Porsche Repair: 78 sc running flat, air fuel mixture, bosch jetronic

Question
hi dave i recently bought 78sc have spent considerable amount of money getting back to acceptable road worthy condition but although car starts well when taken out on the road there is a considerable lack of accelaration although the car wiil gain speed it is quite slow to do so, new injectors have been fitted together with rotor arm timing as been set plus all obvious other items could you please give me your veiws thanks colin nottingham

Answer
Hi Colin,

Thanks for taking a good ol' Porsche and putting its life back in order.

The absolute first thing these cars with Bosch Jetronic injection need is just exactly the right fuel pressure.  Not too much, not too little.  Wrong pressure can be caused by various factors, so you can't always jump directly to the fuel pump.  

If you are going to have the car awhile and get to working on it yourself, one of the best investments is a fuel injection system pressure kit.  Basically it's a pressure gauge and fittings to connect to your fuel line near the fuel distributor and a neat little valve that controls the test process.  Your mechanical injection is completely designed around the ability to get the proper inflow pressure and modify it along the way to get the proper air fuel mixture.  Clever, but it requires a pressure tester to start just about every diagnostic procedure.

The first test is to run the fuel pump without the engine on (by jumping terminals 30 and 87 at the pump relay) and measure the pressure arriving at the fuel distributor.  If it's not 70-75 psi, corrective action is required.  Of course that action depends on whether the psi is low or high to the test value.

I'd suggest checking that first and writing back...no one can have an SC that won't roar through the countryside!

Dave