Gas tank conversion.

[rmacdesign]

Sounds like I gave some work to do. The whole check valve thing gets me do you see it in schematic 1999 Yamaha EXCITER 135 (EXS1200X) Fuel Tank | Babbitts Yamaha Partshouse

 

[I_squared_r]

Sounds like I gave some work to do. The whole check valve thing gets me do you see it in schematic 1999 Yamaha EXCITER 135 (EXS1200X) Fuel Tank | Babbitts Yamaha Partshouse

Maybe the boats are different than the jet skis. I see this on the diagram, part #26 https://watercraftsuperstore.com/products/air-vent-assembly-9204-gp1-u7850-00-00
And it doesn't look to have a check valve built in. It looks like the gas tank is vented to atmospheric pressure. The jet skis always have some pressure in the tank and it helps for fuel delivery. Maybe you can inspect this and see if there's a valve inside, and check that it isn't clogged.

 

[rmacdesign]

Thanks, I will check and see if that vent assembly is a check valve. Still think its a fuel tank pressure problem but not a lot of information on the boats about the fuel tanks out there. Thanks for your time.

 

[I_squared_r]

Thanks, I will check and see if that vent assembly is a check valve. Still think its a fuel tank pressure problem but not a lot of information on the boats about the fuel tanks out there. Thanks for your time.

Why do you think about the fuel pressure? What happens if you remove the gas cap after the boat sits in the sun for some time? Is there pressure, vacuum, or nothing?

 

[rmacdesign]

I think it should have some kind of presure, has nothing.

 

[rmacdesign]

Just checked air vent from tank and air goes both ways so not a check valve or not working. Don't know.

 

[I_squared_r]

Just checked air vent from tank and air goes both ways so not a check valve or not working. Don't know.

I don't think it needs one. It definitely is your carburetors

 

[Beachbummer]

One of the reasons I switched to 4 stroke was no more carb, but there was no alternative for 50+ years, so they are known to work for sure.

To troubleshoot the fuel pump, I have added external vacuum fuel pump and also at times an electric fuel pump to troubleshoot.

Maybe there's someone local, like a motorcycle shop that could do the rebuild for you?


Good fuel filtration will extend their life considerably (within reason) I had 2 fuel water filter separators in series! And that helped quite a bit to extend their life, but also along a more powerful fuel pump.

Best of luck!

 

[I_squared_r]

Maybe there's someone local, like a motorcycle shop that could do the rebuild for you?

It's getting increasingly rare to find mechanics that work on 2-stroke stuff now.

The mikuni fuel pumps don't really have problems. The pump is on the first carburetor and its a diaphragm pump that works off crankcase vacuum/pressure. Thats another thing the OP can check - if the hose from crankcase to fuel pump is damaged in anyway. Those old yamaha fuel lines are great, but they start to deteriorate over the years. FYI jetmaniac over at www.x-h2o.com has the replacement OEM fuel line. Good stuff.

OP where are you located? I have a few good mechanics in NYC that works on 2-strokes

 

[dabomb6608]

FYI the boats have free air vents due to Coast Guard regulations. Jetskis regulations are different due to their higher chance of flipping over causing spills.

Also, each carb has its own fuel pump on the yamaha triples.

If you want to send carbs off for a rebuild, I do offer that service. OP I also responded to your message you sent me.

 

[rmacdesign]

It's getting increasingly rare to find mechanics that work on 2-stroke stuff now.

The mikuni fuel pumps don't really have problems. The pump is on the first carburetor and its a diaphragm pump that works off crankcase vacuum/pressure. Thats another thing the OP can check - if the hose from crankcase to fuel pump is damaged in anyway. Those old yamaha fuel lines are great, but they start to deteriorate over the years. FYI jetmaniac over at www.x-h2o.com has the replacement OEM fuel line. Good stuff.

OP where are you located? I have a few good mechanics in NYC that works on 2-strokes

Lake ontario

 

[rmacdesign]

Went out this morning put chock on and covered 1 intake with hand it started right up and ran good. Seems to be getting better?? Maybe pumps just need to be primed a couple of times. I will put it in the water Friday and see what it does.

 

[rmacdesign]

?? Since I mix oil and don't need intake cover for oil can I use somthing else to cover carbs. Since its a boat and don't have to worry about water can I use a carb filter like a motorcycle

 

[I_squared_r]

Definitely keep the factory spark arresters on there. Especially since its 2-stroke and your carburetors need to be rebuilt. I would want some protection for when it back fires. Because it could. Your carbs need to be rebuilt. In fact, I would resolve it ASAP before doing anything. You don't want to lean out a 2-stroke and destroy a motor.

Companies sell different spark arrestors, but the performance gain is extremely small, if any. Idk how your spark arresters are, but on the jet skis we would remove 1 of the 2 screens. This modification was essentially 0 air filtration and 0 spark arrestor. The single screen was there just to make sure large objects didn't fall inside the motor. And this would slightly impact the pop off pressure on the N/S because of the pressure changes. I still remember what jetting, N/S, and pop off I'd run. In other words, leave your OEM stuff until you resolve the problem.

 

[dabomb6608]

?? Since I mix oil and don't need intake cover for oil can I use somthing else to cover carbs. Since its a boat and don't have to worry about water can I use a carb filter like a motorcycle

You cannot replace/remove the intake without modifications to the carbs. The carbs are jetted and setup for the amount of air restriction the factory intake produces. Any change to that with a better breathing intake setup will alter the air/fuel ratio, run poorly, and burn a engine up if the carbs aren't setup correctly.

 

[dabomb6608]

I mean this in the nicest way possible but you should try to find someone who knows these very well to get you going. These engines leave zero room for error and if not setup correctly you will burn another engine up in very short order.

I hope whoever rebuilt your engine knew what they were doing as well. 99% of the time you can't just slap a top end on them and be done, I see it attempted all the time and it almost always ends poorly.

Rebuild the carbs with genuine mikuni kits only. Set them to 100% factory settings. Confirm you are getting proper pop off pressure. Reassemble the intake as it came from the factory. The factory carb settings work 99.99% of the time on factory engines. If it doesn't run well on factory settings then you have issues elsewhere.

 

[I_squared_r]

I mean this in the nicest way possible but you should try to find someone who knows these very well to get you going. These engines leave zero room for error and if not setup correctly you will burn another engine up in very short order.

I hope whoever rebuilt your engine knew what they were doing as well. 99% of the time you can't just slap a top end on them and be done, I see it attempted all the time and it almost always ends poorly.

Rebuild the carbs with genuine mikuni kits only. Set them to 100% factory settings. Confirm you are getting proper pop off pressure. Reassemble the intake as it came from the factory. The factory carb settings work 99.99% of the time on factory engines. If it doesn't run well on factory settings then you have issues elsewhere.

I agree with everything here. There's a lot of hacks out there. I've gotten a few grenades from "reputable" engine builders. Sleeves not pressed in correctly and dropping. 3x he decked the cylinder and relief cut the head to match before I said "to hell with you and your motor".
Another with a riva racing sleeve, too high compression ratio, and I was told "its a pump gas motor". I melted a piston top, and the ring caught the exhaust port. Carnage.
Then I went with a lightly modded ski that I rode exclusively in the surf. All the sinking and swamping, I was always changing electrical components and stators. Then I quit.
2-strokes are tons of fun, but I don't miss the problems lol

 

[rmacdesign]

I mean this in the nicest way possible but you should try to find someone who knows these very well to get you going. These engines leave zero room for error and if not setup correctly you will burn another engine up in very short order.

I hope whoever rebuilt your engine knew what they were doing as well. 99% of the time you can't just slap a top end on them and be done, I see it attempted all the time and it almost always ends poorly.

Rebuild the carbs with genuine mikuni kits only. Set them to 100% factory settings. Confirm you are getting proper pop off pressure. Reassemble the intake as it came from the factory. The factory carb settings work 99.99% of the time on factory engines. If it doesn't run well on factory settings then you have issues elsewhere.

Project boat just trying to learn can't learn by going to dealer. If it blows up then it blows up. Not a lot of money invested.Maybe the carbs are set up for a oil drip and are to lean for mixed fuel. Going to change mixture to 40 to 1

 

[rmacdesign]

I'm a little confused it runs great just hard to start. If carbs were bad then it would run bad?

 

[Beachbummer]

Does it run well without messing with it? It sounded like you had to mess with it to start it, and to keep it running well.

The choke does that, covers the air path it so it will start easy. Is there a choke on it?