1977 Mercury 1500 starving for fuel at half throttle and sucking primer flat.

[dwilley]

My 1977 Mercury 1500 is hard to start and is starving for fuel at half throttle. They only way to get it to start when it?s cold is to squirt some fuel into the carbs or choke it with your hand. The flapper chokes on the top two carbs don't seal good enough to pull any fuel into the carbs. I have rebuilt the fuel pump, replaced all fuel lines including primer, and cleaned the carburetors. I had the boat out yesterday and it will go to about half throttle then lose power and almost die. I noticed that the primer bulb was sucked almost flat. You could however pump it a little bit and it would pick right up but then would starve again. I removed the fuel cap hoping it wasn't venting good but it didn't help. I do remember that when I got the boat out this year the old primer bulb would pump once then stay flat so I replaced it. I also had an extra brass connector that screws into the top of the tank and it allowed the primer to pump up better. Does the brass connector have anything to do with venting? One other thing I should mention is that when I had the carbs apart I noticed that the float needle valve would stick shut when you pushed up on the lever. If you tap the top of the carb it would open back up. Is this normal, does the fuel pump have enough pressure to push the needle valve back open. I may have to break down and rebuild the carbs. I also tested the fuel pump by letting it suck straight out of a bucket and it has tons of flow. I may try to prime it up then stick the fuel line straight into the tank to see if that cures the problem. I have my suspicions that the primer or brass fitting is restricting flow.

Thanks in advance for your help.

 

[Bondo]

Re: 1977 Mercury 1500 starving for fuel at half throttle and sucking primer flat.

My 1977 Mercury 1500 is hard to start and is starving for fuel at half throttle. They only way to get it to start when it’s cold is to squirt some fuel into the carbs or choke it with your hand. The flapper chokes on the top two carbs don't seal good enough to pull any fuel into the carbs. I have rebuilt the fuel pump, replaced all fuel lines including primer, and cleaned the carburetors. I had the boat out yesterday and it will go to about half throttle then lose power and almost die. I noticed that the primer bulb was sucked almost flat. You could however pump it a little bit and it would pick right up but then would starve again. I removed the fuel cap hoping it wasn't venting good but it didn't help. I do remember that when I got the boat out this year the old primer bulb would pump once then stay flat so I replaced it. I also had an extra brass connector that screws into the top of the tank and it allowed the primer to pump up better. Does the brass connector have anything to do with venting? One other thing I should mention is that when I had the carbs apart I noticed that the float needle valve would stick shut when you pushed up on the lever. If you tap the top of the carb it would open back up. Is this normal, does the fuel pump have enough pressure to push the needle valve back open. I may have to break down and rebuild the carbs. I also tested the fuel pump by letting it suck straight out of a bucket and it has tons of flow. I may try to prime it up then stick the fuel line straight into the tank to see if that cures the problem. I have my suspicions that the primer or brass fitting is restricting flow.

Thanks in advance for your help.

Ayuh,.... You have a fuel restriction, Up-stream of the primer bulb...

 

[dwilley]

Re: 1977 Mercury 1500 starving for fuel at half throttle and sucking primer flat.

I did some troubleshooting today and I think I found the problem. I took the motor side quick connector off and tried to pump fuel out into another container. I found that when I squeeze the primer down it takes a good five seconds to come back. I took the pickup out of the tank and the screen is clean. I blew through it with my mouth and it had some restriction but not to bad. I then took off the brass quick connector and pressed the valve in and tried to blow through it. It had severe restriction. This has got to be most of the problem. The tank I am using is one that was on my dad's little Evinrude motor. I would say it is not sized for a 150 hp motor. From what I have read on here this motor likes its fuel at full throttle. I'm not sure if these brass quick connectors have a hp or flow rating but this one is definitely not big enough. I decided to do away with the quick connector and put a 5/16" hose barb fitting in instead. So now I will just disconnect the motor side and leave the fuel line on the tank, probably not a bad idea anyway to keep the fuel line out of the weather. I did the same test pumping into another container and it pumps tons of fuel and the primer comes back in less than a second. I will test this new setup this weekend and post the results. I am still planning on rebuilding the carbs but if this works I may wait until next year. Thanks