10-06-2013, 07:21 PM #1
99 GP1200 carbs not getting fuel past the needle seat.
I bought a 99 yam GP1200 and it had coded a fuel issue. The original owner told me he had the carbs rebuilt 3 years ago. I tore them down to rebuild them because I was getting fuel to the carbs but nothing in the cylinders.
When I tore them down I noticed that all 3 carbs(SBN 46mm) had fuel in the pump side all the way to the needle and seat. The fuel chamber was dry on all 3 carbs on the needle side(needle seat is 1.2).
The Yamaha service manual is worthless on the carb section. No info on pop off spring.
1. I'm wondering if the needle arm was bent from the other person how rebuilt them. It has to move far to open the needle seat to get fuel through the seat. But I have read alot on this ski and I guess it has high pop off pressure, what is the pop off pressure?
2. I was also thinking that it cant get enough pressure in the fuel lines? Would a fuel restrictor on the return line help with it.
3. The needle seat is 1.2 and cant tell what spring was insalled. I was going to put 1.5 needle and seats in them if that would help.
What am I over looking or doing wrong? I have never had a ski that had the pop off pressure so high. Some people told me it is as high as 70PSI.
Thanks for your time.
10-08-2013, 10:22 PM #2
They are actually SBN 44 carbs.
The problem you are describing is unusual. A bent needle arm could be the problem. They would all have to be bent well below the surface of the carb for the diaphragm to not open the NS. They are supposed to be level with the surface or very slightly higher then the surface. If the needle arms aren't the problem, then somehow the diaphram is getting sucked down to open the needle. Maybe an air leak or low compression?
The stock pop-off is very high. in the neighborhood of 65 to 70 psi. Don't change to a 1.5 NS unless you plan on changing the stock air box to high flow flame arrestors.
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