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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10972
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Have rebuilt Rochester carb for 1998 Baylener Capris 3.0

Customer Question

Have rebuilt Rochester carb for 1998 Baylener Capris 3.0 seems to idle fast
Can't slow it down
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: Idle adjustment on rebuilt Rochester mercruiser 1998 3.0 carb
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: I had replaced the original carb
The connection for gas was different had to add fittings and short piece of fuel injector hose to reconnect
The cable connection was different so had to adjust obarrell to make connection
Had unhooked electrical gas connection at tank and auto choke connection to install rebuilt carb
Submitted: 11 months ago.
Category: Boat
Expert:  Tan replied 11 months ago.

Hello. My name is Tan.

Disconnect the throttle linkage. Then set the idle jets to 1.5 turns from lightly seated. Then with engine in the water warmed up fine tune the jets to achieve the best idle. You will have to alternate between the idle on the linkage and the jets to achieve best idle. If you are on a hose it is very hard to get the adjustment correct.

Have you tried this procedure yet?

Customer: replied 11 months ago.
It idles quite fast should I worry
Expert:  Tan replied 11 months ago.

Idle speed should be 650-700 rpms in the water in neutral. If idle is to high you will cause damage to the drive gears.

Customer: replied 11 months ago.
What do you mean hose
Expert:  Tan replied 11 months ago.

Flushing attachment.

Customer: replied 11 months ago.
Simplify flushing attachment
Expert:  Tan replied 11 months ago.

Do you run your engine on the trailer?

Customer: replied 11 months ago.
Boat in water
Expert:  Tan replied 11 months ago.

Ok then follow the procedure I outlined in my first reply. This should get the idle correct. Long as you don't have a vacuum leak.

Customer: replied 11 months ago.
I will try that
Expert:  Tan replied 11 months ago.

The reason you want linkage disconnected as you want the throttle plates closed. Then when you have to adjust the idle screw on the linkage it won't interfere with that adjustment. You want to get the best idle by adjusting the jets and the idle screw. Once it idles at the recommended rpms then install the throttle cable.

Keep me posted if that doesn't work.

Please don't forget to [positively rate my help as that is the only way I get credit for helping you. To rate click on the stars at the top of the page 3 or more please.

Rating doesn't close the question. Follow up questions are always welcome.

Thank you........Tan

Customer: replied 11 months ago.
Tried your advice
Throttle unhooked
First set both idle screws at 1 1/2 turns
Idle screw set wide open
No change
Adjusted both idle jets to seated did nothing
Expert:  Tan replied 11 months ago.

Idle screw is supposed to be set at the lowest setting not wide open. I never said anything about setting idle jet to wide open.

The adjustment for the idle jets is turn jet in till it seats then back it out 1.5 turns.

Customer: replied 11 months ago.
I had the idle jets set at 1 1/2 turns
Expert:  Tan replied 11 months ago.

What about this setting? Idle screw set wide open And this? Adjusted both idle jets to seated did nothing

Customer: replied 11 months ago.
the idle screw should not be touching anything
Right
Expert:  Tan replied 11 months ago.

Correct. What is your ignition timing adjusted at?

Customer: replied 11 months ago.
I don't have a timing device
Expert:  Tan replied 11 months ago.

Ok if the carb adjustments didn't help you have the timing adjusted wrong or you have a vacuum leak. Did you replace the base gaskets under the carb?

The engine should idle with idle screw out and jets at 1.5 turns. It might idle a little rough but it won't be over revving. Air/vacuum leak or timing are the only things that will make the engine idle very fast. That is if the carburetor was cleaned and rebuilt correctly. This is not a Rochester if it has one idle jet. How many idle jets do you have?

Customer: replied 11 months ago.
It has 2 idle jets
Expert:  Tan replied 11 months ago.

So this is not the original carb correct?

Customer: replied 11 months ago.
Correct
It came with a gasket new gasket installed
Cleaned base where gasket goes well before installing
Expert:  Tan replied 11 months ago.

Has the engine ever run correctly with this carburetor?

Customer: replied 11 months ago.
I just installed this carburetor
Expert:  Tan replied 11 months ago.

Ok are the throttle plates completely closed?

What happened to the original carburetor?

Customer: replied 11 months ago.
Are the throttle plates at the base of the carb
Expert:  Tan replied 11 months ago.

Correct.

Customer: replied 11 months ago.
Someone stepped where they shouldn't and broke the bolt off from the carb (it holds the arrestor
Expert:  Tan replied 11 months ago.

Did the bolt fall down in the carb holding the throttle plates open?

Customer: replied 11 months ago.
No
Expert:  Tan replied 11 months ago.

Are the throttle plates closed?

Customer: replied 11 months ago.
I'll check
Customer: replied 11 months ago.
Expert:  Tan replied 11 months ago.

Ok we are the point we have to check the ignition timing.We have done all we can at this point.

Can you get a timing light?

Customer: replied 11 months ago.
No I'm up on Canada 3 miles from road and docking where I can pull my boat out and bring it to someone who can set timing
Expert:  Tan replied 11 months ago.

Ok We did all we could with the carb adjustments. That was what your question was about. So timing is another till we get the timing checked we can do anymore. You can always post back when you get that checked.

Thank you...Tan

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