I have been reworking a small 1997 15hp. 2 stroke yamaha. I have replaced almost everything... lol This project is getting out of control!!! Well rebuilt the carb, rebuilt the fuel pump ,cleared all the water passages and a bunch of other stuff... So I have been trying to get it started for 2 days now and I don't think it is getting spark. I closed up the garage so it is pitch black with the spark plugs out and tryed starting it to see if it is getting spark, well no spark!! Is that a good way to test the spark?? I don't know, but I thought it might be... Maybe needs coils??? Please help!
Yamaha spark question.
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I unpluged the ground and white wire that come out of the kill switch but to no avail. I seem to think the motor isn't getting fuel. With a rebuilt carb and fuel pump, could it be the reeds? Yes I have a vented gas tank.... that always seems to come up. Anymore suggestions? The motor has good compression.
I bought the motor on the cheap from a guy who let it sit for 6 years. I have rebuilt several small out boards before but this one is giving me trouble. Originally all of the cooling passages were heavily clogged and the main water tube was shot. I pulled the power head and lower unit replaced all of the gaskets and the water tube. Rebuilt the carb just to be on the safe side and the fuel pump was all dried out so replaced all the internals. Now i can get fuel into the bow but after 20 time trying to start is I pulled the carb and the intake has no signs of fuel.
Sitting that long it sounds like jets are clogged, causing it to not pull fuel up from the bowl.
Please dont take this the wrong way, as I dont know your skill set.
Did you take the carbs completely apart, soak em in a good carb cleaner and blow compressed air and brake cleaner thru every little hole and orifice?
You said you rebuilt the fuel pump?
Is it possible a gasket or checkvalve didnt go on right?
For what its worth, a new complete fuel pump costs less than the rebuild kit (dont ask me why)
Please dont take this the wrong way, as I dont know your skill set.
Did you take the carbs completely apart, soak em in a good carb cleaner and blow compressed air and brake cleaner thru every little hole and orifice?
You said you rebuilt the fuel pump?
Is it possible a gasket or checkvalve didnt go on right?
For what its worth, a new complete fuel pump costs less than the rebuild kit (dont ask me why)
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^This, I say it all the time I don't rebuild fuel pumps I buy new ones.
I didn't read every post, but your engine is as simple as it comes.
1 Check Comp.
2 Check spark
3 Fuel
If one is bad find a new engine, if 2 is bad let me or Cut know and we will walk you through it, If 1 & 2 are good then its #3.
How to check spark with out a spark tester, remove both spark plugs from the Cyc. put the plug in the coil wire hold it tight to the block for ground and pull the pull cable the spark will jump the gap and you should be able to see. Repeat for the bottom cyc.
If the plug is not grounded it will give you a little shock but it won't hurt you!!!
*DO NOT DO THIS ON ANY OTHER MOTOR UNLESS YOUR SURE OF THE VOLTAGE, SOME NEWER ENGINES WILL SEND YOUR BUTT TO THE HOSPITAL*
Once you have checked the 1st 2 things, will you be able to diag your engine properly. Until then your guessing!
Most motors I replace the fuel pumps completely after tinkering with them, it was always easier to replace. But this model has the fuel pump built into the carb. When you remove the carb bowl the fuel pump is attached. I did blow compressed air through but didn't soak it in carb cleaner.... I WILL try that.
Did a compression check and it is a little low but almost even in both cylinders. 98 and 96. I know this is a little on the low side, but it should start. The carb bowl is full of fuel but it won't get into the cylinders to ignite. I am thinking this is a reed problem?
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1,544 Posts
It's not a reed problem!
Take a small spray bottle, Oil can works best! mix some gas and oil 50/1 ratio and spray 1-2 pumps into the carb with the handle wide open. Give it 30sec and try and start it, if it starts or tries to start, then the problem is your carb, if it doesn't do anything go back to #'s 1 & 2 and re-check.
96-98 is low should be up around 120-125 even if it starts it's not going to have much power.
??? Are you putting it in a drum or do you have a water hose attached to it?
Take a small spray bottle, Oil can works best! mix some gas and oil 50/1 ratio and spray 1-2 pumps into the carb with the handle wide open. Give it 30sec and try and start it, if it starts or tries to start, then the problem is your carb, if it doesn't do anything go back to #'s 1 & 2 and re-check.
96-98 is low should be up around 120-125 even if it starts it's not going to have much power.
??? Are you putting it in a drum or do you have a water hose attached to it?
Okay after an afternoon I finely said F it and pulled the whole power head. I noticed some suspicious things while taking it apart. Looks like the reeds were replaced and the exhaust cover had been previously taken apart. Yep if it all lines up then this motor swallowed a reed and got stuck in the exhaust housing. Oh well it need new rings and a upper piston. It is heavily scarred and so is the exhaust housing. Not an exact newbie when it comes to this, but at 98psi compression I figured I could get it to fire, my johnny/rude fired with 50psi!!! There was so little compression that the reeds would not open hence why the cylinders weren't getting gas. Thinking about boring it .50 over, modifying the carb, and boyseen reeds just for kicks. I might have $400 into when I'm done and it might become a 17hp. LOL 
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1,544 Posts
Cut no way that number is okay even with just pull starting it. Your right about the gauges though.
No way the reeds weren't not opening with 98psi of compression.
Don't bore it .50 over not even sure you can get a piston .50 over but it won't last. .30 max
Have fun with it and learning good luck need any help let us know.
Tight lines
Usually on other motor that I have played with in the past, I could put my hand over the intake and crank the engine. When I did this in the past I could feel the suction, but not on this motor.
They do make .50 over pistons, but I found a killer deal on oem ones. I can get both new pistons, rings, and pins for the cost of just one oversized piston.
They do make .50 over pistons, but I found a killer deal on oem ones. I can get both new pistons, rings, and pins for the cost of just one oversized piston.
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