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

[SeaRayClyde37]

Hey guys, I have a 86 merc 3.7 170. I have two problems:

1 is the starter. Its turning over really hard. I already checked all of the connections, batteries etc. Cleaned everything. Batteries charged. It turns hard then speeds up then turns hard.

2 is a fuel problem. I stopped getting fuel in the filter. Replaced the pump. First startup when good..filled filter ran and stalled. Also, I'm loosing the pressure. Why is the fuel filter emptying out?

 

[Bifflefan]

Problem 1, starter, it most likely is in need of a rebuild. A good stater/alternator shop should be able to rebuild it for about 75 bucks. Or at the least they can check it out to see if it is in good shape

Problem 2, where is the filter in the line?
How do you know it is empty?
Is there a crack in the hard line from the tank to the pump?
Is there gas in the tank?
Is the filter in the carb plugged up?

 

[SeaRayClyde37]

problem 2. Filter is between tank and pump and its a clear automotive filter, not a water separator. I just bought the boat. I've only had it a couple of weeks.

The line from the pump to the tank is a hose. Half tank of gas. What filter in the carb. I just got done reading a post about an anti-siphon..which I saw on the inlet of the fuel pump but I'm pretty sure when i reinstalled it on the new pump i dont remember seing any type of bearing/flap. I think it was just open. I gotta check that for the hell of it.

 

[SeaRayClyde37]

It looks like the anti-siphon is used between the filter line and pump hookup. The bearing was punched out though. Does anyone know if these mechanical marine fuel pumps are designed just like a mechanical automotive fuel pump? Other than the diaphram failure line that runs back to the carb they are the same right? I don't think anything is leaking between the pump and tank. Why isn't it staying PRIMED???

 

[SeaRayClyde37]

Maybe if the starter would turn over faster it would get to the carb. Gotta fix that next...

 

[Bt Doctur]

the anti-syphon is the very first fitting at the gas tank, If still having problems ,For testing use a remote tank at the fuel pump. an outboard tank .Not a gas can with a hose stuck in it.

 

[stonyloam]

470 starters have a rather long armature that can bend or break over time. When that happens the armature will rub against the field coils of the starter. That will cause the slow/ fast starter. Probably time for a new starter. Check e-bay "470 mercruiser starter".

 

[SeaRayClyde37]

Thanks terry. I found one on amazon by sierra for $130. Forgot to mention...several weeks ago out on the lake I found a bad short from the main disconnect to the bildge float switch. That wire was stuck to the block while I was trying to crank and the starter smoked a little. Ever since then I've had the starter problem. The fuel is a new one.

 

[SeaRayClyde37]

K put in the new starter. Finally had a break from work. Now i dont think its getting spark. In ran shitty for a few minutes. Maybe the slave or coil?

 

[stonyloam]

Most likely points. If it starts, it is not the slave. Coils seldom fail, points fail all the time.

 

[SeaRayClyde37]

Its getting fuel and its getting spark. Maybe too much fuel. When I pulled the carb there was a bunch of fuel in the intake manifold, and #1 wire getting spark. Didn't check the others. Any suggestions? Should I rebuild the carb anyways? Should I just go ahead and install pertronix?

 

[SeaRayClyde37]

It ran descent before the starter failed and before I replaced the fuel pump. There was some hesitation and bogging before but it was intermittent. Also replaced the plugs recently. It always idled low when it was cold, then when it got hot it idled high. Now I just need it to fire period...

 

[SeaRayClyde37]

ok guys it fires but only at 3/4 throttle. Starving fuel I guess I was wrong. Put the carb back on. What this means is.....lol???????

 

[nola mike]

Check your fuel pressure. People have had problems with too much pressure after pump replacement on the 470's. ..

 

[SDSeville]

^^+1

 

[SeaRayClyde37]

I dont know. I rebuilt the carb. It's still doing the same thing. Plugs are dry. It's not flooding. It will start with like 1/2 throttle. It doesn't seem right at all and its running like crap.

 

[SeaRayClyde37]

maybe I should try the fuel pump with the thin gasket instead of the thicker one. Everyone says they have flooding problems without the thick one, but i dont seem to be getting enough.

 

[Bondo]

maybe I should try the fuel pump with the thin gasket instead of the thicker one. Everyone says they have flooding problems without the thick one, but i dont seem to be getting enough.

Ayuh,... Is there any gas in the tank,..??

Can the fuel pump pull it out,..??

To test it, hook up a remote tank to the fuel pump,...

 

[NHGuy]

Try cranking the engine with the fuel line running into a jar. It should give gas whenever the motor turns. Safest way is with a fire extinguisher near by, the kill switch off, and/or the coil wire grounded. Just make sure the fuel does not ignite!
After a rebuild you need to adjust the idle mixture and idle speed. Those could be part of your current issue.
Did the rebuild include replacing the needle and seat? And was the float set to the correct height? Without a correct fuel supply from the pump into the float chamber your carb can't supply the fuel your engine needs.
If it goes dry something isn't supplying the gas you need..

 

[SeaRayClyde37]

Yes there is fuel in the tank. I replaced the needle and seat. The pump is working but I think I should replace the line from the tank to the pump and replace the filter as well. I read the closed sticky about troubleshooting the fuel system. I may have some vapor lock or a pinched line under suction. I made all the adjustments to the carb by the spec sheet. I cant get it running long enough to adjust the idle mixture but I started at 2 turns out. I really need to go out and get a pressure/vacuum gauge. I think the recommended fuel pressure is 5psi. I think I'm heading in the right direction because I tried the old pump and it wont fill the fuel filter. Any suggestions much appreciated. This thing is wearin me out...