Mid Throttle Lean Condition

Goldie627

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1986 Sea Ray
Mercruiser 140 3.0
140 GM 181 I/L4 1982-1986 - 6229718 THRU 0B450800

The good:
Boat starts right up, even with the first cold start. Engine has a small shake but for a forty year old motor, I'm not complaining. Gets on plane, highest rpm i took it was 3200 3300, that was plenty fast enough for me, I'm an old guy :D just trying to get from fishing spot to fishing spot. Gps from phone, showed speed was about 32mph.

Problem:
Boat has no mid range throttle, wants to gasp and/or cut out, seems like a lean condition in the mid throttle range. Occurs between 900 and around 1200 rpm (grains of salt here, that's by the dash tach).

Accelerating up from neutral or a no wake speed will cause the engine to fall flat on its face, you either have to back off the forward throttle or accelerate past the dead spot. Decreasing speed down from being on plane will cause the motor to run real weak and just sputter along in the dead spot.

Im 98% sure its not the accelerator pump, I rebuilt my old carb 3 times before purchasing the new oem carb and the mid throttle lean condition persists.

My compression results:
1 155
2 165
3 170
4 175

My vacuum at engine idle:
Fluctuates between 13 and 14

Things I've done to trouble shoot, improve performance and overall health of the motor:
  • new oem carb
  • new electronic ignition conversion kit, included distributor, spark plug wires and coil (sierra 18-5518)
  • new spark plugs
  • new oem fuel pump
  • new fuel lines
  • pressure tested and cleaned gas tank interior before powder coating exterior
  • new gas tank pick up
  • new metal fuel line (from fuel pump to carb)
  • timing set just a hair above 6 BTDC
  • only use chevron supreme gas
  • disconnected/bypassed the shift interrupt
  • tried coil with 12v and with resistance wire, no difference
  • disconnected the gas tank breather hose
  • ran boat on external gas jug (bypassed boat gas tank)
fuel pump filter and carb filter look brand new​
I'm truly stumped...
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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change your lower shift cable and adjust the shift interupt switch
 

Goldie627

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Hi Scott, over the summer i picked up a new SEI out drive, just before that I purchased a new lower cable around the time I rebuilt the gimbal housing. Boat is coming off a four year restoration and the only time its been on the water was for testing. been fishing a few times. :) I know the cable can stretch but its pretty much new. The boat shifts into forward, neutral and reverse without problem. Should i still pursue your suggestion? You think when the accelerator cable moves its causing the shift cable to move?
 

Goldie627

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After thinking... I remember not being able to adjust the lower cable to spec because the engine would cut off when switching gears, i went out of spec and adjusted it to where it would work... (shift without cutting off)
 

Goldie627

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at one point i thought shift interupt too, i had my niece advance the throttle while i looked at the **** interrupt and i didn't visually notice it attempting to move..
 

Bondo

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Boat has no mid range throttle, wants to gasp and/or cut out, seems like a lean condition in the mid throttle range. Occurs between 900 and around 1200 rpm (grains of salt here, that's by the dash tach).

Accelerating up from neutral or a no wake speed will cause the engine to fall flat on its face, you either have to back off the forward throttle or accelerate past the dead spot. Decreasing speed down from being on plane will cause the motor to run real weak and just sputter along in the dead spot.

Im 98% sure its not the accelerator pump, I rebuilt my old carb 3 times before purchasing the new oem carb and the mid throttle lean condition persists.

Ayuh,.... To Test the carb theory, run it in the Bad Zone, makin' it run bad, maybe til it dies, then shut it off if it hasn't died, 'n check the spark plugs,....
Are they dry, 'n white, or wet, 'n black,....

To Test the shift switch theory, go run it with the shift switch unplugged,.....
Just pull it back in, before ya return to the dock,....
 

Goldie627

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Ayuh,.... To Test the carb theory, run it in the Bad Zone, makin' it run bad, maybe til it dies, then shut it off if it hasn't died, 'n check the spark plugs,....
Are they dry, 'n white, or wet, 'n black,....

To Test the shift switch theory, go run it with the shift switch unplugged,.....
Just pull it back in, before ya return to the dock,....

Hi Bondo, yesterday I took the boat out for a few hours to test a reccomendation. Somebody told me to try gapping the plugs to 40 instead of spec which is 35. To my best memory, all were dry and maybe 2 or 3 were partially white. Next weekend I can take the boat out, run it in the bad zone as much as I can but may be challenging cuz it likes to cut out,

I could get on plane, then drop down to the bad zone then it will just sputter without dying.

I'm checking my manual now for partially white spark plugs... to see what that indicates

Also i put the gap back at 35 because 40 seemed a tiny bit smoother at idle but didn't solve my mid throttle lean condition

Also, I don't think my shift interupt has a plug, it's on top of the valve/rocker arm cover and it has wires on it, when I leave the doc I can unscrew all the wires
 
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Goldie627

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Also color could may be more of a light grey, I'll snap some pics so you can see it, not completely white/grey either
 
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Rick Stephens

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What you can expect on a short test run is a little bit of color. This pic, just dug off a search, is actually pretty good and about what to expect.

Screen Shot 2017-12-04 at 7.24.11 PM.png


Pretty simple. You want a fairly clean looking insulator and light tan electrode, like the pic. Lean will start to show tan or white deposits. Rich is easy, black and maybe even wet.


If you remove the wire(s) from one side of the interrupt switch it will no longer stall the motor. Easy to test, with all wires in place, push the switch to the side and the motor dies. With a wire disconnected, push it and nothing will happen.

Rick
 

Goldie627

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What you can expect on a short test run is a little bit of color. This pic, just dug off a search, is actually pretty good and about what to expect.




Pretty simple. You want a fairly clean looking insulator and light tan electrode, like the pic. Lean will start to show tan or white deposits. Rich is easy, black and maybe even wet.


If you remove the wire(s) from one side of the interrupt switch it will no longer stall the motor. Easy to test, with all wires in place, push the switch to the side and the motor dies. With a wire disconnected, push it and nothing will happen.

Rick

Thanks Rick! I'm taking the boat out Saturday to test the shift interupt and to take pics of my spark plugs after it's warmed up and running for a while
 

Bondo

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and to take pics of my spark plugs after it's warmed up and running for a while

Ayuh,.... For a proper spark plug readin', ya gotta run it in the bad zone, 'n reasonably quickly, kill it,....

The spark plug color is determined by the time run at whatever throttle settin',....
Plugs that have been idlin', reflect Only the idle mode, ditto Wot, or mid-range,...
 

Goldie627

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Ayuh,.... For a proper spark plug readin', ya gotta run it in the bad zone, 'n reasonably quickly, kill it,....

The spark plug color is determined by the time run at whatever throttle settin',....
Plugs that have been idlin', reflect Only the idle mode, ditto Wot, or mid-range,...

Thanks Bondo! The first thing im gonna do after i get away from the doc no wake zone is bypass the shift interupt, after I do that test I'll run it in the bad zone a lil if possibe then make it die, I will not restart the motor until I've checked all 4 spark plugs.... Hopefully the spark plug pics will tell the story...

I'm really hoping it's the shift interupt, my buddy scott wants to bet me 5 bucks thats what it is! Lol

If it turns out to be that simple, oh my gosh...

I've been chasing this ghost for months, this is one of the last two things I have to do before I call my boat done. This and finish fabbin the top of the ice chest.

I do need to change my oil pan gasket but I really wanna have a chance to enjoy my boat for a few seasons before I pull the motor again.

Saturday cant get here fast enough!
 

Goldie627

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I was just thinking... While I'm out there i should test the voltage from the resister wire, if it's too low or too high I wonder could it cause the mid throttle problem? I'm gonna call Sierra marine tech support and double check their coil and distributer required voltages.

I remeber from the install it said to use the resister wire but I don't recall it stating what voltages were required...
 

Goldie627

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So I've been trying to dig up info on my electronic ignition kit in search of proper voltages. I was not able to find a manual anywhere as I have lost the manual that came with the kit. The original manual that came with the kit said specifically to use the resistance wire. However, the kit came with an internal resistance coil. This made me scratch my head.... maybe double resistance is not correct? Meaning, the use of a resistance wire with an internal resistance coil could be causing my mid throttle problem???

I called Sea Star (tech support for Sierra Marine) and the tech said I don't need the resistance wire if I have an internal resistance coil. He said to run 12volts to the coil. While cranking i should get 12volts then in the run position I should get 9 to 10 volts.

During my research I learned that MSD has bought Mallory. 18-5486-2 was originally made by Mallory, part number YLM624AV. So I called MSD technical support. He said that my distributor has a 12 volt module and the coil should be 1.5 ohms. He also stated that if the coil is less than 1ohm I need a resistance wire, if the coil is 1.5ohm or more i don't need a resistor wire.

So.... I think what i need to do is check the coil ohms as it is now with the resistor wire going to the coil, then check the coil ohms again with 12volts going to the coil.

Honestly, I'm a lil confused. But I think this is worth looking at.
 

Scott Danforth

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a Mallory YLM624AV is a V8 distributor for a SBC/BBC motor. one with inductive trigger. I know, I have two of them.

the Sierra part number 18-5486-2 is the same dizzy... the dizzy is now 2X the cost it was prior to prestolite selling Mallory to the MSD group. i paid just about $250 in 2014. they are now $509 when you find them on-sale list price is $750

your motor is a 3.0.

if you have the YLM624AV dizzy, you have the wrong dizzy for your motor. are you sure you have the right part number?

the 2.5/3.0 uses Mallory YLM673AV (induction trigger) or YLU673AV (optical trigger)

however on another note, if your looking at your dizzy, your looking in the wrong spot.... it either sparks....or it doesnt

go to post #7, do the tests
 
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Goldie627

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a Mallory YLM624AV is a V8 distributor for a SBC/BBC motor. one with inductive trigger. I know, I have two of them.

the Sierra part number 18-5486-2 is the same dizzy... the dizzy is now 2X the cost it was prior to prestolite selling Mallory to the MSD group. i paid just about $250 in 2014. they are now $509 when you find them on-sale list price is $750

your motor is a 3.0.

if you have the YLM624AV dizzy, you have the wrong dizzy for your motor. are you sure you have the right part number?

the 2.5/3.0 uses Mallory YLM673AV (induction trigger) or YLU673AV (optical trigger)

however on another note, if your looking at your dizzy, your looking in the wrong spot.... it either sparks....or it doesnt

go to post #7, do the tests
Hey Scott, I apologize for the confusion. My distributer has no downloadable manual and no data sheet. The company that I bought the kit from does'nt tell you the model numbers of each part so i searched the internet for a site that sales the kit and lists the part numbers https://www.********************/sier...onversion-kit/ For sure my kit is 18-5518. Even the 2017 Sierra Marine catalouge doesnt tell you the part numbers in the kit http://sierramarine.com/pdfcatalog/2...earchmain.html

The whole reason i was thinking dizzy is because the coil that came with the kit ([FONT=&quot]18-5435 if this is the correct coil)[/FONT] has an internal resistance and im using a resistance wire to the coil instead of raw 12v. This may make it more resistence than neccessary and i was thinking the dizzy wasnt getting enough voltage. In other words it sparks but if theres too much resistannce maybe doesnt spark hot enough. I know , i know... im a noob!!! :bounce:

just thought of something... if i didnt have good spark i probably couldnt get on plane....

But like you said, go with lucky number 7 :D

if the stuff in seven checks out ok i was tryning to have another trick up my sleave while out on the water.
 

Goldie627

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Hello All, I disabled the shift interrupter, still had the mid throttle lean condition. Drove the boat in the mid throttle area and the engine shut down on its own. I did not restart. I immediately pulled the plugs. And here we are.... Also tried coil with 12volts instead of the resister wire, no difference... 20171209_132520.jpg
20171209_132523.jpg
20171209_132528.jpg
20171209_132534.jpg
 
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