Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

[Roadblock]

Rather than to start a new thread, I'm just going to edit this one as no one ever replied anyway.

OK I got the 1970 Mercury Thunderbolt 500 starting and it seems to idle fine. In fact she turns right over and starts after about one spin from the starter.

I did happen to do a compression test today and my numbers were 125, 125, 110, 125 going top to bottom. Thoughts there? I don't know what the factory spec was.

So yesterday I had posted I was having issues starting the motor. Turned out to be I flooded it I guess. Anyway tonight when I did my compression check with all four plug out happened to look into the engine again and I've still got gas dripping from the same spot as yesterday, even though the boat sat all night and I did not prime the bulb today. I'm guessing the fuel pump pulled some gas in from the tank? Either way I've got this steady trip off what I think it related to a carb? This is my first boat and motor so sorry if I seem like to total noob.


Can someone watch the video and give me there thoughts?

Video:

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

I've updated my thread as I've figured out why the motor wasn't starting. I do have a question about this weird gas drip though!

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

Anyone have any input on this or know where I might find a online forum that might be more active on these older motors?

My friend said something about the float seals being the issue..? He said to buy carb rebuilt kits. Do I also need to buy the floats?

Also I want to take this out and put it into the water tomorrow and see how it runs as a new purchase. If I leave the covers off so fumes don't build up, I should be OK right? The drip when running is about what you see in the video.

 

[racerone]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

This forum is actually very , very active !!-----But ----your video shows nothing but a finger pointing into darkness.----Not sure how you could expect any answers at all.

 

[bilge rat jim]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

It's hard to see anything in the video- There is a distributor in way. Can you post a photo from a different angle, maybe from the other side?

 

[Way Far North]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

I would say your floats are stuck. Probably just needs a good carb cleaning. The seat and needle valve might be worn as well. I would use KleenFlo carb/parts cleaner. It stinks like hell but works like a hot damn. Also get 2 carb gasket kits and possibly new fuel filters. Remove the carbs from the power head and disassemble the carbs. Don't worry about taking them completely apart I would just take the filters and floats out and maybe remove the idle screw as long as you count turns to seat it then remove it.

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

I very politely say you might want to turn on your monitor brightness if you can't see the leak in that video, it's very clear.

Way Far North, that is what my friend thought too. OK I guess I'll start by pulling the carbs out. Thanks!

 

[Chris1956]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

That is an easy question. You are dripping fuel from your throttle plate shafts. Fuel should not be pooling in this area, if the carb floats are set properly and the inlet needles and seats are working properly. You should replace the inlet needles and seats, and inspect the floats. Aw heck, replace the floats. The original floats tended to dissolve in today's alcohol/gas fuel.

Remember to set the float heights correctly.

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

That is an easy question. You are dripping fuel from your throttle plate shafts. Fuel should not be pooling in this area, if the carb floats are set properly and the inlet needles and seats are working properly. You should replace the inlet needles and seats, and inspect the floats. Aw heck, replace the floats. The original floats tended to dissolve in today's alcohol/gas fuel.

Remember to set the float heights correctly.

I was kinda wondering if that might not be what those were. I can see the rebound springs on them so I thought they must turn some how. That makes perfect sense.

Would all of those parts come in a carb rebuild kit? I found some carb rebuild kits on that "Old Merc" parts page. Oh wait looks like the floats are not included.

I can say this though. The gas leak almost completely went away today when I was running it but it's still dripping, like a drip every 10~15 seconds. Still enough that I want to go threw them.

Also does anyone know what would cause a stutter like, um, a missing almost? It clears out when you open it up. I'll post a video, you can kinda hear it when I first take off.

 

[Chris1956]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

It doesn't sound too bad. It is probably partially flooded, and it clears up at high speed. You might check the fuel pumps (you may have one or two of them), and see if the diaghrams are leaking fuel into the crankcase. Just fixing the carbs may fix it as well. Get new gasket kits, inlet needles and floats. That is usually 6 items. Your serial number will help a lot.

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

1970 Mercury Thunderbolt 500 50HP

Serial number 2951315

That video would have been a hell of a lot cooler has I remembered to remove the trolling motor!



I think my next project is going to be to just take it back out again and run some Sea Foam or whatever you guys would recommend to clean it up. Honestly the gas drip got much better after I took it out and opened it up. I hardly noticed much after I actually ran it in the water and not just on a garden hose.

I did find out that my lower unit leaks and gets water in it. I swapped out the gear oil before taking it out and it had water in it, but also the gear case screws has NO seals so I was hoping that was why I had water. I didn't have so much water that gear oil poured out and then water at the end, it was mixed.

Anyway I drained it and let it drip for a few hours before refilling it. I pumped extra fluid in and left it run out the top to make sure if any water was in there it would push it out.

I took it out and drained it after about 5 hours on the lake when I got home, fluid was all milky white/tan-ish colored. It was still pretty thick and drained slowly and no water dumped out on it's own at the end so I'm thinking it's not a ton of water getting in there.

I let it drip overnight and I'm going to fill it up again so it's got oil in it. I will probably just do that for a next couple outings and then maybe drop the lower and do a pressure test when I know I'm not going to take it out for a few weeks so I can leave it apart while I wait for parts/seals etc.

Yea I know I absolutely have to drain the fluid after I bring it in off the lake if I get water in there!

 

[Chris1956]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

You probably need to replace the driveshaft seal. I have found that to be the most usual culprit for gearcase leaks. That seal is located in the base of the waterpump.

 

[carholme]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

You said in post # 11 that "the gear case screws has NO seals so I was hoping that was why I had water." Without a doubt that is the best and most common place for oil to enter the gearbox.


Gerry

 

[Roadblock]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

It doesn't sound too bad. It is probably partially flooded, and it clears up at high speed. You might check the fuel pumps (you may have one or two of them), and see if the diaghrams are leaking fuel into the crankcase. Just fixing the carbs may fix it as well. Get new gasket kits, inlet needles and floats. That is usually 6 items. Your serial number will help a lot.

Mercury Thunderbolt 500 50HP, serial number: 2951315

Would it be worth while to take the boat back out and add a can of Seafoam to the gas and see if that helps clear stuff up before ripping the carbs and pump out?

I did notice that most of the gas leak went away after actually running it but its still does drip a little. Could something have just been stuck?

That said are there any online resources for factory service manual without tracking an old one down on eBay? For most cars, you can practically Google search stuff like that but I'm having ZERO luck on this outboard.

I'm going to guess the carbs haven't been touched in YEARS. I'm also going to guess the fuel pump hasn't either.

How do I tell what parts I need from a parts number stand point? Also where is the best place for old parts? I did find that "Old Mercs" dealer but I don't know what is specific to my motor. Here let me post what I would understand to be for my Merc 500 and tell me if I'm on the right track.

OK first up, carb kit. Doesn't SAY Merc 500 but this is one I get directed to when I look for that model on the site:

http://store.oldmercs.com/product_p/1395-9258a2.htm

Floats, not included in the kit it seems:

http://store.oldmercs.com/product_p/1395-8673.htm

Fuel pump diaphragm:

http://store.oldmercs.com/product_p/23014a1.htm

Fuel pump rebuild kit (includes diaphragm it looks like):

http://store.oldmercs.com/product_p/21-30430a1.htm

Now does the rebuild kit include filters/screens? I can't tell and they don't list.

Ummm so if those are the right parts, if I had to everything is around $80.00 dollars?

I've rebuild engines and transmissions in my Mitsubishi sports cars so I'm sure I can handle this, just a little bit of a learning curve! This is my first boat or boat motor.

 

[oldman570]

Re: Why is gas leaking here? Please look at my video! Mecury Thunderbolt 500 50HP

Look up boatinfo .com for a online manual for the motor. JMO
Oldman570