Gas tank pressure

RdKryton

Active Member
Joined
Nov 6, 2007
Messages
949
First off I did search for an answer but came up blank. I want to know if a Whizzer gas cap is vented. My tank builds a lot of pressure. Is this normal? I wonder if this is why I had a problem with another carb. Maybe it could not hold back the pressure and always flooded the engine. Any ideas?
Thanks

Jim
 


C

cory

Guest
Good question

Thats a good question. My tank is from a new Whizzer kit and it does the same thing but havnt had a problem with the carb.:???:
 
Z

Zomby Builder

Guest
carb

My stock 18 mm carb did that too. Changed to 26 mm no more prob. Don't know why??? maybe because they are restricted from factory & can't breath after modify????
 

bill green

Member
Joined
Jan 5, 2008
Messages
473
Hi all the whizzer fuel cap is eco happy ,It is Aone way vent valve it only sucks in so no vapers get out . So it does build pressure . About the 26mm carb has an external vent line that could be the difference. Hope this helps Bill Green Vancouver Whizzer
 
B

billspirit

Guest
Last year in the heat of summer 90/100 deg, Both of my whizzers 06 /07 NE5's were having running problems like zapor lock, come back from a ride park them in the garage & they had a lot pressure built up both making squeeling noise from the cap, releve the pressure & ride again in the hot sun & they would start running bad, ride with cap loose & they ran OK. I removed the valves from the caps & drilled a 1/16 hole all the way through, never had another problem. I do not fill the tank all the way to the top, so I don't have leakage through hole. Worked for me! Bill B
 

peter nap

Member
Joined
Mar 4, 2008
Messages
79
Last year in the heat of summer 90/100 deg, Both of my whizzers 06 /07 NE5's were having running problems like zapor lock, come back from a ride park them in the garage & they had a lot pressure built up both making squeeling noise from the cap, releve the pressure & ride again in the hot sun & they would start running bad, ride with cap loose & they ran OK. I removed the valves from the caps & drilled a 1/16 hole all the way through, never had another problem. I do not fill the tank all the way to the top, so I don't have leakage through hole. Worked for me! Bill B

I've noticed the same thing with my 07.
 

Quenton Guenther

Well-Known Member
Sponsor
Joined
Aug 2, 2007
Messages
2,149
Yes to Billspirit's comments!
The cap can cause the tank to develope a vacuum. Drill out valve on the bottom of cap, but be sure to remove all particles with an air hose. The reason some tanks don't vent correctly is due to the paint [or lack of] around the filler opening. Some tanks will leak if filled to the top for the same reason. At Portland , IN in 2005 my 1999 was only turning 65 MPH on the dyno until I loosened the cap and it shot up to 68 MPH.
Have fun,
Quenton
 
H

HoughMade

Guest
I am a tad confused- do y'all mean build a vacuum?

I cannot understand why a fuel tank (with a carb, at least) would ever build pressure, that is, increase the pressure inside.

I do understand why it would build a vacuum as the fuel is used and there is no air let in to equalize pressure.
 

peter nap

Member
Joined
Mar 4, 2008
Messages
79
I am a tad confused- do y'all mean build a vacuum?

I cannot understand why a fuel tank (with a carb, at least) would ever build pressure, that is, increase the pressure inside.

I do understand why it would build a vacuum as the fuel is used and there is no air let in to equalize pressure.
Actually, it can and does do both. Gas will vaporize inside the tank when sitting. Put some in a gas can, cover the vent and shake it. when you uncover the vent, you have pressure.

I haven't seen that as a problem. The problem is when the gas won't flow enough to operate the bike at a given speed.
 

sparky

Active Member
Joined
Mar 19, 2008
Messages
1,429
I don't know anyone with a Whizzer, but I am curious about this building gas pressure concept.

My gas cap apparently needs to have a hole or two in it. But my friend's GoPed is completely sealed, and when I take the cap off I can hear the pressure that built up. I thought this was due to the Walbro carb, but my friend claims that it's the tank that builds the pressure.

Anybody know for sure what builds the pressure & why he doesn't need holes in his lid but I do?? Sorry if ya'll think this is a threadjack.
 
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