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First off, hello, I'm new here. 2nd, this is going to be a long post, and I apologize for that in advance. 
To begin, I have a 1988 Suzuki DT75 sitting on a Cobia 177. I bought the boat and engine in non-running condition from a coworker, who I know for a fact had it in running condition at one point. Unfortunately, they let it sit for a year, and then sold it to me cheap since it wouldn't start.
I played with it a little, and got it to where it would fire, but not run for more than a few seconds. I then had the carbs rebuilt my a mechanic, and when I got the boat back, it would start up and run, but only if I held the choke closed (by pushing the key in - that gets very tiring).
Once I let go and the choke opened, the engine would surge and then die after a few seconds. I actually ran the engine once for about 15 minutes with the choke closed to make sure it was good and warm, and it still surged and died when the choke was opened.
Thinking fuel delivery, I replaced the fuel filter and the fuel pump diaphragms, as well as the primer bulb and the fuel line that goes with it. I was using a vented portable gas tank with fresh gas, and the vent was open. My brother's Yamaha ran perfectly on that same gas in that same tank that very morning.
So, I had the mechanic rebuild the carbs again, and my mistake was not verifying that the engine ran when I picked it up from the mechanic. It was raining when I got there and I just wanted to get home.
Thanksgiving morning, I wanted to give it a shot on the water, so I decided to try and warm it up on the muffs first. Of course, it fired up as normal, but also as before it would only run with the choke closed. Only this time, I noticed that after it died, some gas would leak out of the top carburetor.
Obviously, it isn't supposed to do that.
I then took matters into my own hands on the suggestion of some other boating forums, and took the carbs off myself one by one. They weren't as clean inside as I had hoped, so I cleaned them up myself as best I could. I got a steady spray of carb cleaner through the main jets into the throat of the carb, so those passages were clear. I re-adjusted the float height (on one carb it was off, the other two were within spec per the Clymers manual) and re-installed the carbs on the engine.
Unfortunately, this didn't solve my problem, it would still only run with the choke closed. This time, when I let go of the choke and it started to die, I was able to push the choke back closed and keep it from dying several times. After my own personal carb cleaning, the engine seems to run rougher than it did before, probably due to me not being able to balance the carbs myself. (Prior to my taking the carbs off, when it did run, it ran strong)
I have gotten a lot of good suggestions from the other boating forums, and the general consensus is fuel starvation - which makes sense. I did verify that I had strong spark using a spark tester (and my left arm, which happened to be a little too close to the tester..)
This weekend I am going to check for fuel flow through the fuel pump by disconnecting the fuel line and seeing if fuel flows into an empty bottle while cranking. If it does show fuel being pumped, I can assume that the problem is still in the carbs. I am planning to borrow an ultrasonic cleaner from work and plunking the disassembled carbs in that to clean then out a 4th time, and then use compressed air to blow out the passages. I am also going to replace the pilot jets, as they looked like someone had broken them trying to get them out. (Although I am not sure that is related to my problem at all)
I also got a suggestion to bypass the fuel filter and pump entirely, and connect the primer bulb hose directly to the fuel line to the carburetors and see if I can keep the engine running by me acting as the fuel pump. Haven't tried this one yet as I will probably need a helper.
But, I thought I would post here to see if there are any other possibilities or suggestions since this is a Suzuki specific forum. Thanks in advance guys!
For reference:
-When I squeeze the primer bulb, it does feel like fuel is flowing and it will get hard, so I believe that is working properly.
-I took off the fuel lines between the carbs and blew them out with carburetor cleaner. No blockages.
-There is a small pinhole leak in the plastic fuel filter housing. I attempted to run the engine a few times using a see-through plastic fuel filter I got at an auto parts store instead of the leaky OEM one, but it didn't make a difference as far as the stalling goes.
-The compression is 120 on each cylinder measured by the marine mechanic
To begin, I have a 1988 Suzuki DT75 sitting on a Cobia 177. I bought the boat and engine in non-running condition from a coworker, who I know for a fact had it in running condition at one point. Unfortunately, they let it sit for a year, and then sold it to me cheap since it wouldn't start.
I played with it a little, and got it to where it would fire, but not run for more than a few seconds. I then had the carbs rebuilt my a mechanic, and when I got the boat back, it would start up and run, but only if I held the choke closed (by pushing the key in - that gets very tiring).
Once I let go and the choke opened, the engine would surge and then die after a few seconds. I actually ran the engine once for about 15 minutes with the choke closed to make sure it was good and warm, and it still surged and died when the choke was opened.
Thinking fuel delivery, I replaced the fuel filter and the fuel pump diaphragms, as well as the primer bulb and the fuel line that goes with it. I was using a vented portable gas tank with fresh gas, and the vent was open. My brother's Yamaha ran perfectly on that same gas in that same tank that very morning.
So, I had the mechanic rebuild the carbs again, and my mistake was not verifying that the engine ran when I picked it up from the mechanic. It was raining when I got there and I just wanted to get home.
Thanksgiving morning, I wanted to give it a shot on the water, so I decided to try and warm it up on the muffs first. Of course, it fired up as normal, but also as before it would only run with the choke closed. Only this time, I noticed that after it died, some gas would leak out of the top carburetor.
Obviously, it isn't supposed to do that.
I then took matters into my own hands on the suggestion of some other boating forums, and took the carbs off myself one by one. They weren't as clean inside as I had hoped, so I cleaned them up myself as best I could. I got a steady spray of carb cleaner through the main jets into the throat of the carb, so those passages were clear. I re-adjusted the float height (on one carb it was off, the other two were within spec per the Clymers manual) and re-installed the carbs on the engine.
Unfortunately, this didn't solve my problem, it would still only run with the choke closed. This time, when I let go of the choke and it started to die, I was able to push the choke back closed and keep it from dying several times. After my own personal carb cleaning, the engine seems to run rougher than it did before, probably due to me not being able to balance the carbs myself. (Prior to my taking the carbs off, when it did run, it ran strong)
I have gotten a lot of good suggestions from the other boating forums, and the general consensus is fuel starvation - which makes sense. I did verify that I had strong spark using a spark tester (and my left arm, which happened to be a little too close to the tester..
)This weekend I am going to check for fuel flow through the fuel pump by disconnecting the fuel line and seeing if fuel flows into an empty bottle while cranking. If it does show fuel being pumped, I can assume that the problem is still in the carbs. I am planning to borrow an ultrasonic cleaner from work and plunking the disassembled carbs in that to clean then out a 4th time, and then use compressed air to blow out the passages. I am also going to replace the pilot jets, as they looked like someone had broken them trying to get them out. (Although I am not sure that is related to my problem at all)
I also got a suggestion to bypass the fuel filter and pump entirely, and connect the primer bulb hose directly to the fuel line to the carburetors and see if I can keep the engine running by me acting as the fuel pump. Haven't tried this one yet as I will probably need a helper.
But, I thought I would post here to see if there are any other possibilities or suggestions since this is a Suzuki specific forum. Thanks in advance guys!
For reference:
-When I squeeze the primer bulb, it does feel like fuel is flowing and it will get hard, so I believe that is working properly.
-I took off the fuel lines between the carbs and blew them out with carburetor cleaner. No blockages.
-There is a small pinhole leak in the plastic fuel filter housing. I attempted to run the engine a few times using a see-through plastic fuel filter I got at an auto parts store instead of the leaky OEM one, but it didn't make a difference as far as the stalling goes.
-The compression is 120 on each cylinder measured by the marine mechanic
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