2006 gekko gtr top speed/rpm/prop?

[Monkstr6100]

I have a 2006 gekko gtr with the 330hp merc black scorpion in it. I am only able to turn about 4700rpm and a top speed of 42/43. Seems like the last ~700rpm make little change to speed? Is this normal? The prop says 449 13x12.625V L. And also has a 2 stamped on it. The engine runs great, just installed new correct plugs. Look to be original wires and cap. Boat has 370 hours on it. Thanks for any info in advance, Zach J.

[6balls]

@monkstr6100 my brother had same hull/motor and was running close to 50 with driver and no skier, not sure the rpm. We pulled 3, 200 lb footers north of 40 with that boat.

[Monkstr6100]

@6balls yeah that's what I figured, so something must be up!? Been this way since I got it this spring.

[Wish]

My buddy has an 01 or 02. Does every bit of 50mph. Same moter. I'll ask what his rpms are in the upper speeds. Hope he remembers. He hasn't had it out in a month.

[boarditup]

Acme 525 is the best prop for your boat. Did you check your fuel filters (yes, there are typically 2)? The throttle body may be dirty. Clean it out with cleaner and a toothbrush. Clean out the BFA. I have seen the Merc fuel lines collapse at high flow. I had to replace a set due to alcohol swelling - fixed the WOT problem.

[Monkstr6100]

thanks guys. I will check the fuel lines. I will look for that 2nd filter. Just replaced the filter/water seperator. What is the "BFA"? And look into the 525 lower pitch prop.

 

[boarditup]

BFA - Backfire Flame Arrestor - think metal air filter. Since the boat likely does not have a filter on it, but a BFA, they can and do clog up with gunk quickly. I wash mine out with dish soap and then hit it with carb cleaner. The throttle body on boats gets more dust and gunk in it than an automotive throttle body since the BFA is a very coarse filter. So, more frequent cleaning is needed. The second filter, depending upon model, may be where the fuel line attaches to the throttle body - it is a fine screen. If it is there and black, you have fuel lines being eroded by the alcohol into the fuel stream causing high-volume runability issues. You can substitute a K&N air filter for the BFA on most boats (check clearance). If you use blue Sta-Bil or recreational gasoline it protects your fuel lines from the alcohol.

 

[colo_skier]

What are you measuring the top speed with? GPS is way more accurate than the 2 speedo's. You don't mention that you are hitting the rev limiter so the prop is probably not pitched to low/high. Mine ran best with a 3 bade CNC prop on it versus a 4 blade. Sorry I don't remember the pitch. Also I was running at 5k ft above sea level.

[Monkstr6100]

Top speed is with perfect pass and then also with GPS, and def not hitting rev limiter @colo_skier . @boarditup i will check for that fuel filter tonight and check that BFA/throttle body. I only run ethanol free gas in my boats, but who knows what was ran before me.

[Wish]

Perfect Pass cable connections can impede full travel of the throttle cable if installed wrong. Just a thought. Had that happen to me on my old boat.

[Monkstr6100]

@Wish, great point! Had that issue and fixed it already. Had some home made aluminum bracket and a WAY to short cable that would only allow a little over 3/4 throttle. Perfect pass sent me the right cable and correct factory bracket. Picked up a few hundred RPM with that. Cleaned throttle body just now, and it was pretty gunked up. Didn't locate that second fuel filter? Will be a few days till I get on the water and retry it. Leave for work at 5AM and not home till 7pm! Will keep you guys posted. Going to shop for the 525 prop also. Thanks everyone! Zach J.

[colo_skier]

You can also completely disconnect the pp throttle control linkage to see if that is an issue at all. Although if you run with PP off I would think it would be out of the eqn. Does your boat have the water in gas filter? Big white round filter on the bottom left of the motor at the front. May need to empty that. I think I was originally running a 13.5 pitch CNC 3 blade on my GTR and didn't like the hole shot. Went to a 12.5 CNC 3 blade and the top end speed went down about 5 MPH and kept hitting the rev limiter. Did notice that the last 500 rpm didn't really do much to top end. I tried a 14 pitch 4 blade and really ran out of hp before I could get any where near the rev limiter. Remember this was at about 6K above sea level as I was trying this at Navajo reservoir in Colorado mountains. Hope this helps. BTW slalom is 36 MPH max :)

[Monkstr6100]

Called and talked to mark overbye today at Gekko. He said they did a ton of testing and the acme 515 was the BEST prop for the GTR with the scorpion engine. Wonder if the previous owner had the 449 reworked before I bought the boat? Either way, I am quickly running low on time to even benifit from a new prop purchase this season yet. And my wifey will not be to pleased if/when I order this. Mark is setting me up with a good deal on a Gekko cover for my boat for winter storage (inside of course, just for dust/critters) and that needs to be purchased SOON here in WI!

[Monkstr6100]

Also, very recently replaced the water/gas separator filter when I replaced the plugs. The boat has 370hrs on possibly original spark plug wires/cap/rotor?

[Monkstr6100]

So this spring I installed the 515 new prop. NO difference at all in RPM at WOT? Now I am thinking that it may be something with Mercurys Gaurdian system? That's about exactly 90%, and from reading I see that if some sensors are bad it may put it into %90 power? Going to get it scanned this weekend. Any thoughts, and sorry for digging up my old thread here.

[GregHind]

Increasing speed by 10% takes a LOT more than 10% more power. You are down on power by about 25%. Three possible causes. No spark in one cylinder. Fuel restriction. Low compression.

 

Go ahead and change your plugs

 

Run your boat flat out for 20 seconds and switch the engine off while still doing so. Remove each spark plug and look. Is one wet looking? Different colour.

 

If it isn't lack of spark. Do a compression test and report back.

 

If not those then it must be a fuel restriction. You can do a vacuum test to see if it is having trouble getting fuel at WOT. Eg hose collapsing. Blocked filter. Bad anti siphon valve. First do the vacuum test (google it). Then work back to the restriction

 

Could be dirty injectors if it isn't a restriction

 

You need to work it through systematically.

 

The amount of power loss you have suggests to me one cylinder isn't working. Eg no spark. Or spark plug leads are currently fitted to 2 cylinders in the wrong spots (wrong spark order)

 

The scorpion engine is awesome you'll live it when fixed

[Razorskier1]

Mine ran 50mph with that engine.

[Monkstr6100]

Well I did some driveway work to my boat yesterday. Traced down all the spark plug wires and they were all right, then pulled the cap and all the terminals had the green gunk growing on them. I for the time being just cleaned them up with fine sand paper and wetted with WD40. Will be replacing cap and wires. Already did replace plugs late last season. Then opened up floor panel and removed inline fuel filter. Looks to be original mercury 35-864572 filter. Why does it even need the inline AND the spin on? Either way seemed like some gunk came out of it, but no real resistance when blowing through it.

[Monkstr6100]

Also, when i opened up the floor panel I could visually see the trans to shaft alighnment was off. And when in neutral it was pretty darn hard to turn the prop. I know it's crude but I used a straight edges and feeler gauges when coupling bolts were backed off to get it way "closer" than what it was. Now the prop shaft spins much easier. Once I replace the inline filter I will head back out to the lake and test my boat again. Thanks again guys. Will be awesome to get the full potential out of my boat finally.

[GregHind]

@monkstr6100 well then how does it run now??!! It could be your cap. As load increases, it is harder to get the spark to jump the gap. I had that problem with a Yamaha outboard once. Ran fine until max load when it would drop a cylinder and you'd lose 700rpm... That was caused by resistor (noise suppressing) spark plug caps some of which had gone high resistance. Very similar to what green gunk growing in your distributor would do. Keep us up to date.

[Monkstr6100]

@GregHind I have not gotten on the water yet since doing any work to it. I am waiting on the inline fuel filter, cap, and rotor, to show up from amazon. Figured I would just replace all for the low cost of parts anyways. And I do not think it is the Gaurdian system at all, cause the warning horn does come on when I turn the key on, so if it were limiting anything the horn would sound. Will keep you posted.

[Monkstr6100]

So, had it hooked up to merc mechanics computer, no codes and 100% power available. The timing kind of wondered around a lot with a light hooked up to it? I since have installed new Wires, Cap, and Rotor, and that seemed to improve performance a bit, but not perfect. I can now get about 4800rpm but as the day goes on it will go down to closer to 4600 WOT? Ran a bunch of tests today. Fuel pressure at 1800 RPM is 26psi, and supposed to be 43PSI. When I would pull the vacuum hose off of the regulator on the fuel cooler it will increase the fuel pressure by only 5PSI? I could totally unplug the boost pump by the fuel filter/separator and it would not change a thing. Is this pump mainly to prime the system? It for sure runs and you can hear it labor down when key is turned on and then fuel pressure peaks at 33-35, and then drops to 26 when started. If I unplug high pressure fuel pump while running it drops fuel pressure and noticeable difference in the running of the engine. Checked anti siphon valve, tank breather, screen under the fuel pressure regulator, and all clear. Then ran the engine with a short line (10") ran directly into a fuel container from the boost pump, to make sure it was no blockage in the fuel supply, and it ran EXACTLY the same with the same 26PSI! So now is it my fuel pump, regulator, or something else? Sorry for the crazy long post!

[gregy]

Sounds like fuel pump or regulator to me. My 99 Malibu only has one pump on the back of the engine. Some people add a pump at the tank due to vapor lock issues. But its not a merc so might be different. My pump locked up and it was pretty expensive. I bet a regular is cheaper, found the regulator on ebay for a really good deal for mine. Make sure all your grounds are good also.

 

My buddy's 08 MC 197 had a worn distributor gear with about 500 hours. It keeped randomly misfiring. 2 dealerships could figure it out. We finally pulled it because we could think of anything else.

[DanE]

@Monkstr6100‌ Get fuel pressure up to specs first, totally pointless to troubleshoot with low fuel pressure present.

When fixed, good chance you're good to go.

[DW]

@monkstr6100: I would certainly correct the fuel pressure issue prior to any future WOT runs, as it could cause a lean condition which pistons do not like. Wandering timing could be a bad distributor gear.

[RAWSki]

I have that same engine in my Centurion Eclipse, it's been rock solid and have 1100hrs on it. I had the same issue with the prop that came from the factory. It was only letting the engine hit 4720 RPM at WOT, my prop shop checked the pitch and it was true @ 13x13. They said the boat was laboring and the engine needed to run at 5200-5400 RPM WOT. We talked to ACME marine told them what was going on and they recommended a prop they had for one of the larger Malibu's at the time. I think it's a 12.5 x 14 (can check), made a huge difference, besides being a super smooth and quiet prop it allows the engine run at almost 5300RPM and I gained 3mph top end without any issues on the low end pulls. NOTE: You do have to be careful not to let the heat in the box build up on really hot days because you can get a vapor lock, the MPI rails sit right on top of the block under that large metal 'scorpion' plate.

[gregy]

I still think there's a fuel issue. It should be fairly constant.

[Monkstr6100]

The fuel issue is the only thing I am going after right now. This morning with the high pressure pump removed I Jimmy rigged my fuel pressure gauge to it on the bench with a small fuel container to supply fuel. When I would jog the pump I could reach pressures plenty high, easily 100PSI, but when I would run the pump with the drain/bypass open on my gauge it would only run a constant 26PSI, same as when on the engine and running. The pump can not pump the volume any longer at 43PSI, so I just ordered a new pump from Amazon and will keep you all updated when I install it. Wish me luck and thanks everyone.

[6balls]

@rawski that motor was a stinker for vapor lock.

[Monkstr6100]

So I was chasing a unreal fuel pressure. Turns out this engine is supposed to be 30 PSI, and 26 at idle. So my new fuel pump changed nothing. BUT, when I remove the vac line from FPR it jumps to 35 or so, but when I accelerate to 1800 RPM the pressure actually drops a little and this is where it should be at 30PSI? This thing is driving me nuts. Going to drag it to the lake today and see if there is any difference. Will ever do a test run with vac line disconnected from FPR.

[CoolSkiGuy]

Quick Question for anyone that might know - I had my 2006 Gekko GTR 22 out over the weekend - and I took it into a turn above 5000 rpm and it started beeping at me and then become sluggish. When I turned off the boat and started it up again it was fine. Any ideas?

[Wayne]

How full was the fuel tank? Only link I can see is the fuel pickup became uncovered when the fuel sloshed off to one side of the tank. I'm assuming it's fuel injected based on the year of the boat.

[Keith_Menard]

Isn't beeping oil pressure or temp?

[CoolSkiGuy]

Fuel was over half full. Oil pressure seemed fine and Temp was good also.

 

One thing that also happened over the weekend the day before - We were swimming in a cove off the back of the boat after a 10 min ride. When we were ready to leave (after 45min or so), I started it up and went to throttle and the boat tried to get up out of the hole, but just stalled out and I could get it to start - meaning it would turn over and "start" but then it would die like right away, it was like something was flagged and it would not allow it to stay started. So I needed to get towed back in, and the next morning it started right up. Checked the oil, level was fine. temp gage sits around 150 or so. I have had this boat for about 7 years and this is the first real issue I have had with it so I am a little perplexed. I am not sure if it was related.

[Monkstr6100]

@CoolSkiGuy What engine do you have? 150 seems cold off the top of my head? If you got alarms you are best off finding someone with diacom and start there. How old are the plug wires? Depending on engine could be vapor lock.

[Keith_Menard]

@CoolSkiGuy when I had that issue with my other boat it was water in the fuel

[CoolSkiGuy]

@Monkstr6100 Engine is a Mercruiser 350 - I was thinking I would take it in to have someone run a diagnostics on it. Because I am sure that it set off some code or something.

 

@"Keith Menard" - I am hoping that is what it is - water in the fuel

 

[Keith_Menard]

@CoolSkiGuy I have the same engine in my Gekko, I will look at the temp next time out. I think it's this new ethanol crap...but man...let me tell you getting water out of the fuel cell is a b...i...t...c...h.

[Keith_Menard]

150

[Monkstr6100]

I was on mine today and mine runs at 175deg. But I also have the black scorpion. So that's why I thought you seemed cold.