dirty fuel? drain gas?

extremez · Jul 3, 2012

trying to troubleshoot my rough running 3L merc. starts fine and runs great for 15- 20 minutes. go to start again after some relaxing and it gives me a hard time. doesn't want to idle and will stall.

thinking bad or dirty fuel. i will pull the fuel filter when i get time but if it comes down to it, how does one go about draining/cleaning the fuel tank? the tank sits under the sitting area. can you siphon? because i tried to siphon from the line going from the tank to the fuel pump and it's a PITA and i was not successful.

Failproof · Jul 3, 2012

Re: dirty fuel? drain gas?

Electric fuel pump to transfer fuel out. Fastest and easiest!

Bondo · Jul 4, 2012

Re: dirty fuel? drain gas?

extremez said:
trying to troubleshoot my rough running 3L merc. starts fine and runs great for 15- 20 minutes. go to start again after some relaxing and it gives me a hard time. doesn't want to idle and will stall.

thinking bad or dirty fuel. i will pull the fuel filter when i get time but if it comes down to it, how does one go about draining/cleaning the fuel tank? the tank sits under the sitting area. can you siphon? because i tried to siphon from the line going from the tank to the fuel pump and it's a PITA and i was not successful.

Ayuh,... The fitting at the tank's outlet is an Anti-siphon valve,... It could be the problem, or part of it...

Ya can't siphon off the gas, with that valve there...

Pull it, 'n clean it out, then Pump off the tank, as Failproof says..

ENSIGN · Jul 4, 2012

Re: dirty fuel? drain gas?

Remove the fuel gauge sender and pump the tank out.A small electric fuel pump from a auto parts store works great.

extremez · Jul 4, 2012

Re: dirty fuel? drain gas?

gonna have to hire a midget to do this work. i can barely see where the line hits the top of the tank. i see what looks to be a brass 90 degree fitting on top of the tank. from there it goes to the side of the fuel pump then onto the carb. i put a container of seafoam and startron in it and adjusted the idle so it doesn't bog down and shake. it's at about 800rpm now. i started it up and let it run for about 30 minutes. tried to shake the boat around to stir anything up. can't go out on the water till the weekend because i'm on call for work. cut the engine and started it up again and it seemed ok. gonna go back out in a few and start it up after it's rested. trying to simulate some use on it.

fuel filter? shouldn't there be one? don't see one or i'm completely missing it.

Bondo · Jul 4, 2012

Re: dirty fuel? drain gas?

extremez said:
gonna have to hire a midget to do this work. i can barely see where the line hits the top of the tank. i see what looks to be a brass 90 degree fitting on top of the tank. from there it goes to the side of the fuel pump then onto the carb. i put a container of seafoam and startron in it and adjusted the idle so it doesn't bog down and shake. it's at about 800rpm now. i started it up and let it run for about 30 minutes. tried to shake the boat around to stir anything up. can't go out on the water till the weekend because i'm on call for work. cut the engine and started it up again and it seemed ok. gonna go back out in a few and start it up after it's rested. trying to simulate some use on it.

fuel filter? shouldn't there be one? don't see one or i'm completely missing it.

Ayuh,... There's 1 inside the fuel pump, 'n another inside the carb's inlet fittin'....

Adding "Mechanic-in-a-can" to Bad gas, results in More Bad Gas...

extremez · Jul 4, 2012

Re: dirty fuel? drain gas?

found them. manual says i have a water separator. hmmmm not sure why.

anyway went and bought a new paper filter for the one under the fuel pump. the one on the inlet to the carb was filled with crystallized material ?????

i found it easier to remove the entire fuel pump assembly to get to the other filter. also looked down the carb and it looks gritty?? hopefully some carb cleaner will help also.

the seafoam actually helps in some cases. it helped clean my wifes mustang out and we noticed better response and idling. and the smoke show was pretty cool too.

Don S · Jul 4, 2012

Re: dirty fuel? drain gas?

manual says i have a water separator. hmmmm not sure why.

What are we working on?

extremez · Jul 4, 2012

Re: dirty fuel? drain gas?

troubleshooting my poor idling/stalling merc 3L. Nothing in my manual says anything about 2 separate fuel filters. if it does i haven't found it in it. But it talks about a water fuel separator which i don't have but i've read that i should get.

extremez · Aug 5, 2012

Re: dirty fuel? drain gas?

gonna bump this thread instead of starting a new one because the same issue is happening.

Today I went and bought some fuel line hose and hooked up an temporary tank with good new gas. The issue is still here. Starts up fine cold. Idles high until warm and drops back down to 800 or so rpms. When i throttle forward it's fine at 1/4 throttle position. As soon as i get to about 1600-2000 rpms it starts chugging and bogging. If i don't apply throttle quick enough it may actually drop and stall. Then it may require throttle full open to restart instead of in neutral. Obviously I shouldn't only be able to only putt putt around or fly WOT on the water. Can't keep it near a cruising speed.

So I'm skeptic that it's bad fuel in the tank. It may be older fuel and I'll have to figure out how to pump that out. Can't pull the tank because it's under the deck and that would require completely removing the deck. After I drain the tank how do I go about making sure it's clean?

Next suggestion as far as the rough running issue????

extremez · Aug 7, 2012

Re: dirty fuel? drain gas?

bump. Messed around with the carb last night. Didn't take it completely apart guts and all. Took the top cover off and the fuel inside had some gritty deposits in it. I soaked up the gritty gas with a towel and sprayed the carb with cleaner.checked all moving parts to make sure they were free.

my question though is this. Do I need to put fuel in the carb before starting it up the next time? or will it fill itself back up on it's own.

Bondo · Aug 8, 2012

Re: dirty fuel? drain gas?

extremez said:
bump. Messed around with the carb last night. Didn't take it completely apart guts and all. Took the top cover off and the fuel inside had some gritty deposits in it. I soaked up the gritty gas with a towel and sprayed the carb with cleaner.checked all moving parts to make sure they were free.

my question though is this. Do I need to put fuel in the carb before starting it up the next time? or will it fill itself back up on it's own.

Ayuh,.... Pull the carb, 'n Rebuild it...

extremez · Aug 8, 2012

Re: dirty fuel? drain gas?

Any idea which kit I would need?

07 3.0L Merc w/ TKS

Is this something a DIYer can do?

Chobes · Aug 8, 2012

Re: dirty fuel? drain gas?

Yes a DIY'r can do it them selves. I have an 86 Seray 3.0L motor. I pulled the carb, Rochester 2 BBL, Pulled it apart and it was all crudded up with what looked like Corrosion. You have to take it all the way apart. There small brass tubes in side that need to be cleaned really good. It's called the Venturi Assembly.

. Pretty nasty huh. Remove the 3 screws in the center of the carb and the Venturi assebmly is under that.
What style carb do you have?

extremez · Aug 8, 2012

Re: dirty fuel? drain gas?

whoa, the inside of my carb didn't look anywhere near as dirty as the one you posted. Mostly fuel with a little debris. I certainly hope that little debris is the culprit and a good clean rebuild will fix it.

off to figure out which kit i need.

scarpint · Aug 9, 2012

Re: dirty fuel? drain gas?

ENSIGN said:
Remove the fuel gauge sender and pump the tank out.A small electric fuel pump from a auto parts store works great.

What he says....

extremez · Aug 11, 2012

Re: dirty fuel? drain gas?

Here's a clip of what I am dealing with on my 3.0L

It actually seemed to run better after running it up the river a mile or so. I ran it earlier today on muffs for 10 minutes or so till it warmed up. I even put it in forward and let it go up to 1600-2000 rpms a couple times. Seemed fine. So I wanted to take it to the water. Got it on the water and it started doing this. The other strange this is it doesn't stay at a constant idle. If it stalls it may go to 1000 rpms, maybe 700 on restart. And you can see it doesn't actually restart unless I apply throttle to it.

Where is the stamp on the carb so I can find the rebuild kit? I think from reading multiple posts on here that I need the Sierra 18-7098 kit but want to make sure.

Sorry about the crooked neck.

extremez · Aug 12, 2012

Re: dirty fuel? drain gas?

so i took the boat out again today. this time i cold started it in the water. started fine. let it warm up and took off nice and slow. It ran great for over an hour with constant stopping to see if i could recreate it. nothing!! probably ticked people off because i kept passing them going up the river and back down about 30 times. on the bright side i dumped about 1/4 tank of gas.

i stopped for probably 20 minutes and took a swim. started it right back up and went fine.

it finally acted up with about 5 minutes left before i headed back in to meet the wife at the launch.

no rhyme or reason for it.

if it was the carb or a fuel blockage wouldn't i see an issue with fuel spitting into it? when i had the carb apart the accelerator pump was pushing streams of fuel.

anyways i'm getting ready to put an order in for iboats and am still looking for the info on the carb kit i will need.

going to order:

carb kit
fuel water separator??? which one would you recommend? must have a 3/8" inlet/outlet
new prop - looking at a 14.25 x 21 suggestions????
safeskeg

dirty fuel? drain gas?

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