a tachometer problem

[WZ JUNK]

Recently a friend of mine, who drives a model A roadster with a flathead in it, had his garage entered.  He thinks some kids got in there and probably more than once.  The net result is it appears they left the ignition on and ruined the points in the flathead.  He replaced the points,(his distributor has been updated to just one set of points), condenser, and coil.  The engine runs fine.  The Stewart Warner tack however, is another story.  It goes round and round, when the engine is running, like the second hand of a clock on speed.  It does not do this with ignition on and the motor not running.  He replaced the tach and the new one does the same thing.

I checked the most obvious stuff, correct wiring, continuity, and generally looking things over.  

We need a little help.

John

[wayne petty]

thats really strange..


http://www.stewartwarner.com/Tech/faq1.html

[Canuck]

Older tach with a seperate sender that has gone bad?

The 765 tach I have for the coupe has a seperate sender.  The 960 that I had before also had a seperate sender of a different style.

If it is a 765, I have test procedures for the tach and for the sender.

Canuck

[WZ JUNK]

Older tach with a seperate sender that has gone bad?

The 765 tach I have for the coupe has a seperate sender.  The 960 that I had before also had a seperate sender of a different style.

If it is a 765, I have test procedures for the tach and for the sender.

Canuck

This is a newer tach that looks like an older one.  It does not use a sender.  

I read a post on another message board that a filter inline with the tach signal wire might filter out interference that could cause this problem.

Thanks for the help.

John

[Canuck]

Just thinking that, if two tachs show the same problem, one new.  The problem is probably outside of the tach itself. That is why I was thinking of a defective sender.  If the original tach worked OK prior to the break in problem logic says the problem must be in the rest of the ignition system.

Try swapping out the condenser and the coil individually and see if either one clears the problem.  Not to many pieces there to create a problem.  Any other electronic pieces included in the swap from double points to single?  They may be suspect as well.

Canuck[/u]

[Canuck]

Just thinking that, if two tachs show the same problem, one new.  The problem is probably outside of the tach itself. That is why I was thinking of a defective sender.  If the original tach worked OK prior to the break in problem logic says the problem must be in the rest of the ignition system.

Try swapping out the condenser and the coil individually and see if either one clears the problem.  Not to many pieces there to create a problem.  Any other electronic pieces included in the swap from double points to single?  They may be suspect as well.

Canuck[/u]

This may be like not checking the gas tank on the lawn m,ower when it doesn't start, and I have been there numerous times.

Is the tach connected to the (-) side of the coil?

[WZ JUNK]

He is in the process of checking out the distributor components now.  It is not easy as it is a crab like unit mounted low on the front of the engine.

Believe me I checked the connection on the coil.  It is not beyond me to fail to check the polarity.

Thanks, when we find the solution, I will post.

John

Try swapping out the condenser and the coil individually and see if either one clears the problem.  Not to many pieces there to create a problem.  Any other electronic pieces included in the swap from double points to single?  They may be suspect as well.

Canuck

This may be like not checking the gas tank on the lawn m,ower when it doesn't start, and I have been there numerous times.

Is the tach connected to the (-) side of the coil?