View Full Version : FUEL ISSUES I thought I'd share - must read for all carb'd boat owners.

07-09-2012, 11:28 AM
So on Friday evening we decided to run out to the sand bar for a swim considering it was 105F.
So we jump into the bump, lower it into the water, start her up and start heading out the canal.

As soon as I put it in gear and started to move, the motor stalls. No biggie I thought, mustn't be warmed up yet, so I start her again and idle out of the canal and hit the lake and go to give it gas to get on plane and bam, she stalls again. This time I'm thinking this isn't good so we fart around get her started again and then decided to idle to the sandbar where I can take a dip (as I'm sweating like a whore in church at this point), and then look into what's going on.

We get to the sandbar, I anchor up and flip oopen the doghouse to see what's going on.

I start her up again and she's idling but rough, so naturally I assume that there is a fuel issue going on. So I pull the +ve off the fuel pump and see that it make no difference to the way it's (barely) running. Great...I think, fuel pump is shot and I have 2 buddies coming over first thing to go wakeboarding and surfing tomorrow. So after 15 minutes of swimming and cooling off we putt back into the canal and to our dock so I can double check the pump and power wires with a multimeter to confirm that it is shot. At this point it's 7:30pm so my options for going to the auto parts store to get a pump are starting to dwindle.

I run into the house, grab the multimeter and head back out to the boat and check the voltage going to the pump. It gets about 11V at crank and 13V while running, so of course anyone would think the pump is shot if it's not pumping, right.....the funny thing here and key point to note, is that every time I would crank, it would start, so somehow it was getting gas...but more on that later.

So I run back inside, jump on the iPad and search the Moomba forums for info on pumps. I confirm I have a Carter 152-875 fuel pump which cross references to an Airtex E84839 (and P4839). I run out to the local Murray's and Autozone, and none of the local places carry one so I search online and find an O'Reilly's in Centerline 45 minutes away that has one. It's now 9pm and O'Reilly's closes at 10pm. I call them to confirm they have it in stock, so I don't drive all the way from Commerce Twp, for nothing and sure enough they do. So they hold it for me and I zoom out there and get it at 9:50pm.

Next morning I wake up and start swapping out the pump. It's 8am and already 95F! In the process of taking off the hoses I run into isses with the fitting being too tight, so I decide to unscrew the hose from the fuel rail feeding the Holley carb. Like and idiot I don't hold the hex fitting on thre fuel rail with a wrench and instaly crack one of the pipes. MF'er!!! Now, I'm crapping myself. Luckily I remember there is a NAPA nearby and a speed shop next door so one of them is going to carry a fuel rail for this thing. So I remove the feul rail and run out to NAPA. They have two rails in stock. One with a fuel pressure gauge and one without. The one without is cheaper but, it has the wrong spacing for the feed pipes that connect to the bowls, so I get the one with the fuel pressure gauge which turns out to be a plus, later. So at this point IU spent $85 on a pump, $56 on the fuel rail and $10 on a new 1/2" inline fuel filter.

I head back to the boat get it all together and crap....it's still not working right! Luckily with the fuel pressure gauge, I can see it builde pressure 3-4psi during crank, but as soon as the engine catching and it runs, bam I get 0psi! WTF?! At this point my freinds show up on the dock and ask me what I'm doing. I give them the story about my dilemma and they understand - they're both boat oowners and now the constant issues we all face with boats (holes inthe water we throw money into). After trying to start it a few times again, all of a sudden I'm getting 3psi while it's running...great! Lets' go boarding!

So I turn it off thinking maybe there was air in the line or some crap and we load up and get ready to head out.

We back out of the hoist and start up the canal, I lift the dog house agin to check the pressure and my heart sinks 0psi again! :mad:

So we fish out the oar and turn the boat around and head back....I try to start it again and it's working so we decide OK, lets not turn it off and go boarding. So we head out and ride for about 1.5hrs with no issue. and head back to the dock...all the while we are wondering what the issue is?

My buddy call his friend who is a boat mechanic to ask him about what we should look for. He mentions checking the voltage at the pump during crank and then while running we tell him we did and it seem fine, so he says maybe the sock on the pickup it clogged, so we take everything out of the rear locker and remove the panel to access the fuel pick up. Now, I don't know how they put these tanks together, but when you unscrew the pick up tube and try to remove it - there's no way you can pull it all the way out to check or replace the sock - it won't fit through that narrow 1/2" hole. Nonetheless I am able to look down the tube and see the sock it perfectly clean....so WTF? it's not that, and the inline filter is new too!

We're so confused at this point so My buddy Dave calls his mechanic uncle, this time, who says to check the power going to the pump when it's running. We say "Yeah we chacked that already and it's getting +13V". Nonetheless I decide to make 2 jumper wires so we can run direct from the battery to the pump to see WTH is going on, because with the engine running you cannot hear the pump at all.

Now THIS is the first thing I should have done!

We connect the old pump directly to the battery and bam, it works....hmm...so lets check the new pump that's installed, yep, that fires up when we connect it and we get +3psi on the fuel pressure gauge. So we are totally confused. When it's running its getting voltage too(?). So Dave's uncle tells us that the power should come from a oil pressure safety switch that closes the circuit and sends power to the pump after the motors starts - during cranking the power comes from a separate source - the starter circuit. We decide to jump the two fittings with our jump wire and sure enough we get the pump to work!

So this POS oil pressure switch is what is causing all the problems....now either it had a very poor connection that showed 13V, but could support any amperage draw from the pump, or it was intermittently working - either way it's effed. So off we go to NAPA again to get a new switch.

At first the guy is looking up parts in some marine catalog and tells me that it's going to take 3 days to get this switch. I tell him, that I could care less if it's "marine" and just to get a regular 2-terminal oil pressure switch, so he says "OK, but I don't know if it'll work" For $10 I'll take the risk - either that or we'll make a jumper wire until I can get one in.

So we run back with our new switch, install it and viola, everything is working again. SOB! That fiasco caused me to have an ulcer and cost me $160+, but at the end of the day we learned something...at least I did. Don't assume anything test everything first before you start randomly changing (expensive) parts!

This is the oil pressure switch I used:

07-09-2012, 12:43 PM
Holy cow. Awesome write up man. Things like this are what makes this forum so valuable!

Glad to hear you got it figured out and got to get on the water.

Sent from my Galaxy Nexus using Tapatalk 2

07-09-2012, 01:57 PM
Great write up and more comprehensive than the other dozen or so threads on the pressure switch.

07-09-2012, 03:02 PM
First time on forum today. 2nd thread from the top...boom...sounds real familiar. I've got a 2000 outback, carb.

First time on river this season, started fine, ran for 1/2 hour, skied, then started cutting out. Would start and idle but stalled when put in gear. started...revved engine without engaging prop, let run for a minute, then stalled when prop gets engaged. did this a few times and finally it wouldn't start at all. towed back to landing. figured it was bad gas as the fuel had sat in tank all winter (i did put in stablizer and ethanol treatment when winterizing).

Emptied tank by hotwiring fuel pump, changed fuel filter, took back to landing 2 days later in the morning with fresh gas, didn't start.

Took back home, hooked to hose, for some reason boat started. Ran great. Just flick the key and fired right up time after time. Did check the oil at this point and noticed it was above the high fill mark. I thought "what the heck, did I put in too much oil, no big deal, lets go boating!"

Back to landing just after lunch, boat fired right up on trailer, backed off, took off onto river and after about 20 seconds at about 3/4 throttle...boat cuts out. I'm able to get it to catch a couple times and engage prop to give me some momentum back to the landing before paddling the rest of the way. not sure what to do now (except bring to marina).

But my question which is related to this thread involving the oil pressure switch is would this switch cause the engine to cut out if there's too much oil? I went home and drained about a quart which brought it back to the high mark on the dipstick. Haven't tried starting is since. Thought I'd get a little more info before towing back to the river. Thanks!

07-09-2012, 03:07 PM
involving the oil pressure switch is would this switch cause the engine to cut out if there's too much oil?

Welcome to the forum! Well from everything I have read on these oil pressure safety switches is they are only for low pressure conditions.

07-09-2012, 03:54 PM
Thanks for the reply ksmith. Any thoughts on high oil level causing engine to stall under load? Possibly something unrelated to the oil pressure switch? Like what does it do to an engine if you run it with a quart too much oil? (Sorry if this takes thread off topic).

And, it was mentioned a few times above, but what should voltage be at fuel pump? 12volts I assume?

07-09-2012, 04:57 PM
I have never heard of high oil pressure stalling out an engine or keeping it from cranking over. Of course if the oil pressure switch is toast it could be doing all manner of odd things. Buy one and see if it helps, can't hurt, worst case you have a spare for when it does die. If it doesn't help I would be looking at the fuel system, it sounds like fuel issues. Have you ever had your carb rebuilt?

07-09-2012, 05:21 PM
Thanks Kraig. Yeah the carb was rebuilt at the beginning of the 2011 season. I'll grab an oil pressure switch and see if that changes anything. Thanks again!

07-09-2012, 06:41 PM
The intent of the switch is to shut off the fuel flow if the engine failed otherwise you could have gas spewing out until the tank went dry.

07-10-2012, 10:30 AM
The intent of the switch is to shut off the fuel flow if the engine failed otherwise you could have gas spewing out until the tank went dry.
Zabooda is right. The oil pressure switch is just a diaphragm with a spring the separates two contacts. Once the diaphragm sees a certain pressure (I' think it's like 7-10psi, it overcomes the spring and closes the contacts which sends power to the fuel pump. Your high oil level will NOT increase oil pressure. The oil pressure is dictated by the oil pump which is connected to the crank and is regulated by a similar spring contracted orifice. There is no correlation between oil level and pressure, although not enough oil can starve the pump which will cause you to lose oil pressure and possibly blow your engine. Also excessively high oil pressure is also bad as the crank can start sloshing through the oil and cause it to foam up which if you get a lot of can also starve the oil pump as it can't pressure oil foam.

Your isssue sounds EXACTLY like what I was experiencing. A quick test to see if it is a faulty pressure switch it to disconnect the wires at the switch, jump them together to get the pump running and quickly crank/start the engine. If you can keep it running like this then its the switch. My switch had two terminals. One terminal had a purple wire which is a +ve feed (from the battery) and the other was a red and orange wire. The red wire goes to the fuel pump and the orange...I don't know. in any case when you connect the purple wire to the red and orange, the pump will run. I don't recommend running the pump for very long without the engine running as you may flood the carb and damage something. That's why they use that switch; 1) to only provide fuel to the carb when it's running and 2) as a safety shut off is you LOSE oil pressure.

Ideally if you can get the boat to start up normally and then quickly jump those wires together then that would be the way to go if you can do it before the engine quits.

Hopefully it's just the oil pressure switch. It's an easy and cheap fix.

Good luck!