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I get asked all the time about this modification so I decided to make a "how to" and make it a sticky.
This is one of the simplest modifications to do to your carbs. It is intended for multiple carb applications, but can be done on a single carb application as well.
The goal of this mod is tie triple carbs with individual fuel pumps, into a single balanced pressurized system. Rather than three individual systems
One advantage to this modification has been, reduced fuel pump check valve failure. This is a common problem on the older style SBN carbs, used on the GP1200, SUV and many other skis. This failure can lead to potential lean condition, and piston failure. I ran a set of SBN's with this modification in my SUV, and I had over 300 hours on the carbs. When I inspected them recently, all the check valves were in pristine condition. Pretty much unheard of for these style carbs.
When I would get a set of SBN carbs in for repair, I could guarantee the cutomer I would find a creased check valve, and I was right 99.9% of the time.
Another reason for this mod, is the small return orifice in the carb body, gets plugged easily. Either by a foreign object, or corrosion. The orifice is .020" in diameter. This condition results in the fuel pressure getting to high within the carb, which in turn forces the needle valve to open and floods the carb.
There are several ways to do the restrictor either with a jet installed in an inline fitting (Tee or coupler) or threaded into the tee on the carbs.
Novi carbs come with the returns drilled out, I will attach their schematic.
On Yamaha 1100 carbs with the remote fuel pump, the carbs were set up in this manner. They had a restrictor built into the last tee on early models. Later models they went to a small orifice in each cover.
This is one of the simplest modifications to do to your carbs. It is intended for multiple carb applications, but can be done on a single carb application as well.
The goal of this mod is tie triple carbs with individual fuel pumps, into a single balanced pressurized system. Rather than three individual systems
One advantage to this modification has been, reduced fuel pump check valve failure. This is a common problem on the older style SBN carbs, used on the GP1200, SUV and many other skis. This failure can lead to potential lean condition, and piston failure. I ran a set of SBN's with this modification in my SUV, and I had over 300 hours on the carbs. When I inspected them recently, all the check valves were in pristine condition. Pretty much unheard of for these style carbs.
When I would get a set of SBN carbs in for repair, I could guarantee the cutomer I would find a creased check valve, and I was right 99.9% of the time.
Another reason for this mod, is the small return orifice in the carb body, gets plugged easily. Either by a foreign object, or corrosion. The orifice is .020" in diameter. This condition results in the fuel pressure getting to high within the carb, which in turn forces the needle valve to open and floods the carb.
There are several ways to do the restrictor either with a jet installed in an inline fitting (Tee or coupler) or threaded into the tee on the carbs.
Novi carbs come with the returns drilled out, I will attach their schematic.
On Yamaha 1100 carbs with the remote fuel pump, the carbs were set up in this manner. They had a restrictor built into the last tee on early models. Later models they went to a small orifice in each cover.
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