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

[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!

[Kenth]

I have yet seen a marine Quadrajet with large bore primaries, no such animal.
Unfortunately sounds like you´ve got a "frankencarb" car quadrajet from the "remanufacturer" instead of a correct marine unit, thus your issues.

[Pale Rider]

my files are to large so I couldnt post a pic... as mentioned the rochester runs great. the issue is with both the holley and the previous test prior to the Holley on the Rochester. truth be told this rocky runs like a beast up until the demand is high after 43-4400 rpm. not a problem planning off in this heavy gal. I have to agree, the shop built something from something and the bump in the correct position is indeed there. crap I was excited to see this, lolol, anyway I`m still looking for the pressure and or volume drop cause.

Kenth: I don`t doubt at all what your saying. the original had a divorced choke whereas the one I have now is electric choke. I do not usually mess with Rochesters, and most of the mercruiser`s Ive seen or worked on were Rochesters or Carter/Weber/Edelbrock.

[Cliff Ruggles]

Now we are getting somewhere, but I hope your sitting down when you read this.

You have a "remanufactured" carburetor not a "professionally built" unit.  You should have kept your original and had it completely/correctly rebuilt instead.  If that were the case you would very quickly be able to isolate your issues between the carb and fuel delivery...FWIW

I haven't seen a Frankencarb Marine unit to date that was worth two squirts of duck poop, or even had Marine rebuild parts in them, and that includes unit from I-5, National and where you got yours from.  Sure they sell gobs of them, but they are NOT Marine units or do they even really know what to use in them or how to calibrate them for a Marine application.  Those "generic" calibrations they use, driving lead plugs in holes, hacking up/smashing down the idle airbleeds, driving in restrictors, trying to resize MAB's, and the list goes on and on and on ends up with a product that from my observations and testing is a complete pile of bovine excrement.

I don't say any of that to make money or steer any work in my direction, I'm too busy as it is and retired in April.  For the record I'll still be selling parts 2-3 more years and doing a couple of carbs a week for the Bourbon fund, but NO MORE restorations, bottom of the farm pond resurrections, or hacked up junk wanted.

As far as your "Marine" remain, I will just say that I've had scores of them sent here when folks thought they were sending me a "Marine" carburetor and I will NOT rebuild them.  Instead I source out a real Marine carb instead as it will be a home-run every single time when completely/correctly rebuilt using the correct parts.

I just did this for a customer in Washington state after he inadvertently sent me two POS remanufactured Marine carbs that were on the boat he just purchased.  They a MESS, right down to the dog-leg vent tube that blocks incoming air and sits right over one of the MAB interrupting it's function.  I had him source out two original Marine units off of Ebay (different part numbers) but I built him two identical units for his engines and good to go.

So basically if you want help with this project you'll need to locate a correct Marine carburetor and completely/correctly rebuild it.  I'm betting ALL the problems will go away at that point and you'll be able to run a mechanical fuel pump with stock filters, lines, etc........Cliff

[Cliff Ruggles]

PS:  The "blanket" statements from your sources about how much fuel pressure a Quadrajet needs are still inaccurate.

I don't want to write another book here, but there are a LOT of variables involved with fuel control, fuel pressure, float size, type of carb (hinge pin location), size of the float, type of float (brass or closed cell nitrophyl) and size of the hole under the needle.

If you don't understand any or all of that, and messing around with different models, small brass floats, and different N/S assemblies the result will be ALL OVER THE MAP, hence most likely why we see so much varying information posted out there on the subject........Cliff

[Pale Rider]

Cliff, agreed,  yes I understand all that. I immediately saw the cross breeding when I received my reman carb from Guaranteed carburetors. and yes I should have kept my carb that came with the boat, even though I was not 100% sure it was original or not. when I installed the 350 repower into the boat a new Holley was also installed, hence the comparison conversation. The current issue is with either Carb. 1 new, 1 reman, same results.
Your honest information was what I was seeking in moving forward. It would seem its even hard to trust products right out of the box from New Carbs to remanufactured carbs these days. I have seen other companies install the dog leg vent tube in the same exact locations and questioned its position from other brands out there.
Thank you for the tutorial and information. I`ll get this sorted out. 

[Cliff Ruggles]

I hate to sound like doom and gloom and certainly do NOT intend on putting a big black cloud over anyone's project.

Even so I've found that it is better to up front, honest and direct with these things.

Don't know which Holley you bought but I avoid anything from them in the last 25 years or so.  I broke my own rules and got involved with a Street Avenger couple of years ago, only because a good friend of mine got it in trade for tree removal (he has his own company).  What a complete pile of bovine excrement that thing turned out to be.   I told my friend Simon that the next time I saw his dually coming up to the shop for me to take another look at that POS that I was replacing it with a Q-jet.  I must have worked on that carb a dozen times as he had nothing but troubles with it.  Well the day came and he called me from a job site when his truck wouldn't start.  I sent a flat bed for it, got it here, replaced the Holley with a Q-jet Motorhome carb with an electric choke.  His fuel mileage more than doubled, instants starts in any weather (the e-choke on the Holley didn't work and was wired open from day one) and the only time I see him now is when he brings me a bottle of bourbon at Christmas time!

I shot some quick photos of what they are currently selling as "Marine" electric choke Quadrajets.  They are Frankencarbs and I just toss them on a shelf here, source out an original Marine unit and send that back to the customer.  To date that move has been successful 100 percent of the time........Cliff

[Pale Rider]

ooof, I`m sick to my stomach now, wish I had found this forum and your book a lot earlier. I spent a good part of the day bouncing around in here reading peoples threads... Def a kick azz take no prisoners forum with fantastic information.

you and Kenth are correct, this looks more like a franken carb every second. I knew when I took it out of the box and the dog leg vent tube was loose, and it did not resemble what I had returned as a core, it was iffy. looks like they used a different main body, but without the provisions for . egr, timing, etc, they used  a Mercruiser style throttle base plate, and the top piece is secured with more torx style screws than the slotted that was on the original 17080565 divorced choke variety.

I asked for an electric choke model, and they built one. It does have the Merc style throttle lever base plate, but according to the numbers on the reman body it appears to be a M4ME. from what I can pull from an earlier picture in my file > 17085220, the 7th digit may be incorrect.

just for the purpose of this thread I will take some new pictures of the carb on the boat to show ya`ll whats there.
I am more curious as to why I "thought' I saw the bump indicting it was a large bore casting.

lets go back to the repowering the boat for a second. The Seller Lied! no surprise there, the engine was toast despite it ran, I don`t want to waste your time in how I discover automotive gaskets that rotted and caused leaks instead of using Marine gaskets, that`s a good beer story...

The cast iron intake was degraded enough in the thermostat area, I wanted to shed some weight and opted for a weiand dual plane. The Rochester that came with the boat had the very good possibility is was original equipment being only 105hrs on the hr meter for a 1994 boat. At that time I did not want to run it, it was divorced choke and I preferred the electric on the Holley. So I bought a Holley 650 cfm vacuum secondary, the phenolic 1 inch spacer, fabricated the correct length studs and bolted it down. The Holley peformed as expected.
now you say you don`t care for Holleys, I`ve had my bouts with them but for the most part they were ok.  the last run on the boat with the Holley had a weird throttle delay when pushed to the point of engaging the secondarys, then throttle creep with the stick in the same position. What I found was a loose enough vacuum secondary housing to cause a small leak and the delay in response, and no doubt earlier closing than what should have been. the electric choke housing was also loose. and I`m like wtf??? So I had this Rochester sitting right here and installed it and ran the boat, and here we are...
BTW, I did not go mazzo on the last ride bc the Misses was onboard, seas were rough and I want to eat if ya know what I mean... so I did not push the boat for max R`s this last time...

with all the changes to the Rochester over the years, I didnt think it was possible to meatball a carb from a bucket of parts and sell t as reman... silly me... its always the honest guy that gets burnt... live and learn...

[Cliff Ruggles]

The carb in the pics is one of many I have in the "scrap" pile.  Although at a glance it looks like it might be a decent unit it's nothing but a complete pile of bovine excrement and I will NOT use them.   Most customers don't even want them back so I have a shelf full of them.

Rochester NEVER used a huge "dog leg" vent tube on the front and it's a bad idea.  They fall out easily and hang right over the airbleeds on the side of the airhorn they go into.

Holley made some really good carbs over the years but that all stopped quite a few years ago and I avoid what they are currently selling like the plague.

There are half a dozen companies selling these Quadrajet "Marine" conversions.  The biggest outlet is Ebay, and what really amazes me is that they get good ratings so folks jump all over them.  Even so, every single one I've seen isn't going to work well if at all.

What I do see is that when I replace one with a real Marine unit the customers problems all go away and they use less fuel.  Pretty important these days considering how much Marina's are charging for it.........

[old cars]

I have 3 marine carbs on the shelf that I believe to be correct, 17080560,17080561,17080563(restored) 561 and 563 have mapped out the same specs within .001" accept for secondary rods. What do you think Cliff and Kenth

[old cars]

more