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Fuel problem, Please help

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ycart0

Member
The engine is a mercruiser 4.3 gen + lxh, 4bbl webber carb
This has been an ongoing problem on this boat for the last few years. One problem is that I have a cold start. The boat won't start if the fuel tank is not full unless I jump out the fuel pump and let it run for about 30 seconds to a min before starting. Once it starts you have to ease into the gas for the first 30 seconds or it will act like it floods and die. When I get the boat running for the most part it does ok untill we decided to stop on the lake and rest for 30 min to an hour. Now when we go to start it this it what happens. I turn the engine over and hold the key for about 4 seconds. I let off of the key and then turn it again for about 4 seconds, Normally on by the 3rd time of doing this the boat starts but you see a cloud of blue smoke comming from the back. The very last time I took it out One time it took 5 tries. Then later on the day it started on 3 tries but it had a rough idle when it started. I have rebuilt this carb twice. The second time I left the shop do it because I thought I may have made a mistake. when I checked the pressure on the fuel pump it held about 7psi I think. I wonder if the cold start when the tank isn't full and the hard starting on the lake is one and the same.
 
So the choke is closed when cold? And it opens after it warms up ?

pump tank

Now you have a clean fuel system from the tank to the carb.

One way to test before cleaning everything is to run the boat on a external tank of clean fuel say a portable outboard tank.

if you were near me i would lend you 2 so you would have 12 gallons, and have a nice day on the water while testing.

Vent clear i posted about that on the link.

Ok say you tested it or you cleaned the whole system vent is clear what does that leave?

Tune up done last ?

Timing is good ?

Say it is still doing it after you tried everything i posted while on the water and it happens after the first try with a spare spark plug pull a wire and insert the plug and hold it to the block you getting spark ? No spark at the plug then i would be looking to the dist.

But, a big " but " you have thunderbolt ? I don't know the year of your boat .

Post back or pm and we will go from there. All depends on what you post back.

Ether way if we find it's the thunderbolt, then it's 200-300 dollar fix. Easy and you will be back on the water.

I know you sunk money already into her, i just sunk another 100 dollar bill into my pos. It's the nature of the recreational activity we chose.

Keep your chin up might be a zero dollar expense so tell your wifey it will be ok. It ain't major wallet busting time yet !
 
Hey thanks for your help, here is the answers to some of your questions. The choke is closed when its cold and it opens when it is warm. The link to the pump tank doesn't work. Could you send me the detailed information about the vent. I haven't checked that yet. Don't know alot about the vent on the boat. My boat is a 1997 bryant. 4.3 mercruiser. alpaha 1 gen + The timing is good. Tune up was done about a year ago. I didn't change the plug wires but they all ohm good. I put a new rotor button and dis cap on it. This year I put a new fuel separator on it. It does have a thunderbolt. I'll probably go and buy a external tank and try that also, unless this vent thing helps the problem. But again when tank is not full of gas, I have to run the fuel pump for about 1 min to get gas to carb on cold start. After its warmed up I can turn it off on the lake. If i restart it within 1 minute, It starts right up, If I wait 15, then I have the 3 try method that I mentioned earlier. Thanks again for you help.
 
I pumped all the fuel out of my onboard fuel tank when i got it.

You can do one of 2 things, pump the water out of the bottom, or all the fuel out and here is how.

If you just wish to pump just the water out of the bottom of the fuel, you will need to purchase a cheap electric fuel pump from any auto store dc powered.
You will also need about 15 foot of cheap fuel hose from the auto store and clamps to fit the fuel pump.

Install the hose on the fuel pump both ends and cut about five feet on the sucking side of the pump just look for the arrow on the pump.

Remove the fuel pickup tube it's the one where the fuel hose hooks to the tank a 90 degree angel fitting, it's a anti-siphon valve. Unscrew it.

Crank the bow of the boat all the way up, and stick the hose connected to the electric fuel pump 5 feet into the bottom and back of the tank.

Into a clear container pump the water out till you see clean fresh fuel and stop the pump.

Or into a large container pump all the fuel out.

Now check the valve by blowing thru it, check the screen thats its clear.

Install the valve and pickup tube your done.

Question do you have a fuel water separator on the boat, good to have.

Good luck !

Listen where are you located. Lots of people here may lend you a tank.

The anti-syphin valve is the 90 % fitting that enters the tank that the fuel hose connects to that valve i believe is stuck open.

Actually my boat is having a few problems and i will be pumping my tank today, i had a overheat condition, went fishing sat and i am not overheating but i am having a few issues with starting.

I will be checking compression also i have not done so for 3 years.

post back after you pump the gunk and water off the bottom of your tank.
 
Are you pumping the throttle before starting when the engine is warm? If you are try not pumping it and see if it starts correctly.
 
Ok heres an update. I will be putting on another anti syphone valve because I can blow both ways through mine. I went ahead and replaced the pickup tube. Also pumped all the gas out of the boat.
Here is a question for you experts. The book says I need part number 91-18078. to check the fuel pump. Is there another way to connect up without that part. Don't want to spend 50 bucks on a part that Ill only use once. But if thats the only way then I will.
 
after draining the gas and putting 100 percent gas no ethanol I seem to be running alot better. I put a new anti syphone valve on and had to take it back off because it was leaking at the threads. While I had it off I was able to blow both ways thru the new one. When I first put the new one on I couldn't blow thru both ways. So if you guys have any comment there just let me know. And I assume I just need to get that part number 91-18078 since no relpys there. Thanks guys.
 
ycart0
That 91-18078 appears to be a tool for EFI (Electronic Fuel Injection), can't see you needing one with a carbed engine. When checking a fuel pump, pressure and FLOW rate are important. Make sure you pump has a strong fuel flow.
Bert
 
y your syphin valve went twice i don't know, still have the original on my boat 86'

i just checked mine 2 weeks ago, when my boat was down cause of a overheat.

You need only hook into the pump and see if you have between 4-7 psi no less and no more.

You got a webber 4 barrel, think it's leaking out into the mani from the bottom of the bowl ?

Doesn't it have screws that need to be sealed in the bottom of the bowl if it leaks ?

I didn't know you had a webber or missed it, getting old.
 
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