Gastank harmonics issue

GoldenMotor.com

Rambler

New Member
Jul 25, 2009
48
0
0
U.S.A.
I have an interesting problem with my gastank. I want to resume use of my 4L gas tank, but when I used it before, on my 2 stroke, it vibrated in harmony with the engine from 18-25 miles per hour give or take. The issue is not simply vibration, but amplification of said vibrations when the frequency of the engine fire reaches the harmonic frequency of the gas tank, causing over vibration(to the point where even at half a tank, the gas cap would spew a froth of gasoline/oil. In order for me to use this gas tank safely, I need a way to change the acoustic qualities of my gas tank in order to keep it from achieving harmony with the engine. Does anyone have an idea of what I can do to achieve this on little to no budget. I could go back to using my 2.5L gas tank, but I like the range I can achieve with my 4L tank.

Any ideas will be appreciated. I will take all ideas into account.

I was looking at great stuff foam, or figuring out some other way of coating the tank with something that will change the acoustic value of the tank. Any ideas will be helpful. Just remember that I have little to no money to spend. A solution for under or around ten to twenty dollars would be best, erring on the side of ten dollars.
 

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
I would try wrapping rubber not plastic, electrical tape around the top bar, where the straps are.This is the tape that has no adhesive, it sticks and melts to itself.
Make several wraps and get it to about 1/4" thick and see how that works. Also verify that all your engine mounts are very tight.
 

tooljunkie

Member
Apr 4, 2012
663
5
16
Manitoba,Canada
rubberized undercoating,paintable.would probably get 4 coats out of a can.
good drying time before top coating with the paint colour of choice.topcoat should be fuel resistant.

i wanted to insulate my tank from vibration,i slit my old gand grips and cut the flare off the ends,slipped them over the cross bar and mounted the tank.those thicker comfort grips may be an idea too.my tank dosent move at all,btw.
 

Rambler

New Member
Jul 25, 2009
48
0
0
U.S.A.
ok, it's a beach cruiser, so it only really contacts the frame in one spot, is there a way to achieve an artificial straight bar effect, so have the bar contact the tank in at least three areas, or is that one of the benefits of the rubber mounts?
 

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
ok, it's a beach cruiser, so it only really contacts the frame in one spot, is there a way to achieve an artificial straight bar effect, so have the bar contact the tank in at least three areas, or is that one of the benefits of the rubber mounts?
All the above tips will give you the strait bar effect if you have enough rubber or tape under each end of the tank, so that the tank itself doesn't touch the bar. 2 areas of contact is enough.
 

Drewd

New Member
Jul 25, 2008
425
0
0
Colorado
Put about 1/4 spray of armor all or any product containing silicone into a gallon of gasoline mixture. This will prevent frothing. Drawback is that you may have to replace spark plug a little more frequently but never been an issue for me with only replacing plugs once a season/year. This tip is an old tip that folks who fly model airplanes use occasionally when engine vibrations cause fuel frothing.
 

mrchimpo

New Member
Jun 13, 2012
4
0
0
portland, or
I too have had to deal with the issue of vibrations in my fuel tank, lines, and filter. First off I cut the fuel line that came with the kit to almost no slack tolerance, and it shrank over time causing it to become taut... And once the engine hits that 25-30mph mark the vibrations through the frame & carburetor were enough to cause air bubbles to form all through my fuel line, filter, and to my carb. What was happening to me at sustained WOT was for fuel to actually sputter out the backside of my carb ( NT no filter or housing ) and I would have to adjust the petcock slightly more towards the closed side.
I have used foam playground padding (similar to the pipe insulation foam but more durable and compressed) cut to fit the underside of the tank between the main frame bar, and also between the tank brackets and the underside of the main frame bar. It is important when shimming a bracket with foam to do it on BOTH SIDES otherwise the vibrations will amplify to the brackets / studs and cause breaking (mainly engine studs). Hope this helps.