Mid Throttle Lean Condition

Goldie627

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Oct 28, 2013
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1,010
...... If the exhaust shutters are burned out, that could hydro-lock the engine, when the stern wake catches up with the boat. It happened to me once when my ignition switch decided to give up the ghost running at cruise speed, the shutters were burned out and the engine cutting off, resulted in a hydro-locked engine....

I'd run it on plane for 5 min, come off plane quickly and blip the throttle just as the stern wake catches up, then cut the engine. ......

Thanks Dan, last summer I installed a new exhaust shutter, I should be ok, I appreciate the heads up though
 

Davetowz

Petty Officer 1st Class
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Sep 19, 2012
Messages
227
I was having similar odd issues on a different engine, the troubleshooting baffled me. I di everything, carb, IGN Fuel pump. Ended up being the god forsaken anti siphon valve at the fuel tank. Looked like a normal 90 degree NPT to barbed fitting, except for the spring and ball inside :)
. And the grass that was stuck in it. Replaced it and all was good.
 

Rick Stephens

Admiral
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Aug 13, 2013
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6,118
I was having similar odd issues on a different engine, the troubleshooting baffled me. I di everything, carb, IGN Fuel pump. Ended up being the god forsaken anti siphon valve at the fuel tank. Looked like a normal 90 degree NPT to barbed fitting, except for the spring and ball inside :)
. And the grass that was stuck in it. Replaced it and all was good.

Goldie removed and totally cleaned his entire fuel system. And it seems to me a plugged up AS would hit high end more than low end throttle.
 

Goldie627

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The float levels were almost perfect. Spring loaded needle float spec 14mm my float was 15mm. Float drop spec 32mm my float drop was 30mm. After all the screws were out, unfortunately, I damaged the gasket beyond resuing when I lifted the top of the carb off the carb body. I have the stuck on gaskets soaking in some silicone spray lubricant. Hopefully in the morning the gaskets will pull right off. I'll take the gasket from the old carb I rebuilt and install it on the new carb.

Im going out 2maro to snap some pics of the spark plugs so we can see what they look like on plane. While im out there for giggles ill run the motor on a gas can.

After that trolling for strippers!!!

Local tackle shop had no tax friday today so i picked up a few things.

Im seriously thinking about snatching my motor out and doing the oil pan gasket and the acetone test on my intake...

20171215_125356.jpg

20171215_125311.jpg

The worms are trailers for the deep divers...
 
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Goldie627

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I got a feeling, if i take the motor out to do the oil pan gasket, i should just go ahead and do the rear main seal while im there...

I cant find any 1 piece oil pan gaskets, what do you guys think about the 4 piece oil pan gasket? Ive heard to stay away from kork when i can..
 

Goldie627

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Joined
Oct 28, 2013
Messages
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I was having similar odd issues on a different engine, the troubleshooting baffled me. I di everything, carb, IGN Fuel pump. Ended up being the god forsaken anti siphon valve at the fuel tank. Looked like a normal 90 degree NPT to barbed fitting, except for the spring and ball inside :)
. And the grass that was stuck in it. Replaced it and all was good.
Thanks Dave, but like rick mentioned my fuel system is pretty durn clean, doesnt even have a full season on it yet, just test running here and there then dropping in a few lines while im out tinkering with the motor. Your post did make me think though, i havent tried to take the gas cap off to see if it still goes lean in the 1000rpm range without it, I also havent diconnected that air escape line i believe it depreasureises the gas tank. The line is new but the pass through fitting where it goes through the transom is the original fitting. I know its a long shot but i dont have anything to lose checking it out.
 

boatman37

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May 14, 2015
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1,273
Not a fan of cork gaskets here either. I try to always use Fel-Pro. Not sure what the material is but kinda rubbery stuff
 

Goldie627

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Not a fan of cork gaskets here either. I try to always use Fel-Pro. Not sure what the material is but kinda rubbery stuff

exactly! im just not getting my hopes up that i can get a felpro for my application (mercruiser 140 3.0)
 

Goldie627

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As the trouble shooting progresses I'm updating the first post.

These are the spark plugs after 2000rpm for 5 minutes... maybe i shouldn't have used the camera flash...

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Goldie627

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So me and my brother Scott was talking today when I got back from taking the boat out. We are both so stumped. I don't think its Fuel and I dont think its Ignition. I do think Rick is on the right path though... but im not so sure its a internal intake leak persay. One thing for sure is that my vacuum fluctuates between 13 and 14. A healthy motor vacuum has a solid needle around 17 to 22 and does not fluctuate. Mercruiser manual says for my motor 15 to 21 is normal.

So, the low vacuum is causing the carb not to be able to pull down enough gas at low rpm?

There is no external intake leaks i've checked more times than I'd like to admit, always thinking i missed it the last time i checked! :D:rolleyes::)

So the million dollar question is, what is most likely causing the low manifold vacuum?

internal intake leak?
bad valve springs?
bad valve guides?
bad cam?

Rick, could i have an internal intake leak with 13 to 14 vacuum? From what i've been reading an intake leak shows/causes really low vacuum. I don't know if the really low vacuum is from external leaks and maybe the internal leaks cause less vacuum loss?

No water in oil, if it was the head i think i would overheat on plane...
 
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Goldie627

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Also, if i had an internal intake leak, would i see oil on the spark plugs? or in the intake when removed the carb?
 

Bondo

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Messages
70,468
Also, if i had an internal intake leak, would i see oil on the spark plugs? or in the intake when removed the carb?

Nope,.... There's No oil there,....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
47,307
So me and my brother Scott was talking today when I got back from taking the boat out. We are both so stumped. I don't think its Fuel and I dont think its Ignition. I do think Rick is on the right path though... but im not so sure its a internal intake leak persay. One thing for sure is that my vacuum fluctuates between 13 and 14. A healthy motor vacuum has a solid needle around 17 to 22 and does not fluctuate. Mercruiser manual says for my motor 15 to 21 is normal.

So, the low vacuum is causing the carb not to be able to pull down enough gas at low rpm?

There is no external intake leaks i've checked more times than I'd like to admit, always thinking i missed it the last time i checked! :D:rolleyes::)

So the million dollar question is, what is most likely causing the low manifold vacuum?

internal intake leak?
bad valve springs?
bad valve guides?
bad cam?

Rick, could i have an internal intake leak with 13 to 14 vacuum? From what i've been reading an intake leak shows/causes really low vacuum. I don't know if the really low vacuum is from external leaks and maybe the internal leaks cause less vacuum loss?

No water in oil, if it was the head i think i would overheat on plane...

what does your compression look like on all 4 cylinders?
 
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