3.0L will not idle at sea level

SoCalBayliner · Jun 26, 2012

I recently purchased a 2004 Bayliner 175 with a 3.0 Mercruiser, the previous owner only ran the boat at Big Bear (~6700 ft above sea level) i took it to Lake Elsinore (~1300 ft) and it would not idle, I managed to get it out of the no wake zone and it ran fine at high RPM around the lake but when i backed off it would die. I thought it was re-jetted for high altitude but it does have the stock 1.55mm jets. I have read that the timing can be adjusted for high altitude operation, but would that keep it from idle down at 1300'? The previous owner had it tuned to run at high altitude but does not know what they did, i can get it to keep running by holding the choke closed with my hand but when i let it open the engine stalls, like it is not getting enough fuel at idle. Any sugestions on what to check would be much appreciated.

oldjeep · Jun 26, 2012

Re: 3.0L will not idle at sea level

Sounds like the idle mixture screw on the carb needs to be adjusted.

SoCalBayliner · Jun 26, 2012

Re: 3.0L will not idle at sea level

I set the idle mixture screw to 1 1/4 turn out per the manual, should i adjust it out further to see if it helps?

oldjeep · Jun 26, 2012

Re: 3.0L will not idle at sea level

SoCalBayliner said:
I set the idle mixture screw to 1 1/4 turn out per the manual, should i adjust it out further to see if it helps?

If it is idling lean then it seems like it would help. I know that on my 2005 it had to be richened up for the engine to idle properly. Dealer at the time said that the carbs ran too lean at the factory setting, especially on E10.

oldjeep · Jun 26, 2012

Re: 3.0L will not idle at sea level

The fact that you can actually get to the mixture screw actually tells you something too. There is a tamper proof cap over it from the factory

SoCalBayliner · Jun 26, 2012

Re: 3.0L will not idle at sea level

Well i removed the tamper proof cap, but i do not know if it had been adjusted before. I will trying adjusting it out further, it still has the fuel in it from last october which was purchased up at Big Bear, i have somewhat ruled out the fuel since it did run at high rpm around the lake, but could the fuel be the problem?

oldjeep · Jun 26, 2012

Re: 3.0L will not idle at sea level

Anything is possible, but if your problem occurs at idle then I would bump the idle mixture up 1/4 turn and see if that fixes it. You're not going to damage anything by idling the motor a little richer to try it out.

Aatcman · Jun 26, 2012

Re: 3.0L will not idle at sea level

oldjeep said:
The fact that you can actually get to the mixture screw actually tells you something too. There is a tamper proof cap over it from the factory

On a 3.0 with a 2bbl mercarb? Really? Could be but I've never seen it....

3 things generally done to adjust for high elevation..

-1 Lean out the idle. Done by turning the idle screw in. You will need to turn it back out...
--Warm up the engine, hook up a vacuum gauge, and adjust idle screw until you get max vacuum -- out = richer, in = leaner

-2 Adjust timing. You will need to adjust it back.
--Put it in base timing mode (see the manual) and shoot the timing. Adjust to manual specs.

-3 smaller jets. You would need to put the original ones back.
--You said it had the factory spec jets, so this is not your issue.

Sometimes float level is adjusted in lieu of changing jets. I assume you have a carb kit since you checked your jets.
-Use the little ruler and check your float level and drop.

Hope this helps

SoCalBayliner · Jun 26, 2012

Re: 3.0L will not idle at sea level

I will check the float level and try turning out the idle mixture screw, where do i hook up the vacuum gauge?

Aatcman · Jun 26, 2012

Re: 3.0L will not idle at sea level

you'll need to open the vacuum port on top of the manifold -- should be plugged with a 1/4" pipe plug.
You'll need to install an adapter to connect your vacuum gauge to.
Put the plug back when you're done.

Hope this helps

oldjeep · Jun 26, 2012

Re: 3.0L will not idle at sea level

kd7isf said:
On a 3.0 with a 2bbl mercarb? Really? Could be but I've never seen it....

Check out Dons post for one of the most famous posts on the internet about fixing the 3.0L idle problems

From the old BOC before it crashed
http://bocweb.yuku.com/topic/3696

SoCalBayliner · Jun 26, 2012

Re: 3.0L will not idle at sea level

I managed to get the "cap" off with out damaging it or the idle screw, with a flat head screw driver, so it went right back on like new.

fishrdan · Jun 26, 2012

Re: 3.0L will not idle at sea level

SoCalBayliner said:
I set the idle mixture screw to 1 1/4 turn out per the manual, should i adjust it out further to see if it helps?

1 1/4 out is just a starting point, you need to adjust the screw in-out from there for best idle. You'll probably need to adjust the idle speed screw also, idle mixture, idle speed, idle mixture, idle speed, etc, until it purrs like a kitten.

I find it kind of hard to believe that a 3.0 tuned to run exclusively at 6700' wouldn't have the main jets leaned out, I'd check them 4X over to make sure they are stock and unmolested.

As kd mentioned, check the timing as they could have bumped it up for that altitude.

Also, what's the engine RPM at WOT and what pitch of prop is on the boat now? I'm guessing they were using a prop with 2-4" less pitch than you need at 1300'. If the engine is going over 4800RPM, you'll need to swap to a prop with more pitch.

Aatcman · Jun 26, 2012

Re: 3.0L will not idle at sea level

Depends who did the tune. Some guys lower the float level instead of changing the jets..

SoCalBayliner · Jun 27, 2012

Re: 3.0L will not idle at sea level

Adjusted the float level to 1 3/32" per the manual and backed out the idle mixture screw 1/2 turn, but did not have any luck getting it to idle. Should i move to larger jets?

Aatcman · Jul 23, 2012

Re: 3.0L will not idle at sea level

SoCalBayliner said:
Adjusted the float level to 1 3/32" per the manual and backed out the idle mixture screw 1/2 turn, but did not have any luck getting it to idle. Should i move to larger jets?

No You should check the float level.

1 3/32 is the "Float Drop". Float drop doesn't affect fuel mixture, having float drop set incorrect will either cause the needle to get stuck or not open far enough.

The "Float Level" is how close to the top the float gets before it shuts off the flow of gas, Turn the air horn upside down and measure from the dot on the float to the gasket. For sea level, it should be 10mm for a solid needle and 14mm for a spring needle. Yours is probably more than this, making the fuel level lower, making the mix leaner.

Bend the float arm to adjust "Float Level" Bend JUST THE TANG to adjust "Float Drop"

Hope this helps

SoCalBayliner · Jul 24, 2012

Re: 3.0L will not idle at sea level

I rebuilt the carb over the weekend and it is running now, i do believe it was the float level that was causing my problem, but the boat had been sitting for 8 months so it didnt hurt to give the carb a good cleaning. it still seems like it idling a little rough so i purchased a timing light yesterday to see if the timing was also adjusted for the altitude and hopefully i can smooth it out a bit. thank you for all the help, saved me a ton of $ not having to take it to the shop.

3.0L will not idle at sea level

Cadet

Admiral

Cadet

Admiral

Admiral

Cadet

Admiral

At-Sea-Man

Cadet

At-Sea-Man

Admiral

Cadet

Admiral

At-Sea-Man

Cadet

At-Sea-Man

Cadet