1993 70 TLRR power loss issue

[grouper sandwich]

I won't get back down to the coast to run it and do more testing until at least next weekend. And I promise, I'll have my meter and DVA with me this time when test stator charge coil and CDI while problem occuring. I've also made arraignments to borrow a 12 gallon tank and fuel line to test to see if maybe there is a restriction somewhere up the line in my system. But I did think about another symptom that I don't believe was in my original post. This happens with or without the hood being on. After coming up on plane and reaching my cruising speed of about 4400-4500 RPM, if I decide to take it to WOT it bogs at the very top of the throttle range. It's fine until around 5300-5400, and I can leave it there if the hood is off and it will run fine all day. But if I push the throttle the rest of the way home, it begins to bog down. If I back the throttle off a little, it picks right back up. Everyone I've mentioned it to just scratches their head and shrugs their shoulders. Anyone have any clues? Anyone ever experienced a similar symptom?

[99yam40]

It is best to test things you can to eliminate those 1st
monitor fuel pressure and vacuum while problem is there is the best way to see if you have a supply problem
monitor spark and timing also while problem is there

Too much fuel or too little will both cause cylinder not to fire properly
My C40 had main jets that were drilled out by previous owner. It ran best with cowling off and silencer off running into the wind. Took me a year to figure out I needed new jets.

Fuel pump leaking into crankcase will cause problems to #3 cylinder, seals can cause lean conditions on top or bottom cylinders.

[grouper sandwich]

Went to the coast yesterday and picked the boat up and brought it home. Took it to the lake today to do a little testing. The stator charge coil tested fine while the bogging issue was occurring. The CDI was a little out of speck voltage wise on the DVA, but not off the scale. The problem appears to be fuel in the way that it acts and sounds but man I'm telling you, I've got the cleanest, best functioning fuel system in the known boating world. I could put on a clinic or enter a carb cleaning contest at this point! But still, this frustrating issue persists. Every mechanic I've discussed it with or has worked on it has said fuel, fuel, fuel while extending their hands for payment. I've suspected the CDI for quit a while now but have been told "it ain't the CDI, they almost never go bad" for over a year. So today was all about testing that. The peak voltage tests really did not reveal much but still, I was convinced it was the CDI. Almost on a whim we decided to stick an ice pack on the CDI while the problem was occuring. You know what happened? Three guesses and the first two don't count. Yep, the engine sprang to life as if being injected with a massive dose of adrenaline. Pull the ice pack off, bog city. Put ice pack back on, new engine. Wash, rinse, repeat. And when we would do this the little throttle needle on the CDI would advance without touching the Throttle. Now I'm not a mechanic, I'm a desk jockey. But I think I've solved this one. Here's a quick video of one of our ice pack tests.

1993 Yamaha 70 TLRR CDI test - YouTube

[99yam40]

Peak voltages in manual are minimums and should be higher normally, did the in and out of CDI not meet spec while running well and bad?

Posting the numbers would help others see what you saw.

What about the timing? was it changing in and out of spec?

I do not see how an ice pack would change things that fast, not enough time to cool things off and heat back up.
unless the pressure he was putting on it was making the difference.

I Do not understand what you mean by the little throttle needle on the CDI would advance without touching the Throttle.
If it is the wiper on CDI, it is attached to throttle linkage and should not move without the throttle linkage moving also.

Maybe a pic or better explanation

[grouper sandwich]

Wiper, needle...same thing to me. The little pointy thing on the outside of the CDI. And yes, it would move when the ice pack was applied to the CDI. It seems obvious to me why. And it's also why my explanation of the problem set off the "fuel" response from everyone. The throttle advance, or whatever controls the throttle timing (if I'm even sayin it properly) is con*****ed by the CDI. If the the throttle cables are sending fuel to the carburetors but the timing of the spark is not advancing properly, the engine is flooding out and giving performance like what I was experiencing. And yes, it absolutely would cool it off that quickly if the heat tolerance of the device was right on the edge, especially on a 20 year old engine that been run in the hot Florida sun it's entire life. And you saw the video, it doesn't lie. I wish I would've gone with my gut two years and just bought the CDI instead of listening to experts and mechanics and spending thousands of dollars and experiencing untold ruined outings. Live and learn, I suppose.

[99yam40]

The wiper linkage is attached to the throttle linkage, the throttle linkage is attached to the carb butterflies and the cable from controls and none of them should be moving separately from the others.
If this motor is like my 1999 C40, The wiper is just a variable resister inside the CDI that is only moved by the linkage to change the timing electronically. The pointer is just there to indicate where to set it when adjusting the set up.
If the pointer/ linkage is moving, the CDI is not causing it to move, it is moved by mechanical means, the linkage, and if linkage is moving so is the butterflies on carbs


I have read about some one putting something behind the CDI and bolting it down to put pressure on CDI to get a bad connection inside to make up properly, but would not trust that fix for long

A timing light would show if timing was changing, as I suggested weeks ago

[grouper sandwich]

**UPDATE**

Sorry I guess I didn't post on the timing test. We did check timing while the problem was occurring and it was all over the place, on all cylinders. Voltage also dropped, but it was real close to spec. That said, I thought of you mentioning those numbers in the manual being minimums. It also only shows voltage up to 1500 RPM in my manual. It a little further investigation shows that it should be well over 200 volts at WOT, so if I'm getting 120'ish volts when the problem is occurring, I guess I'm well under spec. So, before committing to purchasing such an expensive part (CDI) for such and old motor, we decided to pull the CDI and clean all of the contacts and ground. There wasn't much corrosion on anything, but a little. The CDI ground was the dirtiest. All were polished to shiny nickle new, a good coating of corrosion X applied, a slight crimp applied to the female connectors and off to the lake we went. After an hour plus of running the absolute dog crap out of it (5700-5900 RPM, hairpin turns, stop and starts, etc...), we couldn't get it to fail. Could a slight bit of corrosion on the contacts have caused all of those issues? Here's a quick video of holeshot while waiting for the trailer to backed into the water. I didn't have much room to work with, thus such a short video. Obviously this is AFTER running the engine hard for over an hour. It absolutely wouldn't do this before cleaning the contacts.

1993 Yamaha 70 TLRR holeshot - YouTube

[99yam40]

So are you saying the ice pack was not the fix, probably just the pressure on connections?

[grouper sandwich]

So are you saying the ice pack was not the fix, probably just the pressure on connections?

Maybe, maybe not. Heat was definitely effecting it. And, it was not very hot yesterday (low 80's) so I may not have fixed anything. I'm wondering if the corroded ground could have been causing the CDI to overheat just enough to malfunction. Where the ground is located (behind the CDI mounting bracket) it is impossible to effect it with any sort of pressure on the outside of the CDI box. Pressure on the outside of the CDI box with a block of wood did not change the situation at all while an ice pack did. Then again, I'm not a mechanic so I really don't know. My question is could a corroded ground cause the issues I was having?

[99yam40]

corrosion on electrical connections is never good, you can test you peak voltages again to see if cleaning the ground helped with the reference to ground.

Still do not see how ice pack would cause the wiper needle on CDI to have been moving around by itself without the whole throttle linkage moving

[rodbolt17]

bad connections and poor grounds will create issues.
remember the CDI DOES NOT amplify anything.
it simply takes,rectifies and stores whatever voltage the stator charge coil gives it.
its a stupidly simple capacitor discharge ign system that's been around since the 1960's.

same as all electronics, garbage in=garbage out.

[grouper sandwich]

corrosion on electrical connections is never good, you can test you peak voltages again to see if cleaning the ground helped with the reference to ground.

Still do not see how ice pack would cause the wiper needle on CDI to have been moving around by itself without the whole throttle linkage moving

I'll be honest with you, I don't either. And had I not seen with my own eyes you could've never convinced me it did. It only happened that one day so maybe something was stuck? But it did happen.

Hopefully next weekend all of this tropical moisture will be out of here, it will be hot again and I can really test it. This weekend is all about watching it rain though! But when I do, I'll report back.

[grouper sandwich]

One last update. It appears as if servicing the connections cleared it all up. I've now had two trouble free trips in a row. This past weekend was a good test. I loaded my wife, daughter, father, three coolers full of ice and a kayak and headed across St. George Sound to Dog Island into a stiff wind and ran it at 4800 RPM the entire way with no issues. Dido for the ride home. Air and water temps were both in the mid-80's, which in the past has been the threshold for problems. Thanks to all who helped solve this problem for me.

One other note. For whatever reason I always thought my engine was a 1993 (70 TLRR). I don't know why I thought that or where I got the model number from. In reality, it's actually a 1994 (70 TLRS) and is clearly marked as such on the serial number plate located on the motor bracket. I purchased it new from the dealer in 1996 and knew was an old stock leftover (got a great deal on it), but it's odd that I would've thought for the past 17 years it was a 1993 and not a 1994. Only thing I can think of is that the sales person must've mentioned it as being a 1993 and it just stuck in my head.

[99yam40]

Probably the motor was manufactured in 1993 and is listed on tag.

A lot of people see that and think that is the year model not just year of manufacture