Offshoreonly.com - Fuel pressure loss at high rpm

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - Fuel pressure loss at high rpm (https://www.offshoreonly.com/forums/general-q/353750-fuel-pressure-loss-high-rpm.html)

Twin engines, both setup the exactly the same yet one is loosing pressure. Maybe the carb is dumping to much fuel at higher RPM. Look and exhaust tips and pull some plugs to see if its running rich

it seems to me like the pump can not keep up with the engines demand.might be time for bigger pumps.

Whenever I lost pressure, it was a dirty/plugged filter. I run Fuel/Water sep > 100 micron > pump > 10 micron > dist block w/ return regulator > carb. Is a filter getting dirty? (This is on an electric pump setup).

ALSO, I just noticed one of my lines might be getting restricted coming out of the bulkhead, turning 90deg. I saw it dropping on the gauge last time out, but put the boat away before I could determine root cause. (Filters looked good when I changed them).

Check to make sure you have smooth transitions, and no kinks or collapsing. For it to happen on only one, something is being restricted, or the pump is whooped? (Some of this sounds elementary, which you have probably already checked).

Quote:

Originally Posted by Sonichunter (Post 4624696)

Looking for some help tracking down a fuel pressure issue. Port & star both idle at 7lbs. At around 3800, port begins to fall off and sometimes dumps right off to 1 above 4500. I get out of it at that point so I’m unsure if I’d lose it completely above 5. Occasionally if I walk it up really slowly, pressure will hold. Things I’ve already tried

-swapped upper&lower pump(both new 2x)
-new fuel lines from tank to carb
-inspected tank, no issues or anti siphon
-swapped senders& gauges from other engine(same result)
-ran fuel line directly into 5gal can to eliminate a tank problem
-lobe seems fine in water pump. Changed oil
-bypassed water separator

i did run it in a hose once while looking in the tank. The only odd thing a noticed was that when throttled back to idle quickly, an air bubble spit out of the pick up tube. I have no idea what would cause air introduction since I’ve replaced every line.

maybe a crack in the pick up tube.

Swap the pump from the other motor and see if th problem follows.

Quote:

Originally Posted by AllDodge (Post 4624930)

Twin engines, both setup the exactly the same yet one is loosing pressure. Maybe the carb is dumping to much fuel at higher RPM. Look and exhaust tips and pull some plugs to see if its running rich

It was tuned on dyno. I won’t rule anything out at this point though, I’ll swap carbs and see. Thanks

Quote:

Originally Posted by sutphen 30 (Post 4624941)

maybe a crack in the pick up tube.

I ran it once with a fuel line directly into a gas can. Same result.

Quote:

Originally Posted by indysupra (Post 4624949)

Swap the pump from the other motor and see if th problem follows.

forgot to list that, but I’ve tried.

Did you actually pull the pick up tube out of the tank? Eddie young has often found some funky install issues there from the factory.