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I have a question about how to prime the fuel system on the 496 MAG HO. Since I am poor now, I decieded to do the annual service myself. Everything was a piece of cake, until I went to start it. It started for a moment and then died. I pulled off the fuel filter and it was only about half full. I'm figuring my problem is air in the line which needs to be bled. I have scoured the internet and have found many many explanations about shraeder valves and attaching a primer bottle, etc, but I have yet to find a shraeder valve atop the fuel system nor a place to attach a fuel bottle. Any help would be much appreciated. Pictures would be even better...lol

Bill
 

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just behind the coolant bottle on the hard fuel line, look for a black platic screw on cap (kinda like a valve stem cap on a tire), mine has a hose running over it so it made it a little harder to see, remove the cap and there is your valve.
 

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just behind the coolant bottle on the hard fuel line, look for a black platic screw on cap (kinda like a valve stem cap on a tire), mine has a hose running over it so it made it a little harder to see, remove the cap and there is your valve.
make sure your fuel filter is full and your fuel sorce has fuelin it ( the fuel line hooks directly into the low pressure pump before the spin on filter)cycle the key about 10 times the fuel system will self bleed try to start it if it dosent start repeat the procedure
 

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Tried it all and still nothing. I give up. Know a good mechanic in San Diego?
are you sure its fuel put a little starting fluid in the throttle if it bust off its fuel have you found the fuel pressure port yet don't give up just give us more info what all did you do on your service,how long has it been since it ran last you can prime your fuel system with an outboard primer bulb and a gallon gas can its probably something simple theres alot of boat smart people on this forum just have to have right info
 

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Discussion Starter #6
I replaced the oil in the out drive. Replaced it with the standard high performance mercruiser oil. I changed the engine oil...knarly black...definitely needed to be changed. Replaced with royal purple. Changed the fuel filter, and changed out the batteries.After changing everything out, I put the fake lake on the drive, cranked it over with the kill switch OFF turn bring up the oil pressure. As soon as I saw 40 lbs. I flipped up the kill, and it started and ran for about 10 seconds, then died. The buzzer started beeping so I took a look at the outdrive reservoir and it was empty. I filled it up and the buzzing stopped. I went to start it and nothing. What I have tried thus far....I didn't put fuel in filter when I replaced it so, I yanked it off and filled it up with some 87 and put it back on; nothing. I found the shaeder primer valve, depressed the valve and a small amount of fuel gently bled out. I switch the ignition on and off about 10 times, rechecked the shaeder, nothing came out. I had a buddy depress the shraeder valve as I turned the ignition switch on. Tried that a good 20 times. Still nothing comes out of the fuel rail. I pulled off the fuel filter to make sure there is still fuel in it and it is still filled to the brim. I do hear the pump switch on for about 5 seconds each time I turn the ignition switch.I double checked all the wires going to the batteries and everything looks in order. The boat ran 2 weeks before I started wrenching on it. I'm stumped in this one and know it has to be fuel related, but what is the next step?
 

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I replaced the oil in the out drive. Replaced it with the standard high performance mercruiser oil. I changed the engine oil...knarly black...definitely needed to be changed. Replaced with royal purple. Changed the fuel filter, and changed out the batteries.After changing everything out, I put the fake lake on the drive, cranked it over with the kill switch OFF turn bring up the oil pressure. As soon as I saw 40 lbs. I flipped up the kill, and it started and ran for about 10 seconds, then died. The buzzer started beeping so I took a look at the outdrive reservoir and it was empty. I filled it up and the buzzing stopped. I went to start it and nothing. What I have tried thus far....I didn't put fuel in filter when I replaced it so, I yanked it off and filled it up with some 87 and put it back on; nothing. I found the shaeder primer valve, depressed the valve and a small amount of fuel gently bled out. I switch the ignition on and off about 10 times, rechecked the shaeder, nothing came out. I had a buddy depress the shraeder valve as I turned the ignition switch on. Tried that a good 20 times. Still nothing comes out of the fuel rail. I pulled off the fuel filter to make sure there is still fuel in it and it is still filled to the brim. I do hear the pump switch on for about 5 seconds each time I turn the ignition switch.I double checked all the wires going to the batteries and everything looks in order. The boat ran 2 weeks before I started wrenching on it. I'm stumped in this one and know it has to be fuel related, but what is the next step?
theres 2 fuel pumps a high pressure and a low pressure the low pressure is where the fuel line hooks up to the engine unhook the fuel line get an out board primer valve and a gallon gas can hook up the primer valve between the pump and the gas can you just became the low pressure pump pump the bulb till it gets hard cycle the key you will notice the high pressure pump get quieter then try to start the engine we do this all the time when these engines run out of gas your almost there you can call me at work tomorro 928-855-4720 ask for Bart
 

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I replaced the oil in the out drive. Replaced it with the standard high performance mercruiser oil. I changed the engine oil...knarly black...definitely needed to be changed. Replaced with royal purple. Changed the fuel filter, and changed out the batteries.After changing everything out, I put the fake lake on the drive, cranked it over with the kill switch OFF turn bring up the oil pressure. As soon as I saw 40 lbs. I flipped up the kill, and it started and ran for about 10 seconds, then died. The buzzer started beeping so I took a look at the outdrive reservoir and it was empty. I filled it up and the buzzing stopped. I went to start it and nothing. What I have tried thus far....I didn't put fuel in filter when I replaced it so, I yanked it off and filled it up with some 87 and put it back on; nothing. I found the shaeder primer valve, depressed the valve and a small amount of fuel gently bled out. I switch the ignition on and off about 10 times, rechecked the shaeder, nothing came out. I had a buddy depress the shraeder valve as I turned the ignition switch on. Tried that a good 20 times. Still nothing comes out of the fuel rail. I pulled off the fuel filter to make sure there is still fuel in it and it is still filled to the brim. I do hear the pump switch on for about 5 seconds each time I turn the ignition switch.I double checked all the wires going to the batteries and everything looks in order. The boat ran 2 weeks before I started wrenching on it. I'm stumped in this one and know it has to be fuel related, but what is the next step?
Glad you got it running, one more thing to do to complete servicing

I would change the raw waterpump impeller, sometimes you need to replace the unit. The 496 has a couple different types over the years

This might be better done at a shop like Nordic. It requires pressing on and off the drive pulley and could be tough to get to. We had to pull the rear seat and front engine panel on a twin 28 Daytona for access and replace both pumps

Also we found a bad fuel pressure regulator vacuum hose

It sure helps to have a experienced people like Team Nordic on the case
 

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Discussion Starter #12
Re: ImpellerYour right! I replaced it last year and only went to a local lake once. I bought an extra just in case, but I think I'm going to change it out anyways.
 

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Re: ImpellerYour right! I replaced it last year and only went to a local lake once. I bought an extra just in case, but I think I'm going to change it out anyways.
mercury say's replace the impeller every year on a 496 we surface the back plate it seems that the grooves in the pump don't have much effect on the performance of the pump just the back plate we check water pressure after we do the impeller with the computer if you don't surface the back plate sometimes the pump will not work well at low speed we have the new cp stainless pumps in stock but I have yet to try one
 

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Discussion Starter #14
mercury say's replace the impeller every year on a 496 we surface the back plate it seems that the grooves in the pump don't have much effect on the performance of the pump just the back plate we check water pressure after we do the impeller with the computer if you don't surface the back plate sometimes the pump will not work well at low speed we have the new cp stainless pumps in stock but I have yet to try one
How much for the new pump? I have noticed that more water comes out of the right hand exhaust tube than the left these days.
 
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