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Rpm jumped high on guage

Gvoz42

Gvoz42

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Miamisburg Ohio
Hello all!

This past weekend while cruising through a no wake zone. Had my rams set at 1500 and as I was going they would intermittently jump to 2200ish and come down and jump again. Then out of the no wake at wot I'm usually around 6200 but the guage was reading 7000. Now I didn't have any alarms and my engine , 2021 yamaha f70, didn't sound abnormal nor bouncing off a rev limiter. So as a smart person I back off of the throttle.

So my question is. Do you think my guage is going goofy? Or did I spin the hub on my prop?

Just don't want to cause damage to anything on my beloved boat.

2021 SVL Yamaha f70 with a 13.5 x 9 prop

Thanks!
 
Checking for a spun prop is easy. Mark a line across the rubber part of the hub onto the edge of the prop. Run the boat a bit at high RPM's. Tilt the motor up and see if the prop has moved relative to the hub.
prop.jpg
 
Gvoz42 said:
Hello all!

This past weekend while cruising through a no wake zone. Had my rams set at 1500 and as I was going they would intermittently jump to 2200ish and come down and jump again. Then out of the no wake at wot I'm usually around 6200 but the guage was reading 7000. Now I didn't have any alarms and my engine , 2021 yamaha f70, didn't sound abnormal nor bouncing off a rev limiter. So as a smart person I back off of the throttle.

So my question is. Do you think my guage is going goofy? Or did I spin the hub on my prop?

Just don't want to cause damage to anything on my beloved boat.

2021 SVL Yamaha f70 with a 13.5 x 9 prop

Thanks!
Click to expand...
The likely problem is a loose or corroded connection on the back of the tach...or there is corrosion in the tach selector (selector dial on the back of the tach). Either problem commonly causes the problems you have. Just cured the same issues for ours (again) a couple days ago. Have seen the same problems on our Stingray. The fix is the same there too.
 
I will check that this coming weekend. I took it out again this weekend and was fine 98% of the time. Randomly jumped to 7k. Then back down to normal. And definitely no spun prop made makes to check. So I will do as you suggested and check the guage connections. Thank You!
 
Rssuttle said:
Also check your battery connections to be sure there tight. Maybe a loose ground could cause this. When the rpm’s jump to 7000 rpm’s does the motor sound like its also turning 7000?
Click to expand...
Nope engine doesn't miss a beat or sound any different. Which leads me to think it's what you all have recommended on checking electrical connections. I will check those this week and report back
 
I've experienced similar. When we are on a slow cruise, the tach usually reads 2200 rpm and GPS speed is ~5.5mph. A couple of time s we've been out cruising like that and I look at the tach and it's at 3000, or 2800 or something else. A little while later, back to 2200 rpm. It doesn't happen often enough to make me want to start tearing into things, though.
 
mng8r said:
I've experienced similar. When we are on a slow cruise, the tach usually reads 2200 rpm and GPS speed is ~5.5mph. A couple of time s we've been out cruising like that and I look at the tach and it's at 3000, or 2800 or something else. A little while later, back to 2200 rpm. It doesn't happen often enough to make me want to start tearing into things, though.
Click to expand...
Sounds like exactly my issue
 
PartyBarge said:
The likely problem is a loose or corroded connection on the back of the tach...or there is corrosion in the tach selector (selector dial on the back of the tach). Either problem commonly causes the problems you have. Just cured the same issues for ours (again) a couple days ago. Have seen the same problems on our Stingray. The fix is the same there too.
Click to expand...
BTW: You might want to disconnect the battery to avoid and unintended shorting of hot connections. The wiring behind the dash can be a bit of a rats nest, so use caution. A nut driver of the right size makes the job easier...but who has those? Check for loose grounds around the dash too.
 
I have the same issue with my 2016 F70. Elsewhere on the forum I read that another cause can be the dip switch on the back of the tach may be set incorrectly. Haven't gotten around to checking either as I don't use the tach since I hooked the Garmin up to the motor and get my engine info from there.
 
So finally got the time to get under the helm and check out for loose connections. And the one pigtail is good and tight and no corrosion at all. I did notice and I can't say if it was like it before but the tach with key out of ignition and nothing on is reading about 1500. But does drop to zero when key is turned. Any ideas? Could it be set wrong/bumped from vibrations?
 
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