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Bass tracker merc sport jet 120 binds up when cranking

Biker dave

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Ok this boat was a nightmare to get running right last year but finally found a blown exhaust manifold gasket. Ran great all season then go to start it up this year and it's turning over real slow. Almost feels like it's getting stuck. New battery, new starter, cables good and tight. It almost feels like vapor lock or hydro lock. It will crank to a certain spot then bind up. Take the plugs out and cranks all day. Replaced the head gasket and manifold gaskets last year. Ran great up until stored. It WILL eventually fire up and run with fiddling but it just feels like it shouldn't be binding up like this. I've never gotten into messing with the power head and I'm wondering if maybe it's messed up?? But with no compression (plugs out) it cranks fine. And it seems to have plenty of go once it's running. So I'm confused. This thing has been a Lemon since day one. Always a bear to get it running after its sat awhile. What am i doing wrong? Anyone had this problem or maybe be able to point me in the right direction of where to look? Thanks!
 

Cobra Jet Steering LLC

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Do you see fuel in a cylinder when you remove the plugs and crank it, you may have a float stuck on one of your carbs if not you may have a issue with the pump and between the compression and the drag on the pump it won't turn over so look carefully for impeller to liner contact when I suspect the starter is being dragged down by a swollen liner I spray oil in the pump around the edge of the impeller and if it makes it turn easier the liner is swollen and rubbing on the edge of the impeller this gets worse as the liner sits for a long time like in storage over the winter . Usually once the engine gets running it will keep starting until it sits again even just a week may have an effect on it . Just some places to check out. You could also have a bad ground wire very common problem so carefully check the contacts for the main ground and move the wire if you feel it is soft and pliable it is fine if it feels hard to bend or crackles it is bad you can always run a good jumper cable to the block from the battery and see if that makes a difference.
 

Biker dave

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Battery cables are new, starter is new. Battery is new. I've pretty much eliminated the electrical. As for flooding it doesn't seem to be carbs were rebuilt last season. I took the plugs out and cranked it and it turns fine doesn't seem to be excess fuel in the cylinders. As for the pump seal... I think you are onto something. It does seem like after it sits a few weeks its hard starting, and over the winter real hard starting. But after i ran it a bunch last season it started much easier, until i stored it. How hard is that to check? Is that the power head under the motor? I looked at some videos about it but seems like a fun job so i was trying to eliminate other possibilities first. Where would I put oil in to see if that would solve the issue? If that works I guess the seal needs to be changed? Thanks!
 

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well it is not a seal it is the jet pump liner swelling against the impellor and locking the impellor as it tries to turn
 

Biker dave

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So how would you fix that??
 

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RedBarron55

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I don't think that a Mercury Sport Jet 120 has a liner, the jet body having been machined from an aluminum casting.
There may have been a liner installed, but stock there is none I am aware of as they should be just like the 90 that I have.
 

Biker dave

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Update... I believe I've found the issue. I was going to take the motor off to check the pump and started removing the air box and I noticed that it's filled with gas! So cranking the motor with the plugs out again the bottom cylinder is puking gas out of it. The bottom carb is flooding terrible. First time I checked for fuel in the cylinders I had the fuel line disconnected so it may have cleared itself or I didn't notice. But thats definitely the issue. With the fuel line pinched off it fires right over and runs untill the gas is exhausted from the carbs. No binding up. Carbs are clean as can be inside but the needle tips do look a bit worn. I guess I'll be replacing those before proceeding. Praying to Jesus that's all the issue was. Replacing a pump sounds expensive!
 

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Swampy

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Update... I believe I've found the issue. I was going to take the motor off to check the pump and started removing the air box and I noticed that it's filled with gas! So cranking the motor with the plugs out again the bottom cylinder is puking gas out of it. The bottom carb is flooding terrible. First time I checked for fuel in the cylinders I had the fuel line disconnected so it may have cleared itself or I didn't notice. But thats definitely the issue. With the fuel line pinched off it fires right over and runs untill the gas is exhausted from the carbs. No binding up. Carbs are clean as can be inside but the needle tips do look a bit worn. I guess I'll be replacing those before proceeding. Praying to Jesus that's all the issue was. Replacing a pump sounds expensive!
Had this problem with mine. The tube coming out of the bottom carb. bowl that has a 90 degree fitting, then a hose running up to the fitting out of the top carb. bowl, that has a T fitting, then a hose goes to the air box. That 90 degree fitting is plugged up solid!!!! Check T fitting also!! They are there to let the air out of bowl, which allows the float to float and shut gas off. Pull off carb. bowl and clean them, you may have to soak them in carb. cleaner to loosen that stuff up!!! Make sure when you're finish you can blow air through them. Let me know how you make out.
 

Biker dave

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I did not know that. Makes sense though I'll be sure to check that too. Last time They were apart was when the previous owner "rebuilt them" and now that I'm getting in there it looks like maybe he just cleaned them or straight out lied because the gaskets, needles, everything looks old and original. They are pretty clean inside but I did notice the one float pin was gougued up like they were grabbed with a vice grip. That could also be the float issue. At this point the entire rebuild kit is not terribly expensive so they are getting gone over. Im not a boat tech by any meand but ive rebuilt hundreds of,motorcycle carbs and they look very similar so I'm confident I can do it. Any idea how id go about synching them and setting the pilots? I have a manometer set and tach. I just know you cant run these out of water for long. I have an adapter to set the hose up to the pumo.. Is that enough to keep the pump from burning up while i make adjustments or is it strictly for flushing? Thanks sorry im such a noob to boats 😆
 

Swampy

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I did not know that. Makes sense though I'll be sure to check that too. Last time They were apart was when the previous owner "rebuilt them" and now that I'm getting in there it looks like maybe he just cleaned them or straight out lied because the gaskets, needles, everything looks old and original. They are pretty clean inside but I did notice the one float pin was gougued up like they were grabbed with a vice grip. That could also be the float issue. At this point the entire rebuild kit is not terribly expensive so they are getting gone over. Im not a boat tech by any meand but ive rebuilt hundreds of,motorcycle carbs and they look very similar so I'm confident I can do it. Any idea how id go about synching them and setting the pilots? I have a manometer set and tach. I just know you cant run these out of water for long. I have an adapter to set the hose up to the pumo.. Is that enough to keep the pump from burning up while i make adjustments or is it strictly for flushing? Thanks sorry im such a noob to boats 😆
I did not know that. Makes sense though I'll be sure to check that too. Last time They were apart was when the previous owner "rebuilt them" and now that I'm getting in there it looks like maybe he just cleaned them or straight out lied because the gaskets, needles, everything looks old and original. They are pretty clean inside but I did notice the one float pin was gougued up like they were grabbed with a vice grip. That could also be the float issue. At this point the entire rebuild kit is not terribly expensive so they are getting gone over. Im not a boat tech by any meand but ive rebuilt hundreds of,motorcycle carbs and they look very similar so I'm confident I can do it. Any idea how id go about synching them and setting the pilots? I have a manometer set and tach. I just know you cant run these out of water for long. I have an adapter to set the hose up to the pumo.. Is that enough to keep the pump from burning up while i make adjustments or is it strictly for flushing? Thanks sorry im such a noob to boats 😆
I'm not a boat tech either. I just found that out the hard way! Was 4 hours from the house, up on Lake Ontario and ended up catching the boat on fire!! LOL! I can laugh about it now but it wasn,t funny at the time. Ended up finding out about that issue after I got back. If you take carb off and bowl, blow into fuel inlet and slowly raise float and when float get level and you can no longer blow through fuel inlet then the needle is OK. Try and blow through that 90 degree fitting, with bowl off, if you can't blow air through it, that's the problem. Fuel gets into the fitting and gets hard as a rock not allowing air out, which in return doesn't allow the float to raise and shut fuel off. which then fills bottom 2 cylinders with fuel.
 

Biker dave

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Yikes I guess I'm glad this happened in the back yard than on the lake. No fires here but after all the fuel that poured out I've had the engine compartment open for a few days to let it air out. That definitely sounds like the same issue. I'm gonna start tearing into it tonight and see if that elbow is blocked. Thanks!!
 

Biker dave

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Boy swampy you hit the nail on the head with this one. My vent line to the bottom was indeed blocked with crud!! Gee I would have never thought to look there. Thanks SO MUCH. :winkingthumbsup"
 

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Swampy

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Yikes I guess I'm glad this happened in the back yard than on the lake. No fires here but after all the fuel that poured out I've had the engine compartment open for a few days to let it air out. That definitely sounds like the same issue. I'm gonna start tearing into it tonight and see if that elbow is blocked. Thanks!!
Boy swampy you hit the nail on the head with this one. My vent line to the bottom was indeed blocked with crud!! Gee I would have never thought to look there. Thanks SO MUCH. :winkingthumbsup"
No problem!! Glad I could help! Good luck with that thing!! I have a 98, bought it couple years ago from a guy that said it needed carb work! Ended up, #3 cylinder was wiped out!!! I think from getting washed out with all that gas. Took #3 .060 over (maxed out) I wasn’t happy!!!
 
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