Muddyjeep810
Seaman Apprentice
- Joined
- Jun 10, 2021
- Messages
- 38
I have made a few different threads about various stages of my struggle with my boat motor. I made this post to compile all of the information together and hopefully get this figured out (like the on-my-knees-begging kind of hopefully).
Ok, this post is going to be a long one so buckle up. If you make it all the way through I will be EXTREMELY thankful!
Alright, so 5 weeks ago I bought an old 1978 McFast 15 Bass Boat with a 1977 Johnson 70 horse engine on it. He said the motor ran great and was asking $1000. He said all it needs is a new control box and it’s good to go. He told me the water pump had went out, he had the water pump replaced, and then he could never get it started after due to the control box. The boat itself isn’t in the best of shape but with a 70 horse that runs great how could I lose right?
I’m sure most of you have already guessed it…. The motor does not run great. When I bought the boat, I couldn’t start it due to the control box being half disconnected. I was kind of going into this blind, but I am extremely mechanically inclined and usually if it runs I can fix it. My youngest son recently developed a fishing obsession and I also love fishing so I figured this would be great for us.
Fixing that control box was my first step. I drove 6 hours round trip and bought a used control box for it from a salvage yard. When I got home I realized that the previous owner had rigged two different types of control cables in the old box so I went ahead and bought new control cables. I got that all hooked up, hooked the engine up to water using muffs, and turned the key. It fired right up. I was ecstatic! It ran kind of rough though. I figured carbs but I wanted to test it in the water.
I put it in the water and it didn’t want to start at all. I finally got it started and it did not idle at all. Just bogged out as soon as I put it into gear. We spent the afternoon fishing with the bow mount trolling motor and still had a great day regardless.
Back on the trailer she went. When I got home I pulled the plugs and they were full of water. That’s when my research on this engine started. I found out that these engines are notorious for a blown exhaust manifold gasket which allows water into the engine.
My next step was to check the compression. Cylinder #1 was 115, Cylinder #2 was 105, and cylinder #3 was 112. Not the greatest but compression surely wasn’t my biggest issue. I strongly suspected the blown exhaust manifold gasket. I figured what the hell and pulled the head to take a peek inside. Sure enough, when I pulled the heads and there was a ton of water in the engine. Especially cylinder #2. The cylinders looked good though. No scoring at all. The pistons looked good from the side ports on the exhaust side. I don't think it was ran for very long with the water issue.
I replaced all of the gaskets on the head side and all of the gaskets on the exhaust manifold side. I also rebuilt the carbs. I also put in new plugs, an inline fuel filter between the fuel pump and the carbs, and new fuel lines from fuel pump to carbs. I also changed the lower unit oil and it had a ton of water in it. I pulled the lower unit and removed the impeller to take a peek at things and verify that it was indeed a new water pump. It looked new but I saw gear oil running out of the drive shaft seals under the water pump. I changed those and for good measure changed the O-ring and gasket on the shift rod. I did a vacuum test and it held 15 PSI (or whatever the vacuum terminology is) for 15 minutes or so, and I called it fixed. I also did another compression test and the cylinders improved to 121, 119, 120 respectively. Now we are getting somewhere, right?
Started it on the muffs and it ran great! Idled good and revved strong. When I got it in the water, it was a totally different story AGAIN. It basically still would not idle. The only way to keep it running was to have the cold start throttle lever all the way up. It would then SLOWLY build RPMs from 1000 RPM up to 2000 RPM where it would almost stop climbing. Any movement of the controls at this point required I turn the cold start all the way down and it would stall before I could get it into gear. So, then I left it running at max cold start throttle for five minutes, and after about 5 minutes the engine sounded like it was coming alive and would climb slowly to 3000 RPM. Once it made it up to 3000 RPM, I could slam the cold start throttle off, and slam the boat into forward and it would take off like a raped ape and almost immediately plane and run awesome wide open around the lake until I let off the throttle and let it get below 2000 RPM's again. It would then get sluggish again and I would have to feather the throttle to get it above 3000 RPM where it would run great again.
My next step was to check the ignition. I had spark on all three cylinders, but it was not the strongest. So I checked the coils with my multimeter. Primary circuit first. They all tested at 0.4 ohms which from what I read should be 0.2-1.0 making the primary circuit good. Next, I tested the secondary or output circuit of the coil and that's where I am getting some funky results. According to the specs I found these circuits should test between 200 and 400 ohms. So, I sent my multimeter on the 2000 ohm range. I tested cyl #3 first and it tested at 1289 which is out of spec. I tested cyl #2 next and got no reading at all. When I test cyl #1 it's really weird because the multimeter reads a random/changing resistance and then instantly switches to no reading. I have seen as low as 600 and as high as 1800.
This was two days before we left for a week up north for the 4th. I took the boat up north but the day before I left I bought three new coils and swapped them out. The old coils tested way out of spec or did not test at all. I also was spraying carb cleaner around my intake manifold gasket with the engine idling “smoothly” and the motor stalled right out when I hit one spot.
So I replaced both gaskets between the crankcase and the carbs. When I tore it down, those gaskets were like jelly in some places. I know for a fact it must have been leaking air. I thought for sure that was my major problem. With the new coils the spark is strong enough to jump a 7/16" gap on all three cylinders. The reed valves seemed to be all in good condition.
I put the boat in the water our first day up there. It started kind of rough but when it did start running it ran a lot better at lower rpm and did not immediately stall out when I put it into gear. I could actually use reverse.
The main problem of this discussion still persisted though. It has no power lower in the RPM curve. It stalls out when I shift gears unless I rev it with the cold start lever to get the RPMs up, shift fast, and then give it a lot of throttle. The same goes for forward and reverse gears. It will drive in idle for a few seconds but then stalls.
At that point I took Racerone’s advice and purchased a timing light. The timing is almost dead on using the Reeves method. I think it’s one degree advanced so I didn’t touch it.
We used the boat all week up north. It runs a lot better now, but it still starts hard with a lot of cranking and if you drive at medium or low rpm for 5 seconds or longer it’s almost like it loads up or maybe fouls out. It starts bogging and I have to put it back into neutral and use the cold start lever until it will hit 3000 RPM at which point I can slam the cold start lever down and gas it quickly in gear and it will run, and run amazing at WOT. One of the times when it started bogging I hit the choke to see if it was a fuel issue. It immediately died so my guy tells me it isn’t fuel related. When I am coming into a dock, to maintain motor control I have to keep goosing the throttle from neutral/idle throttle position to heavy throttle position to keep it running and keep it from ‘loading up’. The boat seriously runs fantastic at wide open throttle. It doesn’t load up like it does at medium to low throttle. I could do laps around the lake all day long at 5600 RPM without an issue.
After I got home, I figured I’d take a peek under the flywheel and see if I could visually spot any issues. Everything looks ok except for the timer base retainer is melted on one side. The timer base still rotates freely though you can hear a sound that almost sounds like light scratching when it’s rotating. It does not feel like there is any major resistance though.
How much of an issue is this timer base retainer being melted like this? Would this possibly lead to the problems I am having? I find it doubtful. Are there any other parts I should be looking at that a severe overheat could have damaged that would cause my issues? I know that it was a severe overheat because the plastic poppets in the head were totally melted and even circulated through the head.
I’m very frustrated here. I’ve fixed so many damn parts on this engine that supposedly “ran great”.
Anybody have any insight on this? PLEASE HELP ME!!!! I AM BEGGING!!!! LOL
Ok, this post is going to be a long one so buckle up. If you make it all the way through I will be EXTREMELY thankful!
Alright, so 5 weeks ago I bought an old 1978 McFast 15 Bass Boat with a 1977 Johnson 70 horse engine on it. He said the motor ran great and was asking $1000. He said all it needs is a new control box and it’s good to go. He told me the water pump had went out, he had the water pump replaced, and then he could never get it started after due to the control box. The boat itself isn’t in the best of shape but with a 70 horse that runs great how could I lose right?
I’m sure most of you have already guessed it…. The motor does not run great. When I bought the boat, I couldn’t start it due to the control box being half disconnected. I was kind of going into this blind, but I am extremely mechanically inclined and usually if it runs I can fix it. My youngest son recently developed a fishing obsession and I also love fishing so I figured this would be great for us.
Fixing that control box was my first step. I drove 6 hours round trip and bought a used control box for it from a salvage yard. When I got home I realized that the previous owner had rigged two different types of control cables in the old box so I went ahead and bought new control cables. I got that all hooked up, hooked the engine up to water using muffs, and turned the key. It fired right up. I was ecstatic! It ran kind of rough though. I figured carbs but I wanted to test it in the water.
I put it in the water and it didn’t want to start at all. I finally got it started and it did not idle at all. Just bogged out as soon as I put it into gear. We spent the afternoon fishing with the bow mount trolling motor and still had a great day regardless.
Back on the trailer she went. When I got home I pulled the plugs and they were full of water. That’s when my research on this engine started. I found out that these engines are notorious for a blown exhaust manifold gasket which allows water into the engine.
My next step was to check the compression. Cylinder #1 was 115, Cylinder #2 was 105, and cylinder #3 was 112. Not the greatest but compression surely wasn’t my biggest issue. I strongly suspected the blown exhaust manifold gasket. I figured what the hell and pulled the head to take a peek inside. Sure enough, when I pulled the heads and there was a ton of water in the engine. Especially cylinder #2. The cylinders looked good though. No scoring at all. The pistons looked good from the side ports on the exhaust side. I don't think it was ran for very long with the water issue.
I replaced all of the gaskets on the head side and all of the gaskets on the exhaust manifold side. I also rebuilt the carbs. I also put in new plugs, an inline fuel filter between the fuel pump and the carbs, and new fuel lines from fuel pump to carbs. I also changed the lower unit oil and it had a ton of water in it. I pulled the lower unit and removed the impeller to take a peek at things and verify that it was indeed a new water pump. It looked new but I saw gear oil running out of the drive shaft seals under the water pump. I changed those and for good measure changed the O-ring and gasket on the shift rod. I did a vacuum test and it held 15 PSI (or whatever the vacuum terminology is) for 15 minutes or so, and I called it fixed. I also did another compression test and the cylinders improved to 121, 119, 120 respectively. Now we are getting somewhere, right?
Started it on the muffs and it ran great! Idled good and revved strong. When I got it in the water, it was a totally different story AGAIN. It basically still would not idle. The only way to keep it running was to have the cold start throttle lever all the way up. It would then SLOWLY build RPMs from 1000 RPM up to 2000 RPM where it would almost stop climbing. Any movement of the controls at this point required I turn the cold start all the way down and it would stall before I could get it into gear. So, then I left it running at max cold start throttle for five minutes, and after about 5 minutes the engine sounded like it was coming alive and would climb slowly to 3000 RPM. Once it made it up to 3000 RPM, I could slam the cold start throttle off, and slam the boat into forward and it would take off like a raped ape and almost immediately plane and run awesome wide open around the lake until I let off the throttle and let it get below 2000 RPM's again. It would then get sluggish again and I would have to feather the throttle to get it above 3000 RPM where it would run great again.
My next step was to check the ignition. I had spark on all three cylinders, but it was not the strongest. So I checked the coils with my multimeter. Primary circuit first. They all tested at 0.4 ohms which from what I read should be 0.2-1.0 making the primary circuit good. Next, I tested the secondary or output circuit of the coil and that's where I am getting some funky results. According to the specs I found these circuits should test between 200 and 400 ohms. So, I sent my multimeter on the 2000 ohm range. I tested cyl #3 first and it tested at 1289 which is out of spec. I tested cyl #2 next and got no reading at all. When I test cyl #1 it's really weird because the multimeter reads a random/changing resistance and then instantly switches to no reading. I have seen as low as 600 and as high as 1800.
This was two days before we left for a week up north for the 4th. I took the boat up north but the day before I left I bought three new coils and swapped them out. The old coils tested way out of spec or did not test at all. I also was spraying carb cleaner around my intake manifold gasket with the engine idling “smoothly” and the motor stalled right out when I hit one spot.
So I replaced both gaskets between the crankcase and the carbs. When I tore it down, those gaskets were like jelly in some places. I know for a fact it must have been leaking air. I thought for sure that was my major problem. With the new coils the spark is strong enough to jump a 7/16" gap on all three cylinders. The reed valves seemed to be all in good condition.
I put the boat in the water our first day up there. It started kind of rough but when it did start running it ran a lot better at lower rpm and did not immediately stall out when I put it into gear. I could actually use reverse.
The main problem of this discussion still persisted though. It has no power lower in the RPM curve. It stalls out when I shift gears unless I rev it with the cold start lever to get the RPMs up, shift fast, and then give it a lot of throttle. The same goes for forward and reverse gears. It will drive in idle for a few seconds but then stalls.
At that point I took Racerone’s advice and purchased a timing light. The timing is almost dead on using the Reeves method. I think it’s one degree advanced so I didn’t touch it.
We used the boat all week up north. It runs a lot better now, but it still starts hard with a lot of cranking and if you drive at medium or low rpm for 5 seconds or longer it’s almost like it loads up or maybe fouls out. It starts bogging and I have to put it back into neutral and use the cold start lever until it will hit 3000 RPM at which point I can slam the cold start lever down and gas it quickly in gear and it will run, and run amazing at WOT. One of the times when it started bogging I hit the choke to see if it was a fuel issue. It immediately died so my guy tells me it isn’t fuel related. When I am coming into a dock, to maintain motor control I have to keep goosing the throttle from neutral/idle throttle position to heavy throttle position to keep it running and keep it from ‘loading up’. The boat seriously runs fantastic at wide open throttle. It doesn’t load up like it does at medium to low throttle. I could do laps around the lake all day long at 5600 RPM without an issue.
After I got home, I figured I’d take a peek under the flywheel and see if I could visually spot any issues. Everything looks ok except for the timer base retainer is melted on one side. The timer base still rotates freely though you can hear a sound that almost sounds like light scratching when it’s rotating. It does not feel like there is any major resistance though.
How much of an issue is this timer base retainer being melted like this? Would this possibly lead to the problems I am having? I find it doubtful. Are there any other parts I should be looking at that a severe overheat could have damaged that would cause my issues? I know that it was a severe overheat because the plastic poppets in the head were totally melted and even circulated through the head.
I’m very frustrated here. I’ve fixed so many damn parts on this engine that supposedly “ran great”.
Anybody have any insight on this? PLEASE HELP ME!!!! I AM BEGGING!!!! LOL
