adding electric fuel pump

[elwood206]

I think I may be having a vapor lock issue on my 86 sunbird 175, mercruiser GM block 3.0 140 horse, with an alpha one outdrive.

It will start easy, run great from idle to WOT, but when I kill it with the engine warm it does not want to restart. I checked the ignition system, everything there seems to be fine, if I let the engine sit for about 1/2 hour it will usually start right back up.

Right now the engine has a mechanical fuel pump on the block, my plan is to route my low pressure marine fuel pump I got form NAPA on the firewall or somewhere away from any heat source. Ive got a couple questions about the install and was hoping someone might be able to help.

Right now I have a 3/8 rubber fuel line from the tank to the mechanical pump, then rigid 1/4" line from the pump to the carb.
Can I safely run rubber line all the way to the carb?

The carb has internal threads on the fuel inlet, anyone have a good idea of where to look for an adapter to turn it into an external barb? does it need to be brass?

Should I get a block-off plate for the mechanical pump or just let it run dry?

Would it be worth the effort to tee-in the eclectic fuel pump and have the mechanical pump left on as a back up?

 

[mkast]

Re: adding electric fuel pump

You might want to review USCG regulations.
Troubleshoot your engine before changing your fuel system.
You "think" it's vapor lock.
After you install the pump, and the problem still exists...

 

[elwood206]

Re: adding electric fuel pump

I did, but thanks for the head up anyway.

http://www.uscgboating.org/safety/boatbuilder/fuel/_GIFS_FUEL/FUEL-F12.gif

http://www.uscgboating.org/safety/boatbuilder/fuel/183-524-b.htm

 

[Limited-Time]

Re: adding electric fuel pump

I think I would try and isolate and verify the issue before I put a band aid on it.

 

[shogun95]

Re: adding electric fuel pump

How about insulating the fuel line or cooling the metal fuel line with ice when the issue shows up? May solve the issue or prove it is a temperature issue before going to the trouble of the modification.

 

[chiefalen]

Re: adding electric fuel pump

Ok when you run a carbed engine hard you should let it idle for 2-3 minutes before shutting it off.

Than when you restart let it idle 2-3 minutes before running hard again.

You should not run at w.o.t for more than a few minutes. Not all day every day.

 

[elwood206]

Re: adding electric fuel pump

I understand that about a carbed engine, I dont run it WOT for more than a few minutes per trip, I was just trying to illustrate that the engine runs great in the full throttle range. I do also idle the engine before shunting it off.

I tried cooling off the metal line on the water, i wasn't able to get it that cool, and even if that would fix it I don't like the idea of having to carry ice packs for the engine. Id like to be able to rely on the engine starting every time I turn the key, whether its cold or not.

I took everyones advice who posted and am going to more throughly troubleshoot the engine before adding an electric pump. I just took off the fuel line from the pump to the tank, its in great condition, especially for having 1986 stamped on it. I will probably replace it to be on the safe side. I took out the check valve that is on the top of the tank.

Does anyone know how hard it should be to suck fuel through it? its defenetly not letting fuel back flow into the tank, when I try to blow through it backwards, when I blow throught it in the direction of fuel flow its pretty hard, should if be a free flow forward?


Thanks everyone for the posts.

 

[Eliminator]

Re: adding electric fuel pump

I installed a Carter rotary pump before my mechanical pump and after the fuel filter/seperator, wired through an oil pressure switch. Regs also allow a momentary switch to prime. My back check valve was no good so I just drilled out the spring retainer. No problems!
A rotary or vane pump will act as a restriction should it fail and the mechanical pump will have a tough time sucking through it. An electric plunger style will not cause a restriction problem should it fail.

 

[elwood206]

Re: adding electric fuel pump

I installed a Carter rotary pump before my mechanical pump and after the fuel filter/seperator, wired through an oil pressure switch. Regs also allow a momentary switch to prime. My back check valve was no good so I just drilled out the spring retainer. No problems!
A rotary or vane pump will act as a restriction should it fail and the mechanical pump will have a tough time sucking through it. An electric plunger style will not cause a restriction problem should it fail.

Thanks man, that is a a lot of good info.
I was just wondering about a momentary prime switch.
Can I ask why you installed an electric pump? So you had an electric pump and mechanical pump working at the same time?
I'm not sure what style of pump mine is, Ill be able to tell for sure when I power it up.

 

[Eliminator]

Re: adding electric fuel pump

Wow! This is a busy place! Nice to find a forum that doesn't discriminate against inboards. I really wasn't having any problems but I just bought the boat last year, I needed to re-carpet, do some rewire and it didn't have a fuel filter, proper fuel hose and needed some other repairs and last but not least I had a couple of almost new pumps kicking around I got for nothing. I didn't run it enough last fall after I bought it to find out if it had a vapor lock problem but just figured better chance of not leaning out the engine. Gas sucking 454

I was down to the wire when finishing it the end of June, (kid's done school) when I noticed the back check valve was non functioning and only one I had in my STUFF only had 1/4" NPT fittings so I just turned it into a fitting.

In hind site a back check valve could reduce or eliminate fuel siphoning into the bottom of your boat when not running should a fuel hose start leaking.

 

[chiefalen]

Re: adding electric fuel pump

Alright check the anti-siphon valve on top of the tank at the fuel pickup tube.

Check the screen at the pickup tube. It's on the bottom.

Check the fuel screen at the fuel pump.

Check the screen at the fitting to the carb.

Check the fuel water seporater . I know i spell badly.

Check that the fuel vent is clear. Maybe a vacuum condition.

 

[chiefalen]

Re: adding electric fuel pump

Oh i was gonna ask how you gonna power that electric fuel pump?

And no you can't put a tee in.

Did you ever do a psi test on the pump?

Should give you 4- 6pounds

 

[elwood206]

Re: adding electric fuel pump

I may have found a bad check valve at the top of the tank, I don't know what a "good" check valve should act like, mine stops flow in one direction, and severely limits it in another.

My vent is clear line is clear.

Fuel filter is clear at pump.

Carb screen is clear.

Dont have a fuel water seperator.

 

[chiefalen]

Re: adding electric fuel pump

It should let the fuel flow one way but should be i would say 1 pound of pressure to flow.

You test the fuel pump?

 

[elwood206]

Re: adding electric fuel pump

I was going to wire it in through an oil pressure sensor with a momentary prime switch.

I haven't checked the pressure of the fuel pump yet, just flow and it flows well. I don't have a fuel pressure gauge yet

 

[elwood206]

Re: adding electric fuel pump

I was going to wire it in through an oil pressure sensor with a momentary prime switch.

I haven't checked the pressure of the fuel pump yet, just flow and it flows well. I don't have a fuel pressure gauge yet

 

[chiefalen]

Re: adding electric fuel pump

4-6 pounds you wont need the electric pump.

 

[Eliminator]

Re: adding electric fuel pump

Basicly to verify the vapror lock problem! when it wont start under the conditions you mention, pull the air cleaner off and have someone crank the throttle a few times while you look down the carb without cranking. You should see a pretty good stream of accelerator pump shot down the carb, like liquid spraying out of a garden hose. If you have that and it will still not start you probably have other problems but it should be a steady stream or spray.

Fuel pressure is important and what you are looking for while cranking when it won't start, and little engine like that 4-6 PSI cranking or running. I just want to keep mine a little higher.

In my opinion an electric before a mechanical pump makes life easier for the mechanical by supplying all the pressure the pump needs so it doesn't really have to work but the mechanical also works as a hydraulic accumulator should the electric pick up air etc. Planing the same setup on my other boat i'm building.

 

[elwood206]

Re: adding electric fuel pump

Seems like a good setup to me too, where did you mount the momentary prime switch? back at the engine or route it up to the console?

 

[Eliminator]

Re: adding electric fuel pump

I didn't bother installing a momentary switch to prime, the oil pressure switch starts the fuel pump at 10-12 PSI of engine oil pressure anyways but the reg's do allow a momentary switch. if I did install one it would be on the dash.