Mercruiser 3.7 4cyl fuel not getting to carb - replaced fuel pump and same problem

[nola mike]

FYI, last time I did this the float specs were wrong--don't remember whether the manual or kit specs were off. I think it was the manual.

 

[SeaRayClyde37]

ok I might have found a problem. When you give the carb throttle with the engine off, the jets are supposed to continue spraying correct? Because if i hold it open it sprays and then stops

 

[Silvertip]

You are looking at the accelerator pump squirting when you move the throttle. They do not spray continuously with the engine off. Without going back over the entire thread again, several things you mentioned have not apparently been done.

1) the anti-siphon valve is at the outlet of the tank, not on the fuel pump. What you are looking at on the fuel pump is a simple hose barb. There is no check ball inside those.
2) You mentioned using a clear auto-style fuel filter. Those filters rarely fill completely and in fact may have just a little fuel in them.
3) You have not checked the pickup tube in the tank. It may have broken off or has a hole in it so it cannot draw fuel.
4) You apparently have a rubber hose from the tank to the engine. That hose can deteriorate inside and prevent the pump from drawing fuel.
5) As was suggested, use a portable tank or at least install a primer bulb and see if you can draw fuel and force it to the engine that way.
6) The tank may have an abundance of crud in it that has plugged the filter at the bottom of the pickup tube.
The trick here is to "diagnose" not "shotgun" the problem in hopes you get lucky.

 

[SeaRayClyde37]

Everything has been disassembled from the tank to the intake manifold. There is no anti siphon check ball in the pickup tube, just the filter, and its reaching the fuel, and it is clear not clogged. It has a filter in it thats all. I replaced the barb at the pickup tube. I used thread locker on everything. I replaced the line from the barb to the fuel filter. I replaced the fuel filter. I replaced the line from the fuel filter to the pump. I replaced the pump. I didn't replace the line from the pump to the carb. I rebuilt the carb. I'm gettin fuel to the carb. I couldn't find a compound meter today so I dont know what the fuel pressure is. I dont think I have vapor lock. I really dont know whats going on. And it tries to run only with the mixture screw almost all the way out where it is barely screwed in enough.

The fuel tank vent tube is not clogged and I believe its functioning properly.

The reason I replaced the pump is because it stopped working completely.

The reason I replaced the filter, line, and barb is because the line was thin and not marine grade. I figured it may have been getting pinched under pressure and it was only a few bucks.

The barb at the pickup tube was completely stripped. I replaced it and re-tapped the pickup tube with 1/4"npt pipe thread tap because it had chucks of aluminum stuck in the threads from the barb.

 

[SeaRayClyde37]

The boat ran good until the pump went out. I feel like ever since I replaced it that's where my problems began. Some people say to go electric. Some people say to go aftermarket Sierra mechanical. Thats what I did. Most say not to get the mercruser mechanical. I dont know what to do at this point other than check the pressure when I have a chance to get a gauge.

The people who went to the Sierra say to use the thicker gasket because without it the pressure is to high and the carb floods really bad.

The peope who went to the Sierra who didn't use the thick gasket said that they got shavings in the oil.

 

[Eric 3.7LX Alpha 1]

To only thing you can do is test the pump with a psi gauge. Auto Zone has them... 25 bucks.

Here is the one in stock at the 1535 Laurens Rd, Greenville, SC store.... you may even be able to rent it from them.

http://www.autozone.com/autozone/acc...er=487843_0_0_

You will also need a section of 3/8" fuel pressure hose, hose clamps and small section of 3/8" brake line with fittings and flare ends connected, can be 6" to 12" long.
http://www.autozone.com/autozone/par...estid=12626786

Cut the brake line into two pieces. Remove your existing line from the pump to the carb. Install the two cut brake line pieces on both the fuel pump and carb. slide the the new 3/8" fuel hose over the cut ends of brake line and clamp. Tee in the gauge somewhere in this fuel hose. So now you can see your pressure on this temporary line.

I actually have a permanent gauge connected on my "self-bent" new metal line using an inverted flare tee and fuel pressure gauge. I can tell in a second when I am out on the water if there is an issue what my pressure is.

 

[SeaRayClyde37]

Thank you!