Thread: Tach problem

Last time out my tachometer would swing from 2000-5000 with engine running constant speed. Its on a 150 yamaha. Has anybody had this problem?Also what fuel treatment do you use for E10 gas? I bought star tron but havnt used it yet.

Sounds like the voltage regulator thats where it gets its signal from.Had the same problem on my outboard.

Sea foam is what I have been using. I have read alot of different opinoins on the E10 problem,Not sure what to do! All the gas around here has it in it.

stabil works for me, put it in the lawnmower and weed eater too. i heard since oil prices dropped it cost them more to add ethanol than just make regular gas, stations should be required to post what type they sell!!!

Stabil and sea foam. I think stabil is better for pure gas treatment. I think sea foam is good for cleaning out engine, I used it on an old sailboat I bought to clean out an inboard that hadn't been run in over a couple of years, and it worked great. My buddy used stabil on a salvaged boat and it did wonders even helped the fuel gauge start working again. Tachometer, start with the first things first, is your battery fully charged or working properly, are any other gauges malfunctioning, if battery is o.k. go to your connections, might sound elementary but I always dig way to deep first and always get prooven wrong about starting with the basics.

I had to put one of these on my boat, or the dealer did it under warranty I should say. My tach quit working altogether and the battery wouldn't charge and that was the problem. I don't know ir a voltage regulator will mess up and cause the RPM's to surge like that. I would check connections as that sounds like it might be your problem. Look around the voltage regulator which should be under the flywheel for connectors with corrosion on them. When water gets into them plugs, it can't get out and it takes it's toll on stuff. good luck with it!

I can shed some light on that for you. Tachs work off an AC pulse that comes from the stator. This same pulse is what feeds your rectifier/regulator for charging the battery. This is why the tach lead is connected there. Normally when your charging system stops working so does your tach. Depending on which diode in the rectifier shorts or opens affects how your tach will act. Its real simple to check your charging circuit. Check the voltage at the battery with the motor off. Now check it again with the motor running and if its OK you will see a slight increase in voltage. It gets higher as RPMs approach 2000 RPMs. If you don't see an increase you can test further to see if its the rectifier/regulator or the stator. If you have ever connected your battery up backwards (even for a split second) or caused sparks anywhere there is a 99.9% chance you toasted a diode in the rectifier. Hope that helps.

I would say either Sea Foam or Sta Bil, I don't beleive that one works better than the other. If you buy Sta-bil be sure that you buy the Blue Marine Blend and not the red automotive blend.

I always us ethe Ring Free Treatment for my Yamaha and fill the tank after each use to keep water from forming in the tank.

I have met two people that have suffered from issues related to Ethanol one that spent over $3000 cleaning out fuel lines, tanks, and conditioning the engine. Another who had to replace his engine completely.

The link below has some great info on Ethanol. Fuel Testers -Ethanol Fuel Test Kits -Protect your engines from alcohol blend gasolines.

Thanks guys, if you need to know something, just post it here!

Well...I've had a different tach problem on my Merc 3.0 I/O. Most of the time my tach overreads. I know I'm not turning but maybe 2500-3000 rpm's but my tach will read 5000 rpms. Sometimes but not often it seems to be correct. It sticks at about 1000 when the engine is shut off but will fall to 0 rpms when switch is turned to on position. It doesn't bounce around, just over reads? Anyone have any ideas on this one?