stevesxm

think about it...you had 1/2 a tank of turpentine and put good fuel on top... that didn't make your ond fuel any better... all that meant was that you had 1/2 a tank of garbage mixed w/ 1/2 a tank of fresh fuel.... and yet... still once you did that you got it to run right for a little bit.... now... what could have changed the timing or anything else between then and now ? answer.. nothing...

you have a carb full of corrosion and junk and varnish from the old fuel... it has plugged up some air corrector or fuel passage somewhere and that is your problem... take the carb off ... rattle it to pieces clean it like your life depends on it blow out all the passages with hi press air... throw away ALL the fuel that you still have in the boat along w/ the filters and start over and youll be fine.... never let a carb sit around w/ fuel in like that or run old gas thru the motor... even if it runs it was prob about 70 octane and could ping the motor to death.... that was a bad mistake and i sincerely hope you get away with it...

but the solution to your current problem is easy.

satisfactionII

This is the answer to this problem. New fuel and several fuel filter changes.

speeddemon651

thanks, I changed the filter ran all the old gas out I mean 100% out then filled it up with 93. I'll pull the carb out tomorrow and try changing the filter again. Checking the timing won't hurt, I know that the carb is a webber and is identical to the edelbrock carbs they sell. Can i just use one of their rebuild kits or should i try and get the merc rebuilt kit ? thanks for your time Joel H.

Turbojack

This last weekend was on friends boat. Boat ran good friday night. Saturday was different story. Boat would not plane out. After we tried to get going 3 times he stopped boat and gave me a new rotor and cap. I removed the old one but it still looked good. I put the new one on anyway. After that we were off and running. I would have never have guessed that was the problem.

Griff

To my knowledge, Merc has never made a 454 with 415hp.
A 1996 carbed 454 Mag is 365hp.


I would definately change the cap and rotor before I tried anything else.

Outdrive1

Sounds like a carb issue to me. Accelerator pump is probably bad. You can see if the clear return line from your fuel pump to your carb has fuel in it too. If it does the pump is bad. You can also check your accelerator pump while the motor is not running by disconnecting the throttle linkage or having some-one pump it while your looking down the carb and see if your getting a good spray on both sides. If you aren't then it needs to be rebuilt.
For timing, a good rule of thumb is about 8 deg. advanced but I'm not positive.
Any marine shop should be able to order you a rebuild kit for that carb whether it's a Merc kit or Sierra or what ever.

speeddemon651

Ok I've changed cap and rotor, points sensor, fuel filter, and cleaned and rebuilt the carb. I put the timing light on it dialed the gun to zero and turned the distributor till it was 8 degree's advanced. The engine will idle fine but once a load is put on it and you try to take off. the engine back fires through the carb and won't clear out passed 3,000 rpm. I don't know what else it could be other then that the engine jumped a tooth on the timing. I really really hope it didn't................. And thats a pain in the ass to fix. Last time i took the boat out I changed the plugs it was running great then progressively started running bad. I changed everything listed above but it's still running just as bad, maybe even worse. I'm going to change the plugs again, if thats not it I'm guessing the timing chain. What do you think. thanks for your advice.. Joel H.

jeff32

stupid thing but are you sure your spark plug wires are on the right cylinders? If so, I agree with you, (jumped a tooth on timing) Or last thing I could think of is the electronic box. I've had once a box that did not give the advance needed at higher RPM... Let us know what you find, I can't think of other thing...

Panther

Where the fuel line connects to the carb. there is small filter behind the fitting, check to see if that is clogged. You mentioned points, what year did you say the motor was?? Merc. hasn't used points in a very long time. You may even have a bad ignition module or be using a 6 volt coil when you should have a 12 V. I've seen moisture get into the connection on the ignition modules and reak havoc.

It's really hard to tell with out being on the boat itself.

Worse case you could even have a wiped out camshaft but I tend to think it's fuel..

jeff32

good point, we also had once a coil that was not making 12v and engine was not powerfull and back firing. I forgot about that one. good point.