70 TLRR constant miss

[Joeyvcosyamaha]

I have a 1993 70 Hp TLRR code 6H3L. Was out fishing one night, everything running fine from spot to spot. I went to fire it up & move to another spot & it had a terrible misfire, wouldn't idle, got it on plane & it would kick in the third cylinder & drop it back out constantly. It got me home & I have been chasing this problem since. Wasn't sure if it was fuel or spark, so here's what I did : rebuild carbs ( have been leaking fuel & needing it for ages ), replaced reeds with Boysen power reeds, fixed broken wire on prime start unit, replaced all spark plugs, replaced all plug boots ( two were out of spec ), replaced two coils ( they read out of spec. Ohm wise ), replaced plug wires, checked all connections & wireing for burns, nicks, wear spots etc. The motor fires right up now without having to use the hard start lever, indicating my prime start works again, BUT I still have that damn mis ! The following is test results from ignition / electrical components test : Pulser Coil - 11.2V @ 1500 Rpms.,5.96V unplugged, 321 Ohms. Charging coil - 131V unplugged, 192 Ohms, 242-244V @ 1500 Rpms. Crank Sender Coil - 219 Ohms, BUT only 8.4-9.7V @ 1500 Rpms. CDI to coils - 220-224V @ 1500 Rpms. Compression = #1 - 100 PSI, #2 - 103 PSI, #3 - 90 PSI The only thing I am seeing is the Crank Position Coil being out of spec. Am I missing something & I am assuming this would cause my problem ?? I am NOT a Yamaha trained mechanic, just been keeping this old girl alive for the last 10 years. Thanks, Joe

[99yam40]

check the fuel pump,
might be leaking into #3 and causing too rich to fire properly

[TownsendsFJR1300]

check the fuel pump,
might be leaking into #3 and causing too rich to fire properly

+1 ^^^ ....

Your #3 spark plug is likely also much blacker (fouled) with fuel than the others...

You may to replace at least that one after the fuel pump is fixed...

[Joeyvcosyamaha]

I'll check again, but I believe I've had the plugs out several times since I put the new ones in ( & started the whole investigation process ) & they looked new still. What about the readings I got from the Crank Position Sensor being half what it should be ?

[99yam40]

I have no idea what the specs are or what you are using to measure everything with.

So if using the proper test equipment and things do not meet minimum specs given in service manual, that device or its wiring/connections are suspect.

But it will not hurt to inspect the fuel pump, since # 3 compression is down some. it might come from the extra fuel washing the oil off things

[TownsendsFJR1300]

+1 ^^^

Check the BASIC'S first!!!

It's also the most likely failure with your description...

[Joeyvcosyamaha]

I have no idea what the specs are or what you are using to measure everything with.

So if using the proper test equipment and things do not meet minimum specs given in service manual, that device or its wiring/connections are suspect.

But it will not hurt to inspect the fuel pump, since # 3 compression is down some. it might come from the extra fuel washing the oil off things

Agreed, the fuel pump isn't but a few years old, so wasn't my immediate suspect but I'll check it this week & see if I get any flow out of the back side ( piston side ) of diaphragm using the primer ball. Specs are 20 volts @ 1500 RPM for the CPS & im only reading under 10 volts @ 1500 now, so this was my " hopefully " suspected defective device. I'm using a digital multi meter with a resisted, slow discharge circuit attached to it that I made per specs from a guy on the internet.

[rodbolt17]

long before I messed with a device that has a rare failure rate I would simply monitor the CDI output with a CD-77 or the merc analog peak reading meter.

as you are using a cobbleation and not the DVA adapter or the CD-77 type peak reading meter all your voltage bets are off.
unlike RMS voltage we are looking for the PEAK voltage.
that system uses one pulser to trigger 1&3.
#2 is made up in the CDI based on CPS inputs.

[Joeyvcosyamaha]

DVA, that's what it is, I built one from specs a guy posted on line. This is attached to my Field Piece digital multi meter & yes peak voltage is the intent of using a DVA. The CDI output is 222-224 volts to ea. Coil @ 1500 RPM, which is in spec. according to the manual.

[rodbolt17]

if CDI output is correct on all 3 why are you looking at CPS???
the ign system is working.

[99yam40]

If it is an intermittent miss it maybe hard to see in the spark side, but I would try to look at the peak voltages at the failure point.
Not sure if the DVA would just average it all, but the average voltage would probably go down when it happens.

A inductive timing light hooked to #2 plug wire( or any other plug) if the spark is dropping may show a skip by light dropping out too.Some of the lights also show RPM so if you look at all 3 plug wires with the light if one is dropping spark the RPM would show lower that the others

if the fuel pump is good, then I would see if I could find someone else with a motor just like yours and see what you get reading their motors CPS with your home made DVA

[Joeyvcosyamaha]

if CDI output is correct on all 3 why are you looking at CPS???
the ign system is working.

Just because I'm getting spec volts, does that mean it's in the right order ? Isn't that the job of the CPS ? I believe the CPS tells the CDI " when to fire " doesn't it ? Kinda like a rotor to a set of points ?? Used ta be ?? Kinda ??? As I stated my CPS voltage is under 10 instead of 20 as specs show it should be @ 1500 RPMS, Sorry I'm stupid, but, isn't that a red flag ?

[rodbolt17]

not always a red flag. especially when using non spec test equipment.
it is also why when I chase intermittent things I resort back to the old analog stuff with a needle.
digital buffers to slow to catch it.

[Joeyvcosyamaha]

If it is an intermittent miss it maybe hard to see in the spark side, but I would try to look at the peak voltages at the failure point.
Not sure if the DVA would just average it all, but the average voltage would probably go down when it happens.

A inductive timing light hooked to #2 plug wire( or any other plug) if the spark is dropping may show a skip by light dropping out too.Some of the lights also show RPM so if you look at all 3 plug wires with the light if one is dropping spark the RPM would show lower that the others

if the fuel pump is good, then I would see if I could find someone else with a motor just like yours and see what you get reading their motors CPS with your home made DVA

I'll give the timing light a try & see what that produces. The DVA I made shows everything else in spec, except that CPS, I'm thinking the DVA is working properly. Just weird how this just happened when I went to fire it up after running all night flawlessly, which makes me think something electrical just crapped the bed when voltage was applied to the motor on fire up.