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Mercruiser 3.0L 4cyl starting and idling problem... longer than usual

T

thecca

Member
Hi there, I just bought a Maxum 1800 SR boat (year 2000) and it came with the mercruiser 3.0L motor.

I noticed yesterday that the boat had trouble starting (it takes about 10-15 shots of cranking before it starts and it has trouble idling after (it dies))

BUT when the forward gear is engaged, the motor runs A1 and is really smooth... As soon as I put it back in neutral, it dies within 30 seconds.

Yesterday I got stock on the river for about an hour, the motor wasn't firing...

The previous owner bought and installed a new carb (Reman Carb part no.804617R) + Quicksilver shift cable + new oil everywhere + thermostat housing + exhaust manifold +spark plugs + fuel filter + distributor cap and rotor.

Basically, the maintenance was done, but it's still dying? I thought the problem would be gone after a good ride but it's still there...

Anyone can help? It's really embarassing.
 
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That's what I thought at first... because everything is basically new. The mecanic that did the job probably didn't do it correctly, right?

How hard is it to fix this issue?
 
Maybe the micro switch is sticking not landing in the v groove needs adjusting.

Whats your idle on a warm engine, in gear ?

Choke is opening all the way when warm ?
 
What is the SN of the engine? That carb # doesn't match anything I can find. I'm thinking he may have a TKS (Turn Key Start)carb...no choke.
 
Master mechanic said:
Maybe the micro switch is sticking not landing in the v groove needs adjusting.

Whats your idle on a warm engine, in gear ?

Choke is opening all the way when warm ?
Click to expand...

Probably around 700 rpm? 800 may-be... I'd have to check!

Choke is opening all the way? I don't know... The motor runs fine when in gear and moving, but as soon as it idles (always between 600 and 700) it dies within 30 seconds.

What's the micro switch and the V groove?
 
guyjg said:
What is the SN of the engine? That carb # doesn't match anything I can find. I'm thinking he may have a TKS (Turn Key Start)carb...no choke.
Click to expand...

The engine is OEM from a 2000 Maxum 1800 SR (BOWRIDER). I don't know the SN but I will check tomorrow when I'll go check the boat!
 
UPDATE : I adjusted the carb (idle mixture screw + idle screw) and the ignition timing and it seem to work a lot better!

I'm starting to think that it's the Float inside the carb, even if the whole thing was changed in february...? I've noticed the carb was getting a lot of gaz (it's dripping when I turn off the motor). So I think the float can be stuck in open position?
 
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So my theory could be good? Since the gaz is dripping in the carb even after I shut the motor and when I try to start it again it takes 10-15 shots of crank before it fires because it's floded? On coldstart, it starts right up after 2 shots of crank. (Probably because there's no gaz accumulated in the carb yet?)

Also, I set the idle at 900 rpm (instead of 600 as recommended) so it don't stall anymore, but I don't think it's correct, since the motor should be running fine idling at 600rpm.

I would be glad if this was my problem, since it's not a big deal to change.
 
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Adjust the float and then tie the boat to a dock securely and set the idle speed w/the engine at operating temp. and in gear...650 RPM.
 
OK I'll try this! Adjusting the float is a big tricky I think, but not a pain in the ass. Since I adjusted timing, idle mixture and idle speed the boat runs a lot better and takes less than 5-6 cranking shots to start when engine is warm (it fires right away when it's cold though) so I don't fear to get stuck anymore like I did last weekend. I'll keep you updated thanks for the help!
 
Starting a Carbed engine cold should be 1/2-3/4 push on the throttle to let the choke set and squirt gas into the carb to help with a now dry start as gas evaps quickly. Warm engine starts with in 30m to an hour, usually should be able to just turn the key, though you want to have the throttle in the neutral-throttle only position so you can gas it a little if needed.

Are you using 10% ethenal? Are you using Stabilizer? Putting Fresh Gas in? do you have a water/fuel separator?

adjusting the float if you have a Merc Carb requires the top of the carb to be removed.
With a Holley Carb there is a float adjustment on the top and front of the carb with a site glass/opening on side.
 
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kainon said:
Starting a Carbed engine cold should be 1/2-3/4 push on the throttle to let the choke set and squirt gas into the carb to help with a now dry start as gas evaps quickly. Warm engine starts with in 30m to an hour, usually should be able to just turn the key, though you want to have the throttle in the neutral-throttle only position so you can gas it a little if needed.

Are you using 10% ethenal? Are you using Stabilizer? Putting Fresh Gas in? do you have a water/fuel separator?

adjusting the float if you have a Merc Carb requires the top of the carb to be removed.
With a Holley Carb there is a float adjustment on the top and front of the carb with a site glass/opening on side.
Click to expand...

The boat came emptied and had a freshly rebuilt carb + lots of new parts (see first post), I filled it up with supreme gas (91 octane) with no ethanol in it and ran it for a while. I burnt half a tank since that. I adjusted the timing, the idle mixture and the idle screw (to 900rpm) and it seems to work a lot better. But it's supposed to run clean without stalling at 600rpm so I know I still got a problem.

I have no water/fuel separator since the boat didn't came OEM with that. It's supposed to start without choke when warm that I know and the boat does it sometimes and sometimes not. My guess is that the float isn't working properly and the carb gets floded everytime I turn the motor off so that's why I have trouble firing it up again every time after 1st start of the day.
 
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as Master Mechanic said there is typically a yellow hose from the Fuel Pump to the Carb that when the diaphram lets go in the fuel pump instead of dumping fuel into the bilge it ends up in the engine ( a little less bad than the bilge but still bad ) .. but yea.. sounds like either a bad gasket in the carb or incorrectly set float, or bad needle & seat. Only 1 way to find out.
 
So you're saying that this hose could be damaged? (air going in it?) Sorry, english isn't my first language... Could you simplify what you just said? :) lol
 
So you're saying that this hose could be damaged?
Click to expand...
This hose is a failsafe hose that keeps your boat from exploding when the fuel pump fails by having the carb vacuum suck the fuel into the carb. If you see fuel inside the hose it means the fuel pump needs replaced. If the hose is torn then replace it. Otherwise, leave it alone.
 
Gasket is also a probability but I hope it was changed when the carb was changed last february... I'll check everything tonight! Thanks again.
 
Perfect it's noted! Yes it's a single idle mixture screw. It's a rebuilt one, but probably a mercarb (didn't check the brand on it yet.)
 
If you were able to adjust the idle mixture then it probably has the correct base gasket. If it was the wrong gasket a Mercarb will not change idle mixture no matter how you adjust the screw in/out...it just won't adjust it smooth.
 
Yeah, the engine ran smoother after I opened the screw a bit (went 1 turn and 1/4 as mentionned in the book and played a bit with it after that). I think it's the float, since everything else is working smooth except on the starts after it's warmed up.
 
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