I have been on numerous boat forums, talked to mechanics, and I cannot figure out what is wrong with my boat. I recently bought a 1986 Seaswirl 17ft. with the OMC 3.0L(3.0L inline four, GM) with a two year old rebuilt motor. I’ve taken it to the lake twice now, but it is not running correctly. First time at the lake, I could only pull 3000 rpm on the motor, which should operate between 4200-4600rpm at full throttle. When I try to increase the throttle at 3000rpm, the motor starts to bog down and I have to back the throttle off to maintain that speed. When I returned from the lake I put in new plugs and I checked TDC with a screw driver on the number one cylinder, so I know the mark is correct on the crank. I then checked the timing, only to find it set at 30 degrees above TDC when it is supposed to be set between 1 and 4 degrees above TDC. I set the timing correctly and tuned the carb. It was idling at 550 rpms. Took it to the lake again the next weekend and it wont even start until I advance the timing really high. Now I can only get 2800 rpm out of it. People are telling me it is probably an engine miss, and suggested the mechanical advance in the distributor, which I checked and appears to be functioning properly.
I had a similair problem with our boat engine. The problem turned out to be the timing belt was worn out and was slipping.
With a strobe type timing light, set the timing at around 8 degrees at idle RPM. Then, gear in neutral, advance throttle to 2800-3000 RPM and observe timing. It should have advanced to around 30 degrees total at this RPM if the mechanical advance is working. Boats seldom use vacuum advance.
Then check the VOLUME of fuel delivery to the carb. You will have to disconnect the fuel line at the carb to do this. GREAT CARE IS NECESSARY HERE TO PREVENT FIRE!! Use your head, don’t squirt gasoline all over the place! The fuel pump should deliver AT LEAST a quart every minute at 5-6 PSI…
Points or electronic ignition? I never heard of a 3.0L GM 4cyl engine…
After all this is checked out, and maybe a compression test too, reduce the pitch on the prop to obtain the correct WOT RPM.
if the wrong propeller is used it overloads the engine.
do you know if this is stock, or what the recommended pitch and diameter is?
ensure the correct prop is on the boat before you tear apart the engine.
BTW, the propeller has marking on it. i don’t know what the marks are on your propeller, but write them down, and ask a outboard shop how to decipher them.
since the propeller size is dependent on several factors, do you have a spare prop? if so, switch them.
is the prop damaged? change it. there is a fine line between max RPM and overloading the engine.
You mean timing chain??? Belts don’t slip…they break.
also, when you have it in the water, will it run up to 4200 rpm in neutral?
does this happen all the time? or just when under load?
it is NOT unusual for an older boat to not run to original specs.
believe it or not, all the ‘specifications’ are for minimum gear and equipment. usually a boat owner will add severl hundred pounds of "gotta have it’ gear which staggers the engine and speed.
i once was working at a yacht yard when a customer came in with this exact problem. although it was a larger boat, we unloaded about 2000 lbs of crap off his boat, and viola, it ran as fast as it used to go when new!
Agree…if you don’t check the prop FIRST, you’re making a mistake. Go on line and check standard pitch for your model. Nothing else matters if the prop is wrong. It’s the closest thing to a transmission your boat has.
The added weight as well has a greater affect on a boat than a car because of the increase drag as the boat sits lower. Weight placement is a HUGE factor as well that affects boat performance.
The 3.0 Mercruiser engine is a stroked out 2.5L S-10 engine. It uses a timing gear and I believe that point type ignition was still used on the 1986 model. It seems to be a very reliable and relatively economical engine to operate.
Heh, heh. Reminds me of the story (possibly an urban legend) of the new boater coming into the marina complaining of poor performance. The cause? The boat trailer was still strapped to the underside of the boat! A bit of drag there…
Sorry it took so long guys, lets see if I can answer everyone.
Motor is a 3.0L gm inline four
Yes the timing advances with the throttle.
Only one vacuum line, to the carb, mechanical distributer.
Points ignition
The prop that is on the boat 13 1/4" X 17 which is actually the towing prop.
I have not checked the fuel flow, but the motor bogs when I try to throttle past 2800 rpm, until I back the throttle off A little, which leads me to believe there is no lack of fuel.
All of the figures I have given were running with only myself on board.
I have found other OMC 3.0L owners, with bigger boats(18 and 19 ft.), and they were having no problems achieving 4200-4600 rpm with six people on board.
The added weight as well has a greater affect on a boat than a car because of the increase drag as the boat sits lower
How right you are. Many people have checked everything only to discover that their foam is waterlogged and the boat weighs significantly more than it should.
First step, make sure the prop is matched to the engine AND boat. WOT RPM is established by those parameters. Then make sure that the engine is working correctly. Finally, make sure your boat weighs what you think it does.
A toothed belt can’t skip a tooth if there is a problem with the tensioner pully? I have heard untoothed belts slip. It makes a really loud noise. Belts do slip. Did you mean to say timing belts don’t slip? I would even question that, but only based on what I have heard, not from direct experience.
Arizona boat, only used 3 times this year. I don’t think the hull is waterlogged, it spends way more time on the trailer than in the water.
Not likely to happen in AZ sitting outside due to the arid climate and low rainfall. That’s good information not included in the original post. All I see is “new to me boat used 2 times”. Don’t know where you are, where the boat came from or how it was used or stored.
BTW- a lot of waterlogged boats don’t get that way sitting in the water. It happens when the plug is left in during storage and rain water builds up in the bilge…
plugs out whenever it is not in the water, thanks though
When you say it ‘bogs down’ after 2800 rpm, do you mean that the rpm drops as you open the throttle or just remains steady. If the rpm is dropping as the throttle is openned, the ignition system may not producing enough voltage to spark the increased mixture density. So have the ignition system scoped to see what the maximum voltage is. If the ignition system is up to muster, look at the fuel system. Either the mixture is going excessively rich or excessively lean. Excessively rich would be a jetting problem with the carburator. Excessively lean could be a jetting problem but most likely is lack of fuel flow to the carburator. Lack of fuel flow could be a clogged fuel filter/water separator or the fuel pump.
Well since he Cougar was talking about a timing belt…I was responding to him.
They slip, but NOT in the say Cougar meant it. When a chain or belt slip…they will always slip in the same direction…NOT KEEP SLIPPING BACK AND FORTH. And when it does slip more then 2 teeth…it stops running and WON’T start again until you physically fix it.
i read your replies three times. this question has not been answered that i have seen.
does it throttle up to full rpm with NO load. eg. in neutral? if it will not throttle up under NO LOAD, then it certainly wont with a load.
if it will throttle up, but when under load wont reach full rpm, then likely the prop is the wrong size.
FYI… a boat can ‘soak’ up water when OUT of the water, if the fiberglass is fractured, and the inner balcor or other brand can soak up water making it heavier. does it float at the usual waterline?
Yes, it revs up normally without a load(ie., not in gear).
I have not noticed any difference in the waterline, but I have only had it for a few months.
I have checked the prop and it is actually the towing prop(smaller pitch, easier to spin).
What would I do if the boat has soaked up water?
When I add throttle at 2800 rpm, I begin to lose rpms, until I back it off a little. It then returns to 2800 rpm.
I have checked the fuel filter and it is clean.