1995 Yamaha 70HP TLRT will not advance.

[cclemens]

The symptom:


Cold engine throttles up and runs under load for a good while. Can and will power down and power backup with no stalling, sputtering, or otherwise noticeable problem. Once hot the unit will lose power even while on plane. When throttle is advanced “bogging down” symptoms get worse. Engine will stall unless put into idle then can be advanced again but only carefully. Whether or no it will get back on plane seems arbitrary. It did this for the better part of a year until finally now it will not advance at all under load. Now it sputters and stalls It will run continuously slightly above idle.

Things I have done:

1. New fuel line and squeeze bulb
2. New water separator
3. New Fuel pump
4. Cleaned fuel filter
5. Rebuilt Carbs
   1. Fuel was pooling around intakes and poured out when tilted.
      1. All new gaskets.
      2. New needles
      3. Adjusted floats
   2. Ran under load with top open to see fuel spray which looks good.
6. Tested compression
   1. Plugs Fouled brown/black greasey
      1. Service Manual says bad spark.
7. Tested Ignition coils.
8. Reseated Caps
9. New Plugs
   1. Properly Gapped.
10. Tested Crank Position Sensor
11. Testing CDI

I am mostly convinced something is CAPUT in the CDI. I think this because of the progressive dying, temperature factor to failure, and exhausting fuel issues.

Any Thoughts?

 

[Sea Rider]

Will need to troubleshoot all electrical components : Exciter Coil, CDI, Ignition Coil in that order, that's checking resistance and DVA current while engine is cranked with appropriate multimeters. Seems one of those components is already altered, heats up, shorts and misses badly when engine is given more throttle. Electric oparts doesn't last forever and that's a 22 year oldie..

Happy Boating

 

[cclemens]

According to the service manual I have Pulser, Charge, Lighting, and Ignition coils (See Picture). The manual has listed acceptable testing ranges for resistance but says nothing about DVA Current.

The cold running was an old symptom now it will not advance at all under load. I did advance it once with ears on (I know thats bad) and it did for the limited amount I advanced it but when I dropped the boat in the water CRAPPOLA.

 

[Sea Rider]

Testing electric components just with resistance values is relative, real testing is with DVA values as will know if each component is doing its homework right when engine is cranked. You can even test DVA values while engine is running on water at speed.

DVA values should be found in Servce Manual aside from resistance values. One thing is testing an engine on muffs without load and other much different when testing same with a load. Engines usually misses at load and higher rpm not at slow idle without load.

Have you ever changed cylinder head gasket/gaskets ? If severely hardened, overheated, not torqued back to specs, could have tiny water dropless passing to combustion chamber and engine missing when throttle is applied. A compression test won't spot it.

Happy Boating

 

[cclemens]

I did some readings on the various electrical components and found the pulser coil reading 304 ohms when it should be 3200-4900 ohms. The charge, lighting, and ignition coils tested in range. Could these symptoms be related to the pulser?

 

[Sea Rider]

Any electrical component with way altered resistance could be the culprit of electrical issues. Replace the Pulser Coil and see what happens.

Happy Boating

 

[cclemens]

OK just to complete the full train of thought I looked at what the pulser coil actually does for the engine. Here is the link:

http://racetechelectric.com/ft-752-pulser-coil-ignition-systems.html

From that description the flywheel has a mark that interacts with the pulser coil to generate a signal that the CDI unit interprets as timing for a spark. The PC is set to TDC of cylinder one so that when the motor is advanced the PC signal will always be sent at the same time in the engine's rotation no matter the RPM. It seems clear to me that if that item is defective it could be sending an ill timed signal to the ignition system thus making the unit "BOG DOWN." AND since my plugs came out brown and greasy looking which denotes a bad spark I may very well have found my culprit.

145.00 later and likely removing the flywheel (shudder) and I will find out.

 

[Sea Rider]

Imagine how such a smalll hidden electrical part could screw a whole OB down, Take advantage to clean, shine all electrical contacts and their grounds for a neat electrical connection.

On 2 strokes OB's won't find spark plugs clean as in 4 strokes OB's, are always bit oiled and with use darkened which is normal. Is spark plugs tips are found being dark chocolate color, it's a good indication that OB is working right. Report if PC was the culprit. Good Luck!!

Happy Boating

 

[cclemens]

No it wasn't I am an idiot and cannot use a volt meter correctly. So now I am back to nothing. All the connections I have seen were great. All except the grounds on the ignition coils. Those were corroded like a battery terminal. Cleaning and reseating them did nothing for the problem. And the coils tested good.

Guess its back to DVA values while running under load.

Could something be seizing in the lower making the engine shut down? It will idle forever so I doubt that seriously just spit balling.

 

[cclemens]

SO I keep coming back to one possibility. The 95Yam has alarm sensors and RPM reducer that triggers when the motor is under alarm. While my previous symptoms could have been fixed currently the system might be running under alarm. My gauges are all fuzzed out **** and cannot be read and the buzzer could be dead. I heard the alarm in the past once when I sucked in mud and it overheated and once when I ran low on oil (How I learned about **** gauges). But each time the motor would idle and run at very low RPM in gear. When you try to advance it shudders and stalls very similar to how it is behaving now except no alarm noise.

 

[Sea Rider]

What's the new PC Ohm impedance ? Where all the magnets under flywheel found in good shape and all in place ? Does the OB still misses, bogs down as previously stated or now shuts down and will need a restart to work again ?

Electrical components failures & related issues are a PITA to troubleshoot correctly, worse when cold componets heats up, shorts, misses. Will need to get the DVA Yam specs for that 70 and troubleshoot each electrical component individally flywheel down to Ignition Coils to find the culprit. Get a analog or digital multimeter with DVA reading capability.

Can test each component with OB geared forward while revving at 2.5-3.0 K revs with muffs attached. Just be aware of spinning prop. Has the cylinder head gaskets been changed before or are 22 years old current ones..

Happy Boating

 

[cclemens]

PC Ohm was same on both new part and old. 299 ohms on 20K setting. Manual said it is supposed to be 3.26-4.88k. I originally called it bad because the meter only has four digits for readings so I figured a factor of ten in which would put it at roughly 3k and under spec. But the new one tested EXACTLY the same so now I doubt there is anything wrong with the part.

The fly wheel looked completely unblemished. Every tooth sharp edged and perfect like it was freshly machined. The only magnets I saw were the one on Pulser Coil. It sets up right next to the teeth of the fly wheel and is attracted as each tooth passes by it.

Yeah the boat used to heat up and then start missing. I could be running full throttle on plane and then out of nowhere the unit loses power and eventually stalls unless I take it down to near idle. I got by because there was usually a sweet spot I could get to which would allow it to keep running long enough to get where I was going. If it died it would always crank right back up and I could put around at low RPM until I could nurse it back up to plane.

Now it wont advance at all and nearly got me stuck out away from dock. Maybe two or three percent advancement and then it sputters and stalls.

I have not done the head gasket or know if it has ever been done.

 

[cclemens]

Oh I just remembered there was a time just before total fail where it would be on plane lose power and then get it back suddenly thrusting you back in seat and staying on plane. That only lasted a few trips before dead.

 

[Sea Rider]

Did OB ever overheated ? does this model has a built poverheat sensor that when triggered drops wot revs to safe revs for protection ? If not counting with a overheat sensor, when overheated, where there powerhead funes, impeller destroyed itself due to running dry ? If so, what did you do next ?

Happy Boating

 

[cclemens]

Has alarms that went off in the past. When overheated from mud I shut it down. It never ran completely dry of oil but got real close.

 

[cclemens]

And yes it drops revs when under either alarm.

 

[Sea Rider]

What do you plan doing next ?

Happy Boating

 

[cclemens]

Scour the manual for the sensor that sends that ALARM signal and try to find it.

 

[cclemens]

Guess what I just found, which I did not see in the service manual anywhere other than a tiny exploded diagram.

A TELL TALE.

The motor has never "Peed" so it never really got good cooling and when I pulled the line it was caked in silt all the way back to the port on the exhaust outer cover. Now the motor would "cough" or "dribble" hot water out a different bigger hole but surely this is a problem. Maybe not my power loss problem but a problem none the less.

This weekend I am going to flush the exhaust area, (Run with ears on to get the tell tale flowing) and check the thermostat to see if its working. And maybe inspect the water pump for wear.

 

[99yam40]

I guess I took for granted that people knew the TT was an indicator that the water pump was pumping.
If there was no water coming out of the TT then they needed to find out why,not to keep running it like that

If the TT was plugged up like that there is a very good chance the rest of the motor is full of it also