7.4GI tach problem

SUJA415

Recruit
Joined
Jun 16, 2014
Messages
2
Hello I just bought a 2001 Wellcraft Excalibur 23 with a Volvo 7.4GI, SX drive 1.43 ratio, it has a 19 pitch 3 blade prop on it. Took it out and this is what I saw, at WOT tach showed 3300 rpm trimmed out, but my GPS speed was 53.4 mph. One time after restarting the engine, I noticed the tach reading differently, I had been cruising at 2200 rpm Speed about 29-30 mph, now the tach showed 2800 rpm with same speed, so I go to WOT tach shows 4300 rpm, speed 53 mph.

I am guessing this is a tach issue but before I buy a new tach, is there a trouble shooting guide to use?

Thanks
 

Sparkinator

Chief Petty Officer
Joined
Aug 15, 2009
Messages
423
http://faria-instruments.com/site_manuals/IS0100_Tachometers.pdf

Page 2 of this document has a troubleshooting guide. That 19 pitch prop hooked to a 1.43 gear ratio drive, looks kinda small. I would definitely get a working tach just to verify you aren't over-revving your engine.

I've run a 21 pitch 3 blade stainless and pulled max rpms (4600) with a 1.66 gear ratio SX drive. With that setup, I was running 51 mph. I would think your 1.43 ratio would be spinning that 19 a lot more than that.

My tach recently started acting up like yours, and I think mine will have to be replaced. I plan to mount a cheap one under my dash just to ensure I don't over-rev my engine with different props I'm running.
 

SUJA415

Recruit
Joined
Jun 16, 2014
Messages
2
THanks for the response, I will be looking at this. This boat was bought at the dealership I got it at, and has always been used at the same lake I am at. This is also the original prop that came with the boat. I am thinking it is the right setup, the elevation is 950ft. But It doesn't sound like it is over reving, it sounds right on the money. ANyway will be looking into the tach.

Thanks for the pdf, it helped.
 
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