1976 1150 mercury thunderbolt ignition

[glowbox]

greetings,

i just acquired a boat with a 1976 1150 (115hp) 'thunderbolt ignition' mercury outboard on it and it runs. when put into forward it goes in kind of hard like a rough car tranny and when the throttle is pushed all the way forward the motor does not rev up with it unless the throttle is 'jerked' slightly forward and back and still doesnt reach what i would think is 'wide open'. mind you, i havent had it in the water yet and only use a garden hose setup on the lower unit so i dont really want it to open up. yet. im guessing one of the cables is loose or whatever, but my question is this: where is a good place for me to start out. this is my fist boat and first outboard motor and need to give it a good up and down so i wont have to swim back or rely on my troller the first time(s) out. im hoping this forum is a good start..i'll keep browsing.

thanks

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

just a morning bump.

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Glow, Don't go about 1500 RPM on the hose. it can cause bad stuff to happen.

Run a compression test on all six cylinders. You should have 100+PSI on all six and they should be close in compression. If not, you have some real isssues. Next run it at idle on the hose and put a timing light on each plug wire and make sure they are all sparking. if so, find the "Timing and Synch" post by Clams Canino on this forum and check idel pickup timing and WOT timing. Both of these are done with the engine off. After these steps, if you still have a problem, it is likely dirty carbs. Write us back...

Watch for arcing on the plug wires, especially the lower two.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

thanks for the 'heads up for beginners' reply. ill do as much of what you mentioned as i can and get back to you. preesh.

on a side note i read that this boat (16' 1975 terry) was rated for about a 50hp. i hope this 115hp doesnt cause problems as far as the integrity of the boat itself goes or makes the boat chine walk, which i know almost nothing about except for what i have read.

glowbox

 

[commodore]

Re: 1976 1150 mercury thunderbolt ignition

You should not run the motor full trottle unless you are on a dyno. Not good for the crank. I would check the module by making sure you have spark on all cylenders. I had same issue on my 1976 70HP Merc. I had good spark on number 1, a week spark on 2 and no spark on 3. Make sure to ground your spark plugs lead properly when testing... it's not good for the module and you might get a shock from the leads

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Glow, I think you need to get a smaller motor. If you put that 115HP on a boat rated for 50HP max, the boat will be unstable at speed, fall apart or both, depending on the hull type and condition. You can overpower a bit w/o issue, however you are at about 230% of the power allowed on that boat.

Commodore, That motor has a single coil and a distributor, so spark will be to all plugs or none. provided the plug wires and cap are decent. Your motor had the ADI ignition with three coils

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

ok, so i have had it out a few times. i havent checked to make sure all plugs are firing or that the carbs are clean yet. i just wanted to get it out and run it to see how it did and it did ok. the speedometer said i was going 40mph with the throttle buried and it seemed like 40 to me. seems a 115hp on that boat should go faster though. at low speeds it kind of chugs and putters but when it is above 30mph it sounds much better. i know the 2 strokes like the gas and high rpms. i was hoping that i was sitting for a while and a tank of gas at full throttle would 'clean' it out. doesnt seem to be the case. ill check the spark and timing and carbs and post back.

the hull is in pretty good shape. tri-hull design with very few minor chips and solid. doesnt take on water. rides very smooth at 40mph. im guessing that if the motor was running to its full potential it would go at least 55 and THAT might cause some instability.

 

[jimg984]

Re: 1976 1150 mercury thunderbolt ignition

if it is a 16 ft fiberglass trihull and is in good condition it should be good for a 1976 115 hp before 1982 the hp was rated at the crank which means a 115 would only be 90 hp at the prop after 1982 prop rating would 115 hp

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Glow, It is impossible to predict the speed of a boat exactly. I think 40MPH on that setup is quite low. of course, knowing if the 40mph is accurate, and what the RPM is would help a lot.

You might find that the motor is only running on 5 cylinders. They can run pretty good on 5.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

just an update:

all 6 cylinders are running. i recently cleaned the carbs and while putting them back on found the stator wires to be fried to dust. tomorrow i am going to take it off and look into soldering new wires onto the leads if there is enough to work with.

i read a post here about a guy taking the drip tray and the rubber flap under it out and leaving it out and he said the engine ran better just from that. he way saying it was an 'air intake' (?) i am wondering if it IS an air intake and if it is why the rubber flap? seems like that is to keep water out of the bottom carb. if it is an air intake is taking the tray and rubber flap out a common thing and does it allow water to enter the housing and then the bottom carb?

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Air enters the cowling from several places. One is the rear top cowl handle. I doubt the drip tray will affect performance, or allow water into the lower carb.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

again, thanks for clearing that up.

EDIT:
a question about the stator issue i have been using the other thread for... after soldering 2 new wires to it do i need to know which went where or does it matter? they both go straight down to a bracket which 2 different wires also connect to. so its like they would be the same wire but instead of connecting to each other via splicing they connect via this bracket jobber.

thanks a ton

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

just to reduce clutter on the forum i will keep my individual postings here..

i successfully soldered new stator wires and got my tach working. now im moving onto the link & sync. problem is im not sure what the 'tang' or 'trigger screw' is. i will keep probing until i find out or until someone points me in the right direction.

also, should the muffs be on while performing the link & sync? apparently the motor wont be running but it will be cranking, right?

and, i read a post that chris1956 wrote to a guy using 'friendlier' words to explain the link & sync. here's the quote:

Ok Clam's procedure is quite clear. You are just not "lingo" up yet. Remove the spark plugs except for #1, and install them into their wires. Tape them together so all the bases are touching and tape them to the block so they are all grounded. Remove the prop. Loosen the bolts on the brass economizer collar on the distributor, but leave them snug.

First need to set the idle timing pickup to 4-6 degrees BTDC. Attach timing light to #1 spark plug lead. Turn on the key, motor in forward and jumper the starter solenoid to crank the motor. Have someone advance the throttle until the timing reads 4-6 degrees BTDC. Stop cranking and w/o moving throttle, turn the brass economizer collar on the dissy (about 1/2 way up) until the throttle fork just touches the carb arm on the top carb. Tighten the bolts on the brass collar.

Ok, crank the motor again and advance the throttle until the timing reads 21 degrees BTDC. Stop cranking and turn the max spark advance screw in until it touches the distributor body. Tighten the nut.

OK now advance the throttle until the carbs are wide open. Tighten the max throttle screw to just touch the carb arm. Reinstall the plugs and start and warm the motor. Set the idle speed on the muffs to 1000, using the idle stop screw and throttle cable to change it sufficiently, as is necessary.

now, the one clams wrote says to just disconnect all plugs except #1. chris says to do the same but to also install them into their wires and to tape them together and to ground them to the block. is that step crucial? maybe i am thinking too hard about all of this. i just dont want to assume something and end up causing more work.

could the above quote by chris1956 be used in place of the one by clams or is it to be used in conjunction with it? of course there is the last part of the one by clams about bringing it to the lake. again maybe i am thinking to hard about all of this.

thanks for the long read.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

morning bump.

 

[chum1]

Re: 1976 1150 mercury thunderbolt ignition

Hey glowbox, yes you are thinking to hard, shove the sparkplugs in the boots and ground them with a wire or something, I read somewhere the coils could go bad if you dont do this.

 

[ClassyGlassy]

Re: 1976 1150 mercury thunderbolt ignition

it doesn't matter which stator wire goes to which side as the other two they connect to go to the rectifier. On mine, the two wires going to the rectifier are BOTH yellow with a red stripe after replacing the engine harness with a new CDI harness. The OEM wires were both solid yellow.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

it doesn't matter which stator wire goes to which side as the other two they connect to go to the rectifier. On mine, the two wires going to the rectifier are BOTH yellow with a red stripe after replacing the engine harness with a new CDI harness. The OEM wires were both solid yellow.

thanks classyglassy but i finished up with that already. new rectifier and old tach works good now.

Hey glowbox, yes you are thinking to hard, shove the sparkplugs in the boots and ground them with a wire or something, I read somewhere the coils could go bad if you dont do this.

guess i'd better ground them then. thanks for the input.

and can somebody fill me in on what/where the tang/trigger screw is?

thanks a bunch.

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Glow, I have no idea what a trigger screw or tang is.

 

[glowbox]

Re: 1976 1150 mercury thunderbolt ignition

chris, its in the timing event one narrative:

Timing Event One - throttle pickup.
As the throttle is advanced, the spark timing advances toward TDC and then to before TDC. As the timing is just passing TDC the 1st (minor)throttle pickup should hit and start to open the carbs. Use the timing light. Adjust the tang or trigger screw to make this a reality. All of them are speced different, but if the 1st pickup hits at 3-4 degrees BTDC advance - you win. Use the timing light with a friend cranking it to complete this setting.

i think i read where someone else was asking this same question but i cant find the post for the life of me.

 

[Chris1956]

Re: 1976 1150 mercury thunderbolt ignition

Glow, You adjust the primary throttle pickup on your motor, using the brass collar on the distributor body. Two 5/16" stainless screws need to be loosened, and the collar rotated to just touch the carb throttle yoke, as the timing hits 4-6* BTDC.

Does that work for you?