Setting up a new fuel injection system

If you're thinking of buying a new fuel injection system there are a few things to note when getting it calibrated with your existing setup.

Most fuel injection systems are shipped with a small main bypass which makes the engine run rich. While some systems run richer than others out of the box, they all come precalibrated with their own jetting. In addition, most new systems will run at the higher rpm's with a fuel pressure between 50-150psi. That means that at lower rpm's, the fuel pressure can be so low that the engine runs sluggish.

An Example of What Can Go Wrong

One of the injection systems that we purchased several years ago had a high rpm fuel pressure of around 80 psi and a small main bypass. As we tested the engine, we started using a larger main bypass so that the engine ran less rich and was more powerful. However, the larger main bypass took fuel away from the engine which caused the already low pressure to drop to around 60psi at high rpm and 35 psi at low rpm. There was a very poor response from the engine.

After some trial and error, we made the engine nozzles smaller to boost fuel pressure. The orig nozzles were over .050 in diameter. Later we ended up running nozzles in the mid .040's in diameter. High rpm fuel pressure was around 150psi low rpm pressure was about 80 psi. The engine ran very well with that combination.

Fuel Pressure and Air Fuel Ratio

The combination of main bypass and nozzle sizes determines the system pressure. Low rpm fuel pressures should not go below 50 psi. High rpm pressures are routinely at 80psi and above. As long as the fuel pressure is maintained with the mbp and nozzles, then the main role of the mbp is the change the afr for good power.

Some things to note from various manufacturers

Hilborn is an example of a 50-150 psi operating range. It should be noted that Rons are rated for pressures a little bit less than that. Their low cost system runs really well at around 125psi. Kinsler is pretty much right on right out of the box.

Rons give instructions for changing the main. There is no hs.

Conclusion

Setting up a new fuel system can take some trial and error. Knowing your setup and knowing what to tweak can help you get everything dialed in.

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