M40C Timing

[MarvinGabriel]

I'm doing some checking and found that my timing is way off from the service recommendations. At Idle it was 5 degrees ATDC. But, when I set it to about 2 degrees ATDC, it goes to maybe 20 degrees BTDC at full throttle...there is no play in the connecting rod pivot points. WHat gives???

 

[MarvinGabriel]

So, if the engine is supposed to be 2 degrees ATDC at idle, and 25 degrees BTDC at full throttle, and there is no noticeable damage (rods straight, grommets snug), how do I get it to move the timing plate far enough to reach those two positions? The throttle plate is moving as it should, and opens all the way. Oh, BTW, it's a 1997. I know that doesn't matter much on M40C engines, but thought it worth mentioning.

 

[Sea Rider]

Set gear lever to forward, full throttle to max, stand at middle of both cranckcase's halves line formed between both and take a picture that shows at which timing advance deg the timing plate marks stops at when at full throttle grip.

Happy Boating​

 

[MarvinGabriel]

Set gear lever to forward, full throttle to max, stand at middle of both cranckcase's halves line formed between both and take a picture that shows at which timing advance deg the timing plate marks stops at when at full throttle grip.

Happy Boating​

Ok, moving the gear selector to forward made the difference on full throttle. But the idle setting is nowhere near the specification.

 

[MarvinGabriel]

I should mention the symptom, I suppose: I guess the issue is that it just doesn't idle smoothly enough for me. I have had many 2 cylinder 2 stroke outboards, and they all idle much more smoothly than this one ever has. I've de-carboned it, I've changed to a brand new set of NGK spark plugs, I've cleaned the carburetor until it's spotless, dunked, and soaked it in really caustic carb cleaner (I'm a Mobile Mechanic, and maintain a good supply of professional level cleaners and solvents), blown it out with compressed air, and am now here, still stuck with an engine that idles poorly and shakes. It runs fine, and pushes the three of us at about 30MPH on my 1648. Stalls once in awhile, almost as if it's out of gas. Starts right back up, but almost seems flooded (when it stalls.) Also, if I were to go from idle to full throttle, it bogs way down before it takes off. Almost dies.
I found that the timing was way off. It was about 7 degrees ATDC at idle. It's now at about TDC. Best I can achieve with the 25 degree BTDC at full throttle.

The compression is 125 psi in each cylinder. It's got reasonably close timing, it's getting plenty of air, and gets fuel. So, if I were working on a 1990s car, I'd say "OK, start it and drive it. Nothing to see here.) But there is an obvious issue. Maybe a vacuum leak below the throttle plate somewhere? There don't appear to be any. I used carb cleaner spray around all of the normal spots, to identify any possible vacuum leaks, but nothing. I suppose I COULD put a smoke generator on it an see if it leaks anywhere, but I can't imagine where that could be. It's such a simple system, it's hard to imagine a vacuum leak could form anywhere below the throttle pate. This is just a frustrating issue!

 

[Sea Rider]

As you have witnessed there's an great timing difference between idle and wot when the gear level has not been put to forward.

Some issues : have that motor since brand new or its a second hand one, to know if the timing advance has been messed with. Is it a tiller or remote installation ? Who has changed the standard fuel hose for that one which is darn thick, could be producing already a fuel restriction (pic 2) and a throttle shaft restriction (pic 3) as well. Would suggest replace current fuel hose for an OEM fuel hose or other with much less diam and not routed that tight than current one in pic 2, check original OEM fuel hoses.
​

Idle Time Advance :
Need to loosen nut and turn screw CCW for the timing plate to stop at 0ª, once there with a screwdriver holding the screw head, adjust back tight the nut.



When timing advance is set to 0º will need to backup the idle rpm to lessen it a bit to a point that when geared forward there's a dry clak sound when gears are turning the prop forward and the motor doesn't shut off, if does adjust slight more the idle rpm screw.

Wot Time Advance : Its near perfect set to 25º

There seems to be a hose restriction against the throttle shaft...

General issues :
The M40C uses NGK : BR7HS-10 or B7HS-10 gapped tight to 1.0 mm, the feeler gauge sheet must not fall from the electrode. That motor and the M30 compared to other 2 strokes revs bit nervous at idle, the new timing advance should compensate a bit. Check if the mixture screw is well set.

Let me know if once the idle timing rests at 0 the WOT timing stops at 25º. All my Tohatsu motors have their idle time advance set to 0, shortens the throttle dead range at the beginning of the throttle grip and accelerates way faster from 0 to whatever throttle you like running.

That's an old near bullet proof motor mechanically speaking, check if the new idle/wot time advance and the less diam fuel hose bettered all the described naughty symptoms.....LOL!!

Happy Boating​

 

[MarvinGabriel]

Thank you for the great response. I converted the engine to a tiller last year. I don't like my cockpit cluttered with consoles and junk, so the tiller works great for me. I am the third owner of this engine. I do not know all of the maintenance history, but have witnessed a bit of neglect in the lower unit, so I suspect the rest was neglected as well. I put those hoses on, because it's what I had here for automotive use, and the original equipment hoses were collapsing on themselves, and needed replaced. I'll try to find the OEM hose and order a few feet. In the meantime, I'll reroute that hose to reduce the tight turn. So, these 40C motors really idle rough, huh? It's not terrible I guess, but I'm really obsessive with smoothness, I guess. I don't expect it to idle like a 6 cylinder 150 or anything. But I do a fair amount of trolling, and rough idle stinks! I had a Mercury 25 hp, and it purred like a kitten at idle! I've re-adjusted the timing as you said, and am ignoring the spec, since it seems impossible to get it to go to 2 Degrees ATDC, while having it at 25 degrees BTDC at WOT. The linkages just don't have the length for that. I'll probably get it on the water tomorrow after work, and test it with the new modifications. I have a tach coming Friday, and will set the idle as you have suggested to others (1,000 at idle in neutral, 850 in gear). That may also clear up a bit. I think it's idling somewhere around 700 in neutral now.

Thanks
Marvin

As you have witnessed there's an great timing difference between idle and wot when the gear level has not been put to forward.

Some issues : have that motor since brand new or its a second hand one, to know if the timing advance has been messed with. Is it a tiller or remote installation ? Who has changed the standard fuel hose for that one which is darn thick, could be producing already a fuel restriction (pic 2) and a throttle shaft restriction (pic 3) as well. Would suggest replace current fuel hose for an OEM fuel hose or other with much less diam and not routed that tight than current one in pic 2, check original OEM fuel hoses.
​

View attachment 338436


Idle Time Advance :
Need to loosen nut and turn screw CCW for the timing plate to stop at 0ª, once there with a screwdriver holding the screw head, adjust back tight the nut.

View attachment 338437

When timing advance is set to 0º will need to backup the idle rpm to lessen it a bit to a point that when geared forward there's a dry clak sound when gears are turning the prop forward and the motor doesn't shut off, if does adjust slight more the idle rpm screw.

Wot Time Advance : Its near perfect set to 25º

View attachment 338438

There seems to be a hose restriction against the throttle shaft...

General issues :
The M40C uses NGK : BR7HS-10 or B7HS-10 gapped tight to 1.0 mm, the feeler gauge sheet must not fall from the electrode. That motor and the M30 compared to other 2 strokes revs bit nervous at idle, the new timing advance should compensate a bit. Check if the mixture screw is well set.

Let me know if once the idle timing rests at 0 the WOT timing stops at 25º. All my Tohatsu motors have their idle time advance set to 0, shortens the throttle dead range at the beginning of the throttle grip and accelerates way faster from 0 to whatever throttle you like running.

That's an old near bullet proof motor mechanically speaking, check if the new idle/wot time advance and the less diam fuel hose bettered all the described naughty symptoms.....LOL!!

Happy Boating​

 

[Sea Rider]

You're welcome Marvin,

Personally dislike central consoles as well, tiller driving fast response has always been for me. Yep 40's idle bit rough, seems its the spirit of that beast. Nice to count with an induction tach, can install it side of the tiller grip. ​

Which type of decarbonization has been done to that motor ? Carbon remover fluid poured in fuel tank or any carbon removed sprayed through the carb ?

If wanting to get the max HP out of that motor go for a wot run on flat calm, no wind water cond if possible and report achieved max wot rpm as loaded, probably will need a prop maximization to a less pitch prop for the motor to rev towards its max 5800 wot rpm range where get's its full HP cowl rated.

Can get the both OEM fuel pipes codes at :https://www.boats.net/catalog/tohatsu/1996/m40c-2-stroke-tohatsu/fuel-pump check items 8 & 9 for about $ 11 each set, don't know if one set will reach both extremes.

Happy Boating​

 

[MarvinGabriel]

I did the CRC decarbon on spray treatment last year. I did it as you suggested to me, last fall. It spewed out all sorts of foul looking garbage! I’ll definitely have to get a new prop. Mine is starting to slip the clutch at WoT a bit. The one on it is like 10.6”x11”. Something like that. It’s an old Michigan Wheels 142002 or something. It’s all torn up from the previous owner, and needs replaced. I wish I had access to multiple props, but that’s just not possible here.

You're welcome Marvin,

Personally dislike central consoles as well, tiller driving fast response has always been for me. Yep 40's idle bit rough, seems its the spirit of that beast. Nice to count with an induction tach, can install it side of the tiller grip. ​

View attachment 338443

Which type of decarbonization has been done to that motor ? Carbon remover fluid poured in fuel tank or any carbon removed sprayed through the carb ?

If wanting to get the max HP out of that motor go for a wot run on flat calm, no wind water cond if possible and report achieved max wot rpm as loaded, probably will need a prop maximization to a less pitch prop for the motor to rev towards its max 5800 wot rpm range where get's its full HP cowl rated.

Can get the both OEM fuel pipes codes at :https://www.boats.net/catalog/tohatsu/1996/m40c-2-stroke-tohatsu/fuel-pump check items 8 & 9 for about $ 11 each set, don't know if one set will reach both extremes.

Happy Boating​

 

[Sea Rider]

A pity that current prop was not tached when new or before was on its way to become spun, won't know if revving at wot as usually loaded to at least middle to max wot rpm range which is ideal, go for a new prop maintaining same brand and pitch or to a less pitch prop to pull wot revs up. Once the tach is installed will know...

Happy Boating​

 

[MarvinGabriel]

A pity that current prop was not tached when new or before was on its way to become spun, won't know if revving at wot as usually loaded to at least middle to max wot rpm range which is ideal, go for a new prop maintaining same brand and pitch or to a less pitch prop to pull wot revs up. Once the tach is installed will know...

Happy Boating​

Yeah, I'll probably order the same prop to test, then go from there. What do I do with the unused props? I suppose they'd be cool hung over the fireplace!

I ordered the new hoses from that link. I have looked before, but didn't check the fuel pump area of the website. I went ahead and ordered 8, 9, and 10. I'll probably go ahead and buy a new gas tank and primer hose as well. Mine is old and looking a little tired.

 

[Sea Rider]

Sorry, missed number 10, good to have all 3 hoses brand new. The fuel pump is suspended by 2 side screws, with a screwdriver check that both screws are screwed fully in till stops, air could be entering there and the fuel pump not sucking fuel right.

The motor's posted pic is far away as to check which OEM prop was factory delivered with, whichever pitch it is runs scarry well at wot. Anyway can send the new prop to a prop shop and have it repitched to less pitch in case need to bump the wot revs much higher than were achieved in the previous run.

Once all the new fuel hoses are installed, will be good to turn with hand the advancer arm plate where all the rods meets to wot and check if the timing advance plate stops right at 25 deg independently of the throttle grip following position.. If replacing the old tank and hose, replace them with the 6 gal plastic tank, the 40 used to have a metal tank.

Happy Boating
​

 

[MarvinGabriel]

So. I got my tach today. I wrapped it 6 tight turns around a spark plug wire, set it to 2p1r, and got an obnoxious reading. So I missed around and set it to 4p1r. Looks closer, but not really looking accurate. What is this thing supposed to be set at for an M40C? Looking at the design, it looks like it’s Siamese coil, and will send a spark to both spark plugs with each rotation.

 

[pvanv]

Yes, it is a siamese coil. Both cylinders fire twice per revolution. Once near TDC for power, and again at exhaust.

 

[Sea Rider]

Which tach brand did you finally got, are the idle readings half or double say from 900-1000 K idle readig. Six wraps is too much, just wrap 4 full turns around middle on any spark plug wire. The tach should read well when set to 2 sparks per revolution, my tachs on my Tohatsu horses are set that way and reading fantastically spot on.

If by obnoxious reading you mean the numbers are jumping a bit around the display, that's the spirit of induction tachs compared to a dial needle tach, once passing idle throttle the numbers will jump way much less and should be seen fixed once at full throttle grip.

Happy Boating​

 

[MarvinGabriel]

Which tach brand did you finally got, are the idle readings half or double say from 900-1000 K idle readig. Six wraps is too much, just wrap 4 full turns around middle on any spark plug wire. The tach should read well when set to 2 sparks per revolution, my tachs on my Tohatsu horses are set that way and reading fantastically spot on.

If by obnoxious reading you mean the numbers are jumping a bit around the display, that's the spirit of induction tachs compared to a dial needle tach, once passing idle throttle the numbers will jump way much less and should be seen fixed once at full throttle grip.

Happy Boating​

Ok. I’ll rewrap it, and see what happens. The readings seemed to be way off. Not double, but more than that. The brand is Searon, but it’s the same as all of the other Chinese inductive tachometers on Amazon.

 

[Sea Rider]

Ok. I’ll rewrap it, and see what happens. The readings seemed to be way off. Not double, but more than that. The brand is Searon, but it’s the same as all of the other Chinese inductive tachometers on Amazon.

That's why always recommend to go for a Hardline Tach/hour model HR-8061-2, check Amazon, costs bit more ($ 28.00) but way to go along best investment ever. The motor will be happy counting with it....​

Send the current one back to Amazon, tell them that doesn't work well and trade it for the Hardline and pay the difference...

Happy Boating​

 

[MarvinGabriel]

That's why always recommend to go for a Hardline Tach/hour model HR-8061-2, check Amazon, costs bit more ($ 28.00) but way to go along best investment ever. The motor will be happy counting with it....​

View attachment 338602

Send the current one back to Amazon, tell them that doesn't work well and trade it for the Hardline and pay the difference...

Happy Boating​

Ok, I rewrapped it, and it sounds about right now! Thanks. I’ll change the hoses when they come in, and let you know what happens.

 

[MarvinGabriel]

Ok, I rewrapped it, and it sounds about right now! Thanks. I’ll change the hoses when they come in, and let you know what happens.

Just wanted to give an update. The motor started running OK, and I just sold it. I'd rather fish than work on the engine, and this one seemed to need more care than I want to spend on it. Thanks for all your help with this Sea Rider!