Fresh rebuild; starts fine, then rough, then died...

[Rabbit79]

I had roughly the same problem after my recent re-build..... Mine would idle OK but when I'd get on the throttle it would start to splutter. I had air bubbles in the line between the filter and pump so I figured fuel filter.... changed the filter twice.... still didn't fix it. Eventually I ended up pulling the supply line off at the tank and gave it a couple quick shots of air right into the tank. That would fix the problem for about 50 miles and then it would start doing it again. Finally after about 3 times of doing that it cleared up for good, have about 3000 miles on it since then with no problems. From what I understand there's a screen over the feed line in the tank (although I can't say that with certainty as I've never actually had a tank apart, but seems I remember reading it somewhere), and my guess is it got clogged as it sat for quite awhile. A couple things that worried me about doing it that way was that giving it air like that might rupture the tank or make the sending unit leak..... made sure I had the fuel cap off when I did it..... and the other was that I might blow that screen completely off....... if I did I can't say, but if so it hasn't caused me any problems up to this point. If you're worried about that though might try it from the front as Man53 says. 

[sparkoid]

Final Report.

First of all, thanks guys, your posts were all thought provokers, and all pointed in the right direction.

Looks like the whole thing boiled down to priming.  I did just about every check you guys suggested, including blowing the lines backwards (disconnected the hoses from the tank and routed them into a clear food container so I could see what came out; nothing but clean fuel).  I dropped the tank, looked inside, pulled the screen, it was (mostly) clean as a whistle.  Flushed the tank, touched up some of the rust hiding on the *top* of the tank, back in place.

I also plugged the feed line at the tank side and fired up the Mighty-Vac into the fuel hose going into the pump.  Held vacuum very well, so no leaks.  Now WTF?!?

All that was left was air in various places:  the pump, the filter, the tank line.  So I primed.  Held the filter-to-pump line up and dripped fuel into it until the line filled, and stayed filled.  (This took awhile; that pump can pack in more fuel than I expected, so much so that I started looking on the floor for "excess".  Hopefully, it was sneaking out the return line and back to the tank.)  Before I reconnected the pump, I poured fuel into the top banjo hole above the filter until it topped off.  I expected to *not* be able to top it off, given the fuel would follow gravity back to the tank, but after awhile it did top off.  Go figure. 

Buttoned everything up, said a quick prayer to St. Jude, patron of lost causes, and turned the key.  Immediate, laid back idle.  Stayed that way for 15+ min.  Now it's time to drive it around the block, then 2, then 4, etc, etc, to check the *other* stuff I did.  So much for the scenic route to a vary basic problem I could have nipped in the bud. 

So let that be a lesson to me; moral of the story, if one depends on suckage to get fuel through a 6+ foot soda straw, uphill, air is the enemy...