Staving For Fuel.....

[harleyrider116]

The motor is a 1984 fresh water cooled 5.7 mercrusier. Motor runs fine for a half hour for hours on end then out of no where, it's starving for gas or has no gas shooting into carb if you operate throttle manually at carb....I have replaced; fuel pump (mechanical style), fuel filters, rubber fuel hose from tank to pump, opened up (cut a hole) the fuel tank hoping to find some kind of "filter sock" on the end of pick up tube but nothing there, removed the anti-syphon fitting on fuel tank, replaced fuel vent.....Nothing has changed.
This problem comes and goes like it has a mind of it's own and has been driving me crazy now for 3 or 4 boating seasons. I have had it to mechanics/marinas, contacted Merc, yet no solutions to the problem....I just found this forum and am hoping to find a solution here...any help?

 

[Haut Medoc]

Re: Staving For Fuel.....

Welcome to iboats!....
Is it intermittant or does it occur only at (or near) wot?
Has the carb ever been rebuilt?
What carb are we talking about, BTW?.....JK

 

[harleyrider116]

Re: Staving For Fuel.....

Problem is intermittant... I run the motor 3K rpm and under...sometimes when problem happens the engine will run at 1-1.5k rpm but if I try to give it fuel it dies...other times no fuel shooting in to carb when I manually operate throttle at carb....Carb has never been rebuilt as all mechanics have said if it runs fine it's OK. Carb is a Rochester quadrajet.

 

[Scaaty]

Re: Staving For Fuel.....

Look for somwhere the fuel line might be getting hot, causing vaopr lock?

 

[salty87]

Re: Staving For Fuel.....

have you tried hooking up an external tank yet?

 

[harleyrider116]

Re: Staving For Fuel.....

Yes, tried external tank and it ran great...hooked the main tank back up and problem came back...then went back to external tank...and again it ran great....that's when I decided to open up the main fuel tank, looking for a strainer/filter of sorts on the fuel pick up tube but to my dissapointment none was found....I even replaced the vent on the side of the boat....

Engine has all steel lines from spin on filter up to carb. I have run with spark arrestor, and engine cover off to keep as cool as possible and problem still comes and goes....

The boat ran (on main tank) after the tank was cleaned and filled with fuel for 4 -1 hr. trips with no signs of the problem...then all of a sudden the problem came back 3 weekends ago...!!!!!! Now I took the boat out last weekend and put almost 2hrs of crusing at 3-3.5K rpm's and it never skipped a beat...no problems...!!! I'm really going crazy on this one....I called customer service at mercusier factory and they wouldn't allow me to talk with a tech...told me to go thru a dealer and they would have to call....been there done that to........no luck.

 

[stevieray]

Re: Staving For Fuel.....

Harley - when you tried the external tank, did it run perfect every time, at all speeds & for the length of cruising time you do on the internal tank?

 

[Haut Medoc]

Re: Staving For Fuel.....

I'd like to hear the answer to Stevierays question....
I would take another look at the anti-siphon valve....
I think it may be crap from an old tank....Possibly....JK

 

[harleyrider116]

Re: Staving For Fuel.....

Had a 6 gallon Jerry Jug with me. It ran PERFECT each time it was hooked up....could not run for extended time (as with internal tank), only had the 6 gallon jug and when running with the secondaries open it sucks that fuel right up so I kept rpm's 3K and below where I normally run the engine....

The anti-siphon valve was swaped out for a straight thru fitting. That was first thing I went for 3 or 4 seasons ago....wish it was that simple....

 

[Haut Medoc]

Re: Staving For Fuel.....

Have you checked/changed the water separating fuel filter & the screen at the carb?
The next step would be to check the fuel pressure with a gauge when this occurs.....
I'm still thinking that you are getting garbage from your tank.......
You should be able to get at least 15 minutes at full throttle with 6 gallons....
If you can't recreate the symptom with the external tank, then I would say that your carb is fine & you have a restriction.....
Time for the pressure test......JK

 

[stevieray]

Re: Staving For Fuel.....

Well, this ain't gonna be pretty, but what I'd do next is get a stack of empty jugs lined up, unhook the fuel line from the fuel pump inlet, hook up a pump that will pull at a similar rate to the engine fuel pump, tube the outlet into the jugs & monitor the flow. If you have a problem in the tank or vent line, this should tell you - the flow should shut off after some time just like when you're running.

 

[harleyrider116]

Re: Staving For Fuel.....

I have not been able to recreate the problem with 6 gallon jug. I went out last weekend (with the 6 gallon jug)as I previously metioned and had no problems running with internal tank....I have changed spin on fiter/separator and intenal carb filter. I would tend to agree it's not the carb. How do I check fuel pressure? Where would you hook up a gauge? Is is possible to check vaccum pressure on fuel line also? If yes, how would this be accomplished?...I really appreciate the replies and brainstorming....

 

[Haut Medoc]

Re: Staving For Fuel.....

http://forums.iboats.com/bbBoard.cg.../bbBoard.cgi?a=viewthread;fid=24;gtid=1107009
Courtesy of Don S....

 

[stevieray]

Re: Staving For Fuel.....

If it's not something rattling around loose in the tank that can intermittently stop up the pickup tube, or a restricted vent line (since the fitting was replaced), I'm officially stumped.:=