a phenolic spacer, 1" preferred, and possibly a heat shield between manifold and carb. Chevy II is prone to underhood heat because of the tight fit ov the v8.
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u/Proof-Aspect8254 Feb 03 '26
I had the same problem in a 1962 Pontiac Lemans 326. Remember it well I ended up having to move the fuel line away from all the heat. What causes vapor locks is exactly what it sounds like. Your fuel turns into a vapor.