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What causes vapor lock and how do you fix it. will a fuel pump help?

Common cause of vapor lock is fuel line routed too close to the hot parts of the engine, normally around the cylinder head. You don’t give us much help in diagnosing your problem, like engine numbers or pictures of the fuel line. If you provide more info we may be able to solve your problem without an electric fuel pump, which may get expensive.

Will take a picture of fuel line later

Make sure you post all engine numbers when you post back.

I have also had a couple craftsman riders with the Briggs V twins that had exhaust pipe heat shields that directed the exhaust heat up to the carb and would boil the fuel in the carb after running for about an hour.

ILENGINE said:

I have also had a couple craftsman riders with the Briggs V twins that had exhaust pipe heat shields that directed the exhaust heat up to the carb and would boil the fuel in the carb after running for about an hour.

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how did you solve the problem

raven2955 said:

how did you solve the problem

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The muffler heat shield has two bolts that bolt the shield and the muffler to the frame. There is two fingers that extend over the exhaust pipes from the heads. the issue was the section in the middle came more or less straight up in front of the carb. I bent that section to were it would sit below and somewhat behind the carb. Basically isolating the carb from the exhaust.

ILENGINE said:

The muffler heat shield has two bolts that bolt the shield and the muffler to the frame. There is two fingers that extend over the exhaust pipes from the heads. the issue was the section in the middle came more or less straight up in front of the carb. I bent that section to were it would sit below and somewhat behind the carb. Basically isolating the carb from the exhaust.

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will look to see if I have same configuration

raven2955 said:

What causes vapor lock and how do you fix it. will a fuel pump help?

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Vapor lock is a real problem with many types of vehicles and power equipment today because of the alcohol in the fuel. Pure gas boils at a considerably higher temperature than gasohol (E10), by about 20 degrees or more. Oxygenated fuel ( gasohol) also causes a host of corrosion related issues in fuel tanks and carburetors, AND it ruins fuel system diaphragms in as little as one season of use. I have found one station in my area that sells pure gasoline at about $.50 a gallon more than regular E10. Do a google search for "pure gas" to locate a station in your area. I have ZERO fuel related issues in any of my power equipment or old cars.

I frequently have to repair mowers and power tools for my customers due to use of gasohol, particularly in 2 stroke engines. Moving your fuel line and/or insulating it with aluminum foil to protect it from higher temps may help. A vacuum pulse fuel pump may help get cooler fuel into your carb, especially if you know how to run a return fuel line back to the tank. That way you are constantly supplying the carb with cool fuel and sending warmed fuel back to the tank to cool. Of course this will only work with a larger fuel tank and a larger engine. Probably not worth the trouble on a smaller mower (under 10 HP). The nice thing about the vacuum pulse pumps is that most engines will produce enough vacuum to operate one without any electrical connections. But if you can't find/make a vacuum connection, then electric will work.

Just make sure the gas tank is vented. The cap has a small hole, make sure it is clear.

The temperature the fuel boils depends it formulation. Winter fuels are more volatile in nature. Plus depending on the formulation gasoline can boil as low as 140F. Also the Spring, Fall, and Winter month carb icing can be a problem too. I have had aircraft carburetors to ice over @ 70F depending on the amount moisture in the air. And it is scary for it to happen over a larger city with no place to land.

mikekir said:

Just make sure the gas tank is vented. The cap has a small hole, make sure it is clear.

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After 2012 most caps are not vented They use a separate vent system that is connected to the air intake on the engine. Some push mower caps are vented with a charcoal filtration canister built into the cap. Which can get gas contaminated and brick the material making it not vent.

tadjag said:

Do a google search for "pure gas" to locate a station in your area

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Yep. I have found that I have fewer problems with my fuel systems when I use only "pure gas". There is only one station in my small city of under 10,000 that has pure gas. I found that station via the site in the link below. Check it out for your town/city.

https://www.pure-gas.org/
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You didn't describe the issue you are experiencing. Vapor lock is caused by a liquid being heated enough to cause it to vaporize. When it cools enough, it will go back into liquid form. Like water, if it is under pressure, it takes a higher temperature to vaporize. Rerouting the fuel line away from heat sources could help, or wrapping the line with insulation, like fiberglass, can help. Manufacturers don't usually route fuel lines near a source of heat that will cause vapor lock, but someone else could make that mistake.

I have an older Sears generator that's powered by a Tecumseh 6 hp horizontal shaft engine. (Similar to the one in the pic.) If you look closely, the fuel line from the tank on the back to the carb (which is absent in this pic.) actually passes THROUGH the starter shroud, right past the cylinder. This bad boy always ran like a champion until that little quart-sized fuel tank ran dry. Then, once the flywheel stopped and the cooling air ceased to circulate, that thing was the King of Vapor Lock. I couldn't start it again for at least a half hour, though once that vapor bubble went away, it always started right up and ran like a top until the tank went dry again. Lather, rinse, repeat.....

I was able to completely solve the problem by installing a new fuel line on the outside of the shroud.