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General Minitrail Talk
Tech Area
fuel issue?
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<blockquote data-quote="69ST" data-source="post: 192262" data-attributes="member: 5"><p>These are simple as fuel systems get, really basic setups. Yet, they have a hair-trigger element, i.e. one minor imbalance can cause what seems to be a huge problem. </p><p></p><p>There's not much head pressure to sustain fuel flow and that's the biggest, single, issue. From my experience, locating an external petcock using the upper airbox mount on the frame places it <em>just</em> low enough to allow the tank to empty completely. The routing of the fuel lines, especially the outlet side, can be a make/break proposition. If you're getting a dynamic fuel starvation problem, i.e. the bowl drains under full power, then refills during shutdown, look at float level & line routing as the solution. This, of course, assumes a clean fuel filter, proper tank venting and no pinched lines.</p><p></p><p>Next biggest variable is bowl inlet location + carb mounting angle. With Mikuni carbs in particular, it is sometimes necessary to tweak the float height if the rear of the bowl (where the main jet well is located) sits higher than it would if the carb sat level. Mikunis also have a main jet well O-ring that can be damaged...or shrink; remember all the work kirbby did trying to chase down the optimal jetting on his VM22? That turned out to be a perished main jet well O-ring. That model and the VM26 are really temperamental to dial-in.</p></blockquote><p></p>
[QUOTE="69ST, post: 192262, member: 5"] These are simple as fuel systems get, really basic setups. Yet, they have a hair-trigger element, i.e. one minor imbalance can cause what seems to be a huge problem. There's not much head pressure to sustain fuel flow and that's the biggest, single, issue. From my experience, locating an external petcock using the upper airbox mount on the frame places it [I]just[/I] low enough to allow the tank to empty completely. The routing of the fuel lines, especially the outlet side, can be a make/break proposition. If you're getting a dynamic fuel starvation problem, i.e. the bowl drains under full power, then refills during shutdown, look at float level & line routing as the solution. This, of course, assumes a clean fuel filter, proper tank venting and no pinched lines. Next biggest variable is bowl inlet location + carb mounting angle. With Mikuni carbs in particular, it is sometimes necessary to tweak the float height if the rear of the bowl (where the main jet well is located) sits higher than it would if the carb sat level. Mikunis also have a main jet well O-ring that can be damaged...or shrink; remember all the work kirbby did trying to chase down the optimal jetting on his VM22? That turned out to be a perished main jet well O-ring. That model and the VM26 are really temperamental to dial-in. [/QUOTE]
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