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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3981
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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I have 2002 25hp murcury,put kit in carb and new diapham and

Customer Question

I have 2002 25hp murcury,put kit in carb and new diapham and the only way it will stay running after start is pump the bulb
JA: Sometimes boat issues seem like they'll be really complicated, but 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: I put a kit in carb and replaced diapham,fuel lines and tried different tank and the only way it will run after you start it is pump the bulb
JA: Is there anything else important you think the Marine Mechanic should know?
Customer: Naw
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you.

Expert:  Charles replied 1 year ago.

Would you please post the serial number of the engine?

Customer: replied 1 year ago.
Ot497861
Customer: replied 1 year ago.
Could it be an entinal vacuum problem?
Expert:  Charles replied 1 year ago.

I think that the problem will be on the engine. You eliminated the gas tank when you tried another one.

When you had the carb off, did you also replace the base gasket?

Customer: replied 1 year ago.
No I didn't but did spray carb cleaner around it didn't make any difference on the way motor ran
Expert:  Charles replied 1 year ago.

Was the spring still attached to the plate when you had the fuel pump apart?

Did you also clean the carb, or just work on the fuel pump?

Customer: replied 1 year ago.
Spring is on an I washed it out made sure no port or the jet was stopped up
Expert:  Charles replied 1 year ago.

Did you also open the primer pump?

Customer: replied 1 year ago.
replaced it from parts out of oem kit. It was doing this before so I thought it needed a diapham and the only way I could get was buy a kit.
Expert:  Charles replied 1 year ago.

Do you know the compression on the engine?

When was the last time that it ran correctly?

Customer: replied 1 year ago.
Man I really don't know I just bought it from a guy bout 3 weeks ago and haven't checked compression. But it runs good if you pump the bulb
Expert:  Charles replied 1 year ago.

Ok, is the carb on or off the engine currently?

Customer: replied 1 year ago.
Well I pulled it off to replace the base gasket in process of putting back on. Do I need it off or on?
Expert:  Charles replied 1 year ago.

Good it is off. Make sure that when you are installing the base gasket that you line up the hole in the gasket with the small hole on the block.That is the pulse hole for the fuel pump. If it is blocked, the pump will not work.

Customer: replied 1 year ago.
sir it's lined up.
Expert:  Charles replied 1 year ago.

Did you notice of the old one was?

Expert:  Charles replied 1 year ago.

Since its off, open the bowl and make sure that the needle is not stuck in the seat.

Customer: replied 1 year ago.
Everything looks fine
Expert:  Charles replied 1 year ago.

might as well give it a shot and see if it will run.

Customer: replied 1 year ago.
Also will a flywheel ring and stator on 89 model 20hp mariner work on this motor?
Expert:  Charles replied 1 year ago.

No they wont. they are different part numbers.

Customer: replied 1 year ago.
It ran for 7mins died have to pump bulb and tank has to be up on the bench ssat
Customer: replied 1 year ago.
Seat*
Expert:  Charles replied 1 year ago.

Open the cap on the fuel tank and see if it will run better.

There is water going to the engine, right?

Customer: replied 1 year ago.
Oh yea I got muffs on it with water on lol
Expert:  Charles replied 1 year ago.

Just making sure.

Customer: replied 1 year ago.
Ran for 7 mins again and died?
Expert:  Charles replied 1 year ago.

With the cap open?

When you prime it up, do you hear any hissing from anywhere?

Customer: replied 1 year ago.
No hissing. I got line from tank straight to carb bc I thought maybe the quick disconnect might not been making a good seal letting air get in
Expert:  Charles replied 1 year ago.

Going to need that compression test.

Customer: replied 1 year ago.
I don't see how it could be a compression problem? It runs too good.
Customer: replied 1 year ago.
sir. The spring is real stiff,is that normal?
Expert:  Charles replied 1 year ago.

Yes that is normal.

Customer: replied 1 year ago.
I'm gonna go get a gauge to ck compression. What is compression is good?
Customer: replied 1 year ago.
It has 120 on both cylinders
Customer: replied 1 year ago.
What else could it be?
Expert:  Charles replied 1 year ago.

That is good.

What did you install on the other side of the plate from the spring?

Customer: replied 1 year ago.
Just gasket on carb side.
Expert:  Charles replied 1 year ago.

How does the fuel filter look?

Will it run under throttle, and just not idle?

Customer: replied 1 year ago.
Filter is clean. Seems like it runs longer under throttle
Expert:  Charles replied 1 year ago.

Ok, when you installed the spring and the ball for the primer pump, where was the ball located?

Customer: replied 1 year ago.
On top of the spring
Expert:  Charles replied 1 year ago.

Ok, are you sure that it stayed there?

What is the RPM at idle on the engine?

Customer: replied 1 year ago.
Yea the ball is on top. I filled the bowl up with carb cleaner pushed the primer and it works. Idle higher then then normal. Don't have a tach its on a duck boat.
Expert:  Charles replied 1 year ago.

is the carb off again?

Customer: replied 1 year ago.
Naw still on motor
Expert:  Charles replied 1 year ago.

Ok, I was going to have you inspect the reeds and a divider on the reed plate.

Your idle in gear in the water should be around 850 RPM.

Customer: replied 1 year ago.
Is it easier on motor to put boyesen reeds in it? And how much more power you think it will give it?
Expert:  Charles replied 1 year ago.

They are simple to install, you may get a few extra ponies, not many.

Customer: replied 1 year ago.
Is the reeds what the vacuum works off of for the fuel pump?
Expert:  Charles replied 1 year ago.

No the piston is. The reeds control the fuel charge going into the engine.

Customer: replied 1 year ago.
what you think I need to try next?
Expert:  Charles replied 1 year ago.

When you swapped tanks, did you also swap hoses?

Customer: replied 1 year ago.
I guess it don't pull vacuum it pushes air to the fuel pump?
Customer: replied 1 year ago.
I just got some new 3/8 gas line when I swapped tanks bc the old line looked like the liner was trying to break down
Expert:  Charles replied 1 year ago.

Yes. As the piston moves up and down, it generates a pulse that drives the fuel pump.

did you get a new bulb as well?

Customer: replied 1 year ago.
Naw I haven't replaced the bulb bc pressures up tight?
Expert:  Charles replied 1 year ago.

If the fuel line was coming apart, guess where the stuff from before the bulb winds up..

Customer: replied 1 year ago.
But I haven't seen any trash in the filter. If it was bulb why would it run long when you bring rpms up?
Expert:  Charles replied 1 year ago.

Because the fuel pump draws harder at higher rpm than at idle.

Customer: replied 1 year ago.
what do I need to try next?
Expert:  Charles replied 1 year ago.

Can you run a straight line from tank to the engine? See how the engine runs then.

Im off to bed now. Talk tomorrow.

Customer: replied 1 year ago.
Does the same with it ran straight to the carb
Expert:  Charles replied 1 year ago.

Was that without the primer bulb?

Customer: replied 1 year ago.
Naw. I don't know how it would get gas to it without the bulb?
Expert:  Charles replied 1 year ago.

If the carb is already full, the pump would draw it in, that is what it is supposed to do.

Customer: replied 1 year ago.
Went ran it on lake it runs great wide open 33-34 mph just won't idle runs out of fuel
Expert:  Charles replied 1 year ago.

Wow, you got 34 MPH out of a 25, thats great. How many turns from a light seat is the mixture needle?

Customer: replied 1 year ago.
Bout quarter of a turn from being all the way in.
Expert:  Charles replied 1 year ago.

Back it out to 1 1/2 turns. that is the starting point.

Customer: replied 1 year ago.
Does that have anything to do with what the pump pulls from the tank?
Expert:  Charles replied 1 year ago.

No, but it does control the idle air/fuel mixture. Will not effect the engine at WOT.

Customer: replied 1 year ago.
Then that's not gonna fix it from not pumping gas at an idle. Lol
Expert:  Charles replied 1 year ago.

It will help the engine idle, and you may not need to pump the bulb any longer.

Customer: replied 1 year ago.
Tried it idles too high slams in gear.
Expert:  Charles replied 1 year ago.

Back off the adjustment on the throttle arm. Lower the idle that way.