full throttle in nuetral , to start 3.0 merc bayliner, why?

bob johnson

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Feb 25, 2009
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this is a 3.0 mer in your average 18 ft bayliner. the owner took the carb off and had a mechanic rebuild it, I checked the timing and its dead on according to the book...yes we made the little bypass jumper wire and disconnected some other wire so we got no advance... I thin it was 1 or 2 degrees.

the rpms are just a tad high.... I screwed in the mixture needle....one turn....before that we could hardly start at all!!

now it starts every time If you shift to nuetral and push the thottle ALL the way to the max.... then it starts

seems to be telling me, its getting too much gas.....a few weeks ago when i took the airfilter off and looked down into the carb , it seemed like it was super wet.....like somehow gas is weeping into the carb throat while it sits and when you go to start it...it is loaded with too much gas

anyone got a direction to check?

new plugs
new wires
supposedly professionally rebuilt carb
timed good

???

thanks bob
 

Don S

Honorary Moderator Emeritus
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Messages
62,321
Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

It's normal to use the throttle lever when starting a carbed engine, and it sounds like this boat might be fairly new to you.

Here is a copy and paste from an owners manual on how to start a carbed engine.


Starting And Stopping The Engine

NOTE: Only perform those functions applicable to your power package.
1. Check all items listed in Operation Chart.
2. Place the remote control handle in NEUTRAL.

CAUTION
Overheating from insufficient cooling water will cause engine and drive system
damage. Ensure that there is sufficient water always available at water inlet holes
during operation.


WARNING
Explosive gasoline fumes collect in the engine compartment. Avoid injury or
property damage, operate the bilge blower for at least five minutes prior to starting
the engine. If the boat is not equipped with a bilge blower, open the engine hatch
and leave it open while starting the engine.


3. Push THROTTLE ONLY button and position throttle setting as follows:
a. COLD ENGINE - Move control/throttle lever to full throttle, then return to about 1/4
throttle. In extreme cold it may be necessary to pump lever more than once.
b. WARM ENGINE - Move control/throttle lever to 1/4 throttle position.
c. FLOODED ENGINE - Move control/throttle lever to full throttle. Be prepared to
decrease engine speed to 1000-1500 RPM as soon as engine starts.
IMPORTANT: Do not operate starter motor continuously for more than 30 seconds.
4. Turn ignition key to START. Release key when engine starts and allow switch to return
to ON position.

5. Operate engine for 1 or 2 minutes at fast IDLE (1000-1500 rpm) or until engine temperature
reaches 140-160 degrees F (60-71 degrees C).
6. Inspect the power package for fuel, oil, water and exhaust leaks.
7. To shift into gear, move control handle with a firm, quick motion forward to shift to FORWARD
gear, or backward to shift to REVERSE. After shifting drive unit, advance throttle
to desired setting.
8. Move the remote control handle to NEUTRAL/IDLE and allow the engine to slow to IDLE
speed. If engine has been operated at high speed for a long period of time, allow the
engine to cool at IDLE speed for 3 to 5 minutes.
9. Turn ignition key to the OFF position.
 
Joined
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Messages
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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

Symptoms indicate you're dealing with a flooded carb. Maybe float chamber problem? Did the mechanic "warranty" the rebuild?
 

bob johnson

Rear Admiral
Joined
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Messages
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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

don: its my Gfs boat and It is a 2008 . I have been on the boat the last three years once in a while, and it wasnt that hard to start last year or the year before...earlier this year they got stuck out on the lake twice... thus I suggested they get the carb rebuilt....whe it went back on, things didnt change much... I looked at it and from reading around found the carb mixture needle was out at least 1 turn to far...

but I used the boat yesterday and except for the RETURN to 1/4 throttle.....it does sound like we were operating just like the manual says. although once warm it was a little harder to start.


another guy: I am not sure if it is warrantied, but the guy told my gfs son that he installed the carb on his test engine and ran to verify it was running good...he does that on all his rebuilds....so its kinda hard to tell him its his fault if it runs on his motor , but not ours!

bob
 

Don S

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Messages
62,321
Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

another guy: I am not sure if it is warrantied, but the guy told my gfs son that he installed the carb on his test engine and ran to verify it was running good...he does that on all his rebuilds....so its kinda hard to tell him its his fault if it runs on his motor , but not ours!

Carbs have to be adjusted (mixture and idle speed) to the engine they are installed on, not someone elses engine. Since this is a 2008 model, can we assume it's a TKS carb?
 

bob johnson

Rear Admiral
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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

Carbs have to be adjusted (mixture and idle speed) to the engine they are installed on, not someone elses engine. Since this is a 2008 model, can we assume it's a TKS carb?

thanks for the help Don.... since it isnt my boat, i cant say what model carb it is....the boat is moored on a lake all summer.

if I were to look at the carb how would I verify its indentity? its the base merc 3.0 engine on bayliners 135 hp i think...2 barrel carb

the idle needle ( the only one I could see on the carb at all) was on the port rear of the carb down low

if you have any suggestions...i am all ears

bob
 

Don S

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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

The first thing you will notice about the TKS is there is no choke plate, plus they have a TKS module (a in the picture below) sticking out. They also have a lot of electrical connections on the engine for engine temp ect. Another reason it seems odd that it could be adjusted to another engine.
 

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bob johnson

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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

id say thats not the carb.......i dont see the idle adjustement where I described it....and by the way the GF tells me the boat ius actually a 2007, but she bought it in 2008...hope that didnt confuse the issue.

bob
 

Don S

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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

At this point, I think an engine serial number is in order. The 2007 should also be a TKS. Makes a big difference in how it should operate from a TKS to a carb with a choke. The picture I posted doesn't even show the idle mixture adjusting screw. It's just the basic looks of the carb.
 

bob johnson

Rear Admiral
Joined
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Messages
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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

At this point, I think an engine serial number is in order. The 2007 should also be a TKS. Makes a big difference in how it should operate from a TKS to a carb with a choke. The picture I posted doesn't even show the idle mixture adjusting screw. It's just the basic looks of the carb.

will get that number...on the dashboard, I dont remember seeing any kind of choke....at least not a manual one...thats for sure.


bob
 

bob johnson

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Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

don the serial # is 1a337295

model mcm 3liter

thanks
bob
 

havoc_squad

Senior Chief Petty Officer
Joined
Mar 5, 2011
Messages
693
Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

That's a TKS carb, part #866140A02.

Sounds like you have a carb leaking gas fast into the intake.

The most likely culprit issues I can think of are the following:

1. TKS enrichment circuit still dumping gas into the carb after engine is warmed up.
2. Improper idle mixture adjustment. (Adjusting this out of the water and without load on the engine while at idle equals headaches)
3. Wrong float drop or height (doubtful, but check the Mecruiser float specs).
4. Fuel pressure too high from mechanical fuel pump. (Your serial number pulls up an engine model that uses a mechanical, not electric fuel pump unless converted.)

Key hints of fuel pressure issue mainly would be venturies leaking at idle rpm's and after engine shutdown. Venturies should not drip at idle rpm or after engine is turned off.

5. Last but not least, improper carb rebuild causing it to leak out.


By the way, do you know the TKS carb idle mixture screw requires a special tool to adjust if you don't have it already. That is different than the idle speed screw on the throttle arm. (In case there's any confusion here).


What I recommend you do, others may say differently:

Have this opened when you are trying to diagnosis the real culprit of the problem.

http://boatinfo.no/lib/mercruiser/manuals/mercruiser41.html

1. Check the TKS enrichment circuit per service manual procedures.
2. Check fuel pressure (you never know, it might be flooding the carb with overpressurizing).
3. Float drop and float height (doubtful, but make sure they did it per service manual)
4. Check the idle mixture and make sure its correct while under load at idle per service manual procedure.

If all that is tried but comes up with nothing, dare I say it you probably had the carb rebuilt incorrectly.
 

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,304
Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

That's a TKS carb, part #866140A02.

Sounds like you have a carb leaking gas fast into the intake.

The most likely culprit issues I can think of are the following:

1. TKS enrichment circuit still dumping gas into the carb after engine is warmed up.
2. Improper idle mixture adjustment. (Adjusting this out of the water and without load on the engine while at idle equals headaches)
3. Wrong float drop or height (doubtful, but check the Mecruiser float specs).
4. Fuel pressure too high from mechanical fuel pump. (Your serial number pulls up an engine model that uses a mechanical, not electric fuel pump unless converted.)

Key hints of fuel pressure issue mainly would be venturies leaking at idle rpm's and after engine shutdown. Venturies should not drip at idle rpm or after engine is turned off.

5. Last but not least, improper carb rebuild causing it to leak out.


By the way, do you know the TKS carb idle mixture screw requires a special tool to adjust if you don't have it already. That is different than the idle speed screw on the throttle arm. (In case there's any confusion here).


What I recommend you do, others may say differently:

Have this opened when you are trying to diagnosis the real culprit of the problem.

http://boatinfo.no/lib/mercruiser/manuals/mercruiser41.html

1. Check the TKS enrichment circuit per service manual procedures.
2. Check fuel pressure (you never know, it might be flooding the carb with overpressurizing).
3. Float drop and float height (doubtful, but make sure they did it per service manual)
4. Check the idle mixture and make sure its correct while under load at idle per service manual procedure.

If all that is tried but comes up with nothing, dare I say it you probably had the carb rebuilt incorrectly.

wow, thanks...pretty detailed.....and just what i need...... they are ready to take the boat off the water, but maybe i should go through this before it is winterized.

bob
 

havoc_squad

Senior Chief Petty Officer
Joined
Mar 5, 2011
Messages
693
Re: full throttle in nuetral , to start 3.0 merc bayliner, why?

Yeah, you learn well after 4 1/2 to 5 months off and on of investigating a carb related issue while pulling your hair out in frustration of the poor diagnostic skills of my former service shop, because I don't work on boats as a hobby or for a living, that's what I paid them to address it.
 
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