What are the symptoms of a RV being slightly off?

[JustplainKevin]

I am talking about being slightly out of time, just a few teeth off. My dad has a '95 SP which has an engine that he rebuilt and my brother has a 97 GSX that they rebuild but had the RV installed by a dealer. Both of these boat start easy and idle pretty smooth but just seem weak thruought the RPM range.

I didn't realize how sluggish the GSX was until I got my SPX.

[Bill O'Neal2]

Re: What are the symptoms of a RV being slightly off?

As you may know, SD made several different engines and a few different rotary valve sizes.

As the engines got bigger they needed more duration in the rotary valve to give the intake stroke the time it needs to fill the clyinders, much the same as installing a higher lift camshaft in a hot rod motor. So, you can see that the engine can and will start and run decently even if the RV timing is off a little, but it will not run at optimium performance.

You should confirm that the RV is set correctly. But, do not be suprized to find out that there could be other factors causing your dad's engine to be sluggish. Overly rich carb settings or a bad water regulator or any number of other factors can cause an engine to run sluggishly.

A very common mistake made by amatuers is to think they need to open the high speed adjusters after rebuilding an engine "so it won't sieze". This is a load of garbage. If the air / fuel mixture was correct before the rebuild, why would you need to change it?

Very few people ever even look at a water regulator until they are directed to do so, but they do fail quite often in older skis. When they quit working properly, they inject too much water into the exhaust system and the motor will not reach maximum rpm.

BTW, "a few teeth off" would be at least 35 degrees.

[JustplainKevin]

Re: What are the symptoms of a RV being slightly off?

I didn't know the '95 SP had any kind of water regulation other than pump pressure.

It doesn't have a tach and I am ed'guessing that it will run ~37 mph based on my GSXL which, for some reason, had a pretty accurate speedo compared to GPS. Maybe I am expecting too much from it? It barely pulls away from his 580cc GTS on glass but cannot keep up with it out of the hole.

[Bill O'Neal2]

Re: What are the symptoms of a RV being slightly off?

95 SP's do not have water regulators. I thought you were working on a 1997 GSX. My mistake.

It sounds to me as though the SP could use a new impellor or wear ring or both. The stainless steel impellors wear down over time ( outside diameter gets smaller) and it can really hurt the performance. The 1995 SP should reach speeds of around 42-44 mph.

[JustplainKevin]

Re: What are the symptoms of a RV being slightly off?

Sorry, two boats in one post. The GSX needs help too but it's owner doesn't seem too interested in fixing it. The SP has a new wear ring but I wasn't there when it was intalled so I don't know the condition of the impellor. I did get a little better with the new ring. Less cav out of the hole and a slight gain on top.

The impellor has a large hub compared to the one that my GSi had. Can a small hub impellor be used on this boat?

Thanks,

[Bill O'Neal2]

Re: What are the symptoms of a RV being slightly off?

Either can be used in that pump, but the larger hubbed impellor is the better of the two if it is the correct pitch. There is not alot of difference in the performance of the two in a 587 powered watercraft.