Newb Carb questions!

[dOb]

I?ve spent the last year or so on the resto forum rebuilding this old boat. Now I can start to work on the motor. It?s a 1974 Mercury 500 50hp. It will start on the muffs, but it isn?t very steady and it always had a really strong gas smell. The other day I discovered that gas was pouring from the lower carburetor when I would squeeze the bulb. I read up here, and decided that I should remove the carbs, clean them, replace gaskets and parts, and see if that solved the problem.

I know a little about car motors, and even less about boat motors. But I thought I'd give it a try. So the carbs are off and I have a gallon of carb soaking stuff ready to go. Then I start reading more, and keep coming across people saying that soaking is bad. Now I know from the resto forum that there are different opinions on every subject. But I started getting nervous. I finally decided that with the age of the motor, and not knowing the previous maintenance, I?ll go ahead with the soak.

Now, the question is, how far do I break the carburetors down? Do I just remove all of the plastic pieces and take apart where there are gaskets? I have no experience with rebuilding carbs, but I plan to document everything when I take them apart. Anything else to watch out for? And is it possible to soak for too long?

Sorry for the string of questions. Here are a couple of pics to give you an idea of what I?m working with.

Thanks.

 

[Mi duckdown]

Re: Newb Carb questions!

Serial number?
You need to rebuild the carbs.
Easy to do with an OEM merc manual.

 

[dOb]

Re: Newb Carb questions!

#3819598

Any idea if I can find that manual online? I checked the links in the sticky at the top and couldn't find it there.

 

[Jake.]

Re: Newb Carb questions!

Break it all the way down. There's no point in not doing so. You might initially save a little time and effort in doing a partial disassembly but you'll curse yourself if you hook it back up and it turns out there was still some gunk in a small passage. I almost never soak carbs for more than an hour. Compressed air in the passages does wonders and excessive soaking can strip protective coatings.

It's not likely that you'll find that manual for free online. I've rarely seen online manuals from the 70s, mostly 90s and '00s. Someone else might come along who knows better, though.

 

[aussieflash]

Re: Newb Carb questions!

You should replace needle n seats and all gaskets including engine mount gaskets.Post your serial number and someone will point you to correct parts.I sprayed my carbs with carb cleaner and left for 20 minutes the rinsed with fresh water then blow out with compressed air,then repeated process with Solvent and blow out.Came up nice and clean.
Also check floats arent saturated.If so you will need new ones.

 

[dOb]

Re: Newb Carb questions!

Do you mean the serial number for the carburetor engine. The engine is above. The carb has this number on it:
1339-4664

I think I found the rebuild kit here:
http://www.maxrules.com/fixmercurycarbkits2.html#139592621

If this is not correct, please let me know.

And there are a couple of used manuals out there that I can get online. I am currently trying to download one from the googledocs link in the sticky. The name of the doc has changed, so I'm not sure if it is the right one. We'll see.

I'm back on the fence as far as soaking vs. spraying. I haven't opened the can yet, so I still have the option. I'll have to decide by the time the kit comes in.

 

[MacDaddy21]

Re: Newb Carb questions!

Definitely soak it. A gallon of Chem-dip is more concentrated than the aerosol can of b-12 or gum out. When I rebuild carbs, I disassemble the whole thing and soak it for several hours, then pull it out and rinse it off, and dry it thoroughly.

 

[JPGBU1]

Re: Newb Carb questions!

I would soak those overnight from the look of things. if you can pull them apart, you can rebuild them easy enough. go to crowleymarine.com and look at the schematic if you don;t know where something goes, but def rebuild kit is needed.

 

[dOb]

Re: Newb Carb questions!

Thanks! I appreciate the help. One more question. I'm finding carb "kits" that are just gaskets and a filter, and some other "Kits" that have a lot more hardware for three times the price. I figured I want the kit with more parts due to the age of the motor, but I thought I'd ask in case I'm spending unnecessary money. Thanks again.

 

[MacDaddy21]

Re: Newb Carb questions!

Generally, what you do is buy the gaskets/filter, which cost about 5-10 bucks, then a float which comes separately for maybe 10 bucks or so, then a needle and seat for 5-8 bucks or somewhere around there. The kits that have more parts have gaskets and seals and o-rings and parts you wont need. Even when you buy the Gasket specific set for your motor for 5-10 bucks, it might still have some gaskets you dont need. I'd definitely replace the float and needle and seat and all gaskets/filter. Good luck

 

[dOb]

Re: Newb Carb questions!

Update:
Thanks for the info MacDaddy21. I took the carbs apart and soaked them each for about three hours. I reassembled them and re-installed them. I was pleased that the motor started right up. I made a slight adjustment on the throttle cable, and it kept a steady idle in neutral.

Now, this may need a different thread because I'm not sure if it's carb related.
I got the boat in the water, pumped the bulb twice, and she started right up. nice and steady. We cruised around for about ten minutes at about half throttle, and then started giving it more and more throttle. everything was going fine. We stopped and started several times. The engine started every time. Then... at one point, the wind had picked up, and I was headed back to pick up some people. I was WOT, and everything dropped. Speed, RPMs, everything. So I backed of the throttle, and she stalled. After a couple of minutes, it started back up. But was never quite as smooth as earlier. As I was taking people back to shore, a friend noticed that the inline fuel filter was full. It hadn't been earlier in the day. And he also noticed that it run smoother if he gave the bulb a squeeze here and there.
Does this sound like a carb adjustment issue? Or over heating? The tell tale was working, but the water coming out was pretty warm.

 

[MacDaddy21]

Re: Newb Carb questions!

That is your fuel pump. Whenever you can squeeze the primer bulb and the engine runs smoother and better, that is generally a weak fuel pump. On these old motors, the fuel pump has a diaphragm, 2 gaskets, 2 check valves, and 2 small circular gaskets for the check valves. The diaphragm's are very susceptible to ethanol damage, and they will just get very wrinkled. A new one is extremely flat and taut. The check valves also get old and brittle, and can crack. A rebuild kit is less than 10 bucks, and the rebuild is simpler than the carb rebuild. Do the same thing with the fuel pump. When you take it off, be very careful that you watch how the check valves are oriented. The check valves are identical, but they face opposite directions. So make sure you watch which one is facing which way when you take them out. I recommend that after you take the check valves out, you use a wrench to remove the hose fittings before soaking. There are probably only 2 hose fittings that are threaded, and then there may be one cap screw that can come out also. The other 2 fittings (for the tell tale water stream) are part of the whole fuel pump body. They stay there. I would soak the fittings and the fuel pump body for a few hours, then pull it out and rinse and dry it, put the hose fittings back on, then put the new check valve gaskets in, followed by the check valves, and the gasket/diaphragm/gasket over the top, then bolt it back in place and attach your fuel and water lines. This should get you back in business. Good luck!

 

[dOb]

Re: Newb Carb questions!

I was actually looking at the fuel pump rebuild kit last night online. I'll order it and be back next week with the results.
Thanks again!

 

[dOb]

Re: Newb Carb questions!

Well, it?s been a couple of weeks since I installed the fuel pump kit. I am happy to say that I spent hours on the lake yesterday with no issues. We even hauled a few skiers and the motor didn?t hesitate once. I also went ahead and replaced the two gas lines inside the motor, the one going to the fuel pump, and the one from the pump to the two carbs. The old ones looked dried out and the casing was cracked. Before I cleaned the pump it had been painted black. The chem-cleaner took care of the paint.

I also replaced the gas line from the tank and installed an in-line filter. I figure that after cleaning the pump and the carbs, I might as well be sure that the fuel getting to the motor is clean.

So far, so good. Again, thanks for all of the help.