1970 mercury 500 thunderbolt

[Bjohnson2345]

So I bought a boat that has a 1970 mercury 500 the guy I bought it from didn't know much about it, nor do I for that matter but I have done a couple test runs with it and the second time out the motor felt under powered and it died on me when I tilted the motor up I noticed gas dripping out if the carbs I took the boat home and rebuilt both the carb. After that I took it out again and it still hAs a lack of power it's a 50 hp motor and it won't even plann the boat do my question is what could this be

 

[Way Far North]

Re: 1970 mercury 500 thunderbolt

Did you make sure both carbs are sync'd properly? Does the boat have a tach? If so what RPM are you reaching? Could be wrong prop? I believe you should be getting around 4000 to 4800 RPM out of the motor, but I will double check. Compression Check? Each cylinder should be within 5 to 8 psi and generally around the 110 psi or higher. Bad gas? There is a long list of things that could be wrong, but it could be something really simple. Need to do a little more troubleshooting.

 

[carholme]

Re: 1970 mercury 500 thunderbolt

RPM on that engine should be 4800-5500 and the compression should not vary more than 15 psi between cylinders. Do you have the s/n of the engine?

First thing to check is how the engine is mounted with the anti-ventilation plate being even or slightly above the bottom of the boat. In this link, see where the plate is in relation to your boat.

Outboard Motor Shaft Length

Gerry

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

RPM on that engine should be 4800-5500 and the compression should not vary more than 15 psi between cylinders. Do you have the s/n of the engine?

First thing to check is how the engine is mounted with the anti-ventilation plate being even or slightly above the bottom of the boat. In this link, see where the plate is in relation to your boat.

Outboard Motor Shaft Length

Gerry

The s/n number is 2739033 n I know the gas is good my next step was to rebuild the fuel pump cuz when it died on me I pumped the primer bulb and I got it fired up long enough to get it back to the trailer , do u think this might be a good idea or a waste of the 12 bucks

 

[K-2]

Re: 1970 mercury 500 thunderbolt

Boat ownership = Wasting money
I had a 50HP Mercury on a 17' river sled when I was a kid, tiller steer, pull start,
loved that engine, I had zero problems with it , nice smooth idle with those 4 cylinders.

 

[carholme]

Re: 1970 mercury 500 thunderbolt

If pumping the primer bulb got it to run for you, it certainly indicates a problem with the fuel pump diaphragm or check valves. Good idea to get it changed. But make sure it is mounted at the correct height as well.

Your s/n is a 1970,

50 500 4-cyl 2736807 3008818 1970 USA

From here:

Mercury 2-takt, 4-cyl, 40 - 85 hp, produktions?r, modellguide

Parts List:

MERC 500-7/8 - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is P/N: 90-68647.

90-68647 | eBay

In the interim, here is a link to the condensed version of the Clymer manual if you need it. Download it soonest to your computer as the link is short lived.

MERCURY - MERCURY FOUR-CYLINDER MODELS (1969-1989).: Small Engine Repair Reference Center Home

Gerry

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

If pumping the primer bulb got it to run for you, it certainly indicates a problem with the fuel pump diaphragm or check valves. Good idea to get it changed. But make sure it is mounted at the correct height as well.

Your s/n is a 1970,

50 500 4-cyl 2736807 3008818 1970 USA

From here:

Mercury 2-takt, 4-cyl, 40 - 85 hp, produktions?r, modellguide

Parts List:

MERC 500-7/8 - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is P/N: 90-68647.

90-68647 | eBay

In the interim, here is a link to the condensed version of the Clymer manual if you need it. Download it soonest to your computer as the link is short lived.

MERCURY - MERCURY FOUR-CYLINDER MODELS (1969-1989).: Small Engine Repair Reference Center Home

Gerry

Thank you for all your help
So with the fuel pump needing rebuilt that would cause the motor to feel under powered?

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

If pumping the primer bulb got it to run for you, it certainly indicates a problem with the fuel pump diaphragm or check valves. Good idea to get it changed. But make sure it is mounted at the correct height as well.

Your s/n is a 1970,

50 500 4-cyl 2736807 3008818 1970 USA

From here:

Mercury 2-takt, 4-cyl, 40 - 85 hp, produktions?r, modellguide

Parts List:

MERC 500-7/8 - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is P/N: 90-68647.

90-68647 | eBay

In the interim, here is a link to the condensed version of the Clymer manual if you need it. Download it soonest to your computer as the link is short lived.

MERCURY - MERCURY FOUR-CYLINDER MODELS (1969-1989).: Small Engine Repair Reference Center Home

Gerry

Thank you for all your help
So with the fuel pump needing rebuilt that would cause the motor to feel under powered? And I'm not sure about what you mean by making sure it's the right height, can u explain the steps to me? Thank you

 

[carholme]

Re: 1970 mercury 500 thunderbolt

In this link you will see the plate where the number 1 is pointing to. That is the anti-ventilation plate and it should be even with the bottom of the boat or just above it in the vertical position. What is the position of the plate on your boat?

http://www.crowleymarine.com/mercury-outboard/parts/437_19.cfm

Do you know if a compression test has been done and if so what were the numbers.

I see you said you had done a few test runs with the engine prior to your problem. How did it run on those tests and did it get up on plane?

Gerry

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

In this link you will see the plate where the number 1 is pointing to. That is the anti-ventilation plate and it should be even with the bottom of the boat or just above it in the vertical position. What is the position of the plate on your boat?

Mercury, Mercruiser, Force, etc. - GEAR HOUSING ASSEMBLY, COMPLETE (PAGE 1) - MERC 500-7/8

Do you know if a compression test has been done and if so what were the numbers.

I see you said you had done a few test runs with the engine prior to your problem. How did it run on those tests and did it get up on plane?

Gerry

No I haven't done a compression check and on the test runs the motor only went about 5 mph not enough to even plann at all it barly made a wake

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

So I have a update....
I took the fuel pump off today because I have a kit that should be coming tomorrow well I noticed that some one has been in there before which wasn't a shocker but what did shock me was the fact that the pump has three different bolts in it and only one of the bolts is the right one.. Also it looks like who ever took it off before broke a bolt off and did a really poor job of fixing, what they did was put a way larger bolt in the pump that doesn't even go in to the block of the motor but they taped it and just bolted it back to the other piece of the pump where the bolt hole is on the block it's just drilled out a lot larger and I can see the old bolt down in there still I just don't understand peoples half *** things they do! Will the fact that only two bolts holding this on cause it to run like this? Maybe it's sucking air or something. I do know one thing it wasn't leaking fuel there at all. So could I just rebuild the pump and assemble it the way I found it? I really know better than that tho. My other question is to fix it back to normal can I just drill out the remaining old bolt and fill the hole with JB weld and redrill and tap the right bolt for it I have a different fuel pump from my parts motor to replace the old one that's kinda destroyed, I'm going to try and upload some photos to help to better explain myself I really need all the help I can get with this guys

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

I really need help with this problem I can't sit back and watch fishing on tv I have to make it out for spring salmon

 

[Way Far North]

Re: 1970 mercury 500 thunderbolt

JB weld is about as good as you can get off the store shelf. I can't see why you couldn't easy-out the old bolt and fill/drill/tap again. I'd just make very sure the hole is clean and dry. MEK is great for degreasing/leaving no residue just need gloves when using it. I've used JB weld for rebuilding exhaust manifolds on old CAT generators to bonding new panels on a car body, and never had an issue with it.

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

Does anyone know what lower unit is on this motor or what the part number is for a bearing carrier nut tool

 

[carholme]

Re: 1970 mercury 500 thunderbolt

You started by asking for help with your engine and yet refuse to answer the questions that are asked of you.; In most troubleshooting, you start with the basics and work upwards. We go from a situation where the boat will not even plane to pulling the bearing carrier. Hard to help if you are not going to answer the questions or let people know what you are doing.

Good Luck with your engine!

Gerry

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

I don't understand what questions I didn't answer, n I have a lot of things that need to be done from simple maintenance to the fuel pump issues. What questions did I leave unanswered, no I haven't done a compression check and I'm in the process of putting a tach in the boat cuz I don't have one of them either I have a Manual that I bought and downloaded on my computer but it doesn't say a hole bunch about my problem what's ur input on what I should do about the broke off fuel pump bolt Gerry in my later post. And what questions did I leave unanswered I'll try and do a better job of answering them all... Thanks

 

[bgc]

Re: 1970 mercury 500 thunderbolt

With the pump, I would remove the broken screw to start. Fill the cavity with DEVCON(orJB) and tap it for the correct size. Get the pump on there the way the engineers designed it to be.
Next get a base line reading of the compression, this is important(I learned the hard way).
The first steps with the old gals is Compression, Fuel, and ignition. You know you have a challenge with fuel start with that then goto compression.

 

[Bjohnson2345]

Re: 1970 mercury 500 thunderbolt

Thx kindly I think that's how I'm going to do it I'm looking for a descent yet inexpensive compression tester cuz chances are I won't use it much, any recommendations

 

[bgc]

Re: 1970 mercury 500 thunderbolt

There are several on the market that are "affordable". I prefer the KD for my "on the road" tool kit. When the hose is warm (above 60 deg) it flexes quite well.
There is a challenge with getting any of them threaded into the lower cylinder. Find one that's flexible enough to get it in there and be careful not to cross thread it! The top one, remove the upper cowling on the engine. I have three old Mercs with thread repair coils in them, it doesn't take much to damage the threads


Compression Test Kit

KD Tools 2428 - Compression Tester | O'Reilly Auto Parts

The vast majority of the good folks here have been down the road youre traveling and want to help you.
My Mercs are fussy and there are hundreds of reasons they act up. Knowing the basics about each one lets me know if she needs rings or I have too much grease on the points, again, when there's no power....Keep plugging away at the motor, one step at a time, and we'll have you screaming across the water in no time.

 

[bgc]

Re: 1970 mercury 500 thunderbolt

Where are you located? One of us might be just down the road from you and could offer some hands on experience.