Engine Trouble with '86 5.0 230HP

[Blu]

Hi,

I'm having trouble tracking down an engine issue. The problem is that the boat will only run above 3000 RPM for about 10 seconds before it starts to hesitate and buck. I don't hear an electrical miss. Watching the tach - I will see it drop several hundred RPM and then bounce back up and all over until I drop the throttle back and get it under about 3000 RPM. The water seperater/fuel filter only has about 20 hours on it. The in-lin fuel filter is brand new and the cap/rotor/wires/plugs all look like new.

Can a fuel pump just get weak or something? Any suggestions?

Thanks for looking!

 

[JVM225]

You might want to take a look at your Ignition Control Module. It advances your timing as you increase the RPM. It could be that it is not working properly and the Ignition Timing is not coming all in.
If it turns out to be the problem make sure that you get the correct replacement. They are usually marked V8-22 , V8-24, etc. to correspond with the amount of total advance for your particular engine..

 

[berth control]

Sounds like you are not getting enough fuel, so anything from the fuel pickup in the tank to the jets in the carb. could be it. Start at one end and rule things out until you get it. Most likely it is one of these:

clogged gas tank vent
weak fuel pump
dirty or fouled carb

 

[stevea661]

Sounds like you are not getting enough fuel, so anything from the fuel pickup in the tank to the jets in the carb. could be it. Start at one end and rule things out until you get it. Most likely it is one of these:

clogged gas tank vent
weak fuel pump
dirty or fouled carb

Eric, this is just a stupid boat owner question. The only tests it shows for the fuel pump in the omc manual, for my boat is a vacume test while cranking, before the fuel pump, with the fuel line disconnected and the coil disconnected and a pressure test, after the fuel pump, with the fuel line disconnected from the carb and the gauge on the fuel pump outlet with the engine running, first test is 7 to 10 inches of vacume, second is 6-7 psi. Is there a way to test the fuel pump while running under load?

 

[Blu]

I found a thread that sounds exactly like my issue. He said replacing the anti siphon valve fixed it. I have no idea where it is or how to get to it. I didn't get the manual with the boat. Any idea how I get to it on a 230 Cuddy Cabin?

 

[stevea661]

The anti siphone is the barbed by male thread fitting that screws into the fuel tank outlet on one end and is barbed on the other, and the fuel hose to the water seperator connects to it there. There is a steel ball that is spring loaded inside of it. It needs vacume from the fuel pump to pull it off its seat and allow fuel to flow by it. The purpose is so if you get a leak in your fuel line bellow the fuel level in your tank, you won't fill your bilge up with fuel.

 

[KRB64]

Our '82 is doing similar (I think that might be the thread you found?). Not so obvious at first but getting worse as I fiddle with it...

At first I thought it was electrical, wasn't very noticable but just seemed to have lost that umph. Plugs, points & condensor were new but plug wires were ancient so I replaced those. No luck.

Local marine mechanic said he's rebuilt 62 carbs this year due to increased use of ethanol in fuel here so I replaced the fairly new fuel seperator and added some Star Tron. No luck.

Now it won't even get up on plane. Won't rev over 3,000 unless its in neutral but will start great and idle around all day.

Timing was at 14* BTDC, I backed it down to 10 which made it a little worse I think - or a coincidence. I'm suspecting maybe the advance wieghts in the dist maybe? Marine mechanic thinks its a weak fuel pump. I don't know how to test the fuel pump either other than R&R. If that isn't it then you have a spare for emergencies!?! Just make sure it is CG rated.

 

[tobnpr]

Agree with Eric.
Check the vent (fuel supply restriction). Then have the carb rebuilt or replaced.

 

[belairboater]

Ive spent the last six months trying to trace the source of the exact same problem. What I found was several issues. First, I was advised by a Mercruiser Master Mechanic to knock out the ball in the anti siphon valve. Then I loosened up the fuel fill cap and ran the boat. That didnt fix the problem so I borrowed a known working carb and installed it. The boat ran better but not great. I did some checking and found the prop was the wrong pitch. At full throttle, it was only running about 2900 rpms and loading up the carb. I swapped the prop for a lower pitch and ive been on the water with zero problems.

 

[ferguda]

I had this problem and it turned out to be ethanol in the gas. I emptied fuel/water separator filter and added Marine Sta-Bil to the remaining gas (and add at every fill). Problem solved.

 

[Blu]

Ive spent the last six months trying to trace the source of the exact same problem. What I found was several issues. First, I was advised by a Mercruiser Master Mechanic to knock out the ball in the anti siphon valve. Then I loosened up the fuel fill cap and ran the boat. That didnt fix the problem so I borrowed a known working carb and installed it. The boat ran better but not great. I did some checking and found the prop was the wrong pitch. At full throttle, it was only running about 2900 rpms and loading up the carb. I swapped the prop for a lower pitch and ive been on the water with zero problems.

I'm sure it's not the prop. Before the issue surfaced, I would hit about 4500 RPM wide open.

I haven't had a chance to get to the boat yet. Tomorrow I'm going to first change the water seperator. Then see if I can find the anti-syphon valve and tank vent and check for blockages. Hopefully the tank isn't to hard to get to. I'm going to save the carb and fuel pump for the last checks.

Thanks, for all the replies. I'll let you know what happens..

 

[Blu]

I finally had a chance to work on the boat today. I believe I found the problem. There is a wire mesh filter inside of a fitting that is on the fuel tank pick-up tube (the fitting the anti-syphon valve screws into). It was about 90% clogged. I could barely see light through it. Got it all cleaned out (marina didn't have a replacement) and put back together just before I needed to go pick up the kids.... So, I will water test tomorrow morning and report the results. Keeping my fingers crossed.

 

[ghuskin]

Blu,

That may be the culprit. If you're still having problems, it's the fuel pump. I had the same symptoms last year. cleaned the pick-up tube, anti-syphon valve, and still wouldn't pull over 3k w/o stalling. changed out the fuel pump and all is well. You're engine will run strong when you have the out-drive disengaged, as there is no load. Once the load is there is when the fuel pump can't the demand. all related to ethenol.

 

[KRB64]

Blu,

That may be the culprit. ... all related to ethenol.

Thats what my mechanic is warning me about. I hope that my problems is as "simple" as that too. As I said earlier, he's rebuilt over 60 carbs this year due to, in his opinion, ethanol. My brother and I are trying Startbrite's Star Tron in the tanks now. Guess this winter we all need to leave the fuel tanks as close to empty as possible??? Mechanic says that over time, the sitting fuel will seperate into layers due to the ethanol content?

Hope the screen fixes your situation but until something changes with our fuels this could be a permanant problem? The mechanic has several horror stories of fiberglass or plastic tanks disolving, gunked up carbs, lines, etc, etc...

 

[KRB64]

I finally had a chance to work on the boat today. I believe I found the problem. There is a wire mesh filter inside of a fitting that is on the fuel tank pick-up tube (the fitting the anti-syphon valve screws into). It was about 90% clogged. I could barely see light through it. Got it all cleaned out (marina didn't have a replacement) and put back together just before I needed to go pick up the kids.... So, I will water test tomorrow morning and report the results. Keeping my fingers crossed.

What are you guys using to reseal when you pull the tube? Just regular automobile RTV sealant that fuel compatable?

 

[sbw1]

Hi,

I'm having trouble tracking down an engine issue. The problem is that the boat will only run above 3000 RPM for about 10 seconds before it starts to hesitate and buck. I don't hear an electrical miss. Watching the tach - I will see it drop several hundred RPM and then bounce back up and all over until I drop the throttle back and get it under about 3000 RPM. The water seperater/fuel filter only has about 20 hours on it. The in-lin fuel filter is brand new and the cap/rotor/wires/plugs all look like new.

Can a fuel pump just get weak or something? Any suggestions?

Thanks for looking!

Fuel, spark and air...it's one of the three. Parts looking like new is not the same as new. 20 hours of bad gas will be a killer. I'd see what's in the fuel filter first. If that checks out, I'd run the boat at night with the engine cover open. If you see blue lightning, your new looking wires are bad. Sounds like you could be sucking debris in the tank into a filter, but that also sounds like an electrical issue. If the tank and filters are clean, think ignition components. Are your operating temps normal?

 

[Blu]

Good news. I made it out tonight for a test run and she ran like a champ! The clogged pick-up tube filter was the culprit. Thanks to everyone for their input :thumbsup: One good thing came out this, I learned a lot about the fuel and electrical system...

KRB64 - The fittings were sealed with Teflon tape when I took them apart. The marina mechanic told me to use Permatex "High Performance" Thread Sealant when I put it back together.