I’d like to report success in solving a challenging problem involving ethanol. At 188,000 miles, I placed my 1976 2002 in storage for a few years while we were amid a period of moving, renting, buying, old-house restoration, and so on. I unfortunately discovered that autos most definitely do not like to sit for extended periods, and that gremlins of all sorts can and will take up residence. In my case, a front brake caliper seized, a blockage developed in the left rear hard brake line, and the differential seals dried out and started to leak. The original-equipment starter grew reluctant, and an odd vibration (not guibo-related) manifested itself in the driveshaft, also original. In short, I’d reached the point at which many people lose heart and decide to sell. But I’ve owned this car since 1977, and nothing like it will ever be produced again. So I attended to all the various issues one after another, with each being a bit tricky in its own way (see my writeup of the differential swap in an earlier post below). Yet there was one final nut that proved difficult to crack: my car had never sipped ethanol-blended fuel prior to the storage period, and it was deeply unhappy with the new brew.
Ethanol (another term for pure grain alcohol) lowers the boiling point of fuel notably, and that led to real trouble for me. Fuel makes its way in relatively cool conditions from the tank to the firewall, but once it enters the engine compartment, it has all sorts of time to grow quite warm during the slow journey to the carb. After a good run in any season, and after shutdown of the motor, residual heat gathering atop my car’s intake manifold would focus itself on the carburetor bowl, causing the already-hot fuel to boil audibly and percolate right into the throat of the carb (a Weber 40/40 DFAV, which lacks an anti-percolation feature). This resulted in worrisome levels of fumes, and caused a super-rich flooding condition that made it hard to restart the car when hot. I saw no evidence that this problem was due to actual engine overheating: the gauge was right in the familiar sweet spot (with brand new sender), and when measured with an infrared thermometer after warmup, the radiator, block, and manifold temperatures seemed entirely fine. The troublesome issues arose only after the engine was turned off. Opening the hood wide to dissipate heat after stopping improved things to be sure, but that’s no way to live. I tried all the standard remedies: installed a spacer block under the carb, insulated the fuel lines and pump, insulated the carb bowl, replaced the needle and seat, lowered the fuel level in the bowl by adjusting the float. One BMW expert suggested a fuel pressure regulator between fuel pump and carb, dialed down to 2.5 PSI. Alas, none of this brought any improvement whatever. All the local gurus were stumped, and I was starting to run out of ideas. One far-out tactic did come to my attention: on an internet forum, someone reported that he’d cured this very problem by installing a timed fan that blew air over the carb for 15 minutes after shutdown. That seemed like an unduly complicated workaround, one I was not eager to adopt.
Then came a final inspiration. As part of the emission-control package installed in US models for the 1976 production year, my car was originally set up with a return line that sent fuel back to the tank: just enough went to the carb, with the rest heading back to the tank via a diverter fitting. This return loop had been disconnected many years ago, when the belt-driven air pump (remember those?) and other associated gear was removed. And subsequent to that, I’d installed a Metric Mechanic 2200 Sport motor and the Weber carb (along with a Pertronix unit and a mechanical-advance distributor), taking me even further from the stock configuration.
My new thought was as follows: if I could keep cool fuel circulating, it wouldn’t have a chance to heat up while sitting in the line moving gradually across the hot engine. I located the old hard return line that runs under the driver’s side of the car. The old soft line from the tank to the hard line was completely deteriorated, but was not difficult to replace. The forward end of the hard line ends up just under the steering box, and it was easy to make a new connection there. I then inserted a 5/16″ (8mm) tee downstream from the pump and just before the intake fitting on the carb. Some fuel goes to the carb, the rest back to the tank. This of course means that fuel now circulates continuously and has no chance to pick up heat while sitting in the engine bay. The only “hot” segment of fuel line is the very short portion between tee and carb, and that brief run simply doesn’t afford the fuel sufficient time to warm appreciably. Yes, the carb bowl may be as warm as ever after shutdown, but when the now-cooler fuel reaches it, it no longer boils.
Thankfully, this fix has brought a complete end to the unfortunate symptoms. Nice! Now the car will actually be usable again. Though I wondered if it might be an issue, there appears to be no need to restrict the volume of fuel heading back toward the tank in order to ensure adequate flow to the carb: the stock mechanical pump (which is relatively new) appears to be providing more than enough pressure to take care of all needs. Another aspect of this new setup is that after shutdown, there is no longer a closed section of post-pump fuel line in which heat and pressure can build, potentially forcing unwanted fuel into the carb: the return line to the tank now serves a venting function that would forestall that difficulty.
After all this work was completed, I was still able to detect a faint odor of gasoline in the engine bay a day or more after running the car. The source proved to be the charcoal canister, to which I had paid no attention in many years. Clearly the odor-absorbing properties of the charcoal had long since been used up, and it was time for replacement. The part number is Purolator 00 701, and I found the best price on the part from this source.
What I received was a brand new/old stock canister from the 70s, and the seller was unaware of the actual application until I informed him; other 70s vehicles likely used these as well. As most of you know, hookup of the canister is straightforward: the inlet accepts the line from the plastic fuel vapor tank in the trunk, and the outlet goes to the air cleaner.
Though some claim that such worries are overblown, I’ve heard tales to the effect that ethanol can quickly attack and degrade rubber lines. On the other hand, friends who have rubber lines and use clear fuel filters tell me they are seeing no unusual buildup in the filters after thousands of miles of running standard E10. Just to be safe, however, I have replaced all soft fuel lines in my car with ethanol-resistant line, namely Gates SAE30R9. Others vouch for Tygon, though it is said to be slightly more difficult to work with (and is a bright yellow color that might not appeal to all tastes). On this same topic, Scott Sislane highly recommends StarTron fuel additive, which he and other experts feel is the best available treatment to combat the effects of ethanol.