Why Do I Need One?
Even if you regularly use your classic, it isn’t in daily use. Modern fuel goes stale very quickly when exposed to the atmosphere and as your car sits in the garage what is left in the carbs and fuel lines either evaporates or runs back to the tank. That means that you have to churn over the engine for a prolonged period of time before fresh fuel is pumped up from the tank and eventually into the cylinders. Depending on how powerful your mechanical fuel pump is and how good your starter motor is it can take up to a minute just to get enough new fuel into the engine so it can burst into life. But it gets worse! This very quickly runs your battery flat, puts unnecessary stress on the starter motor and pulls massive electrical loads through your starter wiring.
Further to the starting issues mechanical fuel pumps run off engine speed, in theory the faster the engine is going, the more fuel is delivered. This was all well and good back in the mists of time, but modern fuel isn’t as volatile as it once was and the mechanical pump fuel delivery isn’t as consistent as it could be. The simple fact is that your engine hasn’t got the amount of fuel it needs at the right time.
Getting the Right Pump
There isn’t ‘a one fits all solution’ when it comes to delivering fuel to a carburettor, but the basic principles are the same. Like all good modifications, it all starts with a bit of information. To get the right pump you need to know the following:
- The correct amount of fuel pressure (Usually between 3 and 8 PSI)
- The required fuel flow in litres or gallons per minute
- Where you can fit it – Will it be close to the tank, or close to the engine?
There are a number of different manufacturers, but in low to medium fuel pressures we tend to use an SU Pump and on the higher pressure end a Holley. This is because we have found them to be robust and reliable over hundreds of different applications.