View Full Version : Engine stumbles at high speed

08-11-2004, 06:07 AM
My '88 PS 190 developed a problem during a weekend trip (of course) recently. The problem is that the engine suddenly stumbles at high speed. The problem seems to be intermittent and doesn't happen at a certain place in the power band. Sometimes it happens while I'm cruising along, sometimes right when I pull a skier out of the water.

I'm not sure if its related, but for the past two seasons I've had a very slight, intermittent stumble during idle. Occassionally this will kill the engine, but not normally.

I'm leaning toward thinking this is an ignition problem, because whenever this happens I smell gas or see black smoke on the re-start (i.e. burning rich). I don't think its the carb - I rebuilt it last year and had no problems other than that slight stumble during idle.

Any thoughts of what all I should eliminate before installing an electronic ignition, and would that fix the problem if its an ignition prob?



08-11-2004, 08:09 AM
Fuel filter? When's the last time you took a look at it or changed it? Bad gas? Sounds fuel related to me...

Dan K
08-11-2004, 08:32 AM
I second the fuel relation. Ignition is usually binary, it works or it doesn't. Bad fuel or a clogged filter will act this way sometimes.

08-11-2004, 10:39 AM
I've had a similar problem on a car of mine. It turned out it was just a loose ground connection where the ground cable attaches to the engine. However, the car was fuel injected and not carburated, just thought I'd let you know another possible problem location. So, I would check this after I checked the fuel situation. Good Luck!

08-11-2004, 10:46 AM
When was the last tuneup, including plugs and wires(especially the coil wire)? I replaced coil wires on boats that had run 15 minutes before, then wouldn't even start. If it's flakey, you won't have complete combustion and it can kill and when it starts again, the unburned gas just passes through. Do you need to crack the throttle to get it to start?

08-11-2004, 12:54 PM
Yep, I was going to eliminate fuel filter and water separator first -- sounds like the consensus is fuel so I'll focus on that. As far as tune-up, new points & condenser 6 yrs. ago and new plugs about 3 yrs ago is all I've done. As far as the coil, is that part of the elec ignition package or separate?

Thanks for the replies.


08-11-2004, 02:25 PM
How many hours per year do you put on the boat? 6 years is a long time if you use it much. The wires take on moisture, then the silicone conductor gets brittle and cracks(unless they're solid wires), the whole inside of the distributor gets covered with condensation and corrodes, etc. If the lube on the fiber wedge that rides on the distributor cam dries up, that wears down and then the dwell changes(and not for the better). If the plugs have rusted into the heads, they won't conduct as well as they should and then there's no chance of the spark being as intense as it should be.

Yes, the coil is absolutely part of the electrical system, but if the points aren't adjusted correctly, the coil can't deliver spark with the intensity needed.

08-11-2004, 02:58 PM
Jim, I put 40-50 hrs per year on it. I took the cap off at the lake and looked at it -- there was a little corrosion on the electrodes, but not a ton. I do remove the plugs every year during winterization and they've always looked good -- no carbon rust on the threads, etc.

Your points about the wires are well taken though -- probably time for a new set regardless.

As far as the coil, my question is if I get a new electronic ignition system (the one everyone says is worth every penny), does that replace the coil, or is it something I still need?

08-11-2004, 08:59 PM
The electronic ignition replaces the points and condensor, really nothing more. The coil is still needed. You need to check with whoever you get the ignition system from for the correct voltage to the module. I would think it should be 12V. The reason the points need approximately 9V is that they don't handle current very well without burning. The reason the crank lead doesn't go through the resistor is that during cranking, the voltage drops to a level that the points can handle. Then, when the key goes to the "run" position, the voltage goes through the resistor and the points are happy.

08-12-2004, 07:19 AM
Got it, thanks Jim. I checked the fuel filter and water seperator yesterday -- no sign of anything wrong. I draine about 2 C of gas out of the seperator and saw no sign of water. What's next? I'd like to not just start changing parts. Is there a way to check the function of the coil? I've heard they can go bad when they get hot or the engine is under load, so is that the next place to look?

08-12-2004, 07:57 AM

Know how you feel about "just changing parts"...been there, done that. But, for me, swapping out "regular maintenance items" like fuel filter and separator, plugs, wires, distributor cap and rotor, etc. has resulted in slight improvements - which it seems is what you're looking for...

While it may be a hassle, I agree with JimN and I would try to do some "easy" electrical fixes as well and see what happens.


08-12-2004, 08:38 AM
I'm about the last person who would tell anybody to "just change parts". I mentioned the plugs and wires because they're 6 years old and that's a long time to have them in the motor. I was basing the need for wires on personal experience after changing them(especially coil wires) on more boats than I can remember, all with the 351 motor. Use silicone jacketed wires, not the stiff ones since I have found that they stay flexible longer.

What you seem to have ignored is testing. Anything. You looked at the filter and water seperator. If you want to find a problem with a motor, you need to check the timing, dwell, compression(leakdown too, if possible), and spark intensity. Do you go 6 years on a car between tuneups, whether it runs very little or a lot? I doubt it. If a car with the same motor sits most of the time for 6 years, I doubt that it would even start. Electrical contacts don't stay clean in a wet environment. To run, a motor really only needs 3 things: good compression, the proper air/fuel mixture and spark at the right point in the crank's rotation. The distributor, coil and plugs give you the needed spark, but if they're out of adjustment or old, they can't do it at the right time or with the needed intensity.

I just don't think it's a fuel problem since you said it stumbles, kills and when it restarts, there's black smoke and smells of gas. That tells me the gas is definitely getting to the carb and the cylinders, but something is keeping it from burning. It still could be a carb misadjustment issue, though.

Most times, when a coil goes bad from heat and the motor quits, you won't start up till it cools down.

AR Footer
08-12-2004, 09:11 AM
I was having a similar problem with my 85 and it turned out that the problem was a combination of things. First the points were in terrible condition and needed replacing. They were closing up at high speed. Secondly, this had caused the spark plugs to not get enough spark so they were fouled and new plugs were in order. Unfortunately, my carburetor had not been recently rebuilt so a rebuild kit from skidim was in order. For less than $100 the boat now runs like new. If you put in new points make sure and check or in your case I would go ahead and replace the plugs. No need to take the chance. I replace the points and plugs yearly. A small price to pay to avoid a miserable day broken down on the lake.

08-12-2004, 09:30 AM
I've got an '88 TriStar with the 351 W. Had a very similar problem at the end of last year. I was guessing it was probably ignition or fuel filter/water seperator since the carb had been recently rebuilt.

Instead of trying to figure it out and replace things one at a time I decided it would be a much more efficient use of my time to just go ahead and replace all the maintenance items at once. So I replaced the plugs and plug wires, changed out the points to an electronic ignition, replaced the fuel filter and water separator and the impeller just for good measure (and kept the old one as a spare since it looked ok). I would, like many on this board, highly recommend Discount Inboard Marine. Just give them a call, tell them what type of boat you have, and they will send you the correct parts. They will also help you with installation of any parts if you get stuck.

The boat has run great all summer (except when my starter died - different issue). I don't know which of these it was but once I found time to get everything together, pull the engine cover, get all my tools to the boat, etc. it was just easier to do everything at once. Just my thoughts - good luck.

08-12-2004, 02:42 PM

I hear you. Since the first 3 replies said it sounded like a fuel problem, I went there first. Coil, wires, plugs and elec. ignition is next. Timing is fine -- I check that when I dewinterize every spring. Haven't looked at dwell, but that will be a moot point with electronic ignition. I haven't messed with the points b/c I've never had problems (till now) and frankly am too young to have ever owned another vehicle with points.

Parts are on the way -- I'll let you know how it turns out.


lakes Rick
08-12-2004, 07:16 PM
My 90 Tristar always ran great.. When I sold it in 98 the guy who bought it had it tuned up.. The boat only had 115 hrs on it... During the tuneup the points were really burnt and pitted.. He told me he was amazed at how much better the boat ran.... If I had a points boat again I would check them yearly if not convert it......

08-22-2004, 11:45 PM
I'm having the same issue with mine. It bucks a bit, slows down and stalls. Checked my tank filter and it was good. Wonder if I should drain the tank? :confused:

08-22-2004, 11:48 PM
Mine is doing the same thing. Bucks a bit, slows down and then stalls. Frustrating because all LOOKS well. :mad:

08-23-2004, 01:24 AM
Take a fuel sample before you decide to drain the tank. It could just be a bad pump. Look at the fuel pickup tube if you're looking into the fuel system, too.

08-25-2004, 10:02 PM
I think I found the problem with mine -- looks like I had a bad connection somewhere between my ignition switch and my coil. It must have been intermittently giving low voltage because I would get stumbles occassionally but other times it would run great. After lots of troubleshooting, I finally narrowed it down to that. I don't know for sure if I fixed the problem, since it was intermittent, so now I plan to run a redundant wire directly from the ignition switch to the coil.

08-25-2004, 11:03 PM
Have you checked the safety switch yet?

08-26-2004, 11:22 AM
My safety switch was removed by the previous owner and the leads were twisted together. I soldered them together to make sure that wasn't the problem. There are a ton of potential spots for a bad connection on this circuit -- each guage has two spade connectors, there are two big connectors for the wiring harness, and there is a connection on top of the circuit breaker at the back of the engine. I'm going to run a line in parallel to this circuit, bypassing all of the connections. This will ensure that I get a good circuit that will still have the same on/off action as the original (this assumes the problem isn't my ignition switch which I'm pretty sure it isn't).

08-26-2004, 11:28 PM
I had the same problem with my 88 ProStar, ran perfectly under about 3000 rpm, but would just run out of fuel at high speed. I replaced all my ignition, fuel pump, all filters, rebuilt the carb, still did not solve the problem. It turned out that there is a one-way check valve fitting on the top of the gas tank that had been partially obstructed by small plastic shavings. Once it had been replaced the boat ran excellent. It appears that over time inserting, the gas nozzle into the plastic tank had scrapped the plastic on the neck of the tank and eventually the shavings ended up in the check valve. Turns out I didn't need to spend much money at all. Might be another one of those items we check every year. Hope this helps you


08-27-2004, 09:29 AM
The check valve is something that should have been mentioned earlier. The plastic shavings are more often from when the tank was trimmed for mounting the plate with the pickup and sender. Hard to get everything out through a small hole.

08-27-2004, 11:19 PM
Thanks Jim,
This forum has been a great help to me and I am sure a great number of newbies. I appreciate the time you and others put into helping us.


08-28-2004, 10:04 PM
I had a problem with my 89 where I had a bee lodged in the anti-siphon valve at the top of the fuel tank. It would slow the fuel flow down enough after a run to drain the fuel level in the float bowl and cause the boat to cough and stumble. Going back to slower speed or idle it would catch up. The plug wires will definitely affect performance at load. Good Luck

07-12-2005, 01:22 PM
The electronic ignition replaces the points and condensor, really nothing more. The coil is still needed. You need to check with whoever you get the ignition system from for the correct voltage to the module. I would think it should be 12V. The reason the points need approximately 9V is that they don't handle current very well without burning. The reason the crank lead doesn't go through the resistor is that during cranking, the voltage drops to a level that the points can handle. Then, when the key goes to the "run" position, the voltage goes through the resistor and the points are happy.
Which quickly explains why it is instructed to bypass the resistor when switching to an electronic ignition. Points can't handle 12v, where as the new system can, and performs better with that amount of voltage?