Gas leak

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Nov 14, 2020
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I’m posting a photo showing the area where I’m having a slight gas leak due to dry rotting around a rubber seal/boot. Question. Is there any type of repair sealant or patch that might work for a small leak that you’d suggest? If no other solution other than removing carbs, how difficult is it to get to this area to replace the rubber?


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Mar 25, 2011
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Miami Florida
Are we speaking correctly? Do you mean that you see evidence of a deteriorated rubber donut from the carbs to the VBoost? Because there really shouldn't be a 'gas leak' around there, do you mean, you suspect an intake leak? That's what I suspect that you're describing.

The correct way to deal with this, follows, assuming that your rubber donut is drawing air through a crack, which would make your bike run poorly, this is usually referred-to as a vacuum leak.

Not-knowing your level of knowledge about this (I am only a hobbyist, and am not a professional mechanic) you might be successful in sealing-up a crack in the rubber donut by using some silicone smeared over the area where you suspect the leak to be. However, the correct way is to replace one or more rubber donuts; if one has begun to leak, others probably aren't far-behind. You can go OEM for the item, there are aftermarket pieces available at a substantial discount. I suggest replacing all-four of them at the same time. A cheap-ass 'flipper' is just going to replace whichever one they find is bad: "spending money cuts-into the profit-margin, dude!"

The traditional method of finding the leak, is to use a spray can of ether or starting fluid, sprayed around the areas where you suspect a leak, with the engine running. When the engine's revs pick-up or smooth-out you have found one of the leaks, look for others. Another area where you can have a leak is below the VBoost aluminum manifold to the cyl head, there's a thin o-ring in-there which also can leak. This is definitely an occasion where you want to replace all four of them, once you remove the VBoost assembly. I've never bothered leaving the carbs and the VBoost assembled during removal, and I doubt this would be a time such work would 'work.' Airbox off, carbs off (I disassemble the cables at the little plastic box, leaving the ones into the carbs connected to the carbs), and VBoost off. Assembly is the reverse of disassembly, as they say in the manual. Those tiny screws holding the carb junction box together like to jump out to freedom, never to be seen again, once you un-do them. Be careful. I suggest taking a pic of the unopened box with your cellphone before you start, and them once it's opened. You could even label the two pairs of cables as top/top, and bottom/bottom, to help you assemble them. This really isn't needed, as properly set carb cables will have one 'long' and one 'short' one at the junction box, assuming that the handlebar throttle and the carb cables are still intact and in-place.

I don't know your period of ownership, how-long since you changed the gas filter under the seat/faux tank? You don't need to spend $23 for the OEM Yamaha one, you can find a replacement which fits at your local parts store: O'Reilly's, NAPA, Auto Zone, etc. for probably $5-8. You can use the 'search' function on-here to find an exact part #. Once you have purchased a replacement, cut-open your old one, and see what kind-of crap it's accumulated. Then shine a flashlight into your gas tank, and see what the bottom of the gas tank appears to-be, shiny, bare metal is good. Rusty, gummy dark deposits are bad. A good thing to do before removing the carbs is to drain the gas from each carb bowl into a clear receptacle so you can see if there is any rust or water in the gas. Water appears as a 'lens' of different viscosity floating on the gas, and will cause issues with proper carburetion. If someone sealed your gas tank at some prior point, you may not see a shiny metal interior.
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