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I am having fuel delivery trouble with my 1990 Chaparral 1800 SL.

So far I have replaced what I believe is a perfectly good fuel pump with a new one.

I removed the out line from inside the fuel cell and checked the screen type filter on the bottom end and it is clear of all obstruction.

I have replaced the fuel hose with the upgraded fuel hose from tank to pump, (just in case the line was breaking down internally.)

I have completely discarded the fuel filter, (at least until I get this fuel delivery issue resolved.)

Now this brings me to the forward, 151A, (late model), carburetor.

There is a vacuum line that routes from the flange of the forward carb down to the fuel pump.

The forward carb has very low vacuum and when adjusted for balance it runs like junk.

The rear carb has terrific vacuum and can be adjusted like normal.

I can find no vacuum leaks.

OK, now the past symptoms are as follows;

Drop boat in water.

Fire off the engine and it fires right away.

Sounds really good

Take boat out on the water and run it hard or easy for 15 to 20 minutes.

Stop engine and fish for an hour or so.

Engine will not fire again and there is no fuel in the lines and/or carbs.

I dont understand that vacuum hose from forward carb to fuel pump.

What is that vacuum line supposed to do?

Is that vacuum line there to assist the fuel pump ..... Kind of like a mechanical over vacuum (or vise versa) fuel pump?

Why can I not get any measurable vacuum in the forward carb?

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I just sold my 1990 1800sl. I remember a line going from the front of the carb back to the fuel pump. That line I think was a fail safe. The problem you describe is the exact same trouble I had a few years back. The fix was new plugs, one plug broke in half when removed.

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Ok, got the fuel delivery problem resolved! I added an in line, electric, low pressure, fuel pump and 2 visible fuel filters with a 10 amp fuse. I wired the new pump into an oil pressure sending unit and ignition switch. This way the pump gets 12vdc during starting and once the oil pressure comes up to safe operating pressure the pump then gets its 12vdc from the run position of the ignition switch. If the engine shuts off, the oil pressure drops and the pump is shut down. A great way to safely install and use an electric fuel pump on a carberated engine.

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