Question about 1996 Honda VF 750 C Magna

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Replacing gas cap caused pressure build up in tank

I replaced gas cap which resulted in pressure build up in gas tank. As a result I had gas leaking some place under neath tank. Previous owner had used a sealant inside the tank. He also cut the gasket on the old gas cap by 1/4" wide apparently to release pressure. What else would cause this build up of pressure? Thanks.

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The tank has to be vented, you have a drain line on the overflow that allows air to come in, but it still has to go out, there is usually a tiny hole in the cap somewhere, He may have clogged some of the lines to the tank with the sealant, what did he use?? Most tanks have a map pasted on them where all the lines go, Find one and see what is missing or wrong, if you have to seal the tank, get it off, dry it out, wash it soap and water, get some POR brand tank sealer, works great, and pour it in there , follow their instructions, hope this helps.

Posted on Apr 24, 2010

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Heat causes the build up of pressure. Is the leak coming from the tank, or from the petcock? Also, in my experience, not all fuel tank liners are effective, take it from a guy who spent 2 days getting a Kreem liner out of his Suzuki's tank by shaking it around with acetone, nuts, and washers inside it so he could redo it with a much better product called Red Kote... long story, lol.

Posted on Apr 24, 2010

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As fuel is over flowing the only problem seems to be no (or a blocked) pressure relief mechanism in the fuel cap. So when the petrol heats up the only way for it to expand is by forcing some fuel out of the overflow
I presume its an after-market cap; into which a small hole could be drilled

Ride safe
Bike-Doc
Please mark this as very helpful (if it has been!!)


Posted on Apr 24, 2010

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Pressure build up in gas tank Sporster


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Something else to consider is that a plugged vent would, most likely, cause a vacuum in the tank instead of pressure. (As the tank empties while riding, air can't come in to fill the space vacated by the gas.) The only reason I could expect that you build up pressure is if the vent is plugged and the tank gets heated from an outside source such as the sun.

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My gas tank is building up excess pressure when the bike is on for a while or after riding only short distances. This causes a high pitched squeal when the pressure gets too high. If pressure is not...


G'day.
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clear the blockage or replace the cap & you should be fine.
Under most roadbike gas caps is a cover held in place with two screws-remove them to dissasemble the cap & clear the blockage in the cap vent
If yours is a Canadian(maybe US models are the same)-model then the problem is in the fuel evaporative system. Check out this link.
http://www.mrcycles.com/fiche_section_detail.asp?section=365110&category=Motorcycles&make=KAWASAKI&year=2005&fveh=8485

Hope this is helpfull.
Kind regards Andrew Porrelli

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