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Fuel pressure issue? or volume issue? in a Boat.

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Pale Rider:
Hello All, thanks for the add, let me give a little back story: I`m working on my 20ft Boat which  has recently been repowered (last season) with a non Vortec roller cam 350 SBC. Weiand intake, GLM high flow exhaust manifolds, DUI marine ignition. I have run a brand new Holley 4165 Marine 650 cfm Vac secondary spreadbore and a professionally rebuilt Large bore Rochester set up for this 350.  With that said I was testing out propellers and max rpm threshold which is 46-4800 RPM for my boat last season and experienced the boat falling off at higher rpms if the throttle was held wide open for more than a few seconds. The fuel system is brand new with a Carter 6-7 psi pump and water separator. no real restriction in the stock fuel line routing. For this new season I have installed a Autometer marine fuel pressure gauge (digital/electric/transducer) and an engine vacuum gauge to further test the fuel system. This years run with the Holley, dialed in correctly had the same issue of the boat falling off trying to reach WOT, I felt this @ approx 44-4500 rpm. The fuel pressure gauge reading 6.5 psi at start up and cruising rpms between 2800 up to 3400+ being good and steady. Occasionally I would see the gauge drop to 3.5-4 psi randomly during cruise and wot runs. since this writing I have switched back to the mechanical secondary Rochester and had the boat out yesterday. I was unable to push to max rpms bc the waters were rough, but the boat idled and ran very good with a bit better throttle control with the exception of seeing the fuel pressure gauge drop to 4-3.5 psi. So I didn`t push or load the engine any more from this point. The boat is a heavy Gal, and pretty much needs a lot of throttle to get up on plane a scoot, which really isnt the issue. The issue is at WOT runs trying to test for max rpm and dial in the size prop needed. Right now the boat is happier with the Rochester and 14 x 19 four blade prop. So I am content with the Rochester but still need to find the cause for the pressure dropping off.
After reading from several sources the Rochester needs 4-5 psi and then some have said 6-7 before fuel pushes past the needle and seat. what are the correct specs for my application, and how would I address the pressure issue. According to mercruiser the pump that Im running is good  for the Rochester since its pretty much OEM.
so all new lines and hoses, new pump, new WS/filter, tank has no water or junk in it, vent appears to be fine, and tank does not collapse. I would like to stick with a marine mechanical pump. In speaking with fellow boaters and hot rodders, it seems like out of the box parts these days are not calibrated to spec very well. My Friends have told me out of the box holley pumps are reaching 0ver 10 psi when they should be 7 max.
Most people/boaters would probably not push the boat to test for max rpm/load for prop sizing and or realize there is even an issue. So I either have a defective gauge, not enough volume @ wot, not enough pressure @ wot, or defective Sierra pump (made by carter). Or if there is a sock or filter on the pick up tube in the tank, which by the way is a PITA... something that should not be disturbed... lol
Thanks for reading, what are ya`ll thoughts?
Pale Rider...

Cliff Ruggles:
"and a professionally rebuilt Large bore Rochester set up for this 350."

Tell me about this carb, who did it, what has been done to it, part number that it started life as, etc?

"After reading from several sources the Rochester needs 4-5 psi and then some have said 6-7 before fuel pushes past the needle and seat."

This statement is incorrect, actually absurd.  Anyone telling you that anyplace is simply very poorly informed, little if any real experience with this sort of thing and simply regurgitating old/outdated information they heard, thought they heard or read someplace (happens a LOT on the Internet on a variety of subjects these days).

The only Quadrajets that had fuel pressure issues were very early designs and only then when you tried to use huge fuel inlet seats in them.  Even the early units with the poorly located hinge pin will EASILY take 6-7 psi with a .135" high-flow fuel inlet seat in them.

Later models will be fine with larger .145" or even .149" seats to at least 8-10psi without issues.  I use a later model Q-jet on the engine powering my Ventura.  It has a .145" N/S assembly and fine at 7.5 psi now for over 20 years.  This includes drag racing (1.59-1.61 60' times, and hard braking/cornering).  In all these years it's never faltered once for any reason.

Getting past all that a Qjet only has ONE needle/seat assembly so in high performance/high HP applications fuel delivery and the size of the N/S assembly become important.  I'm sure during your reading you also heard that the small fuel bowl is an issue, another myth because you are either keeping up or you aren't.

I've tested Holley carbs with two .110" N/S assemblies/two large fuel bowls against Q-jets with high flow seats and BOTH fall over at high RPM's when fuel delivery is insufficient for the power level of the engine.  About all saw with this (did the testing on my own engine at the drag strip) was that the big 850 DP Holley I was testing would go just a tad further down the track before power fell off as it took a little longer to suck the fuel bowls low/empty.

Personally I'm not a big fan of mechanical fuel pumps for high HP applications because they are not free-flow, the fuel stops and starts with each stroke of the pump.   Ran in a "dead-head" scenario they can and will cause flooding issues even when the fuel pressure isn't excessive for the type of carb being used.   LOTS of opinions on that one, and some folks get away with more than others so you have to sift thru much of the information involved with that deal, and probably do some of your own testing to find out what works and what doesn't.


.....continued

Cliff Ruggles:

I like electric fuel pumps, especially the gear type (vane pumps are cheaper and louder but work well) because they are reliable in long term service and quiet, but they are also expensive.

I also see a lot of folks using electric pumps as "pusher" pumps feeding high output mechanical pumps.  Varying results with that deal, but if you are using a high flow electric pump the mechanical pump becomes your regulator and restriction in the system at the same time.

I've had the best success here with high performance set-ups using high output electric pumps mounted at or very close to the tank, preferable behind it in if the car is drag raced (good traction) and running them to a bypass style regulator to return unused fuel to the tank when it isn't needed.  This takes the load off the pump, it runs quieter and lasts much longer than running it "dead-head".

Hope some of this helps, I can provide more information once the questions above are answered......Cliff

Pale Rider:
let me see if I can better answer your questions and clarify some things.

This carb is in a Boat. not a high performance boat, but around 270+ HP. Alpha 1 Gen 2 outdrive.

The fuel pressure info I posted was from Summit racing, QuadrajetParts.com, iBoats forums, and several other boating forums posts relating to fuel pumps and pressures. And testimony from shop owners that quality control is an issue from new pump to new pump.

I agree with what is said about the net, but I do my research the best that I can.
My personal high performance experience with Holleys, Ededlbrock, FI, Turbos, and supercharging unfortunately did not include Rochester carbs bc they were considered voodoo back in the 70`s when we all had cool cars... lol

From what I have in my notes, the original boat engine being a 5.0 LX Mercruiser used this carb:
170805565. which had a divorced choke, side inlet.  was widely used between 1982 thru 1995.

I purchased my remanufactured Rochester from Guaranteed Carburetors from Largo Florida, and used my original carb as a core. I should have just kept it for prosperity. I do not have that model number carb in front of me. but on their website it is model Y40-1AE which includes and electric choke for the mercruiser 305/350 260+HP

I have your Rochester Quadrajet Carburetors book # SA113 and have used the information to identify the reman carb that was sent to me as being a large Bore due to the Hump or bump in the primary bore. Typically used in Marine applications.

 

Pale Rider:
continued:



please understand I am not complaining at all of the performance of the Rochester or Holley 650 that I have Ran and compared. Im trying to isolate a possible issue with fuel pressure. I do not race the boat it is for pleasure, but it was necc to max out the rpms to match the max rpm to prop size to be in a specific range of 46-4800 rpms.
currently everything and every part is compliant with USCG rules. The HEI ignition is also wired correctly. all fueling parts from tank to water separator  to pump to carb are all new. So I was indeed surprised to feel a drop off at the higher rpms holding it wide open. With the new fuel pressure gauge I was able to see the fuel pressure drop, BUT technically still in the range according to service manuals and manufacturer of the fuel pump. It could very well be a defective or incorrect pump.
I would like to keep a mechanical pump for the simplicity and that is what came with the boat. If I didn`t push the boat for max rpms, I would not have felt a drop off. I have a few more tests I can perform to check for flow and volume and if all things being normal I could just install a new Holley mechanical that operates between 6.5 - 8 psi...
This was the information I was seeking in my original post. what fuel pressures can the rochester tolerate so I can make the correct choice and if I would need a regulator or not.

I do completely understand what you are saying. I have run numerous fuel delivery systems from electric/canister style filters from the tank sump in the rear in Auto`s and monitoring the gauges ie, fuel pressure and wide band O2s etc in past and recent projects. However in this boat which is for the most part pretty simple, to convert to electric the right way, needs pressure switches an failsafes in the system, and addition lines if Im using a fuel return. I am going to try and keep using the mechanical pump if possible. 
it may be the pick up tube in the poly tank, which I dread to unscrew, if you know what I mean. The tank is clean and was evacuated for the last few years, but who knows if a bug made a home in the vent lines... so far nothing I can see or point to in that regard, bc I have good venting, no collapse and correct flip up tank fill cap...

Thank you for reading and replying Cliff!

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