Carbs running empty at idle only. Any ideas?

I have replaced all fuel lines from tank to carbs. Cleaned tank. Fresh gas. Rebuilt the pump. Ran on smaller remote tank with same propblem. The boat runs great at wot. I thought for sure it was going to be a pin hole in the pump diaphram, it wasnt. The compression is low all six cylinders are between 76 & 80. I saw somewhere that Johnson had a low compression engine, I wonder if this is one of them. It is a 1991 150. I can not get any numbers off of the engine. They are un readable. I am at my wits end here please help with any ideas.

Thanks,
Josh

Re: Carbs running empty at idle only. Any ideas?

Is it a cross flow or a looper ??

Re: Carbs running empty at idle only. Any ideas?

boobie said:

Is it a cross flow or a looper ??

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I think that it is a cross flow. How can I tell the dif?
Thanks for responding.

Re: Carbs running empty at idle only. Any ideas?

A crossflow will have three (3) dual throated carburetors.

A looper will have six (6) single throat carburetors.

Your problem would be caused by either.... a leaking pressure hose between the pump and crankcase, OR a faulty pump, OR poor compression resulting in weak crankcase pressure, OR a failed reed plate (leaf valve) which also results in poor crankcase pressure, OR a sticking Anti Siphon Valve.

However, a sticking Anti Siphon Valve on either type V6 engine would cause the engine's vaccum switch to engage which in turn would cause the warning horn to sound off.

NOTE: A crossflow engine would have a core plug (looks like a quarter size freeze out plug) with possibly the model number on it, located on top of the block near the port cylinder head gasket. A looper would have the core plug located on the rear portion of the engine, centered between the cylinder heads at the top of the bubble shaped exhaust housing.

Re: Carbs running empty at idle only. Any ideas?

It is definatley a cross flow than.
I am leaning more towards not enough crank case pressure which is not sending enough pulse for the pump to work.

Is it possible that the hose connecting from pulse source and pump is too long and too large diameter?
I just changed this recently but worked fine for two days. I have since re checked the connections.

I also removed the one way check valve in this line. Could this be the problem as well?

Thanks.

Re: Carbs running empty at idle only. Any ideas?

Josh Yates said:

I also removed the one way check valve in this line. Could this be the problem as well?Thanks.

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Josh.... A replacement hose must be the same size diameter as the original. And that "one way valve" is actually a flame arrestor that absolutely must be between the engine's crankcase and the pump.... it prevents any flame that exists in the crankcase from reaching the pump!

Re: Carbs running empty at idle only. Any ideas?

Joe Reeves said:

Josh.... A replacement hose must be the same size diameter as the original. And that "one way valve" is actually a flame arrestor that absolutely must be between the engine's crankcase and the pump.... it prevents any flame that exists in the crankcase from reaching the pump!

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I really appreciate the help. If I was to order that hose and flame arrestor what would I call it exactly? Part number would be great.

Re: Carbs running empty at idle only. Any ideas?

You can use any reinforced fuel line, available at most hardware stores... cut it to suit.

The "Pulse Limiter" (proper name) is part number 174540. Note that the plastic side of the Pulse Limiter goes towards the pump!