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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10898
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1990 bayliner with twin 5.0 mercruisers.Both engines get up to roughly 2k rpms an

Customer Question

I have a 1990 bayliner with twin 5.0 mercruisers.Both engines get up to roughly 2k rpms and sputters and wont accelerate past that. I put in pertronic flame throwers but they might be off a tooth? but runs great at low rpm's. Distributors or carbs? thanks Jeff
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
I can rev the engine way past 5k rpms when in neutral. Its when it has a load on the motors!
Expert:  Jason replied 2 years ago.
Hi Jeff, my name is ***** ***** I will be helping you today. . What can you tell me about these engines? When did they last run and make full power? How old is the fuel?
Customer: replied 2 years ago.
The fuel is new. Like I said I changed the distributors and may not have them timed correctly. I bought it two years ago and the sterndrives were bad so I couldnt full throttle I tried and if I remember right theydid the same thing. so I am not sure when they were last throttled up, couple years I know of.I have change everything but the carbs. but the engines only choke when Im under a load (in forward gear over 2k or so). Also when I move the distributors to adjust, they dont change except bad to good (turned an inch or so advanced or retarded) the enginge doesnt idle up when I manually advance them. and the carbs look like they are pretty dirty.
Expert:  Jason replied 2 years ago.
Did you remove the distributor from the engine, or did you just change the points out for the pertronix trigger?
Customer: replied 2 years ago.
I will call around noon Pacific time. I am at work. But I changed the distributors completely and removed the thunderbolt ignition. Do the amplifiers need to be still hooked up to the Pertronic dist.? Replaced the coils too. I honestly think I'm missing something with the distributors but it was doing the samething with the thunderbolt system, if I remember correctly. They dont seem to advance, (like with a vacuum advance) or Would the carbs load up when I'm accelerating in gear?
Expert:  Jason replied 2 years ago.
Phone calls are an additional service at an additional fee. And the way it would work is I would call you. The phone typically goes alot faster for people. Did you want to do the phone call, or did you prefer to stay online?
Customer: replied 2 years ago.
online. If you have an answer or something for me to try or replace I will understand you. Also, My online time is intermittent with work and such and I can keep track. I dont need to go to fast but I sure want to get the boat running correctly. Worse comes to worse I may have to hire a mechanic and my boat stays moored which can get expensive quick
Expert:  Tan replied 2 years ago.
Hello. My name is***** you set the timing since replacing the distributors? Since you have 2 engines doing the same thing what is common to both? Do you have one fuel tank with 2 pickups? Have you tried running the engine on a different fuel source? The engine will rev all day long with no load as they require near as much fuel so when you put a load on the engines they will not pull unless they have a good fuel supply. Running the engine on a different fuel supply will eliminate the boat side fuel system as a possible cause. This will also tell us if you have a fuel supply issue or an engine issue.
Customer: replied 2 years ago.
Very good but I wont be able to try another fuel source and drive it. Both motors are stuffed into the engine bay. the carbs look very dirty and and I'm unsure if they might be the source of my problem.As far as the distributors I got the compression stroke and timed but they only choke out either way when turned, like a car will rev up when advanced these dont. could it be fuel, filters maybe? I could buy new quadrajet carbs and see what happens but kinda expensive trouble shooting
Expert:  Tan replied 2 years ago.
If the carbs are dirty and the fuel is contaminated the engine isn't going to run correctly. The carbs can be rebuilt and we can bypass the boat side fuel system. Now you could have more than one issue so we have to eliminate one problem at a time.To run the engine on a different fuel source all you have to do is one engine. Disconnect the fuel supply line to one engine plug the line then connect the other fuel source to the engine. Now run the boat. Does the engine with the other fuel source run better?If the engine isn't running good the timing will be hard to tell by turning the distributor. As for the timing guessing at where it should be by turning the distributor won't work. You have to set the timing with a timing light then go from there with the other engine run issues. Does this make sense?

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