Why only 7650 RPMs?

[rcguy]

All went fine with boat test today but it could have been better. Light chop, little wind, water temp 76 and air temp 85. Just installed new impeller, Solas 14/19, and new wear ring. Running OK, max RPM 7650, GPS 46 MPH. Most I got before new impeller and wear ring was 7800 RPM and 44 MPH. Don't know why I'm only getting 7650 RPM. Could be the impeller at 14/19 holding the RPMs down since the impeller is actually the governor for the engine. Maybe plugs or 89 octane. Using ethanol free gas and only can buy mid grade 89 octane. Any suggestions. Yes the SC was completely rebuilt last year with steel washers about 20 hours ago. The Seadoo has a total of 74 hours and I just did an oil and filter change. The old impeller has no numbers engraved on it so don't know the pitch. Does anyone know what the stock impeller's pitch is?

 

[Sportster-2001-951C-Stock]

Generally owners manuals contain specifications for acceptable engine operating range.

 

[LouDoo]

Generally I have found the best all around impeller is the stock impeller. Aftermarket impellers are a trade off, some offer more top end, some offer faster out of the hole and will definitely have an effect on engine rpm's. You should be able to find the stock impeller pitch either in the service manual or try to google for it.

Lou

 

[Coastiejoe]

Hands down, it is the load on the impeller that has decreased your RPM's. You gained speed due to the cut/pitch of the impeller. It is more aggressive than your stock impeller. Unless you go to a less aggressive impeller and or do some sort of an engine modification, you will not get back to the higher RPMs you had in the past.

 

[Sportster-2001-951C-Stock]

It's hard to know for sure if the engine is being overloaded absent some knowledge of acceptable range for the application, a worn wear ring can also cause higher than normal WOT RPM's as well? There must be a normal spec the engine was designed for, the wheel should match that and place WOT RPM in the range. What were the original RPM and speed, how much additional weight has been added to the boat since the maiden voyage, a bilge full of "stuff", anchors, extra batteries, etc. can slow top speed some too. It isn't terribly uncommon to resolve loss of top speed to weight gain (for whatever reason).

"It boils down to this: A poorly sized propeller may cause the powerplant to work harder than it was designed to operate. The result can be poor responsiveness, high fuel consumption, high maintenance costs, shorter time between overhauls and/or poor boat performance."

https://marine.cat.com/cda/files/949240/7/Propeller Sizing.pdf

 

[pete63]

most likely all the above, however i did read in some of the tech update sheets that a dirty sc air intake can reduce rpm's.
you can check the tech update sheets, i put the link some time ago in the boat section.

found it

 

[rcguy]

Thanks guys for the help......it is appreciated. When I first bought the boat about 15 months ago it did 7950 rpm. The previous owner said he used 93 or high test gasoline. I changed over to alcohol free gas but the only octane I can buy is 89. My question is if you had a choice between 89 alcohol free or 93 octane ethanol which one would be better for the engine?

 

[LouDoo]

89 no ethanol would be my choice. That's what they sell at our marina.

Lou

 

[Sportster-2001-951C-Stock]

I think whatever fuel Seadoo advises should be the preference. No doubt the SC motor requires a higher minimum octane than the NA engine? Ethanol fuel goes stale much faster, stale = detonation in our heavily loaded marine engines.

 

[Sportster-2001-951C-Stock]

Thanks guys for the help......it is appreciated. When I first bought the boat about 15 months ago it did 7950 rpm. The previous owner said he used 93 or high test gasoline. I changed over to alcohol free gas but the only octane I can buy is 89. My question is if you had a choice between 89 alcohol free or 93 octane ethanol which one would be better for the engine?

I'd also try to find out what kind of speed the boat is capable of normally, seems like you lost 150RPM prior to the impeller swap but that could be the difference of which way the wind is blowing in some prop boats.

Throwing out a few ideas from the hip......... FWIW....

Those have intercoolers too, right? What are the chances the intercooler might be watering the intake or plugged or something? Any signs of moisture in the intake?

 

[rcguy]

I'm sure it doesn't have an intercooler. I believe they came on the 255 hp engines in 2009 and newer.

 

[Albysure]

I just got the solas concord for xmass...was really looking forward to it...I can live with the gas Milage and the lower rpm's as long as it doesn't cause damage on the engine... The main reason I got it is to get a better hole shot when I have a lot of weight on board(people).... So did you notice a better hole shot?

 

[rcguy]

The hole shot was a lot better, so I'm not going to worry about the loss of a few RPM. With boats we usually ride at 5500/6500 RPM 99 percent of the time. Not many boat owners ride wide open for long periods of time. I may be wrong for stating that. I will wait and see what happens when I use up the gas and refill with fresh gas.

 

[pete63]

I'm sure it doesn't have an intercooler. I believe they came on the 255 hp engines in 2009 and newer.

just follow the water inlet hose, if it goes to front of the engine and back out then to the exhaust and not straight to the exhaust manifold then its got a intercooler.

 

[xintersecty]

I'm sure it doesn't have an intercooler. I believe they came on the 255 hp engines in 2009 and newer.

That engine and supercharger combo does have an intercooler. That's how they get from 185 to 215. The 255HP engines have a different intercooler and supercharger combination.

I just saw that Pete replied with the water line information.

I got the same prop, boat, and engine combo. My RPM gauge is busted so I can tell you my RPMS. My hole shot is better and I lost a bit on the top speed.

 

[rcguy]

My mistake about the intercooler.

 

[pvamax]

Choosing 89 over 93 because of no ethanol is silly in a modern boat with this small of a tank. You need the octane points to resist detonation and to get maximum performance.

 

[rcguy]

Choosing 89 over 93 because of no ethanol is silly in a modern boat with this small of a tank. You need the octane points to resist detonation and to get maximum performance.

It has nothing to do with cost of 93 octane or to resist detonation or get maximum performance. Here in central Florida we have a tremendous amount of humidity year round. Ethanol gas at 10% just sucks the humidity (water) right out of the air and water is extremely bad for the fuel injectors and rusts internal parts. Also, ethanol turns to varnish in a short time and gas stabilizers don't help very much. I would use ethanol fuel at 91 octane if I burned most of the tank in less than a month but that is not the case.

My Sea-Doo 180 Challenger/SE 2008 operators guide, page 69, states to use in North America 87 to 91 gasoline containing a maximum total of 10% ethanol or methanol or both and that is for a 215 HP Supercharged intercooled Rotax engine. Also, many gas stations have tested to have as much as 15/20% ethanol plus H2O. Not to change the subject but my new Ford 150 V-8 5L, 360 HP is set up from the factory to run Flex Fuel 87 octane up to 20% ethanol. I use the Ford daily and fill up weekly.

The 89 octane, ethanol free gasoline is right in the middle of recommended range and cost $.75/1.00 more per gallon. No injector problems and no water in the fuel problems. This is the choice I made (silly or not) and will run my Sea-Doo till it runs no longer.

 

[rcguy]

Yesterday, I was oiling the throttle body through the yellow capped tube and tried moving the throttle all the way open. Too my surprise the throttle at the end of the cable still had about a 1/4 of a inch more to open. So I adjusted the cable at the throttle body to open fully. I did this with a 10 mm open end wrench...loosen the outer nut and tighten the inner nut. Now the throttle opens fully. I called my mechanic before I tighten the throttle cable and he said be careful not to tighten the cable too much because this is how you break the cable if you jam the throttle wide open.

Tomorrow , Friday, I'm taking her out for the day and I'll let you all know if this made a difference in rpm. Presently she is running close to 7800 rpm's and 45/47 mph (GPS).

PS: The Shell gas station about a mile away just started selling ethanol free gasoline with a minimum octane of at least 90 for $3.09 a gallon which is .30 cents less than I was paying for 89. Will see if the price difference stays the same. Higher octane better price...one guess where I'll purchase gas in the future.

 

[Sportster-2001-951C-Stock]

Finally, we seem to be getting a break from paid-off DC politicians and their ethanol special interest groups? Oh sat it ain't so!

On the throttle cable adjustment if it's too tight that can break the inner wire due to strain. Here's how I do it: Loosen both nuts and make sure there's some slack, then place throttle controller in full WOT position. Pull cable sheath taught so butterflies are WOT, then tighten both jam nuts to hold that position.

Check idle position, the butterfly bellcrank should rest completely on the butterfly stop adjust screw. If not, the throttle is being held open so recheck previous adjustment.

This way, the throttle plates will reach WOT simultaneously with the throttle controller.

 

[rcguy]

Update... took my boat out yesterday, perfect sea conditions and no change in the RPM's. Engine runs strong but still only 7650 top end and 44/45 mph. We had a great time and are thankful all went well. I can live with the boat as is for now I don't have a choice.

 

[rcguy]

Had the boat out this past Sunday, 5/3/2015, and was running at 7800 rpm's with fresh gas. All working the way it should ...finally!

 

[rcguy]

Using the Doo a lot more and all is great. Had another great day on the water. Other boat owners complimenting the Doo . Dooing 46 mph in open waters. Had a disagreement with the woman about naming the boat. It's our "Doo" period.

 

[X-Runner]

7800 RPM is normal for these boats?

I have 2008 Speedster with the 215 HP 4TEC. My digital gauge is hitting 8100 RPM!! I am GPS'ing the thing at 53MPH with just me in it and a full tank of gas in her.

Does it sound like my gauge my be inaccurate?

 

[rcguy]

GPS's are accurate...so if it says 53mph you are going 53 mph. Your boat is smaller and lighter than mine. I have a Challenger 180 supercharged and with full tank of gas plus me 225 lbs and my girlfriend at 120lbs hit 46 mph. My RPM gauge is analog and it says some where in between 7650 and 7800 rpm. I don't think these RPM gauges are accurate but the GPS at 46 mph is right on.

You may want to check your wear ring because (if accurate) 8100 in not normal for these boats. You should be around 7800 but I could be wrong. My mechanic says 7800 is normal for the 215 hp supercharged engine. If you need a new wear ring you my find out that your Sea-Doo may even go faster than the present 53mph.