Boating How-To’s - Another boggin 3.0 Mercruiser
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06-30-2012, 03:45 PM
I have a 1992 Stingray 536xp with a 3.0 Mercruiser. Boat ran fine last year. Rebuilt 1.5 years ago with about 20 hours of trouble free running on it. I thought since I kept it in the garage where it wouldn't get too cold that I would be OK not winterizing it. Lesson learned I guess. I took it out twice this year. The first time for a few hours it ran fine after topping it off with gas. The second time it ran fine for 1.5 hours or so after topping it off again but after being parked for about an hour on the lake it would not go to WOT when we went back out to tube. Bogged down increasingly until it wouldn't idle at all. Replaced plugs, coil, fuel separator, and rebuilt the distributor. Point gap set at .022". Drained fuel and refilled with ethanol free gas. Fired right up in the driveway with muffs. Ran well for about 30 minutes. Disconnected the throttle so I could manipulate it by hand and all was fine. Then it started bogging again. It bogs down terribly when the accelerator pump kicks in. Looks like a whole lot of fuel spraying to me. Temp gauge seems to be working properly and stays about 150 degrees. Going to recheck the timing as soon as I can get ahold of a light but maybe I can adjust the spray on the accelerator pump? Why does it run great for a short time? Why did it start so suddenly after running great for hours? I have been trying everything I have read on previous forums but nothing has helped yet. All help is appreciated.
06-30-2012, 05:49 PM
Well, i think I have done it now. The thing was running so poorly and vibrating so badly while I was messing around with it that I think I broke the starter bolt. I know one is missing, and there is a broken gold bolt in the bottom of the boat, I just haven't been able to check and see if there is a piece up in the block yet. I had this happen to an old pickup one time and bought all the easy out stuff but in the end it easily backed out with a screwdriver. Hope that is the case here. Going to get a timing light tomorrow but I did make small adjustments either way to see if it helped at all. Nope. Think I might buy a few more feul separators? That's the only thing I can think of that could change so drastically and quickly.
07-01-2012, 12:55 AM
Maybe I missed it, or you did this but didn't list it, but have you opened the carb to see if you have a bunch of crap in it ? Another quest for you : is the engine doing any slight backfire while you go to WOT ? The carbs on those engines are very simple to rebuild and with the current state of ethanol blend fuels deteriorating fuel systems, it wouldn't hurt to check the carb out. One last question for you : have you replaced the filter in the carburetor ? Those are paper filters, and with them located in the fuel fitting, it often gets missed ; depending on your fuel pump, you could have one in it as well, but those were mainly in the older engines. Hopefully some of these things will help you out and hopefully for you, you will be able to get the starter bolt out while laying on your head upside down, and not have to pull the engine.
07-01-2012, 08:33 AM
Thanks for the reply. Actually, I pulled the whole carb down and checked it. Even the bowl was clean. My carb had a screen filter in it though and had very little anything in it. The only weird thing I saw was that when I removed the"jet assembly" there was something that almost looked broken off underneath. Looked like about a 5-6mm x 2mm piece of metal holding a spring in a hole. Never did see where it could have gone to. After I put it back together is when I tried tinkering with the timing a little.
I have been thinking about this a lot since yesterday. The first day that I took the boat out and it ran so well, we pulled into a beach to let a storm pass for about an hour and a half. It rained pretty hard. After that I only ran it for about 45 minutes that day. 3 days after that I topped it off with gas, took it back to the lake, and ran it for about 1.5 hours before parking again on our favorite beach for an hour or so. Everything ran fine up until this point. Started it up, put a kid on a tube and the boat bogged down when I gave it full throttle. It acted like bad gas to me so I made a circle around the lake and tried to clear it up. No dice. Pulled back into beach and emptied fuel separator. Took off and it did ok for about 200 yards then started bogging again. It got consistently worse the longer I tried to figure it out until we had to be towed back to dock. The next part of the story is completed above.
The more I mess with it the more I think it was water in the gas. I am sure that I couldn't drain every bit out of the tank but it has a 28 gallon tank and I put 27.2 gallons of ethanol free gas in it without filling up the filler neck. I still need to reset the timing but the only thing that I have done that seems to affect it is change the separator.
My new question is this, how can water damage the separator? If it was brand new yesterday, shouldn't I be able to just empty the thing out? I still have the original one too that has been sitting out in the garage for 2 weeks. If the element isn't stopped up with trash, shouldn't it work? I know that they empty them on diesel motors and a buddy in the Army says that on their engineer boats they just empty them for PMCS.
Long winded I know but I figure the more information I give the more help I can get.
Oh yeah, what is dwell on the points?
07-01-2012, 11:35 AM
The separator shouldn't be damaged, just by having water in it. Its completely normal to just dump a fuel filter and get the water out of it, but if you are sucking in some trash from your tank then its possible it could be stopped up. Do you have any way to verify that you are actually not loosing fuel pressure from a restriction in the system or are you able to verify that you have fuel in your carb when it loses power ?
07-01-2012, 08:22 PM
I could see a little into the bottom of the tank when I drained it and it "looked" ok but I guess it could have picked up some trash. I don't know any way to see if there is a loss of fuel pressure.
On the broken starter bolt. I read somewhere that it is a common problem and will reoccur if I don't have a "front brace". There is not one on my boat. Where would I find such a thing?
07-01-2012, 09:01 PM
Maybe remove the pick-up tube in the tank and inspect the screen in it to see if its clogged. You might as well get a new anti-syphon fuel fitting for the p/u tube as well, couldnt hurt to change it and for $10 it might be an easy fix. Good luck