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Results 1 to 19 of 19
  1. #1
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default 1971 Mercury 80 hp 800 thunderbolt

    Hello again,
    I am really lost here again, I have been reading the manual and the forums trying to figure out this flywheel situation. From my understanding the flywheel on my Motor is nothing more than to charge my battery and to set the timing. I had to take the flywheel off to get to my distributor gear because the tension bolt under the distributor gear had come loose. After putting this all back together the way it was, making sure my markings were all back in line, we took her out for a run. Starts fine, Idles fine, but when I start to give it some throttle it bucks and sputters, gets up on plane but still misfiring (bucking) max rpm 4200 . Checked the spark plugs and they are wet as if they are not firing right. Battery is at full charge and is charging when running. I am not sure if I should go back and redo my carbs again, they seem to be working fine. I really don't want to give up on this Motor to much invested, New switchbox, new used distributor/trigger, RadioShack rectifier, Carbs. new gas tank, bulb, hoses, fuel pump rebuilt, lower units, etc. Any great Idea's I am game to about anything now. Compression is still at 120 on all 4 give or take 3 psi
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,697

    Default Re: 1971 Mercury 800 thunderbolt

    Are you certain the 'wheel is on the way it came off? It can go on 8 different ways, but only one will work properly.

    I suggest using a timing light to see if the timing is off. If so, that might be the problem. Remove the top carb's throttle lever so you can hold her wide open to check timing.

    Alternately, you can use a timing tool to locate TDC. If the mark on the 'wheel lines up, then you have the right holes.

    Jeff

  3. #3
    Join Date
    May 2010
    Location
    Ottawa, Canada
    Posts
    92

    Default Re: 1971 Mercury 800 thunderbolt

    GET a dial indicator, remove all the plugs, install the dial indicator into #1 cylinder remove the little plate on the top of the distributor rotate the flywheel clockwise until #1 piston pushes dial indicator all the out this is TDC; now on the belt drive pulley on the top of the distributor there is an arrow make sure that the arrow is pointing perfectly towards the center of the crankshaft if the arrow is off one tooth one way or the other you need to re-align the belt. You have to be close now or the motor would not even start.
    Then goto the timing testing and adjusting section in the manual and start from the beginning. setting the primary pickup, then primary to carbs then max spark, then secondary pick-up and finally max throttle stop. If any of these are off the motor will run bad. You say the plugs are wet are they wet with FUEL or WATER. Are they droplets or even coverage of soot, carbon or oil fule mix.
    Regards,

    Dave Scott
    Aim Outboards and Machine
    613-831-1246

  4. #4
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Thanks guy's for responding
    Concerning the wet spark plugs they are wet with gas/oil no soot or water.As for the flywheel just to make sure I get this right when I find TDC on the number one piston,does it really matter how the flywheel is then put back on.I know this may sound stupid but there are really no markings on the flywheel except 3 dots and they have never lined up with TDC marking on the top cowl decal no matter how i put it.
    Thanks

    I just wanted to add when Nr.1 piston is TDC is there supposed to be a little play before the piston starts to go on the down stroke?It seems to me I have about 1/4 inch play back and forth at the flywheel turning it @ TDC,maybe not that much but there is some.
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  5. #5
    Join Date
    May 2010
    Location
    Ottawa, Canada
    Posts
    92

    Default Re: 1971 Mercury 800 thunderbolt

    Correct on both counts. The piston will rock over TDC, I usually use a screwdriver, but it is easier with a dial guage.

    The flywheel location does not really matter as long as your tdc is up, The only problem with that is you have no way to set max timing because your decal is off.

    There should be a decal on the front of the motor with both a degree number and an inch number like 23 degrees or .174 btdc or atdc, you can wind the flywheel clockwise to tdc then turn it ccw to the specified inch number on the dial indicator you may want to go ccw past the number required and then cw to the proper inch number to get over the water pump vanes. Then you can put a spark checker on #1 cylinder wire and turn the key on and then move the throttle actuator arm with the throttle cable disconnected when you hit max spark on the stop the spark checker will jump. I hope this is understandable, I have done it so many times it is like 2nd nature.
    Regards,

    Dave Scott
    Aim Outboards and Machine
    613-831-1246

  6. #6
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Okay let's see if I got this right
    1.Find TDC using a dial indicator.
    2.On my top engine cowl I have a timing strip that goes fom TDC to 50 Degree's BTDC,mark my flywheel @ TDC.
    3.Max advance WOT crank the engine with key on and with a timing light adjust to 23 Degree's BTDC.
    The first white line to the right are the 3 dots and the second white line to the left is TDC.
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    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  7. #7
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Here's is one other thing that seems to bother me on this setup,when setting the distributor gear in reference to the crankshaft the manual say's the arrow on the gear should be pointing to the center of the crankshaft,but what I dont understand is on that gear there is a little tit that is supposed to line up with with the little tit on the distributor mounting bracket which then it doesnt line up.I hope I didnt really confuse any of you.
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  8. #8
    Join Date
    May 2010
    Location
    Ottawa, Canada
    Posts
    92

    Default Re: 1971 Mercury 800 thunderbolt

    Steve,

    Do not worry about the little tang, just line up the arrow with the crank. Max Spark is not WOT. If you do it the way I said to do it you do not need to crank the engine at all and you do not need to worry about the dots on the flywheel. line up tdc on the indicator turn flywheel ccw past the .xxx number supplied on the decal on the front plate of the motor then cw to the .xxx number with the throttle cable disconnected and a spark checker on #1 turn ON the key and actuate the throttle with the throttle lever until you hit the max spark stop on the front plate it should spark on the checker if not adjust your screw in or out until it sparks on the checker just as you touch the stop for max spark then setup the secondary pickup cluster so it is just touching the secondary cluster on the carb (This is done with the screw at the rear of the distributor housing upper tower) Then advance the throttle all the way by hand and adjust the wot throttle screw until there is about .015" play at the top carb cluster that you can feel with your finger anything is good here as long as there is some play and it is not locked up solid against the carb cluster.
    Regards,

    Dave Scott
    Aim Outboards and Machine
    613-831-1246

  9. #9
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    I got it now,I will go tinker with this later today.Its starting to get hot again here in southern Arizona and I am laid off again for the Summer so I have plenty of time to get this right.I hope nobody on here will boycott any advice because I live in AZ.LOL
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  10. #10
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Hello Gentlemen
    I think I have found what has been the trouble maker.I took my Distributor off today to inspect plug wire's cap etc. and found this to be loose.Well it's broke.I guess a new trigger is in order,Bummer......
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    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  11. #11
    Join Date
    May 2010
    Location
    Ottawa, Canada
    Posts
    92

    Default Re: 1971 Mercury 800 thunderbolt

    Yep that'll do it everytime, I am surprised it still ran. You can get those new from CDI. I have lots of used ones if you like. They are not cheap, read the book to take it apart and do not pry anywhere on the rotor or the dwell plate. mark the brass plate before you take it apart, the plate needs to go on only one way.

    There is a nut inside the trigger housing holding the rotor into the trigger and the whole unit needs to be taken apart to change the trigger, there is also a long spacer under the nut I am referring to then there is a spacer between the rotor, dwell (brass plate) and trigger housing, you need to support the bottom side of the rotor between the rotor and dwell plate and a good swift wach with a mallet to knock the rotor out of the trigger housing.
    Regards,

    Dave Scott
    Aim Outboards and Machine
    613-831-1246

  12. #12
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Hi Dave,
    I have been shopping around and yep they are exspensive,so if you have a used one whats your price?
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  13. #13
    Join Date
    May 2010
    Location
    Ottawa, Canada
    Posts
    92

    Default Re: 1971 Mercury 800 thunderbolt

    Steve,

    let me check I have a couple completes off early 850 complete cap, wires etc,,, I will check them tomorrow with the CDI tester and post back for you probably 200$ complete inc shipping.
    Regards,

    Dave Scott
    Aim Outboards and Machine
    613-831-1246

  14. #14
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Thanks Dave,
    No big hurry my finaces right now are not in the best of shape to invest anymore in this motor. I get laid off every Summer for 3 months so things get tight right now.But I will get back to you,Thanks again..
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  15. #15
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,697

    Default Re: 1971 Mercury 800 thunderbolt

    Look for used distributors on eBay. Any 4 cylinder (50 to 80 hp) distributor with the plug wires going straight down will work.

    Jeff

  16. #16
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    Thanks Jeff,
    That is the place where I bought this one and after inspecting it closer come to find out it was JB welded back in place,so you just never know what your going to get.So its a big HHHMMM now,I think I will just kick back and think on this one for awhile.
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  17. #17
    Join Date
    May 2007
    Location
    Ireland,the only country in the world you can go North to go South
    Posts
    1,424

    Default Re: 1971 Mercury 800 thunderbolt

    It took me awhile to work out the damage,if you're in no hurry and fancy a bit of DIY,drill a 3mm all the trough,tap it and screw an allen grub screw through, hey it might even work and keep you on the water till you come up with a replacement.

  18. #18
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    You know I have been thinking about that,because I looked at a new one on line and they look like they have small screws in them.I might just give that a shot now that you have mentioned it,that way I am not the only one with some bright Idea.And I meant that in a good way.
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

  19. #19
    Join Date
    Dec 2009
    Location
    Yuma, AZ, USA
    Posts
    107

    Default Re: 1971 Mercury 800 thunderbolt

    We got her up and running again,my son was nice enough to invest in my boat and bought a new trigger.We havent put her in the water yet but she runs in the drive way.when idleing at 900 RPM seems like she is going to die and runs like as if she has a performance cam like a race car.Cant seems to get her to smooth out when Idleing,carbs are redone,dont leak,fuel pump was rebuilt all new hoses,bulb,etc.Starts up no problem.Compression on all cylinders 130 and nr.1 at 125 PSI.Carbs came off a 85 hp motor and were not re jetted.Also just kinda curious I have watched some youtube video's of 2 strokes running and they all seem to smoke mine doesnt or very little and I do mix 50:1. Also is there a way to clean out the water ways in the motor without taking everything apart,the reason I am asking because at idle my tell-tale hole is just barely dribling,when throttling up she pee's fine.New impeller also installed no difference,I am thinking some blockage somewhere.Used to pee like a champ until I switched lower units.
    [FONT=Impact]Best Regards[/FONT]
    [FONT=Impact]Steve[/FONT] ;)

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