Fuel Pressure Question

**Tittyman** · 06-04-2012, 06:29 PM

I'm still getting my boat dialed in after the valve job. Saturday we ran the boat on a hose in the garage..worked fine. Then put in the water on the ramp and adjusted the timing. When we left the house I forgot to turn off the fuel pump. The pump was hot and the fuse was blown when we got to the ramp..cooled the fuel pump down and replaced the fuse..set the timing.All seemed good. Ran the boat yesterday for the first time..started out good and then had to pump the gas hard just to keep it running. Fuel pressure gauge is at 6.5 lbs. I mickey moused the fuel pressure guage like in the photo..question is could the pump be failing but because the way the pressure gauge is temporarly installed..could I actually be getting a false reading and really could use a new pump..thanks

**Rawhide** · 06-04-2012, 08:28 PM

If you have a gen IV block, why not run a mechanical fuel pump? Also electrical pumps should push fuel with your type of set up.

**Tittyman** · 06-04-2012, 08:47 PM

Originally Posted by Rawhide

If you have a gen IV block, why not run a mechanical fuel pump? Also electrical pumps should push fuel with your type of set up.

It's a mid 70'S LS7..12.5 to 1...It's had a Holley Blue pretty much it's entire life..this pump is only a couple years old. This spring before taking it out for the first time this summer I put on a new pressure regulator because I was always getting float creep. When I put the guage on the old regulator it read 14 LBS. Put the new one on and it's set at 6.5 LBS. Maybe that's my problem, way too low fuel pressure with the compression and cam combination? Then before I could dial all that in I had to deal with the broken valve spring issue..I had the extra stainless line laying around and thought I would just use the other port on the regulator for the pressure gauge.

**jetboatperformance** · 06-04-2012, 09:01 PM

Originally Posted by Tittyman

It's a mid 70'S LS7..12.5 to 1...It's had a Holley Blue pretty much it's entire life..this pump is only a couple years old. This spring before taking it out for the first time this summer I put on a new pressure regulator because I was always getting float creep. When I put the guage on the old regulator it read 14 LBS. Put the new one on and it's set at 6.5 LBS. Maybe that's my problem, way too low fuel pressure with the compression and cam combination? Then before I could dial all that in I had to deal with the broken valve spring issue..I had the extra stainless line laying around and thought I would just use the other port on the regulator for the pressure gauge.

Where do you belive/desire the fuel pressure should be ? and personally I'd mount the pump lower and off the engine Tom

**Tittyman** · 06-04-2012, 09:04 PM

Originally Posted by jetboatperformance

Where do you belive/desire the fuel pressure should be ? and personally I'd mount the pump lower and off the engine Tom

Thanks Tom..it's been right there in that location forever..or I would move it..I'm thinking the fuel pressure should be 7-8 LBS or am I really off base..

**BrotherWolf** · 06-04-2012, 09:30 PM

Originally Posted by Tittyman

Thanks Tom..it's been right there in that location forever..or I would move it..I'm thinking the fuel pressure should be 7-8 LBS or am I really off base..

the reading your getting is that at idle or at 4k 5k 6k? also when you set the timing was that at idle or 3k? etc

**jetboatperformance** · 06-04-2012, 09:50 PM

Originally Posted by Tittyman

Thanks Tom..it's been right there in that location forever..or I would move it..I'm thinking the fuel pressure should be 7-8 LBS or am I really off base..

We tend to run 6.5 to 7 for Holleys and Holley clones (taking into considertion marine float bounce) just like electrics to be well below the fuel cell level and as close to the source as possible and not where they can absorb engine heat ...

**Shaun** · 06-04-2012, 10:26 PM

6.5 is plenty of fuel pressure to feed that engine at idle or cruising, if the problem was at WOT then maybe.

**gn7** · 06-04-2012, 11:43 PM

I tried to think of a worse way to plumb a fuel pump and couldn't. You win hands down. Why would you mount the regulator there. It belongs between the carbs. At the very least, one carb off one outlet and one off the other. Not a tee with the other to your gauge.

My guess is that your pump is no longer running at full speed. But 6.5 lbs is enough to feed twice the HP you making.

**$uperJoe** · 06-05-2012, 12:08 AM

i had a similar issue teh first time i mounted my pump. started with a holley red. wouldnt cut the mustard. swapped to a new blue since the red had served years of service on other applications. still no go. called the holley tech guy and he stated that these pumps are not at all meant to be pullers. mount it below the fuel system and as close to the pick up as possible was his advice. since i cant go below the boat i have it level with the floor of my tank and a seamless stainless line from the tank to the seperator-filter and then into the pump. if i crack a line after the pump has began the siphon it will drain the tank dry with no power. this means no load on the pump for suction. then stainless .500 all the way to the reg mounted between the carbs. less than 14 inches fuel injection rubber line in my whole system.
set to 5.5lbs and never run out of fuel again after the mods were made.

ps rubber hose has a measurable drag psi resistance per foot. with the blue installed at the back of the boat, sucking through about 15 foot rubber hose i watched the pump collapse a clear fuel filter as if it was a stepped on old beer can.

not the best picture but you can see the stainless come in the rear by the starter and the reg between the carbs

**Tittyman** · 06-05-2012, 08:00 AM

Originally Posted by BrotherWolf

the reading your getting is that at idle or at 4k 5k 6k? also when you set the timing was that at idle or 3k? etc

The boat will not idle below 1200-1300K..it will not hold and idle at less than 22*.

**Tittyman** · 06-05-2012, 08:05 AM

Originally Posted by gn7

I tried to think of a worse way to plumb a fuel pump and couldn't. You win hands down. Why would you mount the regulator there. It belongs between the carbs. At the very least, one carb off one outlet and one off the other. Not a tee with the other to your gauge.

My guess is that your pump is no longer running at full speed. But 6.5 lbs is enough to feed twice the HP you making.

I know it's a bad location, but it has been in that same spot for 20 years..with the same setup and the two lines coming up to the carbs from one port on the regulator..I just threw on the fuel pressure gauge

So your saying I could have a fuel pump showing 6.5 lbs of pressure but not running at full speed to feed the carbs even though it says 6.5 LBS? Thanks GN.

**$uperJoe** · 06-05-2012, 08:58 AM

Originally Posted by Tittyman

So your saying I could have a fuel pump showing 6.5 lbs of pressure but not running at full speed to feed the carbs even though it says 6.5 LBS? Thanks GN.

not to steal any from GN, but pressure is not volume. simple and free thing to try. swap the fuel line from the tee with the pressure line that goes to the gauge. put the gauge off the side of the tee if you need a gauge on the line. also pull the cover off the bottom of the pump and see whats going on inside. could be it has just spun to long and the blades are worn out and not sharp anymore.

**jetboatperformance** · 06-05-2012, 09:01 AM

Just a follow up but are you running a bonfide relay with your pump (you mentioned a fuse?)

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Fuel Pressure Question

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