93 Sunsport Low Top Speed and RPM

[Straitcountry86]

Hello all, today I went and checked out a 93 Sunsport. It has the pro boss 351 engine. Overall I liked the boat but was a little concerned when I took it out for a lake test. The boat seemed to run a little rough when cold, but improved once it warmed up. Acceleration seemed ok, though I have never driven a sunsport so I have nothing to compare it to. However, I could not get the boat over 34mph, verified by gps, on totally flat glass like water and hardly any wind. My memory is a little foggy but I believe the rpms were only about 3k at wide open throttle.

Engine hours are 800. My question is, would this likely be caused by an ignition and/ or carb issue? Or could this be a sign of low compression or something more serious? The prop looked perfect. I really like the boat and would have bought it had the lake test gone well. As of now I am still considering it.

Also, temp gauge is not working so, not sure if that might have anything to do with it.

[ckracing]

What prop it is will make a huge difference. Do you know what it has?
For reference - my '86 Sunsport (which is essentially same hull) with a stock Pleasurecraft 351 (Holley carb, 260 HP) on a stock prop would see 40 mph. When I re-propped (Acme 541) and installed new Holley 4160 carburetor the hole-shot increased a ton an the top speed went up to 42 mph. Don't recall the RPM's. Conditions were glass and I was by myself.

[Salty87]

People have posted about issues with the coil packs on the Boss engines. Other possible causes in addition to the prop:
boat carrying excess weight
bottom of the hull creating drag (is it a trailered boat?)
bad fuel or fuel delivery problems
timing, not sure if that's the same as the coil pack issue

More?

[Straitcountry86]

Thanks for the input guys. I don't know what kind of propeller is on the boat, but I can't imagine that alone would be limiting it to such a low speed and RPM. The boat is trailered, but upon inspecting the hull before we put it in the water, I didn't see anything that would be stuck on the bottom creating drag.

I guess my main question is, does this sound like a serious engine problem i.e. low compression? Or something relatively minor like a fuel/ignition issue? If it's the latter it might still be worth buying this boat. If the engine needs a total rebuild, then obviously not.

[Salty87]

Compression test is easy and not reaching proper RMPs is a great reason to request either access to run the test or to request that the boat be taken to a shop for one.

RPMs should probably be 5200 give or take...just guessing. 3k is really low.

Did the seller say anything about it? You might tell him that without any further info you can only suspect a rebuild is necessary and have to price that into your offer.

[Straitcountry86]

Compression test is easy and not reaching proper RMPs is a great reason to request either access to run the test or to request that the boat be taken to a shop for one.

RPMs should probably be 5200 give or take...just guessing. 3k is really low.

Did the seller say anything about it? You might tell him that without any further info you can only suspect a rebuild is necessary and have to price that into your offer.

Thanks. With that in mind, assuming it does need a rebuild, what do you feel would be a reasonable offer? The boat is in otherwise fair condition. The seller didn't say anything about it, and before the lake test said the boat would get up to 40 no problem. When I told them it only made it to 34, they had no explanation.

[Salty87]

Thanks. With that in mind, assuming it does need a rebuild, what do you feel would be a reasonable offer? The boat is in otherwise fair condition. The seller didn't say anything about it, and before the lake test said the boat would get up to 40 no problem. When I told them it only made it to 34, they had no explanation.

That's hard to say without more info and location. I think at this point I'd press for the compression test and go from there. Try to feel the seller out to see if he realizes that a boat that's not in good working condition should be priced accordingly. It could just need a tune-up.

Maybe someone else with a Boss can shed some light on the coil packs.

[Straitcountry86]

I'll probably ask the seller for a compression test and see what happens.

[tryathlete]

Keep us posted of the result. I had a Supra Mariah that topped out at 40 at 3900 rpm. Could not get timing advance to exceed 31 degrees.


Sooner or later your toys own you

[Straitcountry86]

I have not been able to get the comp. test done yet. The local marinas are all too busy pulling out and winterizing boats, and it could be weeks until they have the time to do it. I am thinking of just buying the boat and taking a chance on it. Thoughts?

[SquamInboards]

Does it have the Pro-Tec Ignition system? There's a picture of one here: https://forum.supraboats.com/showthread.php?2129-92-mariah-hesitates-at-acceleration

That system has been known to have issues. Some people have no trouble at all, while many others have simply bitten the ~$550 bullet and converted to an electronic distributor and done away with the coil packs, module, etc.

It is more known for misfiring, shutting down, hesitating, than it is for just running "weak" but it's a thought.

I wouldn't pull the trigger until you know a little more, unless the price is really good. There are plenty of good boats out there.

[wotan2525]

Amazon or Harbor Freight sell inexpensive compression testers and it's a 10-15m job. It's the only way you're going to know if this is a major or minor issue.

[Straitcountry86]

Well guys finally had the compression tested today. Local marina called me back and said they could stop by. The result was 165lb across all cylinders. Seems pretty good to me for an engine with 800 hours.

[wotan2525]

Well guys finally had the compression tested today. Local marina called me back and said they could stop by. The result was 165lb across all cylinders. Seems pretty good to me for an engine with 800 hours.

As long as you believe them (and they don't have a horse in this race) then I'd move forward with your purchase. Compression can't be fixed cheaply or easily. Everything else that is related to your symptoms can. I'd start with a basic tune-up and some fresh gas.

[CJD]

If it runs well, I think you are likely dealing with gages that are all out of calibration. If the temp doesn't work, then you can figure the tach and speedo are probably off. 165 compression is very high, so if it is not making power, it's likely because the throttle is not opening fully. But I bet it's fine and just not reading right.

If you are concerned, use a gps app on your phone to see what speed you are actually getting.

[Straitcountry86]

As long as you believe them (and they don't have a horse in this race) then I'd move forward with your purchase. Compression can't be fixed cheaply or easily. Everything else that is related to your symptoms can. I'd start with a basic tune-up and some fresh gas.

Well, I have no reason not to believe them. They are an independent marina with no affiliation to the seller. I was the one who found them and set the whole thing up. So, I am pretty confident in their findings. They also reported a couple problem areas which I did not even tell them to look out for, such as water in the trans oil. I had already noticed that when I inspected the boat. They also said the flame arrestor was gunked up, so maybe that could be contributing to the problem as well.

[Straitcountry86]

If it runs well, I think you are likely dealing with gages that are all out of calibration. If the temp doesn't work, then you can figure the tach and speedo are probably off. 165 compression is very high, so if it is not making power, it's likely because the throttle is not opening fully. But I bet it's fine and just not reading right.

If you are concerned, use a gps app on your phone to see what speed you are actually getting.

I suppose the tach could be off, but the 34mph reading was off the GPS on my phone, so I know that's accurate. I will probably start with checking the throttle cable, cleaning the flame arrestor and replacing plugs, and see what that does.

[Salty87]

165 compression is very high

Seems odd that all 8 would be there, too.

Have you figured out if it has a standard distributor or the coil packs? Hope it just needs points, etc.

[Straitcountry86]

Seems odd that all 8 would be there, too.

Have you figured out if it has a standard distributor or the coil packs? Hope it just needs points, etc.

It's got the pro tec ignition. So, that could be the culprit. 165 does seem pretty high, maybe it was rebuilt at some point? Also, I should clarify, the mechanic said they were all "around" 165, meaning they were all within range, not exactly 165.

[Straitcountry86]

Hey guys, here is an update. I picked up the boat a couple weeks ago and so far couldn't be happier. Coming from an 85 comp, I am loving the extra room and freeboard. It's a 93 Sunsport and I picked her up for $7200.

The first time I took her out, without doing anything to it, made it up to 37mph and over 4K rpm. Changed spark plugs, fuel filter, cleaned flame arrestor and installed my acme 543 prop, and the boat got up to 41-42 mph with a full tank of gas. So I think I am pretty happy with that. Hole shot seems a lot better too. My only issue is a high sticking idle after cruise, which I will make a new thread for.

Overall though, loving this boat and can't wait for next season! Thanks to all that helped on this thread.