For the most part, fuel tank, lines and carburetion no more challenging than that of similar vintage machines though I’d fit a dual cable control over the single for more accessible/easy adjustment, it’s the petcocks that may prove your biggest challenge.
- Original Carbs?: Both of my machines low mile so no major carb restoration required. Though reproductions now available, you can have your carb bodies bored and re-sleeved in worn. Worn bodies and/or slides will prevent a good idle at a minimum. A good set can be made to work well but probably need shimming to restore accurate float level due to pin/seat wear. Shim either at needle land or by various thickness of base washer. Must have good slides to hope for a predictable idle. Fuel bowls face opposite directions. If aiming for that perfect tick over at idle you have little margin for error in your mixture ratio. Be prepared to have machine want to stall on hard braking to a stop as fuel surge from inertia will richen right hand and lean left hand carb.
I brake with two fingers while keeping ready hand on the throttle to prevent any
surprises. If shimming fails to achieve smooth idle/or the tendency to run rich on one pot with all other elements addressed to "tune" your float level on the fly, you can the carb retention clips on their stubs to rotate the carb bodies very slightly to effect fuel levels in the jet blocks.
- Petcocks: Original style can be made to work but have their limitations. The internal corks must fit and be well lubricated (soaked in olive oil) to ensure good seal and not be vulnerable to having pieces of cork sheered off by the fuel port drillings in the body bores as these will find their way into the idle jets (repeatedly). They also have suspect flow rates which makes it advisable to run both open at highway speed. More vintage in appearance are the Lightening style lever taps. But, running brass on brass with tapered bore, it is imperative they be disassembled and one coil removed to reduce compression pressure as they very easily gall, then leak both into the carbs and externally. Though not original looking and the repro's of suspect quality up till now, John Healey now has very good lever taps similar to those fitted to British machines in the 70's. As of 2010, two pairs fitted have shown no ill effects from modern fuel.
- Fuel Caps: The vent in Vincent fuel caps is easily blocked. Tendency to run on one cylinder or cut out completely under load may be a symptom that your vent is blocked and the tank is now pulling an atmospheric vacuum as fuel level drops. A quick way to tell if you have a vent issue is roll to a stop and allow heat soak from your engine to heat your fuel tank, if you hear any faint whistling and/or removing the cap results in a rush of outward moving air, your vent is blocked. The fuller your tank, the swifter this problem manifests itself as fuel is less expandable than air and a vacuum more quickly drawn
Some recommend drilling through the brass vent mechanism on the underside of the cap, but better is to gingerly remove the gasket and carefully pry it out. Modern fuel formulations do not store well and even after removing crust from long term storage may require a subsequent application of compressed air on infrequently used machines to keep this port free.
- Fuel Tank: If poorly stored on the side/rear stand with little/no fuel inside, Vincent fuel tanks will develop rust perforations on the floor at
the seams just behind the lower front mounting tabs. With today's noxious fuel concoctions, it is better to completely clean one's tank, weld up these pin holes, pressure check at about 3 psi and run them bare without any liners as none available today can
be expected to hit this EPA dictated changing target. Vintage Indians compound
the tank sealing challenge by being soldered and with many seams on the right hand tank. As of this writing the most successful at sealing these yet withstanding the Mid West's high alcohol contents is Red-Kote though I have not tried it in any of mine. Though the VOC Spares lists a fuel tank here, not sure of its regular availability as no price given, I'd avoid current India made reproductions and either repair your own or locate a usable original.
Vincent fuel tanks are durable but a couple of precautions should be taken. Ensure you have the rear distance piece (MO19 - T38) fitted and of correct length, shim with washers or trim if necessary to ensure it can be slipped in between the ears with spreading/drawing them together. The threads within your steering head to secure the fuel tank at its front mounting point are vulnerable to being stripped. The objective is to have the retaining bolts (MO - F81) bottom into the threads against the bolts shoulders without having compress the rubber grommets (MO19 - FT80) in the least. If any compression required, trim the abutting faces of the rubbers back until just barely pressing on the tank ears. If your threads marginal, the rubber grommets can aid in retaining your bolts. Brake the glaze on the bores of the rubber, apply rubber cement as used for tire patches and then secure the bolts with blue loctite. Rear mounting bolts (MO - 172/1) originally had their heads drilled to enable safety wiring them together. This is much preferred but if not, as these bolts are not shouldered to form a stop against upper face of the UFM, do not tighten down excessively, rather blue loctite after tightening to the point where the washers can be seen to compress the rubbers (MO - FT173/1) slightly.
If on the road and find your cap to be leaking, jeopardizing your tank paint, some renewing sealing can be effected by turning it slightly back out of the detents retaining the cap ears so that more of the internal spring can be brought to bear.
- Modern Fuels/Vintage Machinery: EPA changes in reed vapor pressure to reduce fuel evaporation at the pump has had a larger and more noticeable effect on vintage machinery in the U.S. than the transition to unleaded gas years ago. Modern fuel is designed to be atomized at pressures varying from 40 psi (common rail efi) to over 2000 on direct injection engines - not at atmospheric or below as occurs in carburetors. Less effected than antique flat/IOE configurations Vincents
can still suffer from the tendency of the fuel not to full atomize wherein
droplets merely run down the intakes into the engine. This is especially
prevalent during cold start or at low intake velocity/pressure differentials the former as it occurs at idle. Motors are more prone to foul plugs when the carbs tickled indiscriminantly while starting and to have erratic ambient temp related idles requiring more frequent adjustment. To mitigate this annoyance on the Shadow, I pulled a degree out of the timing to 34.5 and slightly raised the idle using the slide screws over the pilots. Incremental adjustments can now be made more readily on the fly by a slight adjustments to the pilots to offset any heat soak occurring in city traffic that may cause the idle rev's to rise. Am not a fan of gear-clashing 1st gear engagements from neural on a dead start so try to keep the idle where good tick over is assured.