Bouncing tach and synch

[petrosell]

Judt complted first trip in my used searay 310 with 350 mpi v drives. The tach started bouncing on the port motor makes it impossible to synch the motors with the gages. have to use sound and experience or feel. Any ideas what i should look for as a cause. ?

 

[Hampton]

Yep.

Lots of the SR tachs have an adjustment on the back to set it for 4, 6, or 8 cyl motors. Remove tach, or access back of tach. Cycle the tiny switch back and forth a few times to scrape away corrosion. Re-set to appropriate setting (8). While you're back there, take connections off and clean or at least shift them around to break through corrosion.

If you don't have a tach selector switch, clean connections.

 

[Redhook98]

Yep.

Lots of the SR tachs have an adjustment on the back to set it for 4, 6, or 8 cyl motors. Remove tach, or access back of tach. Cycle the tiny switch back and forth a few times to scrape away corrosion. Re-set to appropriate setting (8). While you're back there, take connections off and clean or at least shift them around to break through corrosion.

If you don't have a tach selector switch, clean connections.

Yep, exactly. This has worked for evey boat I have had. Since your sync is acting up as well, I would clean the connections on the sync module. Clean connections will make a big difference!

 

[Spot]

If not in adjustment I could be just a bad ground or wire for the tac. One of my past boats did it after some winters (due to me not using (dialectric.sp? grease). All I did was loosten tac wires and then re-tighten them.

 

[petrosell]

Thanks everyone will do.

 

[kpetry]

If the above don't fix it, I had a similar situation on an electric tach on a car. Turned out I had a bad spark plug wire that was arching close to the tach feed wire! The arching was causing the tach to jump. Weird, I know, but keep it in mind.

 

[petrosell]

Yeah I am also losing power on that side have a shimmy. Will check the props but think I may be skipping on that side. She burns more fuel on that side also.

 

[fwebster]

Don't mess with any of that other stuff until you get the engine running right.

The whole tach/synchronizer circuit is electronic and is dependant upon pulses from the ignition system. The jumping tach and screwy synchronizer are most likely from bad plug wires, plug wires arcing to ground, bad ignition module, etc.

 

[Presentation]

I want to check something here.

Pet - do you have a synchronizer gauge?

I want to make sure we are not assuming.

 

[fwebster]

Does it matter?

Both are driven by ignition pulses and until he fixes his ignition problems, neither will work correctly..........but I guess if he doesn't have a sync gauge, it ain't broke and he can't fix it.

 

[Presentation]

Does it matter?

Both are driven by ignition pulses and until he fixes his ignition problems, neither will work correctly..........but I guess if he doesn't have a sync gauge, it ain't broke and he can't fix it.

Hi Frank,

Pet may have an ignition issue such as an ignition wire, distributor cap or spark plug. He may also have no ignition issue, just some corrosion on the tachometer 8/6/4 selection switch on the back.

If both the tach and sync are jumping then it would support the issue being ignition related or at least eliminate the issue being only in the tachometer. If the only issue is the jumping tack then removing and flipping the switch on the tach is a reasonably easy, do it yourself, no expense other than a bit of time next logical thing to try before you start replacing engine components chasing a gremlin.

From my limited personal experience, ignition issues are consistent, meaning you are not going along at a constant speed then the tack jumps as the engine revs then it stops for a bit. I’m not saying it does not happen that way, just that I have not experienced it happening that way.

Ignition issues can cause increased fuel consumption, so can other things.

Jumping tacs due to tachometer selection switch corrosion are inconsistent. They work fine one moment, bounce the next for no apparent reason then go back to working fine.


BTW – Frank, thank you. I do support the concept of this board where things are questioned. I have found your replies to be beneficial. Feel free to question any of my posts and I’ll do my best to explain in more detail as I have done here and admit when I’m shown that I’m wrong.

 

[petrosell]

Yes andf it works at low rpms ? As for engine not running right not sure if it is or not just starting to troubleshoot new boat to me.

 

[petrosell]

yes

 

[Presentation]

yes

Pet, it’s very difficult to understand what you are saying “yes” to.

Also, I could not follow your previous post.

I’m going to try to make this simple:

#1) Do you have a sync gauge? If yes, does it bounce?

#2) Are you confident that one engine is using significantly more fuel than the other measured by multiple refueling and written down to determine a pattern? Not one tank filling, one time. At least 2, better would be 3 fuel fillings. Please post your data.

#3) Exactly what is going on when you say one engine is not running correctly?

 

[fwebster]

I guesss I'm one who likes to avoid fixing things that aren't broken..........


Look down to about post #7 where the OP admits:

Yeah I am also losing power on that side have a shimmy. Will check the props but think I may be skipping on that side. She burns more fuel on that side also.

Losing power, has a shimmy, burns more fuel.....? Maybe he should check the light bulb in his salon closet too. .........Sorry, I couldn't resist.

 

[Presentation]

I guesss I'm one who likes to avoid fixing things that aren't broken..........


Look down to about post #7 where the OP admits:



Losing power, has a shimmy, burns more fuel.....? Maybe he should check the light bulb in his salon closet too. .........Sorry, I couldn't resist.

Good point Frank. I also read this:

.....As for engine not running right not sure if it is or not just starting to troubleshoot new boat to me.

I was talking to one fellow…..gulp….captain and he said his starboard engine burns much more fuel. I asked him how he determined this. Pointing to the throttles he said because when the engines are in sync the right throttle is further forward.

I damn near had my drink come out my nose I was laughing so much.

 

[Therapy]

I had a similar problem with my 410. Turned out that ethonol in the fuel had broken up the garbage in my old tanks and blocked my fuel filters. When the engine sputtered, I couldn't hear it. The sync went wild. Changed fuel filters and fixed problem. I needed to change the filters several times before things ran smoothly