Over the years, plenty of vintage Honda brass floats have been observed in various states of damage, mostly due to the ravages of old gasoline residues left in the float bowl. The acidity of gasoline compounds can easily etch a hole into the brass surfaces, eventually penetrating the metal shell and allowing the hollow chamber to fill with newly introduced fuels. Depending upon the size and buoyancy of the float, sometimes they can be half way to floatation, but often the weight of the fuel is more than the float can handle and it sinks towards the bottom of the float bowl. What that happens, the needle valve cannot rise up to close off the incoming fuel from the seat; then the float bowl fills up to overflowing and the excess fuel exits the brass overflow tube in a steady stream. Anytime that the float valve appears to be clean and shutting off the fuel when the float is raised manually to the normal float level, then you can probably point the blame towards the float itself.
Last year, a restored CA77 Dream customer called to say that his newly rebuilt mount was peeing gasoline down on the floor when the petcock lever was turned to ON or RESERVE setting. Today’s alcohol-infused gasoline attacks any rubber parts within the carburetor body. Usually the main victim is the float bowl gasket. As the gasket faces swell laterally, they can often come in contact with the float lobes, either locking the float up closed or somewhere downwards, preventing the float from rising up and shutting off the fuel flow at the float valve. The “fixes” are 1) replace the gasket, hopefully with one that is alcohol resistant 2) trim the protruding edges of the gasket with an Exacto knife or other razor knife, especially if the gasket has been glued in place 3) gently pinch the float lobes inwards, away from the gasket contact or 4) do all of the above.
In the case of the pissing Dream, the float had filled with gasoline due to a pinhole in one lobe and that was enough to prevent closure of the float valve. A replacement float was all that was needed to solve the problem and the bike still runs well a year later. The gasket was also touching the old float, so some counter-measures were taken to prevent contact with the new float. So far, so good…
Recently, the previously discussed Benelli Sei (six-cylinder) came down with a case of leaking carburetor out the overflow port in the side of the carburetor body. The Dellorto-brand carburetors have plastic floats installed, which generally are trouble-free. Checking the float, still in place, revealed that the float valve was shutting off when raised to the 24.5mm setting by hand, but with the bowl replaced, the overflow condition continued. With the carb rack (3 carbs ganged together) removed, the middle bowl was removed and the float valve checked for debris that might have been trapped between the needle tip and seat. These float valves use a rubber-tipped needle, which might well react to today’s gasoline due to the fact that the float needle is 39 years old. Close inspection of the needle and seat revealed nothing out of the ordinary, however when the plastic float was held and shaken, the sounds of sloshing gasoline were easily detected and felt, especially when the weight was judged against others like it.
The Dellorto floats are made with a central section which is bonded to the float arms at each end, with the float valve closing tang offset from the middle of the float arm. Laying the float on a piece of cardboard, a heat gun was carefully used to give some BTUs to the float lobes and after a minute or so, the appearance of gasoline made itself known. The outer portions of the float lobes are apparently glued onto the center sections. The fine line where the two parts were joined was where the gasoline was leaking from after being heated up. A single-edged razor blade was worked into the offending crevice; however the outer edge wasn’t giving way as hoped. Whatever adhesive they used to bond the two halves together was pretty stout stuff, but somehow the seam opened up just enough to allow gasoline to infiltrate the lobes and both sides seemed to have ingested various amounts of gasoline.
As with all things Benelli (motorcycle), parts are not just laying around on dealer shelves for this low-production, 39-year old machine. Searching for the part number, gained from a US parts book, the only one hit that showed up on an internet search was a used part from a motorcycle salvage dealer in St. Louis for $20, plus $12 shipping. Hoping that sinking floats were the exception and not the rule, a purchase was made and later the part verified as that for a Benelli Sei. Dellorto, in their infinite wisdom, make floats in different weights! You can order a 6gr, 10gr, 12gr and 14gr (if you are lucky) float. The weights are marked on the side of the float lobes, but this is not a feature of any Japanese made carburetor float that I have ever seen before. The Sei specified a 14gr float, but one of the mainstay eBay providers said that he had never seen a 14gr float before. He did have a couple of 12gr floats, so it was worth throwing a few more bucks into the pot to find out what they looked like and if they would affect the performance of the carburetor in any tangible way.
Recent eBay purchases from a seller in the East, who had bought up some Sei parts at an estate sale, came up with one 14gr float with an asking price of $5 plus shipping. Sure! Send it! Fortunately, he offered a new fuse box (early style) at the same time for free. How does it get better than that? The seller is still mining his Benelli parts boxes for any more items of interest for this model, hopefully also at bargain basement prices.
So, if you are confused by a suddenly leaking carburetor float bowl and it appears to be clean inside and the float valve is functioning normally when moved by hand, then the next step is to remove the float and check for the presence of gasoline inside one or both of the float lobes. A final note, however, is that if all of the above items are in good repair and the float bowl continues to leak out the overflow tube, and then check for the possibility of a cracked overflow tube. The crack generally runs vertically down most of the length of the overflow tube inside the bowl, but you may have to take a real hard look to verify that this is the problem. The hairline cracks can easily be overlooked upon casual inspection, but a second check will usually reveal the presence of a fracture in the brass tubing. Again, with age, heat, gasoline exposures and vibration, funny things can happen to the insides of a vintage motorcycle carburetor. There’s always a reason for gasoline leaks, so be safe and fix them right away.