Mercury 500 Thunderbolt 50 HP Four 2 Stroke Serial Number?

Lifeisgood7

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I recently acquired a 1969 Fiberform with a Mercury 500 Thunderbolt 50 HP Four 2 Stroke outboard that hasn't run for several years. I picked up a Solec manual but I really need to find the manufacture date so I can order parts and figure out what part of the manual to start troubleshooting in (I seem to not be getting any spark). I have done multiple internet searches, read dozens of forum threads and found all kinds of webpages showing the year of the motor based on the serial number, however non of the numbers I've found on this motor correspond to a valid serial number... Please see the pictures of the motor below and all the numbers that I found on it. There is no plate on the transom mount where it seems like it is supposed to be on these motors. Any input or direction would be greatly appreciated!








 
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Chinewalker

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Look in front of motor on the pivot bracket, between e transom brackets. Should be an ID plate there. Lacking that, the serial should also be stamped into the motor block, top, rear of the flywheel. Cowling decals look like 1968.
 

racerone

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It sure looks like a 68 / 69 model based on the decals.----What parts are you looking to order ?----Have you done a compression test on it ?----Checked gearcase oil ?
 

GA_Boater

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Welcome aboard,

My '66 has the serial number stamped, not cast, on the distributor bracket. Tried to zoom in, but couldn't see any stamped numbers in your pic. Just a place to check. Also have a plate on the tilt tube - Mine was covered by grease and muck.

mercsn.PNG

ttsn.PNG
 

merc850

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The serial Nr. will look like this: 2736807 no hyphens, look in the area near the fuel pump. All those image Nrs.are part Nrs.
 

merc850

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No that's why they call it Thunderbolt ignition, this model uses an ignition driver (tan colored unit in pic. 3) with trigger coils.
 

racerone

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Thought so---post # 3 suggest cleaning them might be required.
 

Lifeisgood7

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Thank all for the replies! I've collectively spent more then two hours looking for the serial number on this thing with no luck, but thanks to GA_Boater I finally found it! Ended up having to chisel off around an 1/8" of baked on grime to uncover the plate... Looks like it is a 1968 based on the serial number 2478717.

Any thoughts on where to get started making this thing run? I picked up a compression tester so as soon as it warms up a bit that is on my to do list. I've already drained the fuel tank, filled it with 10 gallons of fresh non-ethanol premium and 2 stroke oil at a 50:1 ratio. I put in a fresh battery and after disassembling and cleaning the MerControl unit and choke button I got it to turn over. Next I pulled the plugs (all four of which look great) and found that I have no spark. Yes, I did have a set of muffs hooked up and the hose running while turning it over. At this point I wasn't sure what to do next so I picked up the Solec manual but couldn't start the troubleshooting without knowing the year. I was figuring on order a carb rebuild kit, but not sure if that's really necessary or not. Someone mentioned checking the gear case oil, is there anything else I should look at? Thanks again!
 

GA_Boater

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One of my manuals is a Seloc for 1965-1989 Merc outboard, 40-115 HP, 3 & 4 cylinder. I think you have a Thunderbolt Type II ignition. If you have the same manual, the wiring diagram is on Appendix page A-20.

TB Type II is in section 5, starting on page 23. The troubleshooting part is pretty lame, but it does have coil testing.

I would remove the Ignition Drive (distributor) and clean the rotor and cap. Be careful, the parts are expensive to replace if broken. Also if you have a kill switch, make sure the lanyard is attached. If you have a mercury switch on the side of the motor, temporarily disconnect it.

Probably more to look at, but this will keep you busy. :smile:
 

Lifeisgood7

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Yes, that is the same manual that I have. I was having trouble figuring out if I had the type II, III or IV ignition system... What would a mercury switch on the side of the motor be for?

Also, I wasn't able to find anything in this manual about changing the impeller... Is this just what pumps weather through the lower unit to keep it cooled?
 

GA_Boater

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The mercury switch will stop the motor or prevent it from starting if it is tilted too much raising the prop out of the water, which is unsafe.

Section 10 has the Water Pump/impeller service instructions. The pump supplies all cooling water for the motor. A motor can self-destruct by overheating if the pump/impeller is bad.

Section 12 has regular Maintenance, including draining and filling the lower unit.
 

merc850

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Just a note: in this image it looks like the - cable is touching the starter + terminal, it if it is I would move it farther away to eliminate the possibility of fire.
wiring.jpg
 

Lifeisgood7

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Well I know it's been a while, but life just happened and I got busy. I ended up bringing the boat in to a shop since I didn't have time to troubleshoot any further. I was able to get spark after cleaning up some poor electrical connections but it still wouldn't run. The shop ended up finding that one of the electromagnet choke plates had fallen off and after reinstalling it, the motor fired right up! I went ahead and had them replace the water pump and change the lower end oil too. Unfortunately they didn't notice that there was a fairly large crack in the exhaust housing and it leaked water pretty bad... They did a patch job on it with some JB weld type stuff and said run it till it dies!

The first trip out went pretty good, but I have a few questions being new to this older boat scene. Regarding the warm up lever, how should this be used properly? I got it to fire up and run with the lever in the up position, but after 5 minutes or so it would still die when I dropped the lever back down. I idled it for maybe another 5 minutes and then pushed off from the dock, only to have it die again. I got it started back up by squeezing the primer bulb on the fuel line a couple times (which didn't have any pressure in it) and then ran it with the warm up lever up at a 45* angle facing the stern. This working fine for a while and I was able to drop the lever once underway, but after maybe 10 minutes of motoring around at different speeds, it sputtered and died again.

Squeezing the primer a couple more times let it fire up again for another 10-15 minutes or so of boating. This time we got up on plane for a bit and made some sharp turns, then we slowed down and it died again. Squeezed the primer a couple more times, lifted the warmup lever for start and it ran just fine all the way back in where it died just as I put it into neutral at the dock...

Any thoughts on the matter? I'm thinking it's probably a carb issue as it seems fuel related, but I'm open to suggestions. Is this just how these motors are and am I using the warm up lever properly as an idle control? I tried to avoid driving with the lever up, but it seemed like I had to use it somewhat to keep it running...

The only other thing that I found strange, was that there seems to be a lot of play in the MerControl lever... From the neutral 12 o'clock position I can move it forward all the way to 10 o'clock before anything really happens, then between 10-9 o'clock is where it responds. Is this normal or is there some kind of adjustment? Also, sometimes I could go full throttle forward and the boat would seem to max out at a rather slow speed, then after a minute or two it would start to take off and accelerate all on its own (granted the shift lever was in the fully forward position, it just took a while to get there).
 

Slbaddorf

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Welcome aboard,

My '66 has the serial number stamped, not cast, on the distributor bracket. Tried to zoom in, but couldn't see any stamped numbers in your pic. Just a place to check. Also have a plate on the tilt tube - Mine was covered by grease and muck.

View attachment 247191

View attachment 247192
The serial Nr. will look like this: 2736807 no hyphens, look in the area near the fuel pump. All those image Nrs.are part Nrs.
I’ve been trying to figure out the year of my merc 500 thunderbolt 50hp 4cylnder . My serial number is 2406684, you wouldn’t happen to know what year make it is ?
 
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