Tach problems

I had to replace the tach meter on my 1977 85hp Johnson. At Idle the tach reads fine but when I power up the tach drops off. Any ideas what the problem is?

Re: Tach problems

The tach may be fine. Does the battery charge? A quick easy check is to measure the DC voltage across the battery terminals with motor at a fast idle. If less than 13 VDC, the regulator/rectifier and/or stator may need help. The tach works off pulses from the R/R.

Re: Tach problems

Is the tach new, and is the dial on the back of it set to number six (6)? The 1977 model does not have a voltage regulator, just a rectifier..... and if the rectifier is faulty, the tachometer shouldn't function at all.

Normally that action indicates a bad tachometer.

Re: Tach problems

Joe Reeves said:

Is the tach new, and is the dial on the back of it set to number six (6)? The 1977 model does not have a voltage regulator, just a rectifier..... and if the rectifier is faulty, the tachometer shouldn't function at all.

Normally that action indicates a bad tachometer.

Click to expand...

Joe, I've been trying to figure out if my tach is set right for a few days. I have a 1977 2cyl 55hp Evinrude. I think it is supposed to be set to 10 (5 pulse) based on some searches.....

Also, there definitely isn't a regulator bc my fishfinder (which displays voltage) has read all the way up to 17.2 volts! I typically blast the stereo while cruzing to try and keep the voltage down. I've been told that over 15V is bad for the battery, and I'm kinda worried about the fishfinder and stereo too. Can I add a regulator somehow??

Thanks
Glen

Re: Tach problems

Glen.... The tach operates off of the engine's six (6) pulse charging system, hence the tachometer must be set to number six (6) if it is an OMC tach that has a dial on the back of it. If you have some other kind of tach, the cure will need to come from some other member who might be knowledgeable of it.

There used to be add on regulators but I doubt if they're still available.

Re: Tach problems

Thanks for the info I will give them a try.

Re: Tach problems

Try this: 18-5827 sierra voltage regulator

Re: Tach problems

5P is the correct setting for that motor. Common reasons for high voltage is bad/dirty connections and not using a marine battery.

Re: Tach problems

bhile said:

5P is the correct setting for that motor. Common reasons for high voltage is bad/dirty connections and not using a marine battery.

Click to expand...

... or unregulated rectifier.

Re: Tach problems

I had a problem with mine once. I tapped directly into on eof the two yello wires coming from the stator into the voltage control rectifier regulator. My tach worked low but once past 2300 rpm it was erratic and would only goto 4200 rpm. I switched it over to the other yellow stator wire and BINGO! It works beautifully... go figure! It is worth a try.

Re: Tach problems

Sorry for highjacking this thread kevin... PaulO seems to have a good suggestion to try and I haven't gotten a response for this on the other threads I've started...


OK, this is starting to make a lot of sense, I just want to clarify...

I checked my tach and it was set to 6, which would be the correct setting for my original '97 50.

When I repowered with the rebuilt '77 55hp I didn't change the setting on the tach, and was disappointed with the purchase bc it wouldn't rev over 5 grand.

From what I understand the '77 is a 10 point, 5 pulse system, meaning that the true RPM's would be equal to (6/5)*(tach reading).

This would put me over 6000 RPM WOT, and at risk of blowing the thing up.

I am using a thirteen pitch prop I bought for wakeboarding, because i trashed the original 17P.

I felt that if I can barley turn 5 grand with a thirteen pitch prop moving up in pitch would be over proping. Now, based on my math, I need to reprop because I am currently overreving the motor.

Does all this make sense? I can't get to the lake till the weekend and would like to get a replacement prop ordered today. I think a 17 P is in order, as operating range is 5-6 grand, and currently I am turning (6/5)*(5000)=6000 RPMs

Re: Tach problems

glengold said:

Sorry for highjacking this thread kevin... PaulO seems to have a good suggestion to try and I haven't gotten a response for this on the other threads I've started...


OK, this is starting to make a lot of sense, I just want to clarify...

I checked my tach and it was set to 6, which would be the correct setting for my original '97 50.

When I repowered with the rebuilt '77 55hp I didn't change the setting on the tach, and was disappointed with the purchase bc it wouldn't rev over 5 grand.

From what I understand the '77 is a 10 point, 5 pulse system, meaning that the true RPM's would be equal to (6/5)*(tach reading).

This would put me over 6000 RPM WOT, and at risk of blowing the thing up.

I am using a thirteen pitch prop I bought for wakeboarding, because i trashed the original 17P.

I felt that if I can barley turn 5 grand with a thirteen pitch prop moving up in pitch would be over proping. Now, based on my math, I need to reprop because I am currently overreving the motor.

Does all this make sense? I can't get to the lake till the weekend and would like to get a replacement prop ordered today. I think a 17 P is in order, as operating range is 5-6 grand, and currently I am turning (6/5)*(5000)=6000 RPMs

Click to expand...

start you own thread Glen and soemone will be better able to help you.

Re: Tach problems

Kevin.... Regardless, if that tachometer has a dial on the back of it, it must be set to number six (6 pulses) in order for it to function preoperly with your 1977 85hp Johnson.

Did you get it operating correctly?

Re: Tach problems

????

Re: Tach problems

I am amazed at the amount of info that one can recieve from this site.This is just ( my opion)....... Any time you are going to do any kind of project try and get as much written material from the manufacture as possible.... Now I have the EVENRUDE SERVICE MANUAL. for 79 85-hp v-4 85995r wich i believe is similar to the 77 85-hp if not the same.....The manual states that: 85-hp 100hp 115-hp 140-hp (full throttle operating range for all is 4500-5500 if you are running 6000 and more it is not right.....Also for this particular problem the trouble-shooting section has many solutions...