Fresh Air Page 2

Maintenance Q & A — October 2004
By Capt. Ken Kreisler

Fresh Air
Part 2: A lingering smell, vapor lock, and more.
 More of this Feature
• Fresh Air, and more
• A lingering smell, and more
• PMY Tries... Responder Submersible Flashlight

 Related Resources
• Maintenance Q&A Index

I have a puzzling problem with a Rochester four-barrel carburetor. It’s attached to a 5.6L gasoline engine that starts and runs great. But after a short cruise at 3200 to 3400 rpm, when I bring the throttle back to idle, the rpm returns only to 1200 to 1400 rpm. Turning the engine off for a second and then back on without moving anything else returns it to its normal 750-rpm idle. Removing the cable does not help, and all linkages are clean and lubricated and move freely. Do you have any suggestions? C.Q., via PMY Maintenance Forum
Besides a stuck carburetor float, it sounds like it could be the carburetor gasket swelling due to a fuel leak at the base. The throttle plate is probably barely catching on the swollen gasket and isn’t able to return all the way to the idle position.

Because there is the possibility of a gasoline leak, you or your mechanic should address this problem as soon as possible. When doing the inspection, make sure to disconnect your batteries and take other measures to ensure that no spark or other source of ignition is possible.

I have a boat with a lingering smell coming from the single MSD onboard. I’ve checked for problems but so far, have not found anything wrong. Any suggestions? W.V., via e-mail
Look at the discharge hose that goes from the MSD to your holding tank. Most likely it’s is permeable and is allowing liquids and odors to escape. A good way to test this is to rub the hose with a clean rag. If the rag comes away with an odor, you’ve found the cause of your problem and need to replace the hose with a nonpermeable sanitation hose.

After a sandy grounding, I noticed one engine running slightly hotter than usual. Back at the dock, when I went to check the impeller on my raw-water pump, I found the lid to be stuck to the pump body. What should I do? L.F., via e-mail
First, close the seacock. Then spray around the lid-body seam with WD-40. Let it work in for a minute or two, then tap the lid lightly with the handle end of a screwdriver. You should be able to pry it off, but be careful not to distort either the lid or body. If this doesn’t work, try heating just the lid with a hair dryer—use only moderate heat—while a wet rag is wrapped around the body. The differential expansion should break the seal.

My boat has a pair of 8.1L gas engines. After about two hours of running, the starboard engine started to sputter and eventually quit. Each time it quit I could restart it but had to reduce maximum rpm. Eventually I was able to maintain just 1000 rpm back to port. A cursory inspection of the fuel system showed no blockage or water. The next day, after about three hours of running, the problem cropped up again. Do you have any insight into what could be the problem? K.D., via e-mail
It sounds like vapor lock, an obstruction to the flow of fuel due to the formation of bubbles caused by heat. You can test this theory by placing a wet rag around the fuel line leading into the carburetor. If this prevents the problem, see if the fuel line comes near anything hot like the block or exhaust manifold. If it does, either reroute the line or insulate it with foam or foil. If the problem persists, it’s time to call a mechanic.

Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016, or log onto the PMY Maintenance Forum. Fax: (917) 256-2282. e-mail: No phone calls, please.

Next page > PMY Tries... Responder Submersible Flashlight > Page 1, 2, 3

This article originally appeared in the September 2004 issue of Power & Motoryacht magazine.

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