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Mercuiser 5.7 Sputtering and stalling

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kevin45baker

New member
I have a 1988 Malibu Skier with a 5.7 Mercruiser. The engine only has under 900 hours and used to run great. Ive been having issues for the past year or so where it would start right up but once you put it in gear it would sputter and die. To start last year, I replaced water seperator, fuel filter, distributer, plugs, and wires. It would run great before varnish would fill the fuel filter in the carb, after being cleaned and replaced it would run great. Then we drained the tank and filled it with new fuel. This past winter the carb was sent out to be proffesionally rebuilt and vaccum tested. I fired it up last week with a hose and it ran like a champ. Took it out on the water today, it ran great for about 20 minutes then it would idle fine then sputter on takeoff and stall out. I cleaned the filter and no change. Any ideas the boat was winterized with k100 and Stabil, always run 93 octane. Id also like to add that after the run I noticed a wire spliced into the black wire going to the fuel tank that is grounded on the aluminum tank but was loose.
Please Help!
Thanks,
Kevin
 
What did the contents of the fuel filter look like ? Clean gas or did it have sediment? You mention draining the fuel tank but was it cleaned out of any sediment ?
 
When it dies can you actuate the throttle and see gas squirting into carb?

Are you sure there is NO water or sediment? You have a Weber carb, correct? They have two filters and they are in a weird place in that carb, Did you replace/clean them?

You may need to install a pressure gauge between fuel pump and carb to see if you are loosing fuel pressure

You say you tank is clean, what about the pick up tube? There is typically a screen at the bottom, did you clean/replace?

One suggested the anti-syphon valve, Have you looked at this? It is the fitting on the top of gas tank where soft hose connects.
It is a check valve (ball and spring inside) and may be malfunctioning. Easily replaced with new.
 
Last edited:
kghost said:
When it dies can you actuate the throttle and see gas squirting into carb?

Are you sure there is NO water or sediment? You have a Weber carb, correct? They have two filters and they are in a weird place in that carb, Did you replace/clean them?

You may need to install a pressure gauge between fuel pump and carb to see if you are loosing fuel pressure

You say you tank is clean, what about the pick up tube? There is typically a screen at the bottom, did you clean/replace?

One suggested the anti-syphon valve, Have you looked at this? It is the fitting on the top of gas tank where soft hose connects.
It is a check valve (ball and spring inside) and may be malfunctioning. Easily replaced with new.
Click to expand...
It has a Rochester quadrajet carb. When I give it throttle I can see the lever push down, but not physically see fuel squirting. When taking the fuel put it was perfectly clean. And I just rand it through all of the lines. Checked for water and what not but couldn't see anything. I'm going to look at the tank more in depth tonight.
 
kevin45baker said:
It has a Rochester quadrajet carb. When I give it throttle I can see the lever push down, but not physically see fuel squirting. When taking the fuel put it was perfectly clean. And I just rand it through all of the lines. Checked for water and what not but couldn't see anything. I'm going to look at the tank more in depth tonight.
Click to expand...
Your boat is an '88 & I'd be surprised if there wasen't sediment in your tank. A few years ago I had to replace the floor in my boat & when I pulled the fuel sender for a look see sure enough there was crud on the bottom. For me it wasent a big deal because i had the deck out anyway. I would pull the fuel sender & take a look. And you can't tell by looking at your fuel if there's sediment in your tank. It will settle to the bottom when the boat isn't moving.
 
whiteside said:
Your boat is an '88 & I'd be surprised if there wasen't sediment in your tank. A few years ago I had to replace the floor in my boat & when I pulled the fuel sender for a look see sure enough there was crud on the bottom. For me it wasent a big deal because i had the deck out anyway. I would pull the fuel sender & take a look. And you can't tell by looking at your fuel if there's sediment in your tank. It will settle to the bottom when the boat isn't moving.
Click to expand...
I'll pull the tank and clean it. What's recommended to use? And I plan on buying a new fuel pump. I was thinking about the Holley pump but any recommendations?
 
kevin45baker said:
I'll pull the tank and clean it. What's recommended to use? And I plan on buying a new fuel pump. I was thinking about the Holley pump but any recommendations?
Click to expand...
I used a battery operated pump from Harbor Freight to suck out the old gas, dumped some Gumout in & shook the tank to clean it. I let it sit overnite then vacuumed it out again. That's how I did & it worked for me. I'm sure others will chime in.
 
whiteside said:
I used a battery operated pump from Harbor Freight to suck out the old gas, dumped some Gumout in & shook the tank to clean it. I let it sit overnite then vacuumed it out again. That's how I did & it worked for me. I'm sure others will chime in.
Click to expand...

How much gumout did you use? My tank is like 20 gallons
 
kevin45baker said:
How much gumout did you use? My tank is like 20 gallons
Click to expand...

Did cleaning the tank fix your problem? I also have the exact same boat and I'm experiencing kinda the same issue only difference is mine runs great for 30-40 minutes before it runs rough then eventually dying.
 
Q-Jet rebuild small.jpgAre you using E-10 gas? Was the fuel supply changed at some point in that you used to use straigh gas and now are using E-10? That can cause the exact problem you are experiencing. The E-10 will tend to clean out all the accumulated varnish in the tank. Eventually though it will be clean and you should not continue to have probems, unless you have old fuel lines that are breaking down.
If you have a Quadrajet carb, I can tell you that while they are not hard to rebuild, the idle emulsion tubes are hard to get clean, some say to remove them but I just soaked mine really well in carb cleaner and then blew it out with a good air compressor. Also, I have heard that unless you use a good E-10 resistant rebuild kit the accel pump seal will degrade due to the ethanol. This might be part of your problem. And lastly, a lot of people make a mistake when reinstalling the float and needle on the Q-Jet..the little clip....is not supposed to be in the holes on the lever, its just supposed to hook on to it...putting it in one of the holes, can cause the float to stick and flooding....
 
Yes that's how mine is. I cleaned the tank with a product I use for small nd and atv Carb that's a chemical dip to remove varnish. The problem is still occurring. I cleaned the carb again today and my fuel pump comes in tomorow. I will keep you updated
 
louc said:
View attachment 20875Are you using E-10 gas? Was the fuel supply changed at some point in that you used to use straigh gas and now are using E-10? That can cause the exact problem you are experiencing. The E-10 will tend to clean out all the accumulated varnish in the tank. Eventually though it will be clean and you should not continue to have probems, unless you have old fuel lines that are breaking down.
If you have a Quadrajet carb, I can tell you that while they are not hard to rebuild, the idle emulsion tubes are hard to get clean, some say to remove them but I just soaked mine really well in carb cleaner and then blew it out with a good air compressor. Also, I have heard that unless you use a good E-10 resistant rebuild kit the accel pump seal will degrade due to the ethanol. This might be part of your problem. And lastly, a lot of people make a mistake when reinstalling the float and needle on the Q-Jet..the little clip....is not supposed to be in the holes on the lever, its just supposed to hook on to it...putting it in one of the holes, can cause the float to stick and flooding....
Click to expand...

I appreciate the reply. I pulled the carb apart today and I could surprisingly see dirt inside it. My fuel pump comes tomorow. Hopefully that will solve the issue. The boat has always run on 93 octane e10. It's ran great for 10ish years on pump.
 
kevin45baker said:
Yes that's how mine is. I cleaned the tank with a product I use for small nd and atv Carb that's a chemical dip to remove varnish. The problem is still occurring. I cleaned the carb again today and my fuel pump comes in tomorow. I will keep you updated
Click to expand...

Have found hard sand colored deposits in my carb jets and venturis that no cleaner would dissolve. Ended up having to mechanically remove the deposits with a fine wire. The pros use an ultrasonic cleaner which is out of my budget.
 
kevin45baker said:
I appreciate the reply. I pulled the carb apart today and I could surprisingly see dirt inside it. My fuel pump comes tomorow. Hopefully that will solve the issue. The boat has always run on 93 octane e10. It's ran great for 10ish years on pump.
Click to expand...
New pump came in, ive taken it out twice with it. Still no luck. The tank is topped off and it will run good once it gets up to speed but when you slow down it does not want to go again. I continually clean the fuel filter and spray carb cleaner through the carb and it will fire right up and go like a champ for about 7 minutes or until you slow down to headway speed. Then when you try to take off either quickly or slowly it will stall out and die. I pulled the carb back apart to adjust the needle as you said, but the way you do it simply wont line up, its too offset unless it goes though the 2 holes, maybe the carbs are just slightly different. Any body else have any ideas? Also id like to add that when it doesnt run right ill put the boat in nuetral at WOT and sometimes the rpms will shoot to 3-4k and fall back down and stall, but after i spray the carb cleaner through it the rpm's will hit 3-4k and stay there.
 
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