2012 3.0L TKS runs great with muffs, but slow on lake...

[alldodge]

There is no place to get a vacuum reading from this motor

 

[cyclops222]

Post #3 said your spark gap tester shows a reddish glow ? BAD. Should be white or blue very thin arc in air. Testing arcs with no load on the prop can be useless.
Have you adjusted the carburetor float correctly ? There are 2 dimensions

 

[GeorgioP07]

Post #3 said your spark gap tester shows a reddish glow ? BAD. Should be white or blue very thin arc in air. Testing arcs with no load on the prop can be useless.
Have you adjusted the carburetor float correctly ? There are 2 dimensions

Hi.
The sparks are blue and white and strong. Once in a while, I see a yellow one.
The carburetor float height and float drop adjusted to exact mm listed in the Mercruiser service manual, with no effect to this situation.
Rebuilding the carburetor actually did nothing to make things better, other than some peace of mind on that side of the engine.
I just received the M16x1.5 T-Adapter to measure the fuel pressure at idle and at high throttle, so I will test that in a few hours and post the results with video here.

One last thing that I never mentioned, and maybe because this sounds crazy, is that I noticed that when driving in the speed zone at a local lake at WOT, the engine would "open-up", and run fast as expected (RPM>3200) when making a medium-to-sharp left turn!
If I went to slow down, or if I shut it off, I could not get back to the higher RPM's though.
That led me to think that it might be a sticking throttle or shift cable, or exhaust valve, or something that by moving the throttle lever and cables back and forth, or when that left sided pressure was applied, or right side pressure of that component was relieved, then something "opened up" or got "unstuck", and returned to motor spec, and the motor responded with normal operating parameters leading to expected throttle response.
I could not re-create this phenomenon every time, but it was happening about 1/2 the time.
I should mention that this speed zone runs counter-clockwise, so I didn't get a chance to test a hard right turn at WOT yet.
I know... it sounds nuts.

 

[nola mike]

Hi.
The sparks are blue and white and strong. Once in a while, I see a yellow one.
The carburetor float height and float drop adjusted to exact mm listed in the Mercruiser service manual, with no effect to this situation.
Rebuilding the carburetor actually did nothing to make things better, other than some peace of mind on that side of the engine.
I just received the M16x1.5 T-Adapter to measure the fuel pressure at idle and at high throttle, so I will test that in a few hours and post the results with video here.

One last thing that I never mentioned, and maybe because this sounds crazy, is that I noticed that when driving in the speed zone at a local lake at WOT, the engine would "open-up", and run fast as expected (RPM>3200) when making a medium-to-sharp left turn!
If I went to slow down, or if I shut it off, I could not get back to the higher RPM's though.
That led me to think that it might be a sticking throttle or shift cable, or exhaust valve, or something that by moving the throttle lever and cables back and forth, or when that left sided pressure was applied, or right side pressure of that component was relieved, then something "opened up" or got "unstuck", and returned to motor spec, and the motor responded with normal operating parameters leading to expected throttle response.
I could not re-create this phenomenon every time, but it was happening about 1/2 the time.
I should mention that this speed zone runs counter-clockwise, so I didn't get a chance to test a hard right turn at WOT yet.
I know... it sounds nuts.

Doesn't sound nuts...sounds electrical. Though could also be that the carb is fueling differently because of the angle. Any change when hitting a wake?
Have you checked spark at speed? Rereading the thread I see that the spark was checked at idle, but not under load? I'm broken record about this, but throwing a timing light on the coil wire/each plug wire is invaluable for tracking down a high speed miss. Also, have you wiggle tested the connections? Just grab some wires and see if anything changes when you shake em...

 

[GeorgioP07]

Alright, I did a test run tonight with the fuel pressure gauge inline.
I was reading 4.5PSI at idle and 4.2PSI at 2500RPM.
Tried using a hand-held tachometer to validate the dash tachometer, was not working, will try that again later.
The motor started up well into this run.
Please take a look at the video and let me know what you think.
You can definitely hear the sucking sound of the TKS, as the engine was cold just before this video.
Right after this run, I tried to restart it just as before, and it would not restart, after two tries, I called it a night. Thanks,

 

[Scott06]

Alright, I did a test run tonight with the fuel pressure gauge inline.
I was reading 4.5PSI at idle and 4.2PSI at 2500RPM.
Tried using a hand-held tachometer to validate the dash tachometer, was not working, will try that again later.
The motor started up well into this run.
Please take a look at the video and let me know what you think.
You can definitely hear the sucking sound of the TKS, as the engine was cold just before this video.
Right after this run, I tried to restart it just as before, and it would not restart, after two tries, I called it a night. Thanks,

I think when it doesnt restart take a spark gap tester see if you have spark if you do dribble some gas down the carb , if it restarts then you are missing gas. Just gotta figure out if its spark or fuel. Hard to tell form the keyboard but if yo have good spark and timing is right it should fire if you dribble gas down unless it flooded. if flooded you open throttle wide to clear it just be ready to pull it back if it catches...

 

[alldodge]

After the run did the loud sucking sound stop?

Looking down the carb right after turning motor off, was there any fuel dripping?

 

[GeorgioP07]

I think when it doesnt restart take a spark gap tester see if you have spark if you do dribble some gas down the carb , if it restarts then you are missing gas. Just gotta figure out if its spark or fuel. Hard to tell form the keyboard but if yo have good spark and timing is right it should fire if you dribble gas down unless it flooded. if flooded you open throttle wide to clear it just be ready to pull it back if it catches...

Hi, There is always spark to all 4 cylinders. I already did the spark gap test on all 4 cylinders. Timing was tested a month ago and it is correct. I never replaced the ignition coil because the consensus here was, - it's all or none. Are you saying to pour gas into the carburetor when it does not start? Thanks.

 

[GeorgioP07]

After the run did the loud sucking sound stop?

Looking down the carb right after turning motor off, was there any fuel dripping?

Hello, The TKS Sucking sound stops after a few minutes.
I'll have to take off the flame arrestor and check for gas dripping after turning off the motor.
There seems to be about 4PSI in the fuel line at all times, according to the inline pressure gauge that I installed.
If 4.0 PSI is my baseline inline fuel pressure while not running, and running at idle is 4.5 PSI, and running at 2500 RPM goes to 4.3 PSI, - does that sound like enough gasoline would be reaching the carburetor inlet if I bump it to 3000 RPM when the boat is on the water? I does that when on muffs. Would the fuel pressure inline from the pump to the carburetor change when the motor is under a real load on the water compared to running on muffs?
Thanks.

 

[GeorgioP07]

Also, have you wiggle tested the connections? Just grab some wires and see if anything changes when you shake em...

Hi, I did unplug and re-plug in each wire while running and noticed the same 200-300RPM drop on the tachometer. What else could I do to test for mis-fires? Please watch the video and let me know if you can hear any. Thanks.

 

[Scott06]

Hi, There is always spark to all 4 cylinders. I already did the spark gap test on all 4 cylinders. Timing was tested a month ago and it is correct. I never replaced the ignition coil. Are you saying to pour gas into the carburetor when it does not start? Thanks.

Yes I know you had spark , but when it wont run verify it again to determine why it went from running to not running.

yes dribble some down the carb to see if adding gas changes things.

Also as all dodge suggested look down carb bores when you shut it off to see if bowl is over flowing and flooding it out.

Basically need to look at a few things to see what has changed why wont it run. Do I not have spark now, is there too little/no gas, or is there tooo much gas because carb bowl is over filling and dumping gas and flooding it at shut off.

 

[nola mike]

Hi, I did unplug and re-plug in each wire while running and noticed the same 200-300RPM drop on the tachometer. What else could I do to test for mis-fires? Please watch the video and let me know if you can hear any. Thanks.

I'm talking about all connections everywhere, not just the plug wires. I already mentioned how to test for misfires under load. At 3k rpm you might not hear much. your fuel pressure sounds fine. I'm also in the minority here where sometimes it is the coil.

 

[alldodge]

Hello, The TKS Sucking sound stops after a few minutes.
I'll have to take off the flame arrestor and check for gas dripping after turning off the motor.
There seems to be about 4PSI in the fuel line at all times, according to the inline pressure gauge that I installed.
If 4.0 PSI is my baseline inline fuel pressure while not running, and running at idle is 4.5 PSI, and running at 2500 RPM goes to 4.3 PSI, - does that sound like enough gasoline would be reaching the carburetor inlet if I bump it to 3000 RPM when the boat is on the water? I does that when on muffs. Would the fuel pressure inline from the pump to the carburetor change when the motor is under a real load on the water compared to running on muffs?
Thanks.

Your fuel pressure is good so this is no longer part of the problem

If the carb is flooding the motor than that is why it won't start, but if it's not dripping then it's not fuel and it's spark

It could be after things warm up and motor is turned off something isn't getting enough power. This would not explain why you can't get the rpm just why it won't start

 

[Scott06]

has a sample of fuel been taken and put in a clear jar to see if there is water or contamination?

Did this with my buddies boat this summer and it turned milky in about 5 min...