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Offline moley

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vacuum on fuel tank
on: April 21, 2018, 07:59:18 AM
Hi Guys  Just wondering if anyone else has had this happen . I recently did the pair and flapper mod and the bike was literally transformed into a much nicer machine to ride , However I have now noticed that the vacuum in the fuel tank has significantly increased so much so that the filler cap sometimes actually has to be pulled up when filling up the tank .....any ideas

Offline Notgotone

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Re: vacuum on fuel tank
Reply #1 on: April 21, 2018, 09:17:20 AM
Hi not had it myself but not done the flapper mod I have mk2 can only think that the tank vent pipe is kinked on refitting the tank etc.

Online Skids

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Re: vacuum on fuel tank
Reply #2 on: April 21, 2018, 02:38:44 PM
I have 2 friends who own 14+ VFR800F's who have both had the fuel tank collapse inwards due to vacuum issues. Same engine as ours so definitely worth checking out.
98 VFR800 - 130,000 miles (sold)
08 VFR800 - 76,000 miles (sold)
14 VFR1200 - 20,000 miles
15 VFR800X - 44,000 miles (sold)
18 VFR800X - 9,000 miles

Offline moley

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Re: vacuum on fuel tank
Reply #3 on: May 05, 2018, 04:33:07 PM
Finally found the time to have a look but rather than strip all the plastics off I undid the rear tank bolts and bracket and managed to left the tank 1/2 inch. The main vacuum on the right hand side (looking forward) was clear . I removed the bolt blocking the old vac pipe that used to go to the flapper. On the left hand side of the engine there is a larger diameter pipe that comes off of a tube from the bottom of the tank and goes through the rear tank bracket and follows down under the engine . I pulled this off and blew through it and it was clear . I then made sure it was clear when I re bolted the tank down . I then ran the engine for 3 -4 mins and the "vacuum" was greatly reduced . So I thought at this point it was mission accomplished . I then left the bike for 5 mins without it running . When I opened the fuel cap again it is almost like the tank is gassing on its own fumes. Instead of it feeling like a vacuum ,it felt more like pressure was being released
 >>>>> any ideas ?

 



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