Why only 7650 RPMs?

[xintersecty]

Yeah, the jet-ski guys see 8100. I do in my RXT. However I never had a good working RPM gauge in my challenger. So I think anything around 8K is normal depending on the boat/weight/prop. The Challenger in comparison to the sportster has a lot more wetted area. That's a fancy way of saying water drag. The speed range for a Challenger tops off at 47 to 50 and the more horse powered motors just get you there faster.

 

[X-Runner]

Thanks for the responses. The wear ring has been changed. At around 30 hours, the previous owner sucked up a stick or something. He had the wear ring and impeller replaced. Gave me the repair order(receipt) for it. It actually happened to him twice! I have both receipts. The first one was just for the wear ring.

Anyways, I figure the TACH is not correct. That's the thing about digital gauges though. They look really nice, but i dont care for them.

How does one check the wear ring on these? I am assuming one is checking the clearance with a feeler gauge?

 

[Coastiejoe]

Yep, clearnace is the measurement you are after. .Ten-thousands of an inch is the accepted norm or smaller. Which equates to the thickness of a dime. If you shine a light in from the grate side and look from the back side you will see the gap much easier..

 

[rcguy]

Replaced my wear ring and impeller about a month ago. Could not see the space between the impeller and wear ring without a magnifying glass. Ten-thousand of an inch is much less than a dime in thickness. Put ten thousand dimes together and I think you will have over afoot in thickness....maybe more. Only a guess. Coastiejoe is right about anymore than a dime in space between the impeller and wear ring is not acceptable. You are just losing power and top end.

 

[Sportster-2001-951C-Stock]

In some cases, say if your boat was being used for towing heavy loads for example, a smaller impeller might be the right choice to match the power band of the engine to the circumstances. It's quite common for an outboard engine running at it's intended WOT RPM to outlast by a substantial margin, one incorrectly propped to a lower than spec RPM.

When rigging boats with outboard engines, we always perform a WOT water test to make sure the engine is running in it's designed power band as specified by the manufacturer. The manufacturer requests we do this test and re-prop as necessary, to make certain their warranty costs are minimized.

Weight and size of the craft is why an impeller designed for a smaller and lighter jet ski most likely is incorrectly pitched too large for use in most any boat. I'd wager that if I was to install an impeller intended for a ski into my boat, I would lose WOT RPM and probably run slower, burn more fuel and my engine would develop problems sooner.

 

[pvamax]

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.

Understand the water issue, but your original post was asking what may be causing low rpm. SD says its ok to run 87+ octane, but its not gonna hit the same rpm with 87 as 93. With 89, the knock sensor will be telling the ecm to pull timing and power output will be lowered to keep the motor safe. You will see this with less rpm.

 

[rcguy]

Understand the water issue, but your original post was asking what may be causing low rpm. SD says its ok to run 87+ octane, but its not gonna hit the same rpm with 87 as 93. With 89, the knock sensor will be telling the ecm to pull timing and power output will be lowered to keep the motor safe. You will see this with less rpm.

I'm using 90 plus ethanol free gas now from a new Shell Station and pay $.30 cents less a gallon. My RPM's very between 7650 to 7800 depending on I what the gauge feels like showing. The gauge is not accurate and I ignore it. I installed a new Solas Concord 14/19 impeller with new wear ring and getting GPS 46 mph..... an increase of about three mph with all things being equal (same weight). I'm extremely happy with the results and now I have the tools, the spare parts and knowledge to change the impeller and wear ring myself. I will in the future save a bunch of money doing the job myself and time because the dealers here are very busy during the season and it could take three to four weeks to change a wear ring should I pick up a foreign object. I now can do the job in a few hours with most of the time taken up for the freezer trick. Can't afford to lose the time during the season.