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  90hp Evinrude rpms too low on Katama

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Author Topic:   90hp Evinrude rpms too low on Katama
greyg8r posted 05-23-2004 02:38 PM ET (US)   Profile for greyg8r  
I (finally) added a brand new tachometer on my 1974 Katama with 1982 Evinrude 90 and 13 3/8 inch x 17 inch stainless steel prop and took her for a spin. It rpms maxed out at 4700 at wot. After following this forum, I was under the impression it should be hitting 5200 - 5500 rpms. It seems logical that I should go with a smaller pitch prop (which should help get my lardbutt out of the water on one ski), but should I change diameters?

I need suggestions.

Richard

JohnJ80 posted 05-23-2004 07:32 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I don't think you will need to change diameters. Just reduce the pitch.

sometimes the props will be slightly smaller in diameter, that is not a big deal.

At least that is what the prop guys told me.

Bigshot posted 05-24-2004 01:49 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
That is the perfect prop for that engine, should heit 52-5300 if engine is healthy....is she healthy? Make sure Tach is set right and do a compression test. If both are good then run a can of techron in a 6gal tank and let it sit overnight while in the carbs. This should help ckean some gunk out and possibly bring them up. Dropping pitch will over rev unless engine is tired.
greyg8r posted 05-24-2004 05:04 PM ET (US)     Profile for greyg8r    
Nick,

The boat does 43 mph per a GPS and runs strong. So, I think it's healthy.

As I mentioned, I just installed this tach. How do I know if it is working correctly? Is there a way to verify this?

Richard

TampaTom posted 05-24-2004 06:15 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
I had the same motor and prop for three years and consistently hit 41-42 mph/gps. During that time however, my tach would only max out at 4,800 and over time drifted up to 5,200. Think I posted the dilemma on this forum. My unqualified guess is that the rectifier or corroded tach wire was to blame. Resistance/voltage drop could have been changing due to heat and/or humidity?

43 mph is as good as you could hope for from a 90. I loved that engine.

Bigshot posted 05-25-2004 02:52 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Switch the poles on the tach until one reads about 5200+ and see how that works. The 13.375x17 SST is what everyone including myself runs on that combo. What brand tach is it? This is reason #1 why I only use OEM tachs, I never have good luck with aftermarket except Teleflex(who made most OMC stuff) and Gaffrig which aint cheap. Although Faria and others are good machinery, I "prefer" to run OEM brands, especially on Yamahas.

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