Mercury M-800 Thunderbolt Full Throttle Only Now Help

[MyName]

I bought a1978 Glastron with Mercury 80hp model 800 Thunderbolt 2 stroke 4cyl Ser#500I9751 but soon had running & starting problems. I've replaced/redone all necessary CDI stator trigger rectifier coils starter & solenoid correct plugs wires switch box carb & fuel pump kits fuel lines prime bulb everything! H2o pump ok compression 130#ea But...now at startup the MercControl choke lever must be up and motor runs Only Full Throttle. Putting the lever down does not lower RPM, I can only lower it by hand moving the motor port side vertical Throttle Arm & Spark Arm & go turn off the ignition. There's several adjusting screws, Throttle Actuator Cam, Secondary Pickup and so on?
Question: Can anyone please help? I Called Mercury but they're no help, answering from home eating donuts & SELOC manual has become like my only source since Sacramento Area Marine Repair shops are forever to busy it seems.

 

[Chris1956]

Assuming the carbs are clean, it sounds like you need to do a link and synch.

Remove all spark plugs and the prop and stick a ruler into the top spark plug hole and read the distance to the top of the piston at it's minimum (TDC). A dial indicator is best, a caliper is second best and a steel ruler is third best for this. Now add .464 inches to that measurement stick the ruler into the spark plug hole and turn the flywheel until the piston is exactly that distance from the cylinder head. The timing pointer should read .464 before top dead center. If not adjust it.

Install the top spark plug and put the wire on it. Now install all the other spark plugs into their wires and ground their bases to the engine block. Set the throttle to the spot when the carbs are ready to open, but are still closed. With ign on, jumper the starter and read the timing at that throttle opening with a timing light. It should be 0-8*ATDC. Your Seloc manual should tell you how to adjust it, using the set screws on the throttle arm. You want the idle pickup timing to be in that range just as the carbs open.

Now advance the throttle all the way and read the timing. It should be 21* BTDC. Set the max spark advance screw to that reading. Set the throttle stop screw to allow the carbs to fully open.

Install spark plugs and their wires, Set the idle mixture screws on the carbs to 1-1/2 turns open.

The motor should start and run at fast idle. The rest of the carb idle mixture adjustment must be done on the water, in gear.

 

[MyName]

Assuming the carbs are clean, it sounds like you need to do a link and synch.

Remove all spark plugs and the prop and stick a ruler into the top spark plug hole and read the distance to the top of the piston at it's minimum (TDC). A dial indicator is best, a caliper is second best and a steel ruler is third best for this. Now add .464 inches to that measurement stick the ruler into the spark plug hole and turn the flywheel until the piston is exactly that distance from the cylinder head. The timing pointer should read .464 before top dead center. If not adjust it.

Install the top spark plug and put the wire on it. Now install all the other spark plugs into their wires and ground their bases to the engine block. Set the throttle to the spot when the carbs are ready to open, but are still closed. With ign on, jumper the starter and read the timing at that throttle opening with a timing light. It should be 0-8*ATDC. Your Seloc manual should tell you how to adjust it, using the set screws on the throttle arm. You want the idle pickup timing to be in that range just as the carbs open.

Now advance the throttle all the way and read the timing. It should be 21* BTDC. Set the max spark advance screw to that reading. Set the throttle stop screw to allow the carbs to fully open.

Install spark plugs and their wires, Set the idle mixture screws on the carbs to 1-1/2 turns open.

The motor should start and run at fast idle. The rest of the carb idle mixture adjustment must be done on the water, in gear.

Wow that's real! Thank you so much Chris! I hope as a 'Mercury Moron' I can learn & understand this by attempting it. You seem very knowledgeable! Let's keep in touch buddy.
Kind regards
Stephen

 

[Chris1956]

Those Seloc manuals can have some real bad errors in them. Since that motor is so old, not many mechanics will work on them. You might look around for a factory service manual.

The timing procedure I provided should get around any errors in the Seloc, at least for link and synch.

 

[MyName]

Those Seloc manuals can have some real bad errors in them. Since that motor is so old, not many mechanics will work on them. You might look around for a factory service manual.a question

The timing procedure I provided should get around any errors in the Seloc, at least for link and synch.

Chris I've checked the TDC & .464" ok & pointer ok, but before trying to do the rest to continue to synchronize & get it to idle I have a question which may seem elementary for you but could you explain which throttle is it to set? I suppose the Throttle Arm, not the in boat throttle handle? to "Set the throttle to the spot when the carbs are ready to open, but are still closed" & how to know that position & do it?
Thank you in advance
Regards,
Stephen

 

[Chris1956]

Steve, To check the idle pickup timing, simply remove prop and spark plugs as described. Now advance throttle handle in boat (likely motor needs to be in gear), until carbs are ready to open but still closed. Now you can jumper starter with ign on and read timing.

I expect your timing will be off. The adjustment for both idle pickup timing and max spark advance are on the throttle arm on the port side of the motor. Both are set screws, but throttle arms have changed over the years, so I am not sure what screw does what. I would hope your Seloc manual will tell you which screw is which.

 

[MyName]

Steve, To check the idle pickup timing, simply remove prop and spark plugs as described. Now advance throttle handle in boat (likely motor needs to be in gear), until carbs are ready to open but still closed. Now you can jumper starter with ign on and read timing.

I expect your timing will be off. The adjustment for both idle pickup timing and max spark advance are on the throttle arm on the port side of the motor. Both are set screws, but throttle arms have changed over the years, so I am not sure what screw does what. I would hope your Seloc manual will tell you which screw is which.

I appreciate your replies and instructions so much! Thank you so much for your patience & understanding.
Warm regards,
Stephen

 

[MyName]

Steve, To check the idle pickup timing, simply remove prop and spark plugs as described. Now advance throttle handle in boat (likely motor needs to be in gear), until carbs are ready to open but still closed. Now you can jumper starter with ign on and read timing.

I expect your timing will be off. The adjustment for both idle pickup timing and max spark advance are on the throttle arm on the port side of the motor. Both are set screws, but throttle arms have changed over the years, so I am not sure what screw does what. I would hope your Seloc manual will tell you which screw is which.

You're advise and help is so professional; are you at Chris Marine Redding CA? or?

 

[Chris1956]

Nah, I just had a '77 Merc 1500 and a '73 Merc 850, and now have a '93 Merc 135V6. I do all my own work. The 1500 and 850 share carbs with your engine, and the '93 shares ign systems with small differences, with your motor.

 

[MyName]

Nah, I just had a '77 Merc 1500 and a '73 Merc 850, and now have a '93 Merc 135V6. I do all my own work. The 1500 and 850 share carbs with your engine, and the '93 shares ign systems with small differences, with your motor.

Well it's fortunate you're here to help others & me, since I'm one who will
Break What I Fix! and Fix What Ain't Broke!
Warm regards,
Stephen

 

[MyName]

Hello Chris,
Thanks for your input. I've managed to do flywheel 0° TDC & .464 pointer check, ok the link, sync & timing per the manual & on the plastic carb cover label Pickup +2° TDC & 27° BTDC MAX Timing for 1978 M 800, but still no starting without MercControl manual choke lever up & some starting spray into the carbs. Although the carbs seemed extremely clean, floats are like new, and gaskets were perfect although I did use new ones. With the new correct plugs, CDI stator, trigger, coils, sw box (power pack) rectifier, outboard harness, spark check, engine fuel pump kit, hoses, bulb, good fuel, 50:1 oil. The idle revs up & down & can only be temporarily stabilized for a short time by working the choke lever up half way, or more, to keep it running, so unable to engage in gear without the engine dying trying. I've heard & read that its rare for Merc reed valves to go bad, but 40+ years old with typical old Merc burned rubber coated wires on stator, trigger & engine harness could even be burned reeds, I don't know. Even after all this time & Merc madness stress & a few willing to pay some to take this off my hands I guess I'm still wanting to fix this thing, if my nerves can handle it. Can you advise what might do it?
Regards,
Steve

 

[Chris1956]

Your reed valves are pretty rugged. I would be shocked if they are bad.

Engine must spin 300RPM to choke properly (choke is working?) and make good spark. Clean starter cables. Also look for bulges on cables. This can indicate corrosion under insulation.

I would set max spark advance to 21* BTDC. The original spec of 27* was with better fuel.

Those motors often idle poorly. Most of us pull up the cold start lever, start and warm her up, push the cold start lever down, and put her in gear in one smooth motion and give it some throttle to keep it running. However, you can make it run the best by careful adjustment of the carb idle mixture, on the water, in gear. Use fresh mixed fuel at 50::1 for best results.

Set carbs to 1-1/2 turns open from lightly seated. Start and warm the motor in the water. It should idle pretty well. Put her in gear and idle along. Now give her some throttle and she should hesitate or die completely. If so, open the top carb idle mixture screw 1/8 turn and try to accelerate again. If still bog or die, open lower carb mixture screw 1/8 turn and retry acceleration. Repeat top carb then bottom carb until you get smooth acceleration and reasonable idle.

Generally engine idles best with too lean a mixture to accelerate, so carb settings are a compromise.

If she won't idle with carb mixtures set at 1-1/2 turns open, you have other issues.

 

[racerone]

Maybe I missed it.----What are the compression numbers.----If idle won't come down you need to adjust trunnion on cable.----Or the cable is broken.

 

[MyName]

Your reed valves are pretty rugged. I would be shocked if they are bad.

Engine must spin 300RPM to choke properly (choke is working?) and make good spark. Clean starter cables. Also look for bulges on cables. This can indicate corrosion under insulation.

I would set max spark advance to 21* BTDC. The original spec of 27* was with better fuel.

Those motors often idle poorly. Most of us pull up the cold start lever, start and warm her up, push the cold start lever down, and put her in gear in one smooth motion and give it some throttle to keep it running. However, you can make it run the best by careful adjustment of the carb idle mixture, on the water, in gear. Use fresh mixed fuel at 50::1 for best results.

Set carbs to 1-1/2 turns open from lightly seated. Start and warm the motor in the water. It should idle pretty well. Put her in gear and idle along. Now give her some throttle and she should hesitate or die completely. If so, open the top carb idle mixture screw 1/8 turn and try to accelerate again. If still bog or die, open lower carb mixture screw 1/8 turn and retry acceleration. Repeat top carb then bottom carb until you get smooth acceleration and reasonable idle.

Generally engine idles best with too lean a mixture to accelerate, so carb settings are a compromise.

If she won't idle with carb mixtures set at 1-1/2 turns open, you have other issues.

Thanks Chris, Great Info & Thanks to your help & experience! It worked.
I'm ready to get it out on the lake to do the carb adjust etc. BTW it would not be ready if I had not discovered the "Hidden Mystery" of the New #1 Coil of 4 New Coils. After noticing the timing light Flashing Irradically, or not at all, while attempting to set Primary + - 2° or Max 27°,or a little less, I put #1 Coil to #2 & #2 to #1 then got timing light flash. So, I put back the original Merc coils & she runs like never before & I can put down the choke lever after warm up. Now the mystery gets wierder, if that's a word. Why not simply switch the coil wires to check before switching coils out? I did & No Change! So, new plugs, No change! Ohm tested Coil, Passed! DVA Passed! Called & visited 3 marine mechanics, again/still & one I know personally, after a year of this Agony of Defeat. Here's the general reply & advise I got in a nut shell. We don't use ANY (China Made) CDI electronic ignition parts for that same reason. Many, or most, are junk right out if the box. Steve, why do you think they're half the cost of US made? Save & Suffer or Pay With Pride.
Regards,
Steve

 

[racerone]

Some say------" The bitterness of poor quality is remembered long after the sweetness of low price is forgotten "

 

[MyName]

Assuming the carbs are clean, it sounds like you need to do a link and synch.

Remove all spark plugs and the prop and stick a ruler into the top spark plug hole and read the distance to the top of the piston at it's minimum (TDC). A dial indicator is best, a caliper is second best and a steel ruler is third best for this. Now add .464 inches to that measurement stick the ruler into the spark plug hole and turn the flywheel until the piston is exactly that distance from the cylinder head. The timing pointer should read .464 before top dead center. If not adjust it.

Install the top spark plug and put the wire on it. Now install all the other spark plugs into their wires and ground their bases to the engine block. Set the throttle to the spot when the carbs are ready to open, but are still closed. With ign on, jumper the starter and read the timing at that throttle opening with a timing light. It should be 0-8*ATDC. Your Seloc manual should tell you how to adjust it, using the set screws on the throttle arm. You want the idle pickup timing to be in that range just as the carbs open.

Now advance the throttle all the way and read the timing. It should be 21* BTDC. Set the max spark advance screw to that reading. Set the throttle stop screw to allow the carbs to fully open.

Install spark plugs and their wires, Set the idle mixture screws on the carbs to 1-1/2 turns open.

The motor should start and run at fast idle. The rest of the carb idle mixture adjustment must be done on the water, in gear.

Hi Chris, It's been 3 years since you helped me to link sync & set timing on my 1978 800el Thunderbolt and other advice. It was a super stress but I got it done ok I guess. Now I want to recheck/adjust timing with an advance timing light I got and at cranking speed only. I've replaced many parts like harnesses etc. However, I'm really confused with the 4 adjustment screws. 2 on the Spark Arm & 2 on the Throttle Arm. The Seloc manual is some help, UTube videos some & your post is best. However when it comes to these 4 adjusters Can you please clearly describe exactly which ones & their position on which arm to turn in/out for each step? Idle timing & Max timing. None of what I read ever does say. I'm attaching a photo from Seloc, one of a Flywheel like mine, one of the Arm set like mine I marked up from an Ebay parts site long ago and attempted to label last time but not sure if it's correct or messed up. Possibly you would include a way I could contact you directly.

 

[MyName]

Assuming the carbs are clean, it sounds like you need to do a link and synch.

Remove all spark plugs and the prop and stick a ruler into the top spark plug hole and read the distance to the top of the piston at it's minimum (TDC). A dial indicator is best, a caliper is second best and a steel ruler is third best for this. Now add .464 inches to that measurement stick the ruler into the spark plug hole and turn the flywheel until the piston is exactly that distance from the cylinder head. The timing pointer should read .464 before top dead center. If not adjust it.

Install the top spark plug and put the wire on it. Now install all the other spark plugs into their wires and ground their bases to the engine block. Set the throttle to the spot when the carbs are ready to open, but are still closed. With ign on, jumper the starter and read the timing at that throttle opening with a timing light. It should be 0-8*ATDC. Your Seloc manual should tell you how to adjust it, using the set screws on the throttle arm. You want the idle pickup timing to be in that range just as the carbs open.

Now advance the throttle all the way and read the timing. It should be 21* BTDC. Set the max spark advance screw to that reading. Set the throttle stop screw to allow the carbs to fully open.

Install spark plugs and their wires, Set the idle mixture screws on the carbs to 1-1/2 turns open.

The motor should start and run at fast idle. The rest of the carb idle mixture adjustment must be done on the water, in gear.

It's been 3 years Chris. Can you Help me again with exactly which of the 4 screws, 2 on the Spark Arm & 2 on the Throttle arm & their position on which arm location are adjusted with the steps to use my advance timing light to check/adjust timing at cranking speed only, for idle & Max timing. I cannot find that on any Utube videos or forum descriptions of Which, Where, What Arm adjust screw position, but only to (Adjust IT!) BTWI I replaced several components & both harnesses etc? Please see some pics I hope come through. One is the Spark & Throttle Arm from Ebay I attempted to mark up to identify them 3 years ago. It may not be correct! If Possible, is there a contact # etc for you I might have?

 

[cyclops222]

Linc and sink. The best source of steady retirement income.
I REFUSE to ever touch mine.
" If it is not broke ? Do not fix it. " Quote by 2 best mechanics.

 

[Chris1956]

I am not real sure what you are asking. Throttle arms are a bit different over different year motors. Here are likely identifications. They appear to match your picture.

The bottom set screw on the throttle arm is idle stop. You set that to get the right idle RPM, usually 850 or so. It is set last. Then throttle cable is installed with some preload to push throttle closed.

The set screw just above the pivot is the idle pickup timing screw. You set the throttle so the carbs are closed, but just about to open. Remove plugs and prop, and crank engine and adjust the screw to get the right timing. The setting is 0-9* ATDC.

Above the idle pickup timing screw is max spark advance. Set throttle to full, crank engine and set the screw to 21*BTDC.

Above that is throttle stop. Set throttle for fully open carbs. Adjust screw to stop throttle at that point, so carbs ar not pushed beyond open and damaged.

Did I get it?

 

[MyName]

I am not real sure what you are asking. Throttle arms are a bit different over different year motors. Here are likely identifications. They appear to match your picture.

The bottom set screw on the throttle arm is idle stop. You set that to get the right idle RPM, usually 850 or so. It is set last. Then throttle cable is installed with some preload to push throttle closed.

The set screw just above the pivot is the idle pickup timing screw. You set the throttle so the carbs are closed, but just about to open. Remove plugs and prop, and crank engine and adjust the screw to get the right timing. The setting is 0-9* ATDC.

Above the idle pickup timing screw is max spark advance. Set throttle to full, crank engine and set the screw to 21*BTDC.

Above that is throttle stop. Set throttle for fully open carbs. Adjust screw to stop throttle at that point, so carbs ar not pushed beyond open and damaged.

Did I get it?

Yup Yup. I do believe you got this, to the rescue once again. Ever vigilant, always in time to save the day. Look, up in the sky, is it a bird? is it a plane? No, it's Super Mariner!