Classic American cars


As is often the case our customer came to Probuild American after everyone else had tried in vain to bring the Big Block Mercruiser to life. The Scarab is fitted with the beautiful Mercruiser 454ci 7.4 litre and sitting on top is a Holley List 4779 800cfm double pump carburettor, unfortunately the engine would only fire up for a second or two then die out.

The only way to sort these problems is to go through each component seperately, particularly where others have played before you.

First thing to do was take the big Holley 4779 off and strip it completely, fit new parts as necessary which included gaskets and replacing the secondary float bowl (accelerator pump screw threads were stripped) then refit to the engine using new gaskets on both the carb base and the 1″ spacer already fitted.

Next we checked the fuel pump pressure, this was between zero and 1lb, we were looking for between 5 and 7 pounds. The existing pump looked as if it had seen better days so a new Edelbrock RPM Street EDL1722 High Performance 110 Gallons per hour mechanical pump was fitted, we also fitted a glass inline fuel filter in the hose up to the carb. Then removed, sealed and refitted all of the new fuel lines and connectors/adaptors which had been fitted previously by the owner.

The Edelbrock RPM Street fuel pump is a great pump to use as it is high flow and is internally limited to 6lbs pressure so you do not need a fuel pressure regulator in the system and will support up to 600 horse power.

The only thing to do then was to give it a try. With a fully charged battery, a top up of fuel and a check of the engine oil the last thing to do was to put a flow of water from a hose into the cooling system. We turned the engine over with the coil disconnected to bring up oil pressure then reconnected everything, with 2 pumps of the throttle and only a few turns of the engine the 454ci burst into life.

After letting the engine come up to working temperature it was time to set the float levels, adjust the timing and idle mixture before finally setting the tickover speed. With the engine running very sweetly and with excellent oil pressure of 60lbs when ‘hot’ we were happy.

It is always satisfying to sort these engine problems out where others have failed and this lovely Scarab with Mercruiser 7.4 litre is no exception, very satisfying indeed!

Next step will be to see how it goes under load in the water, watch this space!

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