another lost prime MC8

[rcbeam]

Lost my first post so here goes again.  Been working on replacing the aftermarket alternator that the P/O put on and cleaning up bad wiring for months.  Looked at several options for replacement alternators, and ended up buying a unit from ELREG.COM.  Got a 24V 150A belt drive.  Looks ok as far as alternators go and should be plenty of power since I do not have the bus heat/Air.  This unit does have an IGN terminal on the back and they instructed me to supply this with 24V when the switch is on to excite the alternator.  Did all that, and double checked all my wiring and mounting.  All looks great.  Started up the bus, checked alternator with VOM meter and no voltage.  Not putting out anything.  Problem #1.

Engine lit right off. Hasn't been started since sometime in February, so about 4 months or so of sitting.  Ran for about five minutes and started faltering and quit.  I started it from the rear, and even had my hand on the fuel lever when this happened, so I know it was in the fuel ON position.  I pushed on the throttle and nothing... she just quit.  From my many hours of reading on this board I told my friend with me that she probably lost prime.   Problem #2.  By this point in the day we both were beat and too hot to fool with anything else.

It may be a couple of days or so until I get back to it, but I figure when I take the filters off I'll find them partially empty.  I have two questions really... could it be that she lost prime from just sitting so long without running and there is really nothing wrong?  I hate to waste more time looking for something that isn't there.  My second question is there a methodology to tracing down a lost prime situation?  Do this, then do that, then that, etc.

I'm trying to look on the bright side and figure I might as well get lost prime training now rather than on the side of the road somewhere later on.  Any recomendations for you guys?  Can't start to troubleshoot the alternator until I get the engine back up and running.

[bobofthenorth]

The short answer is that it should NOT lose prime from sitting. Hate to be the bearer of bad news but tracing a vacuum leak can be a real bear. Once you've confirmed a lost prime I'd swap the check valve out first - they're cheap, easy to change and if it doesn't fix the problem at least you'll have a working spare. The workaround if you don't want to waste your life looking for a vacuum leak is to put an inline pump at the tank. That's been discussed to death here - a search will turn up enough threads to put you to sleep.

[rcbeam]

Bob, thx for the reply.  I did some searches on the two boards on 'prime' and got some hits, but was hoping for a method to track this down.  Maybe I'm making it more complicated than it is.  I tend to do that.