2006 GTX 4-Tec 155 44 mph max speed

[JoanEnric]

Hi all!

I would like to ask you for some help.

The max speed of my 2006 GTX 155 is 44 mph at 7200 rpm.

Facts:

- I use the correct key, not the learning key
- wear ring is new
- impeller is new
- sparks are also new
- oil and oil filter (everything was changed in dealer this summer, all BRP original)
- oil level is a little above the max in cold (I know that level has to be between min and max, I need to remove oil)
- OPAS system seems to work well (or this is what I think)
- reverse gate is in place

So, with all this, what can cause that speed of 44? Apart from the impeller and the wear ring, and the fact that the oil level is a bit to high, what other parts are involved in speed? What other things should I look for?

Any suggestion, help, comment or idea would be very appreciated!

Thanks for your time and support!
Regards

 

[Coastiejoe]

Oil level is crucial with the 4-tec. Too high and you get crank case pressure and lose performance.

 

[JoanEnric]

Thanks a lot for your answer!

This is the first thing I'm gonna do! Remove oil and test it if there's any difference.

 

[IDoSeaDoo]

If you're turning 7200 rpm, it's not your oil. Your top speed should be directly proportional top your rpm, unless you have cavitation, or are otherwise losing thrust. Is your reverse gate all the way up? Are you having any cavitation on take off? I ask because even though wear ring and prop are new, you could still be having air coming in from the carbon seal. You can test by flooding the ski to above the carbon seal. Careful though, don't sink your ski

 

[JoanEnric]

If you're turning 7200 rpm, it's not your oil. Your top speed should be directly proportional top your rpm, unless you have cavitation, or are otherwise losing thrust. Is your reverse gate all the way up? Are you having any cavitation on take off? I ask because even though wear ring and prop are new, you could still be having air coming in from the carbon seal. You can test by flooding the ski to above the carbon seal. Careful though, don't sink your ski

Hi!

Thanks a lot for your answer. I'm really new to the universe of the PWC. I only have 28 hours with my GTX, so I'm not sure to know if I have any cavitation on take off. How to know it?
The reverse gate is all way up, and the OPAS also working fine.
The carbon seal is the original one, has ten years (and 149 hours), never was changed by the first owner. Maybe the problem is here?

 

[IDoSeaDoo]

Cavitation is the water equivalent of burning out. Your rpm goes up but your speed take a while to catch up. Most skis have some degree of cavitation, but if you're always sucking air into the pump tunnel, you're just churning that and not moving water. Air is compressible, unlike water

 

[JoanEnric]

Cavitation is the water equivalent of burning out. Your rpm goes up but your speed take a while to catch up. Most skis have some degree of cavitation, but if you're always sucking air into the pump tunnel, you're just churning that and not moving water. Air is compressible, unlike water

Oh, ok! I understand! Well, in that case I'm gonna test it.

With the old impeller and ring I had a lot of cavitation, my top speed was about 36 at 7200, and between 4000 and 7200 it was a lot of noise but no speed. After these changes, I notice that the engine has power in al rpm range.

Maybe it's time to change the carbon seal.

 

[Sea Dood]

Oil level is crucial with the 4-tec. Too high and you get crank case pressure and lose performance.

While it is true that high oil level will cause inability to rev to max RPM, you have the wrong conclusion. It doesn't cause high crankcase pressure.

These engines are a dry sump design. Instead of using an oil pump to scavenge the lower end of the case, they use blowby to do it. Each rod lower end cavity has a tube that goes up to the parting line of the crankcase, and blowby pushes the excess oil out of the sump up these tubes and oil spills into the oil sump. If oil level is too high, it covers the upper level of these tubes and the oil cannot leave the crank sump for each cylinder. The oil buildup acts as a viscous brake on the rotating crank/rod, which slows the ability for the engine to rev to high RPM. It can even overheat the oil.

 

[IDoSeaDoo]

While it is true that high oil level will cause inability to rev to max RPM, you have the wrong conclusion. It doesn't cause high crankcase pressure.

These engines are a dry sump design. Instead of using an oil pump to scavenge the lower end of the case, they use blowby to do it. Each rod lower end cavity has a tube that goes up to the parting line of the crankcase, and blowby pushes the excess oil out of the sump up these tubes and oil spills into the oil sump. If oil level is too high, it covers the upper level of these tubes and the oil cannot leave the crank sump for each cylinder. The oil buildup acts as a viscous brake on the rotating crank/rod, which slows the ability for the engine to rev to high RPM. It can even overheat the oil.

That is an awesome explanation! I've always been told that too much oil is a bad thing, but never had anyone explain it to me. That's why there is a special way to check the oil on these things... Also, this explains why there is such a crazy amount of blowby generated by these motors. I know first hand, because when I first put my engine into my boat, I didn't plumb a big enough PCV pipe to the intake. I had such a huge amount of crankcase pressure, that it forced oil out of the valve cover gasket!

Also, I forgot that the max rpm of the non 215 motor is 7600, not 7200. You are missing about 400 rpm off the top, which could be why you're only getting to 44. I think max speed of the 155hp motor is around 55? Someone else chime in here, as I've only had experience with the 185hp s/c.

So, [MENTION=87374]JoanEnric[/MENTION], do you know the proper way to check the oil on these motors? It's more involved than just pulling the dip stick. If not, google it, there are good explanations everywhere.

 

[JoanEnric]

Hi!

Wow...that's a lot to learn from you!!!

Yep, max speed is around 55, and max rev's around 7600.

Before changing the carbon seal I think it's better to start from the easy stuff, oil level. Yep, I know how to do it. Start the engine, 30 seconds, stop the engine, wait 30 seconds and check level. I'm gonna do it this weekend. I also want to check the spark plugs, in order to see if there is any fuel problem.

I'll check this weekend and I'll let you know how it was.

I really appreciate all your help!

Regards!

 

[JoanEnric]

Hi!

So, a little update. This morning I removed some oil. Now the level is between the two marks. I'm going to check also the sparks. Bad weather these days, so for the moment I can't test in on the water.

Regards!

 

[Coastiejoe]

Spark plugs are one thing the 4-tec engines need to be like new. For some reason, if there is any issue with a spark plug it shows up instantly in regards to performance with these engines.

 

[JoanEnric]

Hi!

Another little update. This evening I've checked the spark plugs, they have now around 20 hours. All three have the same matt white color, they are more white than grey. So, is this a fuel issue?

And also another thing, the carbon seal looks bad. Maybe it's time to change it.

Regards!

 

[Coastiejoe]

Carbon deal will slow the ski down for sure. Sucks air and and allows cavitation which leads to less performance.

 

[JoanEnric]

Yep, I think so.

By the way, the white colour of the plugs is normal?

Thanks!

 

[Hawk388]

Hi!

Another little update. This evening I've checked the spark plugs, they have now around 20 hours. All three have the same matt white color, they are more white than grey. So, is this a fuel issue?

And also another thing, the carbon seal looks bad. Maybe it's time to change it. I would suggest you grong the oil down to a proper level, then run she shot out of it and check the oil level again.

Regards!

Yep, I think so.

By the way, the white colour of the plugs is normal?

Thanks!

Solid white isn't good. You want a solid, Paper-sack brown color. Solid white means too little fuel. Dark brown or black means too much fuel. With your matte White color, I would stop running the ski personally. That means the combustion chamber is seeing too little fuel and it can have major consequences. Are you tuned with a aftermarket air intake? Also, too much oil can be an issue by washing down the cylinders and thinning the fuel. It is CRITICAL you run the oil at half mark to below around the the lower mark. Just the way these engines run well.

 

[JoanEnric]

Hi!

Everything is stock, any modification. By the way, in idle, revs are stable, around 1900. There's no white or black smoke at all in any case. Engine starts always at first attempt, without hesitation, even in cold days.

So, if it was a fuel issue, what symptoms could be there?

Thanks!

 

[JoanEnric]

Hi!

Here's a pic of the spark plug. The other two are identical.

 

[JoanEnric]

And here two pics of the carbon seal...

 

[JoanEnric]

Hello everybody!

Little update. Yesterday finally I got a nice day to run, great weather and good sea, not as good to run at wot, but pretty close.

The first difference I noticed was a powerful response, don't know how to explain it, but the engine runs different, more bright. Now I'm waiting to have the best conditions to test it at wot...

 

[bell99man]

That white plug is still a sign of an intake air leak, dirty fuel jets or clogging fuel lines or filter. I would run it normally for a minute or 2. Kill it at around 4000 rpms and pull a plug out right then to look. If it is still white, trailer it and head to the shop or your garage. Start hunting for the problem checking easy stuff like the filter. Make sure lines are secured tight so no air leaks in. Maybe even start a new thread on here asking specifically about the plugs and fuel issues. White plugs mean hot cylinders and can lead to burning rings and pistons. Hope you find it soon.

 

[JoanEnric]

That white plug is still a sign of an intake air leak, dirty fuel jets or clogging fuel lines or filter. I would run it normally for a minute or 2. Kill it at around 4000 rpms and pull a plug out right then to look. If it is still white, trailer it and head to the shop or your garage. Start hunting for the problem checking easy stuff like the filter. Make sure lines are secured tight so no air leaks in. Maybe even start a new thread on here asking specifically about the plugs and fuel issues. White plugs mean hot cylinders and can lead to burning rings and pistons. Hope you find it soon.

Hi! Thanks a lot for your reply.

I'm going to check fuel filter, maybe after 10 years needs a replacement.

Regards!

 

[IDoSeaDoo]

Engines tend to backfire when they run lean. If yours backfires, that's a good indicator. To check for air leaks, I spray small amounts of carb cleaner at places I'm suspecting/testing while it's running. If you hit it, the engine should slow down some. Careful not to spray too much. Once the fumes start entering the actual intake, the motor will behave differently. Also, keep in mind that you're spraying a flammable liquid onto a hot engine. Don't be dumb about it

 

[JoanEnric]

Engines tend to backfire when they run lean. If yours backfires, that's a good indicator. To check for air leaks, I spray small amounts of carb cleaner at places I'm suspecting/testing while it's running. If you hit it, the engine should slow down some. Careful not to spray too much. Once the fumes start entering the actual intake, the motor will behave differently. Also, keep in mind that you're spraying a flammable liquid onto a hot engine. Don't be dumb about it

Hi! Thanks for your answer.

There's no backfire, no smoke either. Engine runs smooth, no strange sounds or vibrations, any alarm of overheating.

Anyway, I have to check and replace fuel filter.

Thanks!
Regards.