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My ‘69 31 FBC has 1978 454 Mercruisers, with Edlebrock 600 cfm carbs and Prestolite electronic ignitions. She has 1.5/1 gears and 17x15 w/5 cup 4 blades on her (pretty sure about the props–bought them from Dug). She usually runs about 20 knots at 2800, 22 knots at 3000, and 32 knots at 4200. I run her at wide open (4200) at most once a year for a few seconds. The secondaries usually open at about 3150. This spring, the starboard motor ran poorly when she was launched (wouldn’t idle, barely ran), and after finding a weak spark, I put new plugs, wires, cap, rotor, and coils on her (the ignition kit came with cheap coils, and one was leaking, so I just replaced them both with decent coils).

Problem is that both motors will run up to about 3600 rpms maximum, and while the secondaries on the port motor still open at 3150, the secondaries on the starboard motor now open at about 2750. I cannot figure out what’s wrong. I can’t be sure about when the problem with the secondaries on the starboard motor began, but I remember that at the end of last season when I ran her before having her hauled, she only ran up to 3600 or so. At the time, I was hoping it was a dirty hull and running gear, and the season was over anyway. Here’s what I’ve checked.

Ignition- Spark seems good to all cylinders. Timing is correct at idle, and she’s getting full advance.

Fuel- The filters were replaced this spring (Racors and inline billet aluminum Russells), and have been drained off and cleaned. The gas looked fine. Most (not all) of the fuel lines were replaced within the past few years. With the engines running under load, for example, at 3000, there appears to be plenty of fuel in the carbs– a real lot when the secondaries open. I checked fuel flow by looking in the carbs while the motors were running under load (daughter was driving). I am getting full travel on the throttle cables/carbs, and the chokes are opening as they should. I have no way of checking fuel pressure, and am not up to taking the carbs apart. I get my fuel in an ethanol-free county on the Eastern Shore (by Tilghman Island), and as far as I know, she’s never had ethanol gas in her. I’ve checked the EPA maps, and with the owners of the marinas and their distributor, and have been assured that their fuel is ethanol free. The lower part of the Shore has always been non-blended fuel from what I was told. I just bought a new load of fuel today, and it made no difference.

Compression- I checked compression dry on the starboard motor w/the throttle wide open. The numbers (about 145) were consistent, and the same as when I bought her 5 years ago. The #s 1, 6, and 8 plugs looked a little oily and had a few deposits on them. The rest of the plugs on the starboard motor looked fine.

Intake- The engines run the same with the spark arrestors on and the boxes closed, or with the spark arrestors off and the boxes open.

Exhaust- I put new 3" hoses and Ys on her this past winter to replace the old cast iron Ys that were falling apart. I have no real way of being sure, but I think the exhaust flow is fine.

Running Gear- I can spin the shafts by hand easily. I scraped the barnacles off the shafts (picked up about a knot), and the wheels look fine. The hull is clean.

Oil pressure, water temp are fine.

She starts up fine, idles fine, and runs smoothly all the way up to 3600 on both motors. If I run her at 2700, she sounds just fine. I believe the tachs are accurate, because I get the same speeds per rpm at 2800, 3000, and as I remember 3600 (about 27 knots) that I’ve gotten before. The starboard motor, outside bank has what I think is a slight lifter tap on start-up, that goes away within a few seconds. There is what sounds almost like a slight exhaust leak on the outside bank of the starboard motor, but I can’t find any leak.

I have no idea as to what may be the problem, and am about to bring her to a mechanic for the first time since I’ve had her. If she’s in need of major surgery, I may go diesel, or sell the boat as is. She won’t be going to the mechanic for a couple of weeks, so I have a little time to check additional things. I’m pretty much out of ideas (what does a bad cam/wiped lobe sound like? Both motors? Ugh), and any advice would be greatly appreciated. I may have missed something simple, or it might be a big deal. I just don’t know. Thanks fellas.

John F.

john...pull a plug and take a look.....if it looks like it was painted with black enamal....its ethanol that was snuck in there somewhere.....have the same problem.....(not ethanol) and pretty sure its the carbs

John

I have never experienced a wiped out Cam but years ago a friend of mine had a 31, actually the same year as mine a 75 with 454 Mercruisers. He had a cam go. Wore the lobed down. Could not get it above 3000 RPM's. It never made any type of noise, just wouldn't wind up. Strange its both engines though, that makes me think its fuel. Although I had a cam go on an old Firebird with a 305 Chevy engine in it. I had blow back through the Carb. I guess it depends if its intake or exhaust that goes. Good Luck. Tony Meola

I know you said you scraped the gear but it sounds like bottom/gear fouling, I couldn't reach 3000 when I to the boat to the yard after sitting all winter.

Could you have the boys at the end of your creak give you a short haul to look at it out of the water?

Other than that I'd say maybe plugs/wires???

good luck.

John

It's the carbs. Bring 'em down to the shop and clean 'em up!

John,

I agree with Capt. Dick Dean,

Where the fuel line goes into the carbs, there is a filter screen there, make sure it is clean. If that screen is clean, then pop the top of the carb apart and check the inside bowl for dirt & trash.

DQ

John, are the secondaries vacuum or mechanical?

I looked at the manual for the Edelbrocks, and it didn't show an internal screen filter like Quadrajets have. The carbs have vacuum secondaries. Five of the plugs look fine, 3 looked slightly oily/rich, with a couple small deposits on them, so it doesn't seem like it'd be an ethanol problem. I'll try to check the starboard carb today for trash, and maybe set-up a short haul down the creek just to be sure. I had checked the running gear with a mask and about 1' of creek visibility. Thanks, and keep it coming.

John F.

John, this is probably a foolish question but how old is the gas? Today’s gas doesn't last long and new mixed with old and some conditioner is just a patch job. You may try running one on a five gal can of fresh and see if it helps. I had similar problem last year and after a month of frustration we went with diesels.
RussP

Someone else needs to verify this as I am not familiar with 454's...

Could you be overpropped? From what I read you would only get 4200rpm at WOT last year, I thought 454's should run up higher at WOT.

Are the props new to you? I don't care what the props are labeled as the pitchometer could have been calibrated wrong. Your old props or the new ones could be off. Sometimes the style/brand of wheel makes a big difference as well, even if the same pitch diameter and cup are used. If you have the means swap back to the old ones and give her a try I'd consider that.

Aside from that I'd replace filters again, only one? No in-line filter or filter at the carb to replace or clean. Otherwise I'd go with carb overhaul as mentioned, but two at once is strange unless a bad batch of fuel...bringing you to what was mentioned by Russ, run from fresh jerry jugs.

Good luck
Carl

Had the boat shorthauled this am. Cleaned the bottom pretty well, and got the port motor up to 3900-3950 WOT and starboard up to 3650 WOT--but the secondaries on the starboard still begin to open at 2750. Pulled the inlet fuel line off--clean as a whistle in the inlet--no screen like Quads, but a small screen the looked like new.

The props were from Dug who had 440s in his B31, and worked for him and worked for me for the last few years. Don't think its the props. If it was the fuel, don't see how the starboard motor would be so affected while on port I'm only losing about 300 rpms while dragging a motor. I fueled yesterday though--took on 130+ gallons, ran for an hour os so, and no change. Going to check timing again just to be sure.

The starboard motor still makes some noise that seems to come from the outside cylinder bank. Still wondering about the cam.

Thanks for all the responses. Any other ideas greatly appreciated.

John F.

Russ- Window work looks good. Maybe diesel is the answer--I just need to find an affordable way to do it.

John,

I have 2 thoughts.
Either the advance on the vacuum secondaries is off slightly or
there may be a problem with the timing chain on that motor. If you're getting a chattering sound on the outside bank, it sounds similar to what happened to me before the port motor let go. And you know why my motor let go.

Try pulling the valve covers and see if you can tell if the valves are traveling the full distance or if the rocker arms are loose. Tony Meola

John and I just got back from a short ride on the 24ft Baja which also has a 454. After running my 31 for years its fun to get in the little go fast and take her out in the river for a few minutes at rediculous rates of speed. We both drove the thing wide open for a while and the smile just eases up on your face.

John hope you find out whats kicking that secondary open early on that one engine. If you need any more therapy come across the bridge anytime & bring your gas card....lets go bar hopping. I need practice- Thudd's coming down next month.

I thought about this after you left- do these engines have timing chains or gears ? I know with engines with older worn single row timing chains tend to act like this and it's very difficult/impossible to time them as the crank and cam aren't in/won't stay in synch. I pulled a Range Rover v8 apart @ 150k and put a Cloyes dual row setup in and it made a world/4mpg of difference. I'm sure Bruce will weigh in.

The ride was great therapy--thanks. Going to try the vacuum gauge this pm if I have time and see what I come up with. Again--great ride.

I don't know what chain it has on it. When I had a chain jump on my GTO years ago, it barely ran. Doubt thats it, but I don't know.

John F.

John,

The tapping sound on start up could be the fuel pump vent hose. My 351s have made that noise when the mechanical pump is bad. That could lead to loss of power as well if the pump was not pushing the required volume. If it has been sitting for a while I would rebuild carbs. I just went through a couple weeks of issues that centered around a bad 1/4" o-ring in the carb. If you have spark and air then I would look at fuel. I think anything major like cam or timing would not let the engine get past 1000 - 1500 rpm.

Other item would be exhaust risers leaking but that would cause idle issues, at least that is what I have seen.

Jim

John: Do it systematically. Before you do anything else, swap carbs and see if the problem changes sides. Edelbrocks are Carter AFB clones. Very simple and reliable.

Rechecked the timing--it was at 6 BTDC rather than 8. Checked the vacuum. About 16 at idle on port and starboard but really bouncing around within a narrow range on the starboard motor. Manual says that 15 to 20 OK, but bouncing is indicator of leaky valves. Both motors up to the low 20s (I have it all written down somewhere) when the rpms are brought up, doing just what they're supposed to do.

Took her out. Ran up to 3750 on starboard, 3950 on port according to the tachs. Manual says that normal WOT is 4000-4200 (or 4400, I forget). Pretty close on port. Secondaries on both motors open at about 3100--impressive amount of fuel going down the throats at WOT. Swapped carbs--no difference. Maybe the 200 rpms is from leaky valves, or whatever that noise is on the outside starboard bank.

Going to leave it alone for now. When I have time, I'm going to bring her in for a motor check-up and price on repower to diesel.

Thanks for all the advice.

John F.

Oh yeah--when I had the carbs off and looked at the carbs/manifold, it all looked pretty clean. No sign of ethanol I guess.

John: The other thing is that you should use a tach/dwell meter or optical tach to check the tach readings. They could easily be off by 200 rpm's.

Where can i get a photo tach for reasonible $$?

Concening gas motors how crucial is loading, when people refer to diesels, it seems to be #1 concern.

My owners manual also gives a broad range for max RPM---i think it is 4600-5000, where should i be?

Seems you're forgetful .... " (I have it all written down somewhere)or 4400, I forget". .... At AC, it looked like you were fine but then again, some things are not what they seem to be.

Are you "on" anything?

Let's talk!

John,
Have you popped the rocker cover on the noisy side to see if you have broke or bent a push rod?
A common problem with the 454.

Craig,
A motor is a motor. Its loading is important being gas or diesel.

Its true that gas engines have a wider range than do diesels. But the gas should be at its minimum reccomended loading.
In your case it would be 4600.

But you could run up to the 5000 limit.

As a kid my dad had a cruising buddy that owned an old Owens with a gas motor who consistantly over propped it and every season despite warnings from my dad, he would throw a rod and replace the motor in the winter.

Dick- The manuals are in the boat, and...forgot what I was going to say...

Bruce- That motor broke a rocker and bent 2 pushrods when I first got her. I may take the cover off, but the sound is coming from down in the motor, not from the head.

Rawleigh- Don't have an optical tach. I can't be sure that the tachs are accurate, but I can tell (I think) from the motors' harmonics whether they are in sync or not, and it sounds like my port is running up higher than starboard.

Thanks-

John

John, I have an optical tach I can loan you if needed, but they are pretty cheap nowdays, think I paid about $75 for mine.

UV

UV-

Thanks for the offer. For $75, I'll get one up here.

John

I bought this one for $49 and it works fine. http://www.web-tronics.com/lastacdt.html

Eddy G.

Bruce confirmed the WOT rpm I had in the back of my head.
Your max rpm of 4200 from last year means you are overpropped or tachs are off. When you get motors running correct again, check tachs, if tachs are not out, really consider losing some cup and/or pitch. In my opinion I'd rather run higher RPM to keep your cruising speed with less load on engines.

The 454s in my 1978 B33 have stamped on the Merc decal on the valve covers that WOT is 3800 rpm. The Bert manual that came with my boat has the operations chart showing Bertram testing the B33's with gas motors to a WOT of 4000.

My last boat was a 1984 & the operating spec for the Merc 454 was 4100 > 4400 rpm.
Al

That is a huge difference, I stand corrected.

I just "kind of remember" a guy on our dock that said he was told to run his 454's at 3600rpm for cruising and said he topped out in the high 4000-5000 rpm range. Sounds like they made several versions, guess thats why they supply manuels.

2 years ago, when all was well, I was getting 4400rpm at wot. 18 x 18 3 blade nibral no cup. Last year, I was down to 4200 starboard and 4000 port....and then kaboom!! This year, port motor gone, starboard sleeping. We all know the rest of the story.

Its important to follow the manufacurers specs for your engine.

Not all 454/7.4L engines are rated the same wot rpm's.

John,
Just went through the same thing. Ticking noise was the cam lobe and lifter wearing out. The cause was a sticky valve. Something scored the valve guide and more force was needed to open and close the valve causing excess wear. Had to change the cam at anchor while on a trip in the Keys. Heads just came off and are going to the shop.
Not saying this is your problem, but I had the exact symptoms before mine let go.
Brgds,
Matt W

Bruce wrote:Its important to follow the manufacurers specs for your engine.

Not all 454/7.4L engines are rated the same wot rpm's.

Bruce,

my manual calls for 4200-4400 rpm at wot.
That's why when she started dipping lower, I figured I had a problem.
Now I have a project.