2003 90TLRB - Need Help

[newboater]

2003 Yamaha F90TLRB – Serial # 61P L 1000850 – 548 hours on the motor

The boat sat for a about 2 months due to a pending move. I always add Yamaha Ring Free and Stabil fuel stabilizer to regular ethanol gas (87 octane). The previous owner ran it for 10 years so I continued to run it.

When I started it for a day of fishing, it sounded like crap, likes it’s misfiring. It idles rough and spits and coughs intermittently, but I can’t actually pinpoint where it’s coming from (carbs, exhaust, etc).

Installed new spark plugs and plug wires – same results

Compression is 204 – 208 – 202 – 180

On the cylinder drop test spark plug wires 1, 2, & 4 have an effect on performance/RPM. Pulling the wire on cylinder 3 has no effect. There is no audible change.

Adjusting the idle screw on Carb 3 full in or full out also has no effect (no audible change)

Pickup Coils – ohms check is in spec
Pickup Coil # 1 reads 12 Peak Vdc at 1300 RPM
Pickup Coil # 2 reads 11 Peak Vdc at 1300 RPM

Ignition Coils – ohms checks are in spec
Ignition Coil # 1 Primary reads 179 Peak Vdc at 1300 RPM
Ignition Coil # 2 Primary reads 179 Peak Vdc at 1300 RPM
Service manual says both ignition coils need to be replaced.

Cylinders 1 & 2 read around 1300 RPM using a GTC TA500 SmarTach
Cylinders 3 & 4 read around 2600 RPM
Burn Time is around 0.90-0.95 mSec on all 4 cylinders
Peak KV Readings (Min – Max)
Cyl 1 – 16.8-21.4 KV – Cyl 2 – 13.6-24.7 KV – Cyl 3 - 6.1-18.3 KV – Cyl 4 – 12.3-20.3 KV

Swapping the ignition coils has no effect (same results)

Drained the carb bowls and they all had the same amount of gas in them.

Swapped carbs 1 & 3 since they have the prime start ECVs and there was no change. Drained the carb bowls again.

Connected a new 3 gallon tank with new REC90 gas, new primer bulb, and new gas lines – no change

On another day I was checking the carb sync and it would blow the vacuum tube off of cylinder 2 or 4 every once in a while when it would cough. – Don’t really know what that means.

Could this be a CDI/TCI problem, or is it mechanical requiring opening the motor for an internal inspection of the valves, pistons, rings, etc.??

Bob Murry
Cape Coral, FL

[rodbolt17]

your compression numbers are off.
next step is a leak down test.
if it manages to pass the next step is cleaning the carbs/fuel system and properly re syncing them.

[newboater]

Rechecked compression and did the leak down test. I'm a little suspicious of the leak down results but I double checked to insure everything was set up correctly.

Comp Cold: 204 - 208 - 202 - 175
Comp Warm: 205 - 208 - 205 - 185
Leak Down: 2% - 2% - 2% - 2%

I would certainly think the leak down values should be higher. The gauges aren't calibrated but they do have a +/- 2% accuracy at 100 PSI.

Pumped gas from the fuel tank into a glass jar and the fuel was clear and clean out of the tank and after sitting for 6 hours.

Guess I'll be cleaning the carbs again. I did it about 6 months ago and installed the repair kits but did not replace the jets. I guess this time I'll order some degreaser/carb cleaner for my ultrasonic cleaner and replace the jets as well this time, so they'll be rebuilt when they go back on this time.

[boscoe99]

Something is not adding up. Maybe it is me.

Compression ratio on that model is 8.9/1.

Standard atmospheric pressure is 14.7 psi. Multiply 14.7 times 8.9 and you get 130 psi. Now add another 14.7 psi converting from absolute to gauge pressure and you get about 145 psi. Add a bit more pressure rise from the heat of compression but you are still a long way from 200+ psi. Was the gauge calibrated and certified to be correct?

If the compression values are really as high as you indicate I might think there was an excessive build up of carbon in the combustion chamber.

But with excessive carbon one might expect the leakage rate to be higher than what you indicate. Your numbers almost seem unrealistically low. What was the input pressure that you used?

I am betting on the carburetors being the problem but it is just a guess.

[TownsendsFJR1300]

If you didn't pull the jets out and visably look thru them, it doesn't count.

Some of the jets have verticle openings that you cannot see unless their pulled. Their usually easily cleaned.

The idle jets also have very small orifices that easily clog up. The Ringfree usually works pretty good at keeping them open but perhaps it was mixed on the thin side and the jets clogged anyway. Sounds like the idle jets clogged up, no or little fuel in the lower RPM range..

My $'s on the idle jets being clogged up.. You don't need new jets unless they've been altered...

I'm also on the Cape if you need to double check your compression #'s or leakdown, I have some decent equipment (pretty accurate). PM me...

I also have a Morgan Carbtune, (stainless slides for a 4 banger) FI'/carb syncronizer if need be. I'm assumming you had the restrictors in the hoses?

It'll work on my F150 so it shouldn't be an issue at all on your 90.

Question, when you moved the carbs, did the misfire (or lack of noticable performance) follow the #3 carb?

*If your other cylinders are hitting, I'd be pulling carb for cylinder #3 and simply pull the jets and inspect/clean..

[newboater]

boscoe99

Thanks for the reply. I wonder about the numbers myself. The service manual calls for 135 PSI minimum for compression, and I would totally suspect that the leak down values should be higher. I’ve checked them several times though and they keep coming out the same (unless I keep doing something wrong).

I don’t have the experience yet and it’s pretty much all theory to me at this point, so I’m always learning something new. I do lock down the flywheel after I put the cylinder to be tested at TDC for the leak down..

My previous boat, which I wish I kept, had a 4-stroke Honda 50 that got 195 PSI in ALL cylinders which was actually a little below spec, but I don’t know what its compression ratio was. The manual is packed away, but I’ll have to unbury it because now I’m really curious.

The gauges have a 2% accuracy but they are not calibrated. I used 100 PSI for the leak down test pressure.

Townsends FJR1300

Thanks for your reply.

I pulled all the jets and looked at them through a magnifier loupe. Ran Brakleen and compressed air through them, then ran everything through an ultrasonic cleaner.

I do have to add though, the first time I pulled carb 3 this time around and reinspected everything the main jet looked like it had corrosion on the outside of it. I cleaned everything with Brakleen and compressed air and put it back on the motor because I thought I had found the problem. It didn’t change anything.

When I swapped carbs 1 & 3 it did not change anything. I still had the problem on cylinder 3. Adjusting the idle screw and sync screw (with carb 1 installed), and pulling the plug wire had no effect, no audible change in RPM.

Adjusting the idle screw, sync screw, and pulling the plug wire on cylinder 1, with carb 3 installed on it, all effected the RPM.

I guess I could try cleaning carb 3 one more time. I’m thinking I should get a good carb degreaser/cleaner specifically made for ultrasonic cleaners like Shrpertek 1220 and run the carb through it again, just to make sure I’ve hit every little hole and crevice, and haven’t overlooked anything.

I’m certainly open to any suggestions from all of you though, who offer your assistance to us in need.

Thanks to everyone who has replied !!!

[TownsendsFJR1300]

I pulled all the jets and looked at them through a magnifier loupe. Ran Brakleen and compressed air through them, then ran everything through an ultrasonic cleaner.

I do have to add though, the first time I pulled carb 3 this time around and reinspected everything the main jet looked like it had corrosion on the outside of it. I cleaned everything with Brakleen and compressed air and put it back on the motor because I thought I had found the problem. It didn’t change anything.

When I swapped carbs 1 & 3 it did not change anything. I still had the problem on cylinder 3. Adjusting the idle screw and sync screw (with carb 1 installed), and pulling the plug wire had no effect, no audible change in RPM.

Adjusting the idle screw, sync screw, and pulling the plug wire on cylinder 1, with carb 3 installed on it, all effected the RPM.

I guess I could try cleaning carb 3 one more time. I’m thinking I should get a good carb degreaser/cleaner specifically made for ultrasonic cleaners like Shrpertek 1220 and run the carb through it again, just to make sure I’ve hit every little hole and crevice, and haven’t overlooked anything.

I also have a good spark testing tool we can use / test while the engine is running on #3 cylinder. It'll show if we're loosing spark or even have spark just to rule that out.

It does sound like you got those jets clear. I'll give you a call later on today.

spark tester;


Morgan Carbtune;

[99yam40]

I am not sure if the fuel pump for that 4 stroke is pulse driven like the 2 stroke , but would not be a bad idea to check for leaking pump.

Never mind I looked it up and it is not like the 2 stroke

[rodbolt17]

your posted voltage values look ok, why would you think the ign coils are bad?
Yamaha posts MINIMUM voltages not maximums.
your CDI peaks are about as expected.
does the ign timing advance and retard per service manual?
the doubling of RPM during the same tests tells something.
remember its a waste spark system.
if #1 fires then so does number 4.
if #2 fires so does number 3.
if #3 fires so does #2.
if #4 fires so does #1.

has spark plug lead resistance been tested ?

[newboater]

My Yamaha service manual reads:
The CDI unit output peak voltage (input to ignition coil primaries):
107 V at 400 r/min (cranking)
110 V at 1,500 r/min
111 V at 3,500 r/min
Below spec - measure lighting coil output
Above spec - replace the ignition coil

I bought all new spark plug wires because the tips at the coil end pulled off the old #2 and #3 wires. I re-crimped the old wires and they ohmed out ok but I didn't want to have to rely on them, so I installed new Yamaha wires. I did not ohm the new wires, but I did swap the wires between the #2 and #3 cylinders, which had no affect, then put them back where they belonged.

[rodbolt17]

lighting coil has absolutely nothing to do with CDI charge coils.

each plug wire has its own specific ohms value.

[newboater]

rodbolt17,

I totally agree with you on both counts. I simply wrote what the Yamaha service manual said word for word, as shown in the attached PIC 1 image. The text in red is my corrections.

The spark plug wires do have their own specific values as you say, and as shown in the attached PIC 2 from the service manual. Each wire is basically a resistor with a specific value or range. They also have a fairly wide resistance range though.

The resistance of my original wires showed about a 500 ohm difference between plug wires 1 & 4 and between plug wires 2 & 3.

I believe the resistance range and measured values are close enough that the Spark Plug Wires for Cylinders 2 & 3 can be swapped with each other for troubleshooting purposes without causing any damage, but they should only be swapped between cylinders 2 & 3.

One should also be able to swap the Spark Plug Wires for Cylinders 1 & 4 with each other, and once again, only between cylinders 1 & 4.

I’ll never see what’s inside the CDI so there is no way to calculate any LC, RC, or LCR time constants or the effect, if any, the resistance value of the spark plug wires may have.

I would not leave the wires swapped, but you should be able to swap them long enough to see if it makes any difference and make sure the wire isn’t breaking down under load when the engine is running, which may not show up in the resistance measurements.

In these older engines, I don’t think the TCIs or CDIs are sensitive enough that it would make a difference. I’m not swearing to that, because I have limited experience, which is why I rely on the information you all are kind enough to pass along. I would not hazard to guess on the newer computer con*****ed ignition systems, but I think they would be designed to take some abuse

[newboater]

Sorry, pictures are attached to this post.

[newboater]

Sorry,

I'm a little slow and don't understand why cylinders 1 & 2 read 1300 RPM and cylinders 3 & 4 read 3600 RPM during the same test with a digital tach/timing light.

I understand cylinder 1 fires at the top of it's compression stroke, and the spark is wasted on cylinder 4 because it's at the top of it's exhaust stroke. Then the same thing happens for 3 & 2, then 4 & 1 and finally 2 & 3 (for a firing order of 1, 3, 4, 2).

If the wiring diagram is a true representation, the pickup coils are 180 degrees out of phase. That would cause the trigger pulses to the CDI to be out of phase to insure the CDI fires the ignition coils at the proper time to send spark to the cylinders at the correct time.

If I could even find a generic schematic or block diagram for a CDI or TCI I'd understand how it works but I can't find anything useful on the internet. I'm sure its all manufacturer specific proprietary information anyway. They have to have some type of programmable chip or transistor logic array for the oil pressure, thermosensor and TPS signals to effect timing. I believe the rectifier output voltage may have some effect as well.

I don't understand why you get the different RPM readings, but am trying to learn as much as I can through these posts. Could you please tell me why it does it, if it's normal, or what it is, that it should be telling me?

[throrope]

I know nothing about your outboard as I only have experience with our 3 cyl 2-stroke.

I dropped a cylinder fortunately at the end of a trip and cleaned the carbs. On the test all was aces for the first half hour then back to the problem. Thinking ignition, I schlepped it to the dealer and forked over big bucks for them to tell me the carbs were clogged. Included in the job was three hundred bucks to clean the tank and lines plus $3.25 to dispose of each gallon of "bad" fuel. The problem was the junk in the fuel system which promptly undid my work above.

I replaced the tank and everything upstream of the engine connector myself for less. Using a $26 electric fuel pump, I now pump all fuel from the boat to the truck and leave the tank open and upside down when putting the boat away after the trip. And I mean after that trip, not the season. This may be a bit over the top, but for me, no fuel means no fuel to go bad and I haven't had issue since.