Iv'e got a clear fuel line hose and noticed alot of air moving to carb. Every time it sputters or backfires I see a surge of air coming out of fuel pump. Could the fuel pump be sucking air and pushing it to carb causing it too backfire, or is the backfire causing the surge of air? Backfires thru air intake at midrange, can't even get it to wind up all the way. Fuel supply problem? New main jet, diaphram. Carb has been cleaned, can't find any leaks in the boots. Plug is always dry, even if I kill at half throttle and check. Have tried different plug, cleaned gas tank, and tried without inline filter. Any ideas? I'm about out of them and getting frustrated.

 

your fuel pump could have a torn diaphragm or leaking gasket, and is pumping air. if you have checked everything else, then thats where i would look. especially if you can see air bubbles coming from the fuel pump. $40 for the diaphragm kit.

X

 

What is the year and engine size of the Magnum?

 

Its a 96 425. Also checked cam, lobes aren't flat. If timing got "off" would that cause a miss thru out the range, and on every stroke? Still leaning towards the fuel pump, there shouldn't be any air in gas line, right?

 

Have you checked the fuel vent line for being plugged or pinched?Also a bad cam could cause this too along with a bad fuel pump or even a bad coil.
If you wanted to try a good fuel pump I have one PM me on that.

 

Hey FTWFLH are those pumps driven by crankcase pressure pulse. Fuel pump diaphram, I wonder for testing purposes whether it would run on gravity. Don't know never tried it.

 

They run off crankcase/engine vacuum

 

As long as the quad doesn't have the "large" tank (5 + gal tank design that extends down in front of the engine) the fuel pump is not necessary - if you have the normal flat bottomed tank you can bypass the fuel pump with no problems.

 

I beg to differ.All Polaris 4stroke use this pump it helps on constant fuel delivery.

 

<div class="FTQUOTE"><begin quote>Originally posted by: ftwflh

I beg to differ.All Polaris 4stroke use this pump it helps on constant fuel delivery.</end quote></div>

Hints: the word "helps".(no pun intended) i believe if the gas tank is positioned above the carb/engine the pressure in the tank will put enough gas in the carb to run fine. maybe your intake valve is burned i am not that familiar with these bikes.