Hi Phils,
I was away from the Forum for the past week--on Spring break, travelling w/ family in CA. We went up to Mariposa to see our land, and then hopped over to Yosemite. Our son took his first ski lesson at Badger Pass which has a 10 foot base, and was snowing to beat the band while we were there.
On the vapor lock problem, I too experienced this last Summer, and had a great discussion w/ <font color="red"> pairodime </font> about it. I also had the problem w/ detonation at shutdown.
I used our race car pyrometer and measured the air temperatures adjacent to where the OEM fuel filter was located (just inboard and below the muffler). Temps were in the 300 degree + range. Gasoline boils-off completely at 260. No wonder there was a problem! You don't have to be above the boiling point of gasoline to have vapor lock, but being above it will guarantee the problem. I have changed over to thick black SAE rated fuel-vapor hose, 1/4" ID (~$1/ft at Auto Zone), and replaced the fuel filter. My OEM filter had an outlet of 0.18" ID, and the new one, a generic off the shelf unit has outlet of 0.25" ID. I also relocated the filter to be forward of the black steel barrier between the engine and battery.
I also wrapped the exhaust manifold with racers exhaust header wrap made by
DEI Products I stopped the wrap just before the manifold connects with the muffler. Unlike pairodime, I have experienced absolutely no sag nor warp anywhere in the exhaust system.
I also applied DEI's hj-temp adhesive "Floor & Tunnel Shield" (look under heat shield area of products) to the entire engine side of the black steel barrier located just aft of the battery. What a difference that made. Everything forward of that barrier is now cool enough to touch immediately after shutdown. The battery is no longer too hot to touch, and the gas tank is cool as well.
I also sheathed the entire fuel line and fuel filter with a DEI heat sheath w/ velcro closure. We use these in our race cars, and they are also used a lot in aircraft where vapor lock might be more of a problem than for us. It comes in a 3 foot length which is more than enough for our units. DEI doesn't sell direct, but you can get their products from
Summit Racing where it is discounted from the MSRP.
I conveyed all this to Terry at PT. He was initially surprised about the temperatures, and indicated that he would talk to staff about going back to the thick black SAE rated gas-vapor fuel line. The clear plastic Tygon tubing was never intended for this harsh a service application. Mine was clear Tygon. Pequeajim's was the yellow fuel rated Tygon. Before I replaced it, mine sagged at least a foot into the bottom of the tub!
In our machines, the fuel pump is downstream of the tank, and it is sucking fuel to supply to the engine. The fuller the tank, the higher the pressure head at the pump (vapor and/or liquid), and the easier it is for the pump to deal with entrained gas vapor. Reason we don't see vapor lock in modern cars is that the pump is upstream, in the tank itself, so the fuel is being pushed from an area with fuel at a lower temperature directly to the carb or the injectors.
BTW, while I replaced the fuel line and filter, I also installed a dripless"quick disconnect" in the line upstream of the filter, between the filter and tank. That way, I can remove the tank easily and w/o losing gas from either end.
On the matter of detonation, I use 91-93 octane gas, as was recommended to pairodime by Jack Robin. He also recommended, and I am using the lead substitute which is found at Wally World. Terry at PT confirms this, too. Terry recommended shutting down directly from 1/2 throttle, i.e., do not bring the engine down to lowest idle and then shut down. I didn't believe it until I tried it. Since I started doing shutdown from 1/3-1/2 throttle, I rarely have the detonation problem.
Hope this helps Phils. If you need any specifics on product numbers, etc, drop me a PM...
