not pulling fuel
 

working on a buggy for a buddy of mine and having some issues.
its a GS storm and has an HPI .21 motor.

we cant make it pull fuel to save our life. if we prime it by blowing fuel into carb, it will fire up first try, but it wont pull on its on.
we checked the base of the carb and back plate, but cannot find a leak. also tried new fuel hoses, etc.

can anybody give me some ideas as to where to go to next?
i know the motor runs, but without the vacuum, the motor wont pull the fuel.

this thing has stumped me for going on 3 days!

Now I'm the first to admit I'm a newbie here, but I was under the impression these thing don't pull fuel by vacuum, but push it by exhaust pressure? Is your tank lid sealed tight? Any exhaust leaks in the header to engine or header to pipe? I'm certain some more experienced people will come on here and clarify

There are actually quite a few reasons you have no pressure. Of course they all have to do with an air leak or blockage.

Front bearing on the engine is leaking.
Engine case has a crack somewhere.
Fuel tank has a split at the seam, or a crack, or a hole
Pipe has a clog in the pressure nipple
Pressure nipple on fuel tank is clogged.
Pressure line has a hole in it.
Cooling head and button are loose
Carb is not tight.
Pinch bolt leaking.
Hole in the carb slide boot.
Fuel line is clogged or leaking.
Carb nipple is blocked.

There may be more but I'm tired of typing.

Start going through the list one by one. Good luck.

All motors pull some vacuum as they suck in through the carb. But with the amount of fuel ours need, gravity feed tank and vacuum, like on your lawnmower for example, is not enough. So it is supplmented by exhaust pressure.

Zkid, are you blowing in the exhaust pressure line and you get fuel to the carb? If so I think first guess would be exhaust seals as it works until the engine is running (ie no exhaust pressure)

Jaz's list is good

thanks guys.
it was running when he got the thing a few weeks ago but now it wont.

im going to check exhaust then work through that list