How to Check and Fix Vapor Lock on a Harley-Davidson®
Bob LaRosaDescription
Why does it happen? Most fuel systems have a vent in the fuel cap. Let’s review how to check and fix Harley Davidson vapor lock.
Let's take a moment to discuss vapor lock. All fuel systems need to vent. They need to vent to the outside atmosphere. This is done through a number of configurations throughout the years. This particular model, there is a fixed, left side fuel cap with a fuel gauge. You never remove this cap. You fill the motorcycle from the right side only. Most fuel systems, the vent, is in the fuel cap. You'll see on this right side fuel cap, there's a small area right in the center of the cap, that has a small check valve in it. As pressure builds in the tank, it causes the vapor pressure to push upward on that check valve, and release the pressure out into the atmosphere. If you happen to be riding along, usually it happens in very hot climates or on very hot days. The pressure will build-up in your fuel tank, if it doesn't vent correctly, what it'll create is a vapor lock situation, where the fuel in the tank becomes stagnant. It can no longer flow to the carburetor or the throttle body and it can no longer vent out the fuel cap. When that happens, you'll most likely hear, a release of heavy fuel vapor, when you crack your fuel cap loose. You'll hear, as you release the cap. If you hear that, when you go to fill your motorcycle it's not uncommon, due to the fact in a motorcycle, that's almost empty. The fuel tank is full of vapor, and there's not much liquid fuel. When the fuel tank is full, you should have very little vapor, if you release the cap. Again if you're riding your motorcycle for short distances in hot conditions you're getting excess heat rising from the engine. You're getting hot air because of the environment you may encounter vapor lock, if that fuel cap vent is not working correctly. I highly recommend not trying to modify a factory fuel cap. A lot of people in the past, they've taken, this small, release valve and drilled it out. What that creates is a constant flow of fuel tank vapor to the atmosphere. You don't want that, especially if you parked your motorcycle indoors after a long ride. the inside of your garage will begin to smell like fuel, as the vapors release from the tank when they're not supposed to. If you do encounter, a fuel filler cap that's defective, don't modify it, replace it with a new cap. Make sure the fuel tank is at least 2/3 of the way full. Make sure the cap is secured tightly to the fuel tank. Take your motorcycle for another ride. If you did have a defective cap and your engine was shutting off due to vapor lock the problem should be corrected just by replacing the fuel cap.
Can't get fuel to EFI. Had to remove tank and now no fuel. Starts if I put fuel into butterfly.
THANKS!! The best and the only site that explains to me the lack of Power in my 883. I recently bought a new cap and I've noticed the vapor release when I opened it. My bad ´cause the cap is one that I bought in that "wish" app
I am having vapor lock issues on my 2008 ultra classic
ADORE your shorts - i would seilrusoy love to explore your wardrobe and accessory collection, but i think you already know that by now! hehehewhat beautiful para-sailing photos, i took a few when I was in Thailand last Aprilx Lauren
Good info for the New owners. It also should be pointed out that this problem can effect all mechanical engines that run on fuel, both Bikes & cars. Thanks for the info, once again brilliant presentation & delivery. Would expect nothing less from your crew & fix my Hog! Cheers from down-under!