bertram31.com

Here is my setup-

454 / 340 hp (Gen IV?)
1 3/8" shafts
3 blade 17x19 nibral props
lightweight SF boat with no tower or top

At the end of last year I noticed that my WOT only got to 4000 rpm - port and 3800 rpm stbd. At the begining of last season I was aroung 4150/4200 on both sides. I had not chaged the stbd carb fuel filter and my flame arestors were dirty so I figured that I would take care of it over the winter and worry about it this season. I asked my mechanic about it and he mentioned that I may have a weak fuel pump.

I changed all filters and cleaned flame arestors before I went in the water last April. Still can't get the stbd. engine to go past 3800. Also, I have noticed that I need to push the throttle control further on the stbd. engine to get both engines to my normal 2800rpm cruise.

Does this sound like my fuel pump is starting to weaken or should I be looking for somehting else? Given the high number of blow boats in our town, it is tough to find good gas engine mechanics. Any input is greatly appreciated.

I had a bad spark plug that provided similar results.

Have you given a good tuneup? Checked timing and make sure it's advancing as it should.

Shafts turn freely? Could alignment be off. Rope, bag or something fouling the running gear? A bent blade?

As it's both engines with some issue could it be bad gas or old gas? You could try to run fresh quality fuel from a seperate tank and see if performance improves.

If your wondering about the fuel pump can you install a fuel pressure gauge to check it?

All good suggestions. I hadn't thought about a bad plug since it otherwise runs well at all RPM ranges.

Tuned up about 200 hrs ago. Cleaned the bottom recently and no issues with bent or fouled props. Replaced the fiberglass fuel tank the winter before last and have many full fueld ups since then. I also use Star-tron with each fill up.

I don't have a way to check fuel pressure but I am suspicious.

Any thoguhts Bruce?

Do a compression check, or better yet, a leak down test to see how your rings and valves are holding up. Check timing!! I lost an engine to that last year.

Crae-

I have a good compression tester if you need it. I'll even deliver it to you because I want to check out your tank install again to prepare for my winter project. If those are last year's plugs (and were fogged), I'd also replace plugs while doing your compression test. Take a look at the plugs when they come out--mine weren't oil-fouled, but showed signs of oil, in each of the cylinders that came up low. Check your timing and make sure you're getting full advance (I think it 8 degrees at idle, 30 degrees at full advance, but check a manual, amd make sure you get the rotation right). I'd expect more of a miss with alot of problems, including fuel, rather than running well and just loosing some off the top. I don't have a fuel pressure gauge. Hate to say it, but sounds like my motors--run great but lack their old power. Mine are just worn.

John

Mack Before you go and do all that make sure the vent to the tank is clear? Mud doubers shit I cant speel Sorry got to go do the dishes before the Bride gets home.
Chris

Are you sure that the tachs are correct.....is it possible that the motors are indeed running correctly but the tachs are off.......probably not since both are acting up but something to look at.

You guys may not believe this but........when I first got DeNada she would turn 4100 WOT........I always thought that it was a little low but.....

Then one day I decided to fix something that had always bothered me and that was to level up the carbs. The setup was 454's and the Quadrajunks were bolted directly to the intake manifold.......engines mounted at 14/15 degree then add the running angle......the carbs were sitting at such an angle that it bothered me......badly.

I purchased 4, 7 degree carb wedge plates and put 2 of them underneath each carb.

Me and DeNada went for a boat ride.....I throttled up to 1500 RPM or so then nailed it all at once and almost wet my pants......she jumped like I had never seen her jump before and I helded the throttle until she maxed out at 4650 RPM.......just by leveling up the carbs.

I'm not thinking that this is the problem your trying to solve but it was amazing what it did to DeNada.

Harry

I used to get 4400 rpm at wide open throttle, same engines, same shafts, 18 x 18 nibrals, no cup. Then I started to develope the same symptoms. 4000 rpm port, 4200 starboard. Everything looked clean. Then I lost the port motor. Then discovered the gas tank was disolving. Tore down port motor and it was covered in the dreaded black goo from the fiberglass tank disovling. I certainly hope this is not the case for you as it has proved to be an expensive proposition for me. But it is something definitely worth considering.

Harry, I think the quadrajet carburetors are the best carburetors you can get for a marine application. They need little maintence, are very efficient at cruise and when you open them up there is all the fuel you can handle. Why do you call them "QUADRAJUNK"??????

ScottD

Scott....thats just an inside joke between myself and some of my hotrod buddies........they all like Hollies........I don't care for the Holley carbs myself......I have a 20' Shamrock with a 351 Ford engine and a Holley carb........it may be that I just don't understand how to set them up but the Shamrock always smells like its running to rich.....

I also have a 69 Vette, 350 engine and a Spread Bore Holley......if it pops back thru the carb just one time you have to replace the power valve.....not so with the Quadraj....

I took the Quad off of one of my boats one time and bolted it onto the Vette motor and I actually believe that the engine performed better......your right as long as you don't crack the secondarys fuel economy is good.

There are a lot of good carbs out there but my pick of the litter is the QUADRAJUNK.

I am repowering DeNada with diesels and the thing that I quite often think about is how much I am gonna miss the deep throated roar of the quadrajets feeding that pair of big blocks..........I just hope that screaming turbos give me the same satisfaction........

By the way Mack........have you found the problem yet???

Harry

I'm with you on the Holley's Harry! They may be OK for hotrods, but not for boats or heavy truck use. I have Carter AFB's (Edelbrocks are the same carb) and they are bulletproof in this application. I like to follow the KISS principle when it comes to boats. Holley's are too complex. I don't need fast acceleration, just solid performance just below where the secondaries open up.

Rawleigh
Back when I was a kid (about 3 years ago ha ha) one of the sweetest setup was the Chrysler 318 CID 225 HP with the Carter Carb.......dependable, bullet proof and economical

A good running engine with a 4 BBL carb WAO just send chills over my whole body......

One of the first things that really turned me on to the 31's was on a sea trial.......hatches opened and I was standing between the engines.....all of that horse power screaming, 4 BBL's roaring.......now that the kind of thing that gets me going

Harry

My QJets seems to fill up with alum. corrosion or something from all the salty air they sucked down. Quick rebuild would get them back up to snuff.

Thanks for all of the insight guys.

I am going to dive deeper into it this weekend and plan to start by looking at the plugs. I pulled my fiberglass tank the winter before last (prior to this problem) so I don't expect it to be related to that. Been running the aluminum tank for 2 seasons now. I also added a second set of Racor's about mid way between the fuel pickup and the engines when I replaced the tank.

However, John F. and I used to run down to another county (non-ethanol before the entire state converted last year) to put non-ethanol gas in our glass tanks two years ago. He is having a similar issue so I hope it is not related.

Tune up may be in order as well. I realize opinions may vary, but how many hours between tune-ups?

harry...you should like this

I do like it Randall..........don'tcha just love to hear a well tuned 4 barrell just bellow at about 4000 RPM?????

I wonder why I never get decent fuel economy?????

Harry

i get great fuel economy...i limit opening the secondaries to just a few seconds here and there.......mostly ....."watch this". she'll hit 28 with the secondaries closed.

thatsaid i really do like the way these engines sound.

Edelbrock.
Running one of the marine versions for 6 years without ever missing a beat, or needing to be touched. I do talk nicely to it from time to time just so it doesn't feel unappreciated.

I used to tune up once a season, thats when I ran the boat. About 150 hrs or so. I'd pull a few plugs here and there while doing oil changes and the like to see how she was burning. Have you pulled a few plugs to see if she's running lean, rich and or fouled etc?

My super expensive Heavy Duty, High Performance Silicone blah blah blah plug wires used to degrade around 200hrs or so, but I usually felt a mis-fire here and there more then a loss in rpm. But an easy check, open the hatch when its dark and look to see if you have arcing across wires or to block. Also a good way to check for a bad plug.

Just to toss some wood into the fire, I have been told not to add extra filters in the line. When I was having the ethanol problems I had intentions of adding extra filters in the lines and was told that was a No-No, because it would restrict flow and cause other issues. I'd verify that before yanking it out of the system, especially if it was rnning well, but thought I would pass it along anyway.

Spark plug wires often look great and people keep them a bit too long IMO. My ford crown vic needed a new set each year to get optimum effeciency.{even the oem wires dont last} Go with a set of 100.00MSD wires every two years. Good old mechanics at the GM service dept told me that they will often even ck good on the machine but will not be 100%. In boats i also like a good strong performance coil.

Thanks for all of the input guys. Looks like I found the solution.

I changed the plugs, wires and cap last week and ran her over the weekend. Turned her up to 4300 (port) 4200 (stbd). Two plugs looked a little fouled, others fine. I checked my records and I noticed that I was running on the plugs and wires that were changed out when I converted to electronic iginition about 250 hrs. ago. Looks like I need to stick to the 150 tune up interval. Like I said earlier, stb. engine seemed to otherwise run fine before I did anything. No misfires, idled at 750 rpm just fine.

Probably the biggest difference can be heard when the engines are in sync while cruising at around 2800 rpm-

Hey thats great news, don't you love it when it's something fairly simple.

Drifter31 is right about the high performance coil. I switched over a couple years ago to peformance coils. I did it as one of my customers is a tuner for those rice burners, he said it was a quick easy way to get better performance and economy plus he owed me some money.

I figured what the hell I'll give it a shot. I changed on one engine first and noticed it definetely started better, as to performance I really could not tell but did see a slight improvement in my gph burn. So I swiched the other out as well.

I was also told to swich to MSD ignition, but never got around to it.

Thanks Mack
I always enjoy hearing the out come to the question posted here.....kinda wraps up the conversation

Glad she's running top notch again

Harry