points question

[john cole]

on my 1987 OMC 4.3l gm engine i have been working thru some issues with it. the biggest gremlin appears to be my points. i just change them because i couldn't get up on plane and looking things over it appears i somehow managed to forget on not noticed the spring missing for them causing points to float. anyways i put in some from napa and told my marine store contact about what i did and he said that i just wasted my money cause they're not "marine quality". well to make a long story short, the motor ran good for about a hour of run time and last time out, i did some fishing and when coming back in my engine sputtered a couple of time and then ran ok but wouldn't come up to full power, so now i'm wondering if my points are going bad already or burning out and just not allowing the right voltage to go thru or maybe the condenser is crapping out. any thoughts to this.

 

[Lyle29464]

Re: points question

Your contact is full of it. I would not rule out other problems. I would start with water in the gas as my first thing to check. Do a search on here but dont put points in it. just stick with the symptoms.

 

[bruceb58]

Re: points question

You should always replace the condensor when you replace points.

You did set them with a dwell meter and then check your timing afterwards right?

You also have a ballast resistor in there right? To see if you do. Have the points closed with the ignition on and measure the voltage at the coil. Should read around 7V or so. If its less, you have other issues you need to look into like bad connections. If its 12V, your ballast resisitor isn't in the circuit which can cause your points to be burnt as wel las lowering the life of your coil.

I agree with previous poster. You need to look at everything.

 

[john cole]

Re: points question

pretty sure the fuel is ok. i have been doing the additives and changed the filter and have added plenty of fresh gas to it, but i won't rule it out. on the dwell, no i haven't used a meter on them, just gaped them and checked timing, still trying to find a friend with a meter to use. i ditched mine years ago. as far as voltage goes thanks for the info cause i didn't know what it should be. also i havent even seen a ballast resistor in this circuit, is it possible that it didn't have one or most likely some one yanked it and never put it back in?

 

[Lyle29464]

Re: points question

If the points are damaged from too much voltage or being set too close they will have turned color, look old or pitted. If they are bad I would look at the items bruce listed. Check an OMC manual to see if it list or shows a ballast resistor or the wiring diagram list a resistor wire going to the coil.

 

[john cole]

Re: points question

would it be worth while to invest in one of these online manual that i see i boat supports? does it have the diagrams i need? either way i will be down to the boat store in the am looking over thier books to see what they show. thanks for the help. looks like i should have this running good just in time to pull it for the winter.

 

[bruceb58]

Re: points question

Go on ebay and get a factory OMC manual.

 

[proshine43]

Re: points question

Dont feel bad, i replaced my points about a month ago, about an hour becore i went on our camping trip to the lake. Started it before we left. It ran for ten seconds before i shut it off. Next day, launched it, started it, went to take off and it would die, worked on it for about 3 hours before i realized what that thin piece of metal that came with the new points was for. (The spring for the points) like you i jyst gapped them, i dont have a meter either. Except for having to rebuild carb all is good now. Good luck.

 

[bruceb58]

Re: points question

For you guys that don't have dwell meters:

http://www.amazon.com/Actron-CP7605...YUUS/ref=sr_1_1?ie=UTF8&qid=1317178838&sr=8-1

 

[john cole]

Re: points question

thanks, for the link. looks like i will need to invest in one.

 

[john cole]

Re: points question

on the carb, watch that float adjustment. it will cause you a boat load of problems too if not done right.

 

[NetDoc]

Re: points question

Points... I love them and am glad that cars don't use them anymore.

A ballast resistor was mentioned earlier, but not all coils need them. It is usually marked on the coil so do check. I would go with a coil that does NOT require an external resistor unless you are bypassing it during starting. That was standard in the auto industry and were used for cars that needed a hotter spark to get going when cold. We usually don't go boating in that kind of weather, so the internal resistor coils are just fine.

A coil is nothing but a step up transformer. A condenser is nothing but a capacitor. When the points break the 12V circuit, the magnetic field in the coil collapses and is amplified into enough voltage to jump the gap on your spark-plugs. The resistor, whether it is internal or external, keeps the sparking to a minimum on the points, preserving them. The condenser also does this as well as give the spark a longer duration so it can adequately light the compressed air/fuel mixture. I agree with the previous poster that the condenser and points should be replaced as a unit.

Point float is quite unusual below 5-6K engine RPMs and you really need an oscilloscope to accurately diagnose this issue. Check the dwell (or duty cycle) against specs, adjust if neccesary and look elsewhere. Always be sure to check your timing AFTER any dwell adjustments. FWIW, Carbs are far less reliable and things like a restricted fuel supply (water in gas, semi-clogged filters) are far, far more likely. A carb that runs fine at idle runs far differently if the fuel pump can't keep up with the demand and might well result in a lean miss-fire situation (loss of power) at higher RPMs. I use a Fluke 88V/A meter as I can check a lot of electrical issues with as well as check RPMs and duty cycle.

 

[bruceb58]

Re: points question

That engine originally came with a ballast resistor or wire so if the coil is has an internal resistor, its because someone changed it out. An external ballast resistor is preferred so that full voltage can be applied to the coil at start time. When the engine is started, you have a large voltage drop due to the starter cranking. Bypassing the ballast resistor basically is compensating for that voltage drop during cranking.

Netdoc, his points floated because he forgot the spring. Of course he would easily have realized this earlier if he had used a dwell meter.

 

[john cole]

Re: points question

thanks again for the reminder about the dwell, will be getting a meter this afternoon so i can set them right. like the saying goes never have time to do it right the first time but always have time to do it a second time:facepalm:. and will look into the ballast resistor part of it some more too.

 

[bruceb58]

Re: points question

Get that set correctly along with the timing and then go on to look at other things. Another thing that is useful to do while you are checking the timing is to make sure you get full distributor advance. If you have an advance type timing light that is an easy way to check it otherwise you can make marks on the harmonic balancer or use timing tape.

 

[NetDoc]

Re: points question

The biggest problem with nichrome wire resistors is corrosion. Even when they are potted, heat and elements make them weak. Again, they are most needed during colder weather, since things are harder to get going. If an engine starts with an internally ballasted coil, then that's one less thing to go bad. Normally, when the external resistor goes out, the engine starts but won't remain running. Of course, if the engine came with one, I would tend to keep it stock... until I had the first issue with the coil. Then, all bets are off and I would probably change the entire system. I am already researching electronic ignition solutions for my 3.0L OMC. There's a reason you won't find points on a modern car. Solid state solutions are far more reliable and you don't have to set the dwell or worry about forgetting a spring.

 

[NetDoc]

Re: points question

If you have an advance type timing light that is an easy way to check it otherwise you can make marks on the harmonic balancer or use timing tape.

That's overkill. Just accelerate the engine with the timing light on. Does the mark advance from where you set it? There are two basic ways to modify timing: vacuum advance and centrifugal. In the former, timing is retarded somewhat during acceleration (low vacuum) to reduce ping caused by pre-ignition. The latter will advance timing rather smoothly as engine RPM increases, giving the mixture time to combust giving you a good power stroke. If you have a vacuum advance, disconnect it to check the function of the centrifugal (weights) advance. Some pollution controls of the seventies and early eighties really messed with how the vacuum advance worked, but for most applications plugging it in at idle or just off idle should result in increased timing.

 

[john cole]

Re: points question

the timing does advance when you accelerate the engine. not sure if it is advancing all the way thou, but it the weights do move freely when checked by hand. so right now i have to back up a step and recheck my points to be sure i didn't burn them up (maybe the gap was to small) not really sure at this point, waiting to get back up there and do some checking and everyone has given me a few good tips on what to look for so we shall see what i come up with here, hopefully this evening. but with everything i have done to this motor up to this point i am leaning toward a voltage issue with be it the points condsensor or coil.

 

[bruceb58]

Re: points question

That's overkill.

If its overkill, how come all service manuals show a chart of the advance curve so it can be checked? Also, boats do not EVER have vacuum advance so it doesn't apply here. My point is you do all checks possible otherwise you will be going back and doing it again. At least for me, I try to do a thorough trouble shoot so that I don't miss anything.

If springs are too tight or there is corrosion on the weights, the advance curve can be affected. That's why it is useful to measure every 500 RPM to verify that the distributor advance is occurring at the proper time. Not only is this important for performance if the advance is coming in too late but also for engine longevity if springs are weak and the advance is coming in too early.

]There are two basic ways to modify timing: vacuum advance and centrifugal.

Also electronically based on RPM and knock sensors on solid state distributors.

 

[NetDoc]

Re: points question

If its overkill,

It won't cause a sputter as indicated in the OP. While a bad wire going to the points could cause this during advance, a firm pull that does not yield would verify that its integrity. Excessive dwell could cause this, but that should not be affected by the timing advance mechanism. If dwell and timing are set, the prudent technician would check fuel and fuel dilivery. A sticky/bad advance mechanism would cause sluggishness or low power, but I can't see it causing a "sputter". YMMV.

Timing is important to maximize the power of the combustion stroke. It takes time for combustion to start so you initiate it (usually) before TDC. The faster/leaner the engine, the more advance you need. Think about it like a swing. If you push too early, things get hurt (ping). If you push too late, you don't get that much power into the push. You have to time the push just so.