I need help, boat runs rough and stalls. I pumped new gas and lots more.. I need help

[Bayliner3.0]

The choke valve rod was hanging up on some pitting where it passes through the carburetor. I could have polished it out while the carb was on the boat (if I knew that) and kept boating.
After tearing the carb down it was not it that bad of shape, but $50 for a new carb soak bucket, carb spray, paper towels, some new brushes blah blah. I will just put that money toward a new carb.
So a loose plug wire (from 1997) lead to ignition tune up and lead to choke being stuck… It is never a simple diagnosis for me lol.

Good news is this old boat of mine is almost totally renewed. The engine looks amazing. In a few days I will follow up if the problem is solved with the new carb.

Thanks for the help everyone.

 

[Bayliner3.0]

Ok so last update. I can not seem to tune the carb. I am going to start a new post. There is an updated carburetor from mercruiser but it supposedly goes from 1.55 to 1.7 jet and they said I should leave it, as it may have to do with the 1997 carb and new ethanol mixtures…??? They are not mechanics on the phone, but they said to adjust the float and pump arm the same as the old carb as there are no new specs….
Please look for the new post. Thanks.

 

[Bayliner3.0]

Engine serial is: 0K148873

I installed a new carburetor and I am having trouble tuning it. I am at sea level - 100ft above.
Original Carb Part# 3310-807504A 1 (807504A)
New Replacement per Mercruiser Part# 3310-8M0045397

Mercruiser told me to adjust everything the same as specs for the original carb (float level, drop, pump arm linkage) but the new carb is supposed to have a 1.7 jet vs the original 1.55 jet size. They had no memos about new specs for the new carb and no updated manual. They said keep 1.7 as it may have to do with ethanol mixtures starting after 1997 (my original boat carb year)

Ok I start with idle touching choke cam then 2 full turns in. I start with the mixture screw 1 1/4 out.
Vacuum gauge hooked up and when I drop the idle it seems to need more mixture (more than 1 1/4). Then I just keep opening up the mixture screw and reducing idle screw until the idle screw NO LONGER touches the choke cam.
By this time it seems ok but I rev the engine and it just holds rpm and takes a few secs to drop. I can smell fuel from exhaust too so I am assuming way to rich..
I try and try, but do not know what I need to do.

Any tips, my engine idled great before and reved up and down fine. Also I reached 4500rpm with a 21p prop no problem at 43mph. ALL BEFORE SWAP.

 

[alldodge]

I merged the threads because this is the same issue, just installed new carb

Where are you connecting the vacuum gauge and what is the reading?
Has timing been set correctly? Meaning was a shut used and interrupter bypassed?

Smelling gas means to much fuel, backing out the mixer just gives motor more fuel

Is the throttle cable disconnected from the carb?

 

[Bayliner3.0]

I merged the threads because this is the same issue, just installed new carb

Where are you connecting the vacuum gauge and what is the reading?
Has timing been set correctly? Meaning was a shut used and interrupter bypassed?

Smelling gas means to much fuel, backing out the mixer just gives motor more fuel

Is the throttle cable disconnected from the carb?

No prob about merge. Thanks.

There is a plug to the right of the carb on the manifold, that is where I put the vacuum gauge. The reading is about 15-16 until I make adjustments.
I have read that 19.5 is perfect for sea level, but I am starting to think that this motor may be around 16 at sea level.

I have not checked, or even adjusted the timing since I owned the boat (couldn’t hurt to check it I guess).

The boat seemed to run perfectly prior. Spark plugs looked great when I changed them, RPM range and top speed was good.
Throttle cable connected but does have some slop at carb cable end guide (that plastic cable holder) I am looking at how to adjust that and specs now. Can’t find it in my manual it’s hiding from me.

 

[alldodge]

Adjust carb with cable disconnected until done

A marine carb does not have a return spring like on a car. The throttle cable "is" the return spring

The throttle carb is adjusted with motor idling at correct RPM. Apply a slight pressure to hold the carb closed and this should not effect RPM. Once this is achieved, adjust barrel on cable so that the barrel just slides in place along with end on carb post.

At this point, remove cable and turn barrel one turn further out. This turn is what will help hold the carb closed at idle

 

[Bayliner3.0]

so vacuum is 13-14 and idle is 1000 and it stumbles and after a min or 2 will shut off.
this is with idle mixture at 1 1/4 turns. Exhaust smells like gas for sure.

So should I be increasing idle and screwing in the mixture since the exhaust smells like gas? I assume this will bring the idle back down..? Thanks again for your help

 

[alldodge]

A new cab doesn't mean things didn't change from the factory

Get it idling as low as you can and look down throat of carb, if there is dripping fuel the cab needs to be opened. Need to check float level and float drop

 

[Bayliner3.0]

A new cab doesn't mean things didn't change from the factory

Get it idling as low as you can and look down throat of carb, if there is dripping fuel the cab needs to be opened. Need to check float level and float drop

Ok I think I get this, if there is fuel dripping in at idle then the level is set too low. I should increase the level measurement. Is that right?

I could throw in the old carb float and see what happens. New and old float level was set to spec, but drop was way over I assume the old carb float was set right even though it was about 42mm drop vs the 29mm drop spec in manual.

No more day light, will continue tomorrow.

 

[nola mike]

Ok I think I get this, if there is fuel dripping in at idle then the level is set too low. I should increase the level measurement. Is that right?

I could throw in the old carb float and see what happens. New and old float level was set to spec, but drop was way over I assume the old carb float was set right even though it was about 42mm drop vs the 29mm drop spec in manual.

No more day light, will continue tomorrow.

Did you check timing? It will affect everything...
Low vacuum can be due to timing being off or engine running rich. Like AD said, look for fuel dripping down your venturis. Jet size shouldn't affect idle.

 

[alldodge]

Ok I think I get this, if there is fuel dripping in at idle then the level is set too low. I should increase the level measurement. Is that right?

No, fuel level is to high.
The float is not shutting the fuel off soon enough, the tang might need to be bend ever so slightly more. The drop is not that important but needs to be correct. The drop is just the max the float will drop

 

[nola mike]

No, fuel level is to high.

I was reading his post as being that the float *measurement* was too low, float itself is sitting too high in the bowl.

 

[Scott06]

Additionally if venturis are dripping at idle start with float adjustment but also too high fuel pressure can overcome the float. If needle and seat adjustments don’t cure it measure fuel pressure

 

[Bayliner3.0]

No, fuel level is to high.
The float is not shutting the fuel off soon enough, the tang might need to be bend ever so slightly more. The drop is not that important but needs to be correct. The drop is just the max the float will drop

So my manual says 14mm for the level that seems to leave the float too high (measurement too small), so what do you think I should go with? 15mm, 17, 20?? I saw on a youtube video (mikes carburetor parts) to go level with the gasket. As in parallel. That would be I would guess 17mm or so.. Or start small? I am tearing it apart now.
Any thoughts? Otherwise I might go with level or first try the original float from my old carb.
Happy Easter everyone! And thanks for all the help!

This is mainly going to affect my idle only right? Once I open the throttle the other jets take over and the float is less important.?

 

[alldodge]

I'm unable to see what you are , and don't see an old float being better then new, only maybe it's adjusted different

Float level is more for running then idle

 

[Bayliner3.0]

My old carb ran great for 3 years. I assume the float was adjusted pretty good. So switching to the old float may take out the guess work that is what I meant.
Unless the new carb has different specs slightly, which I can not seem to find.
My goal is to not damage my engine. If I adjust the current float to sit lower so that it shuts off faster, how much lower I measured 14mm currently. Should I measure 15 to start or 17? Just trying to get a starting point. I do not want to go too lean either.

 

[Bayliner3.0]

Ok I have the idle at about 800-1000 fluctuates any lower it will die. I look in carb with choke open and engine warm and I can not see fuel I tap throttle and see fuel. I shut off the engine and can not see fuel dripping either.

 

[brodmann]

What you need to be correcting is the point where the float turns fuel flow off. The drop of the float is unimportant. It will sit on the bottom of the bowl. With the carb off, slip a piece of clean fuel line on the nipple where gas goes in and blow on it. Lift the float with your hand and see if the air stops flowing when the float is parallel and even with the bottom of the gasket. Or, just lay the carb upside down with the gasket on it and see if the float is level with the gasket when the needle is seated, like it will be when the carb is laying upside down. Again, the drop of the float is not your problem. That measurement is not something to worry about.

 

[brodmann]

I've had motors that were 50-60 years old and have never replaced a carburetor on any of them. I don't understand the need to replace a carb.

 

[airshot]

Are you making your carb adjustments while the boat is in the water and underway ?? You cannot get a proper carb adjustment on a trailer. The manual clearly states this. Had a similar problem with my 3.0, after a complete carb rebuild I could not get the idle good. Put the boat in the water and fine tuned the carb underway....600 rpm and nice and smooth.