1997 40 hp 2 stroke 3 cylinder, Help with rough idle?

[99yam40]

that is a very good question,I do not know myself and I would like to know this also.

seems strange that if the secondary was open it would have been the same as you pulling the plug wire off.
or when you said no reading did that mean 000.0 ohms

looks like that c40 has 3 pulser coils one for each cylinder to tell when to send spark.
I wonder if the voltage from bad coil could cause voltage/current to run through grounds on other coils, or it just caused the timing light to get false reading.
let me know if you find an answer as I have a motor close to what you have

[zenoahphobic]

Not knowing the timing light and how that was connected, it seems from here that it is picking up the other pulses on the line. This is just its sensitivity and doesn't necessarily mean that there is any arching between leads. But probably there is earthing problems.
If that the case I would clean etc all earth connections including the mounting surfaces of all the coils.
To be sure that the coil you suspect is faulty, you have to sure the secondary ohm reading is infinite (very high); it will never be zero.
Keep in mind even with a open circuit reading it could still actually work if the break is in the lead. The spark simply jumps this gap and then jumps the spark plug gap.
All the above faults can send pulses everywhere, and a faulty coil can take some energy away from the good ignition.
Difficult from here to diagnose!

[redexredex]

basics

Hi,
I am new to the forum, but have you tried all the basics first ? Correctly gapped new plugs. If it appears to be a problem with one cylinder swap the coils and see if the problem moves with the coil. If the problem stays with the original cylinder, its not coil or plug !
Check the reed valves on the affected cylinder if you can, also look for air leaks, check the check valves on the crankase oil scavenging pipes if fitted.
Check the float level and slow running circuit. I would ignore suggested settings and open the idle screws up an extra 1/2 to 3/4 turns, usually gives a better (dirtier) idle anyway !!! its all about emissions !
Timing is unlikely to be an issue unless you have changed it. After all it was working fine before !!!
After all that you are only left with pick up coils and cdi (try substitution if you can "borrow the parts")
(I am ignoring the possibility of crankcase seals, deal with the easier options first !!)
Hope that helps, good luck, Mad Prof (aka Neil)

[bedwar44]

I've done the basics, compression, spark, fuel (fuel several times). The timing test was goofy. The timing light picking up the signal from the other leads sounds reasonable. They are pretty close together, and it isn't the cream of the crop as far as test equipment goes. Reed valves and seals were next on the list.

The coil for cylinder two was definitely bad, however. There was no conductivity between the high tension and ground wire testing as manual instructed. But... It also makes sense that it would still function enough to pass spark test, etc., which I have done, but under compression could be too weak to fire, or only fire intermittently. Visual inspection of pistons and cylinder seems to confirm that. The HT leads are short, and basically bend at a 90 to go to the plugs, so I can definitely see where over 20 years (its a 97 model) the lead could come loose from the internals. To check, I stripped the insulation on the bad coil, and sure enough, a VERY slight tug pulled the HT lead loose from the coil.

New coil is supposed to be delivered today. I will update the thread after I install and test motor.

Thanks again for all the help.

[bedwar44]

Solution! sort of...

Got the new coil in and put all the electronics back together and fired right up. Purring like a (angry) kitten... Will idle now for as long as I leave it on the muffs, but it is still a bit rough. Haven't been able to test higher RPMS on water yet.

Couple questions for the experts:

1) when I was checking/setting the timing, with the pointer at the factory mark indicated by manual on the CDI, timing was past 10 ATDC, about 14 I think. Should be 7. I got it to 7 by adjusting the pointer linkage, but I had to turn the pointer, advancing timing, about 1/4 inch downward. The timing stays steady at this point, and increases as it should if I manual rotate the pointer downward farther, but I am worried that this is bad news. Is it possible the CDI is somehow just off by a set amount? i.e., when I run at WOT should I expect to need the pointer to go the same distance past the factory mark for full advanced? Has anyone ever seen this amount of bias on the CDI units? This is really bothering me.

The other question is about carbs and idle passages versus main jet fuel flow. The idle spec for the motor is 800 rpm. Unless I have the butterflies basically all the way closed I can feel some fuel coming out of main jets with my finger while at idle. If I adjust the idle screw so that the butterflies are more than even a hair or two open, there is definitely gas coming through main jets. Is this normal for these carbs?

[99yam40]

Back on post #11 I told you what problem I had with my C40TLRX.

Sounds like the same as yours, timing too far retarded at idle.

causes you to increase the idle speed with the screw and opens up the butterflies just to make it idle.
Might check WOT timing to just see where it is

[bedwar44]

99yam40, gotcha.

After some searching I actually found your original forum posts when you were having your issue with the CDI. Sounds almost the same.

I find it simply mind boggling though. Mine seems to operate normally. It throws spark to coils and the timing changes when I move the pointer, so the rheostat is not fried, nor is the discharge system. Timing is advanced at startup until temp switch kicks in. All normal. Pulser coils ohm out good. No shorts to each other detected. It could be having an intermittent problem too fast for me to detect though (I have no DVA).

Just very strange. It is off by about 7 atdc degrees and with the pointer in the correct location starts at about 14 to 15 atdc at idle. Its almost as if whatever it uses as the initial reference is fried, so rather than starting at TDC and retarding by 7, it is starting retarded by 7 and then retarding an additional 7. But... I manually moved the pointer to increase advance, and everything on the btdc side of the spectrum seems normal and the pointer is at about 25 btdc at the mark on the cdi, i.e., the 7 degree bias is either gone or much less. Alas, the service manual doesn't do much in the way of explaining the system design, just how to check it (I know, I should be able to figure it out from that; not that smart...)

I hate to spend 400-500 bucks on a new one but it certainly seems to not be working correctly.

Out of curiosity, did use an oem model or something like cdi electronics to replace yours?

[rodbolt17]

my first guess is you have a 98 C$ or newer.

this guess would be based on the 97 had 2 cylinders.

can you post the full model number ?

[bedwar44]

C40TLRV. block is 6H4

[99yam40]

99yam40, gotcha.

After some searching I actually found your original forum posts when you were having your issue with the CDI. Sounds almost the same.



Just very strange. It is off by about 7 atdc degrees and with the pointer in the correct location starts at about 14 to 15 atdc at idle. Its almost as if whatever it uses as the initial reference is fried, so rather than starting at TDC and retarding by 7, it is starting retarded by 7 and then retarding an additional 7. But... I manually moved the pointer to increase advance, and everything on the btdc side of the spectrum seems normal and the pointer is at about 25 btdc at the mark on the cdi, i.e., the 7 degree bias is either gone or much less. Alas, the service manual doesn't do much in the way of explaining the system design, just how to check it (I know, I should be able to figure it out from that; not that smart...)

I hate to spend 400-500 bucks on a new one but it certainly seems to not be working correctly.

Out of curiosity, did use an oem model or something like cdi electronics to replace yours?

If you read my post about the problem I had with timing, it was difficult to adjust the threaded connection far enough to get it to correct idle timing and then it was off on the top end.

I bought the Yamaha CDI and all was good again

[99yam40]

my first guess is you have a 98 C$ or newer.

this guess would be based on the 97 had 2 cylinders.

can you post the full model number ?

Made me look up the 97.
it shows 3 pistons and 3 carbs

[zenoahphobic]

Just a thought.
Usually a "black box" piece of electronics fails in its power circuits or in this case expect failure of the high voltage conversion inside (weak or no spark); not in the input parts.
So, how does it get its input for the timing? Is this a pulsed coil? I would check this very carefully as gap to magnet, as well as triggering on the fall and not on the rise of the electric field, at slow speeds all could add some retardation .
Just a left field thought, as you hope to spend the minimum required. Sometimes buying a new component compensates for a weaker component and because the fault seems to have been fixed, there still lurks a component not pulling its full weight.

[99yam40]

seems this style of motor has the TPS built into the CDI, so that is what changed things is my thoughts.
At the mark for idle timeing it should be at or close to proper timing but it is not.
trying to remember when I was checking mine, at start up cold the timing is set electronically to before TPC, then drops some for warm up, and once motor is warmed up it drops to the idle timing.
Once I changed my CDI everything was back to spec

[bedwar44]

Zenoahphobic, I also had the thought that maybe the flywheel key sheared, or another mechanical issue, had changed the timing at the pulser coils, but everything looks in order there. The small rectangular magnet (or maybe just indicator, not sure) that is raised from the surface of the flywheel finishes its pass of each pulser coil right about TDC as far as I can tell. I assume that is how it is supposed to work to set up the signal to the CDI. Seems logical. The gaps don't look adjustable, the pulser screws into a little mount on side of wheel with two screws that don't appear to have any wiggle room.

Original symptom was bad misfire at idle. Sure seemed like fuel issues. Improved with updating fuel system but miss still there. After all the checks etc, the symptoms now are:

1) Timing is retarded about 7 or so degrees too much at idle with all the correct service manual linkage, pointer, etc adjustments. Haven't tried WOT since I discovered this, too scared of damage.

2) Coil 2 had gone bad. Maybe because of CDI also? I cant say because I don't have access to a DVA tester. Didn't see any shorts, etc in any wiring, cleaned all grounds, etc.

3) Replaced coil 2 and it is better still a regular miss. It seems to kind of surge (I know that's not right word), like a good good good bad good good good bad pattern on the firing and miss, with the god parts being a couple seconds. This is with adjustment to the timing pointer to where timing light reads correct idle timing. The plug in cylinder 2 appears to be firing less based on visual inspection. If I pull that plug wire the misfiring smooth out even though its only on 2 cylinders. Really hard to tell but if I point timing light hooked to 2 at black surface you can kinda see it too. Don't see it on 1 and 3.

Given the similarity in CDI issues 99yam had, I think it is pretty safe to target the CDI as the culprit. Even if it isn't causing the miss as well, It is the only thing that could introduce the bias to the timing. Doesn't really make sense to me but it seems it must be so.

Gonna be a while (2 or 3 weeks) before I can afford one, but when I can I will post and say if it fixed everything or not.

[bedwar44]

CDI fixed the timing problem

Found a used CDI unit that matched. Timing issue is gone.