Engine Surge at WOT

Good morning,

Im having a minor issue at WOT that bothers me a bit on our 96' Ski. Engine is 351w carbed. Boat runs flawlessy throughout power band, except when at WOT after about 30-45 seconds. Engine will loose a little power for a few seconds, like it isnt getting fuel, then it will pick back up to full speed and have no issues. Only time this occurs is when I am footing at WOT, other than that, it runs perfect. Last week I replaced the fuel line, and ASV. Could this be a fuel pump issue at those higher rpms? Appreciat the help guys.

Mark

Might be as simple as setting the secondary floats as the bowl may be running dry.

Thanks for the input guys. Brian, I have that exact in-line filter, and that is the only one in the fuel line. I replaced it in the spring and have put a little over 50hrs on it so far, so I am going to replace that first thing and see what happens. If I still have the issue, I will take the carb off and see whats up with the secondary bowl like suggested. Hopefully the new fuel filter solves the problem. I will report back when I get the new one on and tested.

Mark

O.K., one more update. Got the new inline filter installed after work and pulled the secondary bowl. I adjusted the float to parallel when inverted. I must have misread the 3/8" measurement for the float setting. It would of been sitting lower than it was originally set at. So I put it to parallel like I said. Anyway, I sprayed the heck out of the needle and seat area while working it up and down. Reassembled, hooked up the hose and no leaks. I wont be able to get the boat out till Friday to test it. Hopefully the cleaning, readjustment of float, and new fuel filter will cure this issue. I will post the results as soon as we get her out on the water. Thanks for the help.

Good evening everyone, finally had a decent afternoon today and went out for the first ski of the season. As you know from previous posts in this thread, I had surging issues when at WOT, not that I run it that hard much, but I thought I solved the issue, and sure enough at the end of the day, went for a little speed run and it did it again. This what it did. I gave it full throttle and picked up speed just fine, and about 8 seconds into it, surged big time, like almost dying, and then it would pick back up to full speed and surged again like it was dying. It did this a couple times and the last time it did it, it really slowed down and jerked a little and picked back up like a bat out of hell and never slowed down again like it got some debris or something out of the way and had plenty of fuel flow. Before the beginning of the season I took off the secondary float again and readjusted it and cleaned up the needle and seat again, hoping to clean out any debris. I was pretty bummed when it started to surge again. It runs flawless when skiing at 36, just happens at WOT or when footing. I would appreciate any more input and suggestions. If you read previous posts, I replaced the fuel lines, filter, anti syphon vavle, and adjusted floats and cleaned needle and seat previously. Stumped on what to check out next. Thanks for the help.

Mark

Chris, next time out I will check the fuel vent with the cap off. I have not watched the secondary butterfly to see if it is closing. The carb was new in 2010 and it did not start doing this till last year. We'll see how the weather is this weekend and hopefully get out to check on things. When I first bought the boat I took it to a dealer near us to check things out and the mechanic said that the fuel pump on the boat was not the right one, but would work fine. I didnt think anything of it till now. Maybe there is an issue with that pump and wore out? I'll check the vent and secondary butterfly first and will be in touch. Thanks for the help

What ignition system is on this motor? And is there an ei conversion on it?

Ei = electronic ignition conversion. If it has one clean it and check the spacing, I had one that gave these symptoms

Just an update, we hit the river this afternoon for some runs and I ran the boat WOT a few times and never had any issues! She ran perfect. Thanks for the advice and help everyone.   Mark

levinmark wrote: He told me to pull the cap and check the spacing between the fins and the rectangular piece and that it is recommended to be set at .010", however they set them up at .006". Mark

do you happen to have a photo of this??

I'll add my experience for the next guy also. 93SN 351W, holley carb, electronic ignition. Same symptoms as the OP, only worse. Slightly different conclusion.

Look under the coil packs for resin on the transmission housing. My electronic ignition system was in the process of melting and the cutting in and out at high speed was the first major symptom.

The engine started immediately when cold. Ran perfect at ski and wakeboard speeds, until it was time to haul a**. Open the throttle, and the engine sounded like it has a high and low power switch cutting in and out. Top speed was low 40's.
At first I blamed it on clogged filter, alcohol in the gas, clogged check valve, etc. etc. Rebuilt the carb, no change, changed power valve and jets, no change, replaced the carb, no change(the rest of the carb circuit was finely tuned, but the initial problem remained.)

I had also replaced the plugs and wires earlier. From the forum research, I knew the only thing left was the ignition module, but the failure symptoms didn't match anything I could find that was previously discussed. I purchased a DUI ignition and called my old-school mechanic to help me swap it out since the old ignition pickup has seized in the block and I couldn't pry it out.

The first thing he said when we opened the engine cover was, "What's a GM coil pack doing on a Ford engine?" The second thing he said was, "Look at all that resin that has melted out of the circuit board." as he pointed to the bell housing directly under the coil pack. The third thing he said was, "Do you want me to rebuild the coil pack? They are only 30 bucks at the junkyard. Cadillac modules work best." I allowed that since I had already sprung big bucks for the GM based HEI ignition system that I'd pass on the rebuild offer.
That was the problem, no more missing, stumbling or cutting in and out. Top speed is now right around 47 MPH on the speedo. Dunno if it's accurate or not, but it runs great now.

Regards,

Ed

MI-nick wrote: levinmark wrote: He told me to pull the cap and check the spacing between the fins and the rectangular piece and that it is recommended to be set at .010", however they set them up at .006". Mark do you happen to have a photo of this??

I searched the 'net for 15 minutes & this is the only picture I could find of the sensor (kit, not assembled).

You just loosen the retaining screw & move the pickup until you get the proper gap between sensor & the fin. In the instructions it warns to use a non-magnetic feeler gage.

Do you have the original electronic ignition, with the separate coil packs? If so, check underneath them for resin dripping out of the bottom of the box and/or onto the transmission housing. That was the symptom on my boat that indicated that they were overheating. The resin looked like amber colored sticky grease by the time it had melted and dripped out. Replaced the electronic ignition with a DUI and my cut-out/hesitation problem was solved.

Unfortunately I haven't read of an inexpensive way to test the OEM electronic ignition system, apparently a swap out is the preferred test method. Could get pricey if it didn't fix the problem.

I'd guess that an old 351W distributor and coil from the pull-a-part junk yard would be the cheapest way to test the ignition, if you had the time to pull one out. If that fixed the cut-out, you could then decide which type of ignition would suit your needs. Compare the two cam gears and re-use the cam gear at the end of the boat's distributor pickup on the junk yard distributor, it reverses the direction.

With the DUI unit, I removed the OEM distributor pickup, and the electronic module with the coil packs on the top, along with the plug wires. The DUI has the coil inside the distributor, so it's self contained.

Thanks for the replies, I believe the post before Brians was referring to a pro-tec ignition, which I do not have. Here are a few pics. Im getting pretty frustrated. When I foot, I usually go off the fly high pole, so it shouldnt be an issue. Where exactly should I be looking for sparks. My wires and plugs are 3 years old, so they are probly ready for replacement this winter?

Thanks for the reply Ed, watching da Bears at the moment, I'll go dig into it at halftime and see what it looks like under the cap.