Trojan Boat Forum

At 2600 RPM you should be getting around 14knots if running gear and bottom are clean, and trim is good. Also, the 16x16 props are right, as long as they are cupped.

My money is on distributors - either timing is not set right or they are not advancing fully. They use a centrifugal advance mechanism that has a tendency to bind after a while due to moisture/corrosion. I had an engine that wouldn't go past 3000 RPM - it was only getting about 1-2 degrees of advance. Replaced with a rebuilt (with full advance) and all went back to normal.

no improvement. 2600 RPM max and still only 11 - 12 mph. Exhaust smells rich, heavy gas smell, at max RPM's. Timing was just re-checked but perhaps the points are bad, gapped improperly or for some reason failing. I will check the distributers more thoroughly and may replace. Any advice is welcome.
What are the odd's of both engines suffering the same non fuel related problem at the same time?

The speed your getting and way the engines are running all point to fouled running gear . even if there was something wrong with the engines you should be a little faster at 2600 .captainmaniac
gets around 14 knots at that rpm (14 knots = 16.1 mph) . running good or running bad 2600 rpm is 2600 pm and boat speed is the same ,I know you said its clean but in your area a few weeks is all it takes . my props were clean but I was losing 3-4 knots just because of dirty shafts and rpm was down .

dove the boat yesterday before we left the dock. Ex U.D.T. and recovery diver. One question though, there are no zinc's on the shafts. Never have since I've had the boat. I know it is a different subject, but is there a simple answer? Zinc's are on the rudders and tabs.
I took notice as well of captain maniacs post, I have no explanation. Unless my tachs all are off by the same amount and I am turning less RPM.

or both props are damaged /bent . I would put shaft zincs on it

sorry but i would still like to hear what the full advance of your timing is at say 3000 rpms. i know you say timing has been checked but is that at idle? what is it? at say 3000 rpms? with the advance all in. you need to have an idea of what degrees of full advance you are getting
if you are running original chrysler distributors i would stop doing anything else till you open them up and see if the rotor will snap back when you try moving it with your hand. i know of this problem first hand as well as some others on here.

replaced my original chrysler igniton with this

http://www.summitracing.com/parts/MAA-YLM579AV/

you asked what the chance of 2 engines having the same non fuel related problem at the same time. it could be the previous owner had a problem with one engine and didnt use the boat enough to realize he had a problem and now the other dist in this case(my opinion) has developed a problem and you now have the probem you are having but the problem really didnt happen at the same time

GM 350ci engine should have 24 degrees of advance @ 3000rpm. Typically 8* BTDC at idle. You will need timing tape to check this and its very easy to confirm the distributors are advancing properly.

I've had an issue with my port engine going above 3000 RPM since I've owned my boat. Still unresolved here, but what your checking is on track.

Good luck. I'm down to a carborator issue or prop sizing. I've replaced everything else with new with no results. Fuel pump, Distributor, filters and rebuilt carb.

Another reason for possibly lower speed at same RPM is trim angle, carrying too much weight aboard, bad weight distribution, or waterlogged hull carrying an extra thousand pounds or so... If it's ploughing or squatting, a lot of the power being delivered is just going into pushing water. If you can't climb onto plane the extra power is not going into speed.

just got off the phone with my mechanic. Timing is good and advancing properly. Electronic ignition - standard mercruiser ignition. At this point I am concerned about a water logged hull. That would be a worst case scenario. Perhaps the carbs need rebuilt from sitting from the previous owner. Or a tune-up. Strong gas smell when WOT. Maybe. Is there a sealed cavity in the bow area that I cannot see to check for water?

Have you checked the fuel filter in the carb if applicable? Checked that you don't have a clogged gas tank vent? Having said that, I'm with g36, and also believe it's ignition related. Odds of happening to both engines at the same time? probably pretty good if there were poor maintenance practices before you got it. If the mechanic say's he's getting full advance, your next question should be what is it, and he should be able to answer right away. A couple of degrees off on initial timing will give you lower rpm and not getting full advance will make things worse, it all adds up. You must make sure you're getting full advance, not only for performance sake but you can do serious engine damage trying to push it without full advance. The smell of fuel may be that not all cylinders are firing so you're expelling unburned fuel. I don't recall seeing ignition type but if it's breakers, check gap and dwell, and voltage to the coil. Bad condensers can cause issues too as well as internally shorted tachs (disconnect one tach and try). Do a cylinder power test by running the engine and removing one wire off the cap at a time and see if it makes a difference in the way the engine sounds. If nothing changes after you pull a wire off, that cylinder is not firing...simple test. You should also hook up a vacuum gauge; it can tell you alot once you learn how to read it....lots of info on internet. If you change parts, change only one at a time and test or you won't know what caused the problem.

Get a five gallon marine tank for an outboard with new fuel and hook it up to your engine a with a hose and clamp somewhere between your fuel tank and filters. Then see if it will run up over 2600. Can it rev up above 2600 in the slip or just does not rev up under load while out on the water?

have you checked to make sure your transmission has proper oil level and full engagement with the lever when put in gear?

Drain your onboard fresh water tank and have the head pumped out and take off as much weight as possible to see if you get any improvement.

Not that you couldn't have an engine issue, but I think Paul is on the right track here. If all the information you provided is correct- and it's very important that it is, you have a boat problem- NOT an engine problem.

Here's why- At 2600 RPM with 1.5 gears and 16x16 props- your "shaft speed" will be 1733 rpm. Forget about engine condition- 2600 RPM is 2600 RPM- the prop doesn't know if the engine making that RPM is sick or healthy and the prop is what "moves" the boat.

Now at 2600 RPM, your props are cutting through the water at a theoretical 26 MPH- If your only traveling at 11-12 MPH- you have close to 60% slip!!!! Most twin inboard boats run between 15-30% slip. Your fully 200% over the normal maximum. This has nothing to do with the engine- this is likely because you have a prop issue (fouling, damaged, wrong pitch) OR you have a hull drag problem related to weight, fouling, and/or other drag factors like tabs or other appendages creating undue drag.

One other "remote" possibility would be if you had some kind of shaft binding issue which is causing the shaft not to spin at 2/3 the engine speed. The additional "bind" could load up the engine preventing it from spinning while at the same time keeping speed down by virtue of reduced shaft speed. Not likely- but possible.

The easiest course would be- confirm shaft RPM at 2600 engine RPM with a photo tach. If the shafts are indeed turning 1733 RPM (engine rpm/1.5) then you for sure have a prop or boat problem- no sense looking at the engines as these won't be the issue.

what ever he finds i would hope he will share with the rest of us. seems like alot of times people ask a question like this and never report back what was the actual cause of the issue

good luck riptide

Transmission levels checked out. Motors seem perfect at idle or putting along. docks great, props bite hard and drive system reacts well. Boat is a dream in close quarters. Motors spool up instantly in neutral, 4000-5000 RPM easy and almost instantly. Never tried to max them in neutral.
Motors start right up, idle perfectly, transmissions shift smooth with no clunk.
I will bring a moisture meter with me this afternoon. I have some soft spots in the fore deck that I am in the process of drilling and filling with CPES. I am fairly well versed in this procedure and have had success in the past. The flybrdge deck was treated the same by the last owner. Do you think that soft spots in the cored decks could - or would - lead to exdcess water weight in the hull?
Today I will run the motors from a seperate gas tank with more new gas.
And definitely I will keep this board posted.
Thanks to all who have responded mucho.

If the engines run smoothly and will run up to 4000 rpm and not sputter or surge in neutral then I think there is not a fuel problem and you should look at the possibility of a water logged hull or stringers or deck. Did you have the yard that launched your boat tell you what it weighed in the slings? I would think with full fuel, and gear it should weigh around 13,500 lbs. If it were to weigh around 16,000 lbs then I would suspect a water logged issue. Empty weight is 12,000 lbs.