Garage find 1974 JOHNSON 40hp won't start.

[gm280]

Thanks for the tips! I'll look into that stuff and see if I can make a spreadsheet of costs etc. I wasn't sure if I'd need new ignition set up or not under the flywheel. Probably an alternator and rectifier etc too.

Quick question since our motors are almost the same set up, does yours have bolt holes on the clamp bracket to bolt the motor to the transom? Or are these motors supposed to only be attached to the boat by the two clamps?

My '76 40HP Johnson used the screw clamps at the top area but also has two lower holes for bolts as well. Look at the clamping bracket to see if your's does as well. Probably so if I am thinking correctly.

As for the ignition system, there are probably the exact same. So I don't see any need to change that. The alternator is located under the flywheel and outputs via three yellow wires. Those three wires goes to a rectifier and then to the battery. There is no regulator on mine. And the rectifiers are available everywhere. Nothing unique. They used that same configuration for a lot of their engines.

If you don't already have a manufacturer's engine specific HP, year, model shop manual, you need to buy one. It explains everything about your series engine and probably explains the hand start version as well as electric start version. I know they cover both in my manual. That way you can see the differences and parts needed as well. And there are lots of break downs or parts and wiring and schematic diagrams and whatever you ever wanted to know about the engine.

As for the low speed plastic screw, yes that is located by the throttle handle slightly under neath. If your is bad, they still are available as well. It should be plastic (nylon) with a metal button at the very end.

If you want a tach wired up, you will need to have an alternator and the rectifier. Because the tach output comes off one of the pre-rectifier connections from the alternator. And that wire is usually gray and attaches to the rectifier where the yellow wires attach from the alternator but only attaches to one of those yellow wires.

Hope that helps a little. :noidea:

 

[hardwater fisherman]

No Title

I think that motor had a tiller when it was new. Because the gear for the end of the tiller is exposed and if there was no tiller then there would be a box around the gear. And a little toggle type thing for raising and lowering the throttle by hand at the motor. Also every motor with rope start and manual choke that i saw had a tiller. If it was for remote controls I think it would at least have an electric choke. I converted mine to electric start by finding a donor motor. The starter bracket ,starter and solenoid will be easy to find new or used. But the flywheel with the ring gear is expensive. The photo is of the manual throttle control.

 

[gm280]

I think that motor had a tiller when it was new. Because the gear for the end of the tiller is exposed and if there was no tiller then there would be a box around the gear. And a little toggle type thing for raising and lowering the throttle by hand at the motor. Also every motor with rope start and manual choke that i saw had a tiller. If it was for remote controls I think it would at least have an electric choke. I converted mine to electric start by finding a donor motor. The starter bracket ,starter and solenoid will be easy to find new or used. But the flywheel with the ring gear is expensive. The photo is of the manual throttle control.

Yep, that is the throttle knob, for lack of a better word. Mine is electric start with remote controls, but it still has all the controls at the motor for manual use as well.

 

[hardwater fisherman]

Also to do the electric start conversion right you will need a neutral safety switch and the lever and linkage that goes along with it. So it can really add up when you price out everything you need to do it right. It might be as much as what you paid for the motor if you price everything out. Like I said I found a donor motor to do mine. And the solenoid and the neutral safety switch were bad. So the conversion cost almost half of what I paid for the motor. But I am glad that I dont have to pull the rope anymore. Also I now I can charge my battery while the motor is running.

 

[Gjkelley31]

My '76 40HP Johnson used the screw clamps at the top area but also has two lower holes for bolts as well. Look at the clamping bracket to see if your's does as well. Probably so if I am thinking correctly.

As for the ignition system, there are probably the exact same. So I don't see any need to change that. The alternator is located under the flywheel and outputs via three yellow wires. Those three wires goes to a rectifier and then to the battery. There is no regulator on mine. And the rectifiers are available everywhere. Nothing unique. They used that same configuration for a lot of their engines.

If you don't already have a manufacturer's engine specific HP, year, model shop manual, you need to buy one. It explains everything about your series engine and probably explains the hand start version as well as electric start version. I know they cover both in my manual. That way you can see the differences and parts needed as well. And there are lots of break downs or parts and wiring and schematic diagrams and whatever you ever wanted to know about the engine.

As for the low speed plastic screw, yes that is located by the throttle handle slightly under neath. If your is bad, they still are available as well. It should be plastic (nylon) with a metal button at the very end.

If you want a tach wired up, you will need to have an alternator and the rectifier. Because the tach output comes off one of the pre-rectifier connections from the alternator. And that wire is usually gray and attaches to the rectifier where the yellow wires attach from the alternator but only attaches to one of those yellow wires.

Hope that helps a little. :noidea:

I will definitely look for the manufacturers manual. I have one for my old (but chronologically newer) motor that's 1989 johnsons and on.

My motor doesn't have any wiring harnesses except for the kill switch wires that run under the flywheel and the pressure ignition stop switch part (square part with tube leading into cylinder attached to switch up near flywheel) so I guess I might need some extra parts for conversion.

Looks like there are only the clamps. No casted in bolt holes on the bracket like other motors have. Here are a couple of pics.

https://i.imgur.com/V35nMAL.jpg

When titled though, there are what look like threaded holes "inside" the bracket that are only accessible when the motor is tilted up. Here is a pic: https://i.imgur.com/hLwihof.jpg

I don't know what those are for but seems kind of stupid to be th ransom mount holes since they are so inaccessible. Do you think using just the clamps is a secure method for keeping the engine on the boat when running hard? I'll keep it cabled to the boat. Want to get this thing out on the water!

Thanks for all your help.

 

[Gjkelley31]

I think that motor had a tiller when it was new. Because the gear for the end of the tiller is exposed and if there was no tiller then there would be a box around the gear. And a little toggle type thing for raising and lowering the throttle by hand at the motor. Also every motor with rope start and manual choke that i saw had a tiller. If it was for remote controls I think it would at least have an electric choke. I converted mine to electric start by finding a donor motor. The starter bracket ,starter and solenoid will be easy to find new or used. But the flywheel with the ring gear is expensive. The photo is of the manual throttle control.

There's definitely a spot for a tiller, but one was never used because the paint on the doesn't have even the smallest scratch or mark where that tiller would bolt on and be able to swivel up and down. All the connections to attach control cables are there so it can be used remotely no problem just have to pull to start rather than push a key at the console.

There is no hand toggle for the throttle so only way is with a control cable in its current config. A tiller didn't come with it so idk.

 

[hardwater fisherman]

No Title

This is what I used to mount my motor. I put it around the stern bracket and used large washers inside. Also I drilled a hole through the plate that is up against the transom by the tilt pin. I did this because it would always work itself lose. And also it helps stop thieves.

 

[Gjkelley31]

This is what I used to mount my motor. I put it around the stern bracket and used large washers inside. Also I drilled a hole through the plate that is up against the transom by the tilt pin. I did this because it would always work itself lose. And also it helps stop thieves.

That's a good idea. U bolts are great. I'm not visualizing where exactly you have it though. Any pics of the motor itself and the hoes you drilled? Thanks!

 

[gm280]

I will definitely look for the manufacturers manual. I have one for my old (but chronologically newer) motor that's 1989 johnsons and on.

My motor doesn't have any wiring harnesses except for the kill switch wires that run under the flywheel and the pressure ignition stop switch part (square part with tube leading into cylinder attached to switch up near flywheel) so I guess I might need some extra parts for conversion.

Looks like there are only the clamps. No casted in bolt holes on the bracket like other motors have. Here are a couple of pics.

https://i.imgur.com/V35nMAL.jpg

When titled though, there are what look like threaded holes "inside" the bracket that are only accessible when the motor is tilted up. Here is a pic: https://i.imgur.com/hLwihof.jpg

I don't know what those are for but seems kind of stupid to be th ransom mount holes since they are so inaccessible. Do you think using just the clamps is a secure method for keeping the engine on the boat when running hard? I'll keep it cabled to the boat. Want to get this thing out on the water!

Thanks for all your help.

Gjkelley31, if those hole you posted with the engine tilted up can be used to bolt the engine in place along with the screw clamps, I would most definitely use them as well. My engine bracket has two holes at the very bottom of the bracket that are used to bolt the engine on the transom. And I would not rely solely on just two screw clamps to hold the engine on the transom. I would use at least two other bolts to help hold it in place. That would also help to keep your engine from growing legs and walking off. JMHO

As for converting yours to electric start, you can figure out the parts you will need and buy them along the way while you still use your engine as it is. Then once you do procure all the necessary parts, change it over at that time. It doesn't have to be one huge cost at one time. Just collect the parts over time and change it if that is what you want to do. There is no reason to put your engine out of commission waiting for parts.

I had to change the way I steer my setup remotely, via stick steering, because the engine I have, and probably yours as well, doesn't support the typical steering cable setup through the pivot point. I think Johnson change that setup in 1977. So I had to buy an adapter part to allow a typical steering cable setup. And if fits under the screw clamps on the engine to hold the steering cable. So I have no idea how you plan to set your up for steering.

 

[Gjkelley31]

Gjkelley31, if those hole you posted with the engine tilted up can be used to bolt the engine in place along with the screw clamps, I would most definitely use them as well. My engine bracket has two holes at the very bottom of the bracket that are used to bolt the engine on the transom. And I would not rely solely on just two screw clamps to hold the engine on the transom. I would use at least two other bolts to help hold it in place. That would also help to keep your engine from growing legs and walking off. JMHO

As for converting yours to electric start, you can figure out the parts you will need and buy them along the way while you still use your engine as it is. Then once you do procure all the necessary parts, change it over at that time. It doesn't have to be one huge cost at one time. Just collect the parts over time and change it if that is what you want to do. There is no reason to put your engine out of commission waiting for parts.

I had to change the way I steer my setup remotely, via stick steering, because the engine I have, and probably yours as well, doesn't support the typical steering cable setup through the pivot point. I think Johnson change that setup in 1977. So I had to buy an adapter part to allow a typical steering cable setup. And if fits under the screw clamps on the engine to hold the steering cable. So I have no idea how you plan to set your up for steering.

I made this bracket to hold a steering support tube https://i.imgur.com/7hlDkPU.jpg

And mounted it like this. https://i.imgur.com/QPuSnjf.jpg

It seems to work I just can't tilt the motor up for trailering without disconnected the link to the motor which isn't a huge problem.


I definitely need to tune the idle. Tried the Joe reeves method but I think I just made it worse not better. I tried to line up the throttle link with the two marks on the cam under the flywheel and then set the idle screw but it just doesn't sound right/ as smooth as it should be. When I shift into gear the rpms decrease. It's not super rough but the jump is noticible. Idk how smooth that needs to be.

 

[hardwater fisherman]

No Title

This is on my 4hp motor but it should give you an idea. Also I agree that the two clamps will probably not stay tight.

 

[hardwater fisherman]

Better to set the idle when motor is warm and in gear on the water, and not in the driveway.

 

[Gjkelley31]

This is on my 4hp motor but it should give you an idea. Also I agree that the two clamps will probably not stay tight.

that's perfect thanks. I'll install some u bolts just like that. And ok I'll try and tune the idle while out on the water! Thanks for all your help!

 

[oldboat1]

I have to disagree with some of the suggestions.

The screw clamps will secure your motor with no difficulty if in good condition. They are sized just fine for that purpose. If you rig up u-bolts or something similar, you risk breaking the aluminum bracket at best. I don't know what hull you have, but a larger concern is the integrity of the transom core. If you have an old hull with a rotted transom core, you need to replace it.

You have no high speed carb adjustment, and can set the idle adjustments (that's mix and throttle stop) before you get on the water. Tweak it when you launch if not satisfied with idle operation.

Finally, you don't need to go through the expense and complexity of adding a charging system if you are using the battery only for starting, or starting and a fish finder. Those motors were made and used for years without charging systems, including electric start versions. Alternatively, you can add a simple starter system very easily if you can round up a few parts (starter and bracket to fit, along with a flywheel with ring gear. Buy an outboard solenoid, and use a starter button for simplicity. Fashion your own harness.) A donor motor is always a good idea, whatever you decide -- and particularly if interested in more sophistication.

btw -- assume that remote throttle cable in your clip is just sitting loose behind its proper location (pictures can deceive). It fits over the post.

 

[Gjkelley31]

I have to disagree with some of the suggestions.

The screw clamps will secure your motor with no difficulty if in good condition. They are sized just fine for that purpose. If you rig up u-bolts or something similar, you risk breaking the aluminum bracket at best. I don't know what hull you have, but a larger concern is the integrity of the transom core. If you have an old hull with a rotted transom core, you need to replace it.

You have no high speed carb adjustment, and can set the idle adjustments (that's mix and throttle stop) before you get on the water. Tweak it when you launch if not satisfied with idle operation.

Finally, you don't need to go through the expense and complexity of adding a charging system if you are using the battery only for starting, or starting and a fish finder. Those motors were made and used for years without charging systems, including electric start versions. Alternatively, you can add a simple starter system very easily if you can round up a few parts (starter and bracket to fit, along with a flywheel with ring gear. Buy an outboard solenoid, and use a starter button for simplicity. Fashion your own harness.) A donor motor is always a good idea, whatever you decide -- and particularly if interested in more sophistication.

btw -- assume that remote throttle cable in your clip is just sitting loose behind its proper location (pictures can deceive). It fits over the post.

Thanks for your post! I feel better about having just the clamps. I'll take it out tomorrow and see how it goes.

Good point about just needing a starter motor and solenoid etc. just need it to pop up and turn the flywheel which isn't using a lot of juice for extended periods. Does the flywheel have to be the right weight as to not hurt anything or can they be swapped without problems?

And yes that throttle cable was purposefully removed from its correct spot to adjust the stop screw but thanks for the heads up!

 

[oldboat1]

Look for a sister motor with factory electric (parts motor), while zeroing in on parts numbers for what you want to add: http://www.iboats.com/40-40455S/dm/cart_id.281375630--session_id.877393100--view_id.1550137 May cross walk some parts numbers when shopping.

Generally, similar vintage and hp. Go from there. (might be able to add a ring gear to your manual flywheel, for example, although it might not be cost effective over a used flywheel. On the other hand, a starter bracket appears to be available.)

Can be kind of labor intensive, or may fall into what you want right away -- all fun, though.

 

[TN-25]

I love those old 40s. 1974 models got a heavier crank and driveshaft for added durability (not that they were needed). Being a manual start means that your motor will have an automatic decompressor (something the electric start models omitted). The manual start 40s included a tiller handle as standard as of the 1971 models so yours would have been crated with one installed.
As I recall, there was a kit to add electric start to these motors, but if it wasn't an electric start model from the factory then the charging system was not something easily added (probably due to numerous parts like flywheel and such). Incidentally, the 40 was the last OMC motor to still use a generator as opposed to an alternator; 1974 they finally switched to an alternator. Pre-1974 electric start 40s did not come standard with a charging system and still had the starter handle through the hood. 74 electric start 40s stopped putting the starter handle through the hood.

My thoughts are that the twin factory clamps should be sufficient; OMC would not have used them on the Bigtwin-derived motors since 1951 if they were iffy. Think about it. Maybe you could find one of those OMC transom plates (I bought one from a dealer recently). They have little recesses to positively locate the clamp pads, and if one loosens at all, you will hear a rattle.
You got a good, rugged, understressed motor there.

 

[Gjkelley31]

I love those old 40s. 1974 models got a heavier crank and driveshaft for added durability (not that they were needed). Being a manual start means that your motor will have an automatic decompressor (something the electric start models omitted). The manual start 40s included a tiller handle as standard as of the 1971 models so yours would have been crated with one installed.
As I recall, there was a kit to add electric start to these motors, but if it wasn't an electric start model from the factory then the charging system was not something easily added (probably due to numerous parts like flywheel and such). Incidentally, the 40 was the last OMC motor to still use a generator as opposed to an alternator; 1974 they finally switched to an alternator. Pre-1974 electric start 40s did not come standard with a charging system and still had the starter handle through the hood. 74 electric start 40s stopped putting the starter handle through the hood.

My thoughts are that the twin factory clamps should be sufficient; OMC would not have used them on the Bigtwin-derived motors since 1951 if they were iffy. Think about it. Maybe you could find one of those OMC transom plates (I bought one from a dealer recently). They have little recesses to positively locate the clamp pads, and if one loosens at all, you will hear a rattle.
You got a good, rugged, understressed motor there.

Good to hear! And that makes sense about the clamps I don't have to worry about theft either because I'm currently trailering the boat as opposed to having a mooring/slip.

I guess I don't need the motor to charge the battery just need the starter motor to pop up and turn the flywheel to get it cranking. All I would need there is a different flywheel with the ring gear, a starter motor and bracket, and starter solenoid, and then make a wiring harness with a start button correct? This is all just for future thoughts. The motor is quite easy to pull start for now. I appreciate all of the input! Making me feel good about buying this motor!

 

[hardwater fisherman]

This is from my OMC factory service manual. Allow engine to run at half throttle or slightly more until it reaches operating temperature before adjusting low speed needle. With motor at operating temperature, run in gear at slow speed (700-750 rpm) with test propeller in tank or on a boat. I guess they did not know what they were talking about when this was written. You can disagree with me and the manual also. But you may find that just because it runs good in the driveway does not mean it will run good under load on the water.

 

[oldboat1]

yup, boat is best. Get it close, then tweak it after launch.