sleeper_dave

I'm going to get started getting the boat ready this weekend, and I had a few questions. Important parts in bold if you want cliff notes. 1991 Fountain, single 502 mag, carbureted, bravo 1.

I have the seawater pump setup where the fuel pump is driven off the seawater pump. I'm not planning on doing the impeller this spring, it was done when the motor was freshened up about a year and a half ago. BUT... do I need to lubricate the seawater / fuel pump? The service manual says something about a chamber full of gear lube, does this need to be checked, changed, or what? Can I change it without pulling the water pump out of the boat? I figure i'll replace the impeller next spring, unless i start running into cooling problems before then.

I know I need to grease the coupler, is there a specific marine grease I should use for the coupler? I also plan to change the gear lube, just going to use the Merc HP gear lube again. It's a Bravo, and the u-joint was changed last spring as preventative maintenance (paid someone to do it). Do I need to pull the outdrive to do any maintenance, such as grease the u-joint?

Also doing an oil change, tune up, installing an oil thermostat, getting some spare v-belts (existing ones still look good), cleaning it up, etc. As part of the tune up I want to overhaul the carb, make sure everything is adjusted properly since it seems to be running rich. It looks like a Weber carb (based on comparison to the pics in the clymers manual) and the overhaul looks pretty simple after reading the manual. One thing isn't covered, though: how do i find the proper adjustment on the idle mixture screws? Along the same note, what are the proper stock jet sizes for a 502 mag? The manual just says to check the position of the idle screws when removing them and put them back where they were. I don't think they're adjusted properly, so that isn't going to fly. I will tweak based on spark plug readings if necessary (should be easy to do since it's just idle mixture) but I want a good starting point. I just want to verify that the jet sizes are correct while i'm in there.

Thanks to anyone who takes the time to read and answer some of my questions.

Griff

If you've got a year and half on the impeller, I would replace it. You are on borrowed time. At the same time, change the lube for the fuel pump. Use the Merc HP gear lube.

Merc makes a special spline grease for the coupler, but you can use others. I use the same good quality grease for the coupler and gimble bearing. Don't remember the brand.

As far as pulling the drive for maintainence, it depends. The only real reason I know of would be to check alignment. If you have solid mounts, its usually not an issue. My drive has been off a couple times and the alignment is always right on. I do have solid engine mounts.

Jets don't control idle mixture--at least not on Holley's. The idle circuit is separate. I think the Weber's use the same principles. The idle mixture almost always leaves the plugs dark and I doubt you will be able to set it that way. You only have the 2 idle mix screws on the front---right????
Just keep turn them in slowly, a little at a time, to adjust/lean out the mixture. When the engine slows/stumbles turn them back out about 1/8-1/4 of a turn. I am not 100% sure of this, but I think I'm right. You can also adjust using a vacuum guage, but I've never used one to do it.
Also, the webers are know to have internal leaks which can cause hard starting when warm and a rich idle condition.

t500hps

I change the impeller EVERY year.....and still find need to inspect it during the year. I also carry spares with me just in case.

hillbilly24

Defenitly do the impeller, it should be done every year at a minimum. You will want to change the oil in the littel crankcase for the cam that runs the fuel pump, same oil as you use in the drive.

Merc. Spline grease is the recommended lube for the coupler but any high quality grease will work. I would recomend pulling the drive to inspect the u-joints, shift cable and transom rubber. If you find water in the shift cavity or u-joint bellows you have a leak that should be addressed.

For the idle mixture you should start with the screws about 2 turns out. When you close them do not tighten them, just seat them, you can damage the seats if you tighten them down. From 2 turns out you want to slowly turn one in until the engine just starts to stumble then back it out until it just starts to stumble again and then center it between the two points. Then repeat the same for the other screw.

sleeper_dave

My dad has the same water pumps on his cruiser and hasn't touched the impellers in probably 5 years. I have a water pressure gauge and I watch it (and the temp gauges) diligently. If water pressure starts to look iffy, i'll put the boat on the trailer and swap out the impeller. I might do it as preventative maintenance anyway once I have everything else out of the way and a couple of boat rides under my belt, though. I hate to ask for advice and not listen to it. I will check the lube in the little cavity. I would think the impellers would last more than 120 hours of engine operation without risk of failure. This one was replaced when the motor was refreshed, mid-august of 2005, but I know it has seen some sand.

All the bellows and the u-joint were done last spring, but I can pull the drive to check everything out anyway. How do I check alignment, I need a special tool don't I? I have the solid engine mounts on the front of the engine, the rear of the engine is supported on the transom housing. That's what you mean by "solid mounts", right? Pulling the drive will give me a good opportunity to check everything out.

As for the carb, I will adjust the idle mix with the idle screws, but i plan on overhauling the carb anyway because I'm getting fuel in my oil. According to the serial number on the block, it's an MPI motor, but according to the carburetor on top, it's not. Thus I know it's not original, and I don't know if someone screwed with the jets or not. I want to try to verify that the jet sizes are correct while I have it apart, if anyone knows the stock jet sizes for a weber carb on a 502 mag. Hopefully any internal leaks will be taken care of in the overhaul process.

Thanks for the advice on the idle mix screws, Griff and hillbilly.

I'll go pick up some merc grease at west marine this weekend. Is the same stuff good for the gimbal bearing?

IM4A2Z

Make sure you replace the gear oil between the water pump and fuel pump. It get's contaminated with fuel(Even on New units) and that causes the oil to breakdown and loose its ability to do it's job.
I just replace my impeller with only 32 hours on it, Bought new 05, and was surprised to find fuel in the gear oil when I drained it... already!
I always change the raw water pump impeller every other season, in every boat I have owned. It's realatively easy to do and cheap ($25) insurance!

sleeper_dave

And after some research, I've answered my jet sizes question.

Thought i'd put the info here in case anyone comes across this thread on a search.

weber / carter carb on a 502
primary is .110"
marking was 120 410, which is an edelbrock number
p/n from mercruiserparts.com is a 823432, crosses to a .110", which crosses to the 120 410 edelbrock number marked on the jet

Secondary is .101", 811650, 120 401

awsomethunder

can you guys tell how many pumps of grease you put in bearing and coupler.not really sure how much to put in.

Griff

I do about 5 pumps for each every 25-30 hrs just to be safe.

Kidnova

[QUOTE=IM4A2Z;2068452]Make sure you replace the gear oil between the water pump and fuel pump. It get's contaminated with fuel(Even on New units) and that causes the oil to breakdown and loose its ability to do it's job.
QUOTE]

I realized the need to change the gear lube in the pump after reading a similar thread last year. After reading the thread then checking the lube, I'll bet it was 25% gas and 75% gear lube. Not good, but no apparent harm done, yet.

I'll be changing the gear lube in the pump as annual maintenance from now on.