No fuel pressure on a 1975 merch 8500

[tompowers85]

I checked my fuel pressure from the line coming off the fuel pump by cranking the engine and the fuel coming out is speratic. It comes out as a trickle and then it stops altogeter. When I prime the bulb it comes out fast. I replaced the diaphram and check valves about 3 weeks ago, so i was wondering if maybe a pressure leak in the tank or fuel line might cause this or anything else or could it only the fuel pump.

 

[dynapac]

Re: No fuel pressure on a 1975 merch 8500

Does the engine run? Pump works off of vacuum from one cylinder of the engine. The flow should be sporadic. Priming will cause the lines to fill. The trickle could be from the pump and line draining. Have you replace the fuel filter?

 

[tompowers85]

Re: No fuel pressure on a 1975 merch 8500

i replaced the fuel filter. the engine does run if i push the throttle all of the way up after the engine starts to fire, and then when i prime the bulb the engine rpms increase to were they should be with the throttle up that high.

 

[dynapac]

Re: No fuel pressure on a 1975 merch 8500

Let me see if I understand you.....<br /><br />Full throttle setting and the engine will idle, prime the bulb and that seems to increase fuel flow to the carbs and you see an increase in RPMs. Was the motor running OK prior to rebuilding the pump?<br /><br />Stupid question.............<br /><br />Did you put the gaskets and diaphrams on in the right order, howabout the check valves?

 

[Ben Konopacky]

Re: No fuel pressure on a 1975 merch 8500

did you check the vac./press.on the cyl.port that is pulsing the fuel pump.this port (hole) could be partly plugged and restricting the operation of the fuel pump..also if the spark plug of this cyl. is wet its an indication of a leaky diaphragm .

 

[tompowers85]

Re: No fuel pressure on a 1975 merch 8500

i did not check the port. I never even thought about that, but i can feel a little push of air coming out the end of the fuel line when I crank the engine. The engine was not running ok before i changed the diaphram. I put the gasket and check valves on correctly, i used a repair manual.