gas tank presure

Ok, i guess a maxi tank holds like 3/4 or .8 gallons or some shit, so check this out: when my tank is like .4 gallons from full (full to the brim!!) it just wont run. The bike acts like it is out of gas and it seems like air is coming through the jet cuz i lean way out. Idle is high (like 4-4.5thousand rpms) and i can barely give it any throttle or it dies. Doesn't make any difference to run without the gas cap. It IS a ported and moded bike, but the problem did not arise when i did all this, it happend later. Now it gets worse and worse. (it started not running when it had only about 1/4 gallon, now it has to have at least like .4 gallons to run. Whats up? New petcock?

Re: gas tank presure

make an auxiliary tank and then try to run it. if it works then it might be something in the tank or petcock. and if it doesnt work then move to the carb and look at it if it needs adjustment.

i dont understand your question because you said it doesnt work when its .4 gallons away from full and then you say it has to have at least .4 to run. the latter sounds like thats just the reserve. the first statement sounds awkward and i wouldnt know whats wrong.

Re: gas tank presure

oh yeah put your mouth against the caphole and try to blow into it making a seal with the outisde of your mouth. and make it force gas through the petcock and see if it runs better

Re: gas tank presure


by the way hear is what i meant:

my bike holds .8gal

.4 from full means it stops running at about 1/2 tank (i think, only because i don't know the actuall size of tank. what i do know is that it stops running, and then i top it off and gas pump says i put in .4 galons)

reserve is nowhere near .4, it's something like .1 or .2 gallons at most. BUT, it doen't make a difference to put it on reserve.

i don't think i'll be able to blow through caphole while riding for these reasons:

1. i will look really really stupid (and feel stupid)

2. i think i might crash

3. thats gross (even though i like to breath gas, i may throw up)

4. sorry to put down your idea, but thanks for the input

5. I just realized that you were joking

6. boy, now i feel dumb. hehe

Re: gas tank presure

lol i wasnt kidding. i dont mean ride and blow it hahahaha. i mean put it on the stand go WOT while blowing it.

now that i understand your situation better im thinking its your petcock being clogged.

your petcock may be clogged a slight bit to the point that. whatever .4 gallons weighs isnt enough pressure being exerted to push that gas through the petcock. the weight of more than .4 gallons may be whats pushing the gas into the petcock. you might need a tank cleaning. pull the gas line off and see if it flows. it might flow but not fast enough to feed the engine for extended periods of time. drain the tank take out the petcock look at the filter on the petcock. then try to clean it with carb cleaner or something. it might save you from having to buy another petcock. then get some acid stuff to clean your tank mix with water. remember always put acid in water and never vice versa

and then skip the kreeming part. rinse it out with soap. and water. then water. then let it dry. you can use a blow dryer but i broke mine in the process. then test if petcock will flow enough by running water through it. if it does then you can use it i suppose if its dirty beyond repair go get a new petcock. either way a new petcock will benefit you most. unless you really needa save money. then put some fresh gas and oil mix in there and run.

this is all assuming you have a dirty rusted tank and cloggged petcock. if not then i just type a whole lot for nothing

Re: gas tank presure

Here is what you do:

fill it up all the way with gas, get a gas can that can hold a gallon or more, take the fuel line off your carb, stick it in the gas can, turn the petcock on to run, turn it to reserve, you should get a full flow on both settings, if it's slow then you have crud in there, after emptying the tank, take the petcock off, and clean it out, and you are done.

if for some reason with a full tank you get full flow out of the line, then it's in your carb, maybe an air vent is blocked? or a cloged filter?

but basicly, if you are not getting gas, start at one end, and work your way twards the other, untill you either find the problem, or knock something loose and fix it accedently, and if all else fails you have gas, all you are missing is a match.

Re: gas tank presure

check the filter in the banjo bolt

Re: gas tank presure

i feel so dumb now, i have come to a milestone in my moped carreer fixing bikes on the fly, porting engines, building engines, and the fucking ffuel line filter was clogged. Huh, i guess i should just try what makes sence next time instead of trying to do it all in my head.. fucking filter, thanks anyways guys. fucking filter will be the end of me

Re: gas tank presure


He he, pretty funny. I think we've all done this.. About two months ago, a certain person I know spent the better part of an afternoon trying to start a motorcycle with the ignition turned 'off'.

Re: gas tank presure

Leon Swarmer /

Actually just blowing into the tank while it is sitting still not running has helped sometimes..but I prefer to put a sheet of platic with a slit in it between my lips and the tank. I saw one guy try this with an air compressor and he blew out a seam in the tank..ooops. Your lungs aren't strong enough to break the tank.

I love the visual of trying to do this while driving it down the road.

Re: gas tank presure

Happens to everybody at some point.I think its called a mental block.Peace.Jerry.

Re: gas tank presure

can you put a 2stroke top end on a mental block? or do they run diesel? haha moped joke

Re: gas tank presure

that banjo bolt is what got me once as well.

carbs this small have problems with fuel filters, or so has been my expearnce with motorcycles, you have to be carful with your low fuel presure not to get an air bubble traped in the line around the filter that gives you a vaporlock like affect.

Re: gas tank presure

thats what would happen, air would go through the line and lean me way out. i would have to idle my way to the gas station at 20mph. Very carfully acclerating

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