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
Last edited by glowbox : September 2nd, 2008 at 08:13 AM.
Reason: title change
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.
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.
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
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
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.
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
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.
1976 1150 mercury thunderbolt ignition
Re: 1976 1150 mercury thunderbolt ignition
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