View Full Version : 87 prostar skipping
07-26-2011, 11:03 PM
Okay we arrived at the lake on Sunday and are staying all week. After I launched the boat and got underway it loses power as I begin to accelerate. It starts fine, idles fine, and revs fine in neutral. It kind of stutters when you take off until around 2200 rpms. It will also run hard as long as you gun it and the secondaries open. At around 3000 you can hear and feel a skip. Ran fine last weekend. Since then I have changed plugs, filled with gas, replaced the thermostat, and the kill switch. It has also stayed at a fast idle a couple of times 1100 today even though it was warm. Any ideas for a quick fix at the lake? I've run it like this for 2.5 days it is aggravating but has not let me down yet.
07-27-2011, 12:31 AM
I see you changed spark plugs, Probably got your wires crossed up. Since it didn't do this before you changed them out.
07-27-2011, 12:39 AM
I assume you have the ford 351, if so then, counterclockwise 1 3 7 2 6 5 4 8 is the firing order.
07-27-2011, 02:13 AM
Yeah 351 hope its something like that. If not I'm wondering if I goofed one of the wires up when I changed the plugs a coupled were pretty hard to remove.
07-27-2011, 02:21 AM
Btw the cylinders are numbered starboard side is 1 2 3 4 and port is 5 6 7 8.
07-27-2011, 04:57 AM
I have a 1985 s&s Ford 351w I am having the same problem I am down to changing the disturber and the full pump I have change everything else. So look in to those.
07-27-2011, 08:12 AM
Most problems are electrical in my experience. Why would you change the distributor? Something wrong with it? I have seen distributors wear out and get so corroded they weren't worth the hassle. Most times mechanical fuel pumps work or they don't work and leak. If I suspected anything fuel related it would be old fuel/ water in fuel or fuel filter.
07-27-2011, 08:15 AM
Boat ran fine? Why did you change all those parts out? Have you looked to see if your carburetor is returning to the idle screw and if the choke is open?Okay we arrived at the lake on Sunday and are staying all week. After I launched the boat and got underway it loses power as I begin to accelerate. It starts fine, idles fine, and revs fine in neutral. It kind of stutters when you take off until around 2200 rpms. It will also run hard as long as you gun it and the secondaries open. At around 3000 you can hear and feel a skip. Ran fine last weekend. Since then I have changed plugs, filled with gas, replaced the thermostat, and the kill switch. It has also stayed at a fast idle a couple of times 1100 today even though it was warm. Any ideas for a quick fix at the lake? I've run it like this for 2.5 days it is aggravating but has not let me down yet.
07-27-2011, 09:58 AM
I changed the thermostat because it was reading 20-40* hotter than the actual water temp, kill switch line was screwed up so I replaced the whole switch, I usually change the plugs every year regardless of hours and had not this year, and it won't run at all without gas. To rephrase the engine rand fine with no skipping or hesitation. Headed to the dock now to have a look at the plugs. Thanks for the replies ill give an update if I figure the problem out.
07-27-2011, 02:01 PM
I hate these kinds of problems. I would still look at fuel filters and the fuel itself. I am paranoid about gas here. Our humidity and ethanol they add makes fuel a real problem sometimes. I will not buy fuel at a lot of the places on the water--good people but if they don't move enough fuel it goes bad. Which carb you running? I would still look at the carb. You change plugs annually and doing all you have done your not afraid of your tools. If it was me I would check my plugs again and firing order. Look at my rotor and distributor cap. Then me and my carb would be spending some quality time together before I took it off of the boat. I would check my linkage and choke. Accelerator pump and then I would be pulling the top off to look at floats and needle valves. Just a warning---I figure you know this but I have to say it anyway. Don't drop anything into your intake manifold pulling all these screws loose. Then depending on what I find I would either rebuild, replace, or call a friend.
07-27-2011, 03:29 PM
Check the bearing in your siphon tube on top of the tank. Its the fitting your fuel line attaches too.... The new Ethonal gas gumms them up good....
07-27-2011, 04:22 PM
Plug wires are correct I will start looking at the fuel system stuff tomorrow. I ran it for a couple of hours this morning and still sputtering but running nonetheless. I can live with it for now but it sucks compared to the usual throttle response. I truly appreciate all of the replies. Thanks guys.
07-27-2011, 04:44 PM
I'm looking at this from another direction. From the original post, it is the off-idle to the point that the secondaries kick in that is the problem. Sounds like fuel delivery within the carb to me. One thing to can do without a lot of effort is to remove the mixture screws and blow the passages out with carb cleaner. Make sure you slowly screw them in until they are seated counting the exact number of turns (and writing that down) so you can properly replace the mixture screws. A little gunk in these passages could cause the symptoms you describe.
07-27-2011, 05:22 PM
I'll pickup some carb cleaner when I head into town.
07-27-2011, 07:17 PM
Power valve in carburetor maybe blown.
07-28-2011, 03:25 PM
J.mccreight I think you are the winner. My parents showed up today to see the grand kids. My stepfather rode with me to the marina. He listened to it let the hood down and asked if this model of marine carb had a power valve. He said it sounded just like a power valve went out on an old spreader truck Jr use to have that had a 391 with a holley on it. Be said ee could replace it when I get back home. Thanks for all of the replies and I will be sure to let everyone know if that fixes it. I changed the fuel filters this morning before he arrived. He said it was definitely card/ fuel related and not spark / electric.
07-28-2011, 04:35 PM
Are you seeing any black exhaust or black discoloration on your transom? When the power valve goes out is runs extremely rich and typically easy to see some indications of this.
07-28-2011, 06:13 PM
Haven't really noticed any but it is still idling funny too.
07-28-2011, 06:16 PM
Sounds like it's worth checking.