OMC stalls and hard to idle when hot

[KM7]

OMC 4.3 V6 2bbl rochester carb

Starts and runs great when cold and for a couple of hours. Then is hard to idle and stalls.

Temp on dash is fine.

Timing and dwell are dead on. 6 deg BTDC and 39 deg

Plugs are just a little rich looking

The resistance through the coil (disconnected) is 2 ohms across the primary contacts + and -.
And 10.3 K ohms from + or the - to the high voltage contact. That also seems within spec.

But spark looks more orange than blue/white to me.

Using a tool that connects to the end of the spark plug wire, the spark will jump a gap of at least 5/16 .

Voltage drop thru the key resistor seams high 8 v when book says should be 3.2 max.

Could that be overheating coil?

Where is is "key resistor" located??

Can you buy them ?

Thanks

 

[Howard Sterndrive]

Re: OMC stalls and hard to idle when hot

egads..what book uses the term "key resistor"? I have never heard that, but will take a guess they mean ballast resistor or are referring to the resistance wire in the ignition circuit.

"Voltage drop = voltage difference. So, if the battery positive+ terminal is 12V and the drop through the resistor is 4V, you will see 8V at coil + terminal when referencing ground with your meter.

So, are you seeing 8V at the coil, or an 8V drop?

 

[KM7]

Re: OMC stalls and hard to idle when hot

Howard

Thanks for the reply.

I have 2 shop manuals. A 1991 year old Clymer and a 1991 Seloc book. The boat is an 87.

The Seloc manual refers to the "Primary resistor" and shows it in the circuit from the battery through the ignition switch (in the on position) to the coil. So it would drop the voltage to the coil to lower than at the battery.

Apparently in the start position the coil gets the voltage directly from the battery with out going through the resistor.

To answer your question I did a test voltage **at coil** while cranking and got what the book says 8 volts.

Is the drop from 12 at the battery due to the starter??

The manual says to disconnect the resistor and measure the resistance. Should be 1.3 - 1.4 Ohms. I could not find it and did not do the test.

The clymer manual has what I think is the same test by measuring from the + wire of the coil (disconnected) to the purple wire (S) on the alternator (also disconnected) Book says 1.5 to 2.5 ohms but I get 4 ohms

There is another test of the voltage drop through the circuit in the on position: With the points closed and the ignition ON. Measure from battery + POST to the positive side of the coil. Book says 3.2 but I got 8 volts. I might have to do this test again.

The book says to look for corrosion at one of the connections. I cleaned the ones I could find.

The book refers to the "Ballast resistor" in this circuit and then also refers to the "Key Resistor" as if they are the same
But it must be the same as the "Primary resistor" above. I hate when manuals do that

So bottom line: Ballast/Key resistor is suspect but possibly coil as well. I doubt I will change the whole wire harness for a ballast resistor.

What do people do in this case? Can I buy a Ballast/Key resistor?

Thanks

Sorry for the long post

 

[Levinz11]

Re: OMC stalls and hard to idle when hot

The manuals you have are terrible. Here is an actual FSM...large download but very helpful... OMC Manual.zip

I think most of us who have had a resistor wire fail buy an alternator w/internal resistor or one that runs 12V constant. Then wire it straight to the alt.

 

[Howard Sterndrive]

Re: OMC stalls and hard to idle when hot

I think Levinz meant coil instead of alternator and that's how I did mine. You have to be darn careful to never leave the ignition key on if you go that route. There are some benefits to the factory setup.
Your resistor you are looking for is part of the wire. I think it is purple with a red stripe. PU/R in this diagram. You would have to disconnect it from the alternator and the coil to check the resistance. I'm not sure what's going on with that "splice"

 

[KM7]

Re: OMC stalls and hard to idle when hot

Thanks for all the input. Took her in and after checking coil and resistor wire they said just carb adjustment and running a bit hot due to old impeller and possible wrong heat range thermostat.

Thanks everyone.

 

[KM7]

Re: OMC stalls and hard to idle when hot

The OMC manual you suggested had a NASTY VIRUS or the site it came from was trying to infect me!!


Updated: February 15, 2012 3:15:47 PM
Type: Other
Risk Impact: High
Systems Affected: Windows XP, Windows Vista, Windows NT, Windows Server 2003, Windows 2000

Behavior
WS.Reputation.1 is a detection for files that have a low reputation score based on analyzing data from Symantec’s community of users and therefore are likely to be security risks. Detections of this type are based on Symantec’s reputation-based security technology. Because this detection is based on a reputation score, it does not represent a specific class of threat like adware or spyware, but instead applies to all threat categories.

 

[Levinz11]

Re: OMC stalls and hard to idle when hot

The OMC manual you suggested had a NASTY VIRUS or the site it came from was trying to infect me!!


Updated: February 15, 2012 3:15:47 PM
Type: Other
Risk Impact: High
Systems Affected: Windows XP, Windows Vista, Windows NT, Windows Server 2003, Windows 2000

Behavior
WS.Reputation.1 is a detection for files that have a low reputation score based on analyzing data from Symantec’s community of users and therefore are likely to be security risks. Detections of this type are based on Symantec’s reputation-based security technology. Because this detection is based on a reputation score, it does not represent a specific class of threat like adware or spyware, but instead applies to all threat categories.

Weird....I never heard anyone else on here say that. I have Windows 7 and Microsoft Security Essentials.

 

[KM7]

Re: OMC stalls and hard to idle when hot

The virus may have been on the Download Manager file that the website was trying to get me to download Before downloading the actual manual. I have Norton 360 a top antivirus program. Anyone else try it?

 

[Levinz11]

Re: OMC stalls and hard to idle when hot

The only anti-virus you need if you run Windows is Security Essentials. Do a scan from time to time with MalWareBytes and call it good.

 

[wellcraft guy]

Re: OMC stalls and hard to idle when hot

I have Norton 360 a top antivirus program. Anyone else try it?

Norton 360 is a horrible resource hog and is known for throwing all kinds of false positives. As Levinz11 said, uninstall that crap and use Microsoft Security Essentials, and an occasional Malwarebytes scan.