Merc 3.0 does not start easy when warm

[Bullrider]

1995 mercruiser 3.0
New coil,new plugs,new cap n rotor. This engine starts like a champ when cold and purs well. When it gets warm it gets harder to start.I have to start it as if it were flooded when hot. It diesels like mad when I shut it off hot as if my idle is set too high.

My real question is could my automatic choke be a part of the problem? The butterfly valve stays wide open even when I unlatch it while cold. I would think It shouldnt start so well cold with an open butterfly valve but it appears this is happening. Im thinking a defective automatic choke could hamper hot starts.
Or could my issue be the engine is flooding as I shut it down from a too high an idle setting and making a hard start when hot?
Im reading about 1200 RPMs at Idle with my gauge but the engine sounds to me like 800ish and doesnt sound like it could go much lower. I assumed I have an inacurate gauge...
any thoughts?

 

[s.hadley81]

Re: Merc 3.0 does not start easy when warm

Not sure but did you check your timing and set idle mixture screw also I would definetly look into that high idle it's not good shifting in gear with a high idle I have 2.5l and my idle in the water is around 650rpm. Just my 2 cents

 

[alldodge]

Re: Merc 3.0 does not start easy when warm

1995 mercruiser 3.0
New coil,new plugs,new cap n rotor. This engine starts like a champ when cold and purs well. When it gets warm it gets harder to start.I have to start it as if it were flooded when hot. It diesels like mad when I shut it off hot as if my idle is set too high.

My real question is could my automatic choke be a part of the problem? The butterfly valve stays wide open even when I unlatch it while cold. I would think It shouldnt start so well cold with an open butterfly valve but it appears this is happening. Im thinking a defective automatic choke could hamper hot starts.
Or could my issue be the engine is flooding as I shut it down from a too high an idle setting and making a hard start when hot?
Im reading about 1200 RPMs at Idle with my gauge but the engine sounds to me like 800ish and doesnt sound like it could go much lower. I assumed I have an inacurate gauge...
any thoughts?

Your correct the choke plate should be closed are almost closed when cold. Only thing that could change that is if the outside temp is hot. Pull the plugs and have a look, I'm thinking they are probably black. Agree with s.hadley, need to check the timing and get a hand held tach and have the idle set correctly.

 

[airshot]

Re: Merc 3.0 does not start easy when warm

Sounds like you need a factory service manual, If my memory serves me correctly the idle is 600-650 while in gear in the water. May also have a need for a rebuilt carb, from your story it may be that it is running so rich that it starts easily in the cold but way to rich for warm starts. Sounds as though a complete tuneup and rebuild may be in order. The carb rebuild will give you the proper settings for your elec choke as well.

 

[thumpar]

Re: Merc 3.0 does not start easy when warm

A high idle and rich mixture can cause dieseling. Most tachs have a switch on the back. Move it around a bit and then back for 4 cylinder setting. Sometimes they get dirty.

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Thank you for the great input!

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Along with this I have some old gas in there (about 2/3 of the tank) I figure as soon as that is out I can make a more acurate judgment. The previous owner said he used Stabil always for wintering.Ive been told to use some Seafoam. I thought the deiseling could be from a loss of octane as too. When I did a test run before purchacing this boat It did not have an issue. That makes me think ethanol gas sitting for months is a factor.
My shop manual suggests taking that gas out and running it through the car. Funny! Either way I dont mind rebuilding the carb if I have too.

 

[UNSUREBOATGUY]

Re: Merc 3.0 does not start easy when warm

I had the same problem with an otherwise great running engine. My carb was leaking a little bit after shut down and flooding a bit-made it pretty hard to start after sitting for a few minutes when warm. Rebuilt the carb ans it starts much better warm now. Timing and correct idle speed are important as already stated, but you might have a hard time getting the idle down and have the engine run smooth if the carb needs work. Just based on my little experience Good luck.

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

I had the same problem with an otherwise great running engine. My carb was leaking a little bit after shut down and flooding a bit-made it pretty hard to start after sitting for a few minutes when warm. Rebuilt the carb ans it starts much better warm now. Timing and correct idle speed are important as already stated, but you might have a hard time getting the idle down and have the engine run smooth if the carb needs work. Just based on my little experience Good luck.

Wow thank you! Good info

 

[tinkerguy70]

Re: Merc 3.0 does not start easy when warm

Along with this I have some old gas in there (about 2/3 of the tank) I figure as soon as that is out I can make a more acurate judgment. The previous owner said he used Stabil always for wintering.Ive been told to use some Seafoam. I thought the deiseling could be from a loss of octane as too. When I did a test run before purchacing this boat It did not have an issue. That makes me think ethanol gas sitting for months is a factor.
My shop manual suggests taking that gas out and running it through the car. Funny! Either way I dont mind rebuilding the carb if I have too.

I don't think the fuel is your problem, it's usually takes longer than a few months for pump gas to get bad enough to cause issues.

 

[havoc_squad]

Re: Merc 3.0 does not start easy when warm

Sounds like you have a slow fuel leak through the venturies or the idle mixture circuit into the carb body.

A high idle speed set by someone will try to mask the issue of the too much fuel and not enough air mix at the setting where normal idle speed should occur. A higher idle speed adds extra air to prevent the engine from choking itself due to flooding.

Does opening the throttle to full when you start it warm in the water allow it fire and run when you pull the throttle back down?

If so you have a slow flooding/overriching issue with your carb.

Recommended steps:

Buy a multi-meter that supports tach readings or learn by ear what 650-700 rpm at idle sounds like. You better be accurate if you are using your ear.

Get a timing gun and check that timing first per service manual specs while the engine is at service manual spec idle in base time mode. This you can probably at home with the muffs.

Next, get the boat in the water and bring a helper. You need to get the engine fully warmed up, go for a 5 minute 25 mph run and return back to a place where you can have the boat at idle in gear. You'll want to do this out of heavy boat traffic, but near others if an emergency comes up.

Take the flame arrestor off while engine is running and put it in gear in idle. Get that idle speed down to 550 to 650 on that engine. Keep a close eye on those Venturi bowls on the Mercarb while another drives the boat. No vapor or dripping of fuel should be happening, if it does you have carb issues.

There is the possibility of a slight flooding condition upon engine shutoff and when running if the carb's needle and seat is not giving a complete seal while at idle when the fuel bowl is full.

If nothing obvious is found after at least 5 minutes of being in gear at idle, stop the boat, let the engine run for 30 seconds in neutral, then kill the engine.

If it diesels still, it sounds like you have an overly rich mixture or slight flooding. You could possibly try to adjust the idle air mixture screw to fix this, but you have to know the service manual limitations of changing this. Idle air mixture adjustment will not fix a carb needing rebuilding.

The only other option not mentioned originally is fuel pump over-pressurizing. If you have a flooding condition, make sure you have 5-1/4 - 6-1/4 PSI at specified at 600 to 700 rpms going to the carb. If it is higher than this, you have a fuel pump issue. Such an issue is usually easy to notice with fuel dripping from the Venturies at idle, which they should not dispense fuel at low rpm's.

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Sounds like you have a slow fuel leak through the venturies or the idle mixture circuit into the carb body.

A high idle speed set by someone will try to mask the issue of the too much fuel and not enough air mix at the setting where normal idle speed should occur. A higher idle speed adds extra air to prevent the engine from choking itself due to flooding.

Does opening the throttle to full when you start it warm in the water allow it fire and run when you pull the throttle back down?

If so you have a slow flooding/overriching issue with your carb.

Recommended steps:

Buy a multi-meter that supports tach readings or learn by ear what 650-700 rpm at idle sounds like. You better be accurate if you are using your ear.

Get a timing gun and check that timing first per service manual specs while the engine is at service manual spec idle in base time mode. This you can probably at home with the muffs.

Next, get the boat in the water and bring a helper. You need to get the engine fully warmed up, go for a 5 minute 25 mph run and return back to a place where you can have the boat at idle in gear. You'll want to do this out of heavy boat traffic, but near others if an emergency comes up.

Take the flame arrestor off while engine is running and put it in gear in idle. Get that idle speed down to 550 to 650 on that engine. Keep a close eye on those Venturi bowls on the Mercarb while another drives the boat. No vapor or dripping of fuel should be happening, if it does you have carb issues.

There is the possibility of a slight flooding condition upon engine shutoff and when running if the carb's needle and seat is not giving a complete seal while at idle when the fuel bowl is full.

If nothing obvious is found after at least 5 minutes of being in gear at idle, stop the boat, let the engine run for 30 seconds in neutral, then kill the engine.

If it diesels still, it sounds like you have an overly rich mixture or slight flooding. You could possibly try to adjust the idle air mixture screw to fix this, but you have to know the service manual limitations of changing this. Idle air mixture adjustment will not fix a carb needing rebuilding.

The only other option not mentioned originally is fuel pump over-pressurizing. If you have a flooding condition, make sure you have 5-1/4 - 6-1/4 PSI at specified at 600 to 700 rpms going to the carb. If it is higher than this, you have a fuel pump issue. Such an issue is usually easy to notice with fuel dripping from the Venturies at idle, which they should not dispense fuel at low rpm's.

Thank you so much for the great input!
I am going to rebuild the carb for a god start. Ive decided to siphon the gas out and start with fresh and noticed a crack in my fuel line between the filter and pump, not sure if that aggravates the issue. Also trying to siphon from the fuel line to the pickup tube in the tank was difficult so I opened the sensor hole to pull out the gas. There are a lot of chunks in the fuel.
The engine didn’t struggle at WOT so I guess the engine didn’t notice some restrained fuel feed…or could that make it run lean and hot and diesel?
I checked the temp after a few minutes out on the water at full speed. The temp gauge said 160,the hand held laser said 116-121 all around the head and around the spark plugs.
I am believing there is varnish in the carb causing things act up too.

The engine still fires as soon as I touch the key when cold. After warming up a little the idle drops lower and lower till it wants to stall. A quick pump brings it to life for about a half minute.
Your question about “fire and run after dropping throttle” does not happen. All throttle action gives a good response either way.

 

[havoc_squad]

Re: Merc 3.0 does not start easy when warm

Get the timing verified first per service manual procedure, then check the fuel pressure to the carb.

Extremely doubtful you have a fuel flow restriction, your issue is too much gas, not too little.

If both those check out as okay, I'm suspecting flooding from the carb.

The reasons for this statement:

Starts well when cold. (Cold engines require a richer fuel/air mixture to run and stay running, warm engines require a leaner fuel air mixture). That's why a choke plate restricts the air flow for a cold engine.



Idle drops lower and keeps dropping slowly til it wants to stall (Slow flooding condition, the fuel mix becomes more and more dense to the point which the engine starts to choke on its own gas).

If you have to work the throttle ANY to get it started immediately after the boat dies from stalling, you are clearing a flooding condition. A boat engine should have enough fuel vapor in the intake manifolds to immediately restart the engine for a carb'ed engine.

Also, if you pump the throttle, you are only allowing extra air to stop the flooding condition. The carb doesn't put out much gas until you start getting at high rpm's, +1800 rpms.

 

[oldjeep]

Re: Merc 3.0 does not start easy when warm

Simple thing to check. What octane fuel are you running. Regardless of what the manual said, my 2005 3.0L didn't run worth a crap on anything under 91 octane. When I used the lower grades of fuel it would diesel like crazy on shut down, had hot start issues. With 91 all those issues went away.

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Thank you guys!

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Get the timing verified first per service manual procedure, then check the fuel pressure to the carb.

Extremely doubtful you have a fuel flow restriction, your issue is too much gas, not too little.

If both those check out as okay, I'm suspecting flooding from the carb.

The reasons for this statement:

Starts well when cold. (Cold engines require a richer fuel/air mixture to run and stay running, warm engines require a leaner fuel air mixture). That's why a choke plate restricts the air flow for a cold engine.



Idle drops lower and keeps dropping slowly til it wants to stall (Slow flooding condition, the fuel mix becomes more and more dense to the point which the engine starts to choke on its own gas).

If you have to work the throttle ANY to get it started immediately after the boat dies from stalling, you are clearing a flooding condition. A boat engine should have enough fuel vapor in the intake manifolds to immediately restart the engine for a carb'ed engine.

Also, if you pump the throttle, you are only allowing extra air to stop the flooding condition. The carb doesn't put out much gas until you start getting at high rpm's, +1800 rpms.

I have finished rebuilding my carb. I replaced the solid pin in the needle valve with the optional spring and pin. This is said to reduce the flooding issue.
After reassembly I noticed the throttle lever that actuates the accelerator pump is manufactured WITHOUT the adjustable tang to bump the choke open a little. I have asked around and am looking online to see if I have an odd 9562-2 (1602) two barrel made in 1995. It appears the only thing affecting the choke is the bimetalic coil.
Anyone experienced with this anomally?

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

I installed my rebuilt carb and it works well. I no longer have the flooding issue. The springs and post on the needle works better than the solid pin.Thank you all for your input!!
Now to get out for a sea (lake) trial!

 

[alldodge]

Re: Merc 3.0 does not start easy when warm

Sounds great, it is boating time

 

[havoc_squad]

Re: Merc 3.0 does not start easy when warm

Good to hear, the spring loaded needle usually should end up being the last option in the flooding resolution list.

I believe Mercruiser put out a service update regarding this matter and the diagnostic procedures. It's probably easily findable through a Google search.

Hopefully the lake trial goes well.

Don't forget all, the Allstate mayhem man can't be far behind now that boat season is soon to arrive. If there's an idiot that can be on the water or something that can fail on the boat, he's not far behind.

Mayhem man: "I'm the worn out impeller in your boat's outdrive that cooks the engine like a burnt steak because the previous owner told you it was lake ready and well maintained."

 

[Bullrider]

Re: Merc 3.0 does not start easy when warm

Good to hear, the spring loaded needle usually should end up being the last option in the flooding resolution list.

I believe Mercruiser put out a service update regarding this matter and the diagnostic procedures. It's probably easily findable through a Google search.

Hopefully the lake trial goes well.

Don't forget all, the Allstate mayhem man can't be far behind now that boat season is soon to arrive. If there's an idiot that can be on the water or something that can fail on the boat, he's not far behind.

Mayhem man: "I'm the worn out impeller in your boat's outdrive that cooks the engine like a burnt steak because the previous owner told you it was lake ready and well maintained."

Good advice. Thank you.