Need advice on how to correctly manage vapor lock
- Thread starter Rentalman
- Start date
That's why 'modern' FI systems have MAF vs. CTS decay to either increase timing and/or pull fuel on startup with other temperature related enrichment strategies. The ethanol of pump gas recently with the plagued war of the world and all of its greed, has halted the federal volatility standards of ethanol in fuel to prevent shortages. In some cases up to 15%. Higher pressure of liquids will raise the vapor formation (vapor lock), at 6 psi and hot, fuel can easily boil - especially when you shut off an engine after operating. Temperatures often go above 240 within minutes. All fuel will be vaporized in the carb rather quickly or bleed out due to the increased pressure relating to the float valve. The vapor will always over-power the liquid pulling force of the mechanical pump. Modern injection system see 50-70psi at around 200lph and are way less prone to vapor locking, but it still happens. Of course proper venting of the tank is needed for everything to work correctly, you need a PURGED air source from the engine with a check valve like I have already mentioned. In conclusion, your carburetor is not designed to work with modern fuels and you are either forced to compromise or go FI.
Rentalman
Active member
Hi Winchested, thanks for reaching out. Prior to the end of July, how I would typically start my Scout is I would pull the choke out, press the gas pedal quickly once, turn the key and it would fire. Then I would push the manual choke in half way or so for a smooth idle. Every time since the summer time heat arrived ( I live in the I.E. of Riverside County, temps have been 100 to 108 daily) when I would try to start it this way it would flood every time. To get it started I'd have to floor the gas pedal everytime to clear the fuel circuit out and it would start. I've also tried starting it choke in, no gas pedal added, turn key. It will fire for a moment ( firing on the vapor or liquid gas in the manifold from the garage heat. My garage is 103 deg and so is the Scout) Then die. I would turn key again, engine would crank but not start. Once again I have to floor the pedal to clear the circuit she fires, then I pull the choke out halfway to keep it running and push it in as it warms up. I took out for a 18 mile drive in light work traffic Friday. The trip was 49 min long. The carb never stumbled, runs great, I was even stuck at a light for 6 cycles. Coolant temp rised but went down after a miles drive. When I shut off the engine after a drive for 5-10 minutes, when I go to restart it, I press the gas pedal down slightly just to open the butterfly, no gas added, no choke, she fires. If I go to restart it say 8 hours later after a drive, all that I do is turn the key and it starts. But now when it sits in the 100 deg garage for 3 days or longer it gives me attitude. Finally I thought I had this carb figured out on how it liked to be started. I'm open to any suggestions.
Scoutboy74
Moderator
You'll probably just have to fiddle fart and babysit it each startup until the oppressive heat subsides. Once cooler ambient temps return, you'll likely be able to revert to your previous tried and true methods.
Rentalman
Active member
Hi Zaed, thanks for the reply. I did follow your instructions and finalized the hook up of my charcoal canister. The liquid/vapor separator is hooked up to all the correct fuel tank vents. There's a 5/16" line that runs from the separator to the fuel tank port on the canister. I've got a 1/4" line with a Holley size 50 jet coming out of the purge line on the canister ( 1" from the canister) going to manifold vacuum. I also have a sealed gas cap. My system is sealed.
Not being a mechanic, you don't know what you don't know. I did not plan on the fuel issue with the Ethanol. But I sure am learning.