Low Dwell Reading

[wrosales]

I just finished adjusting the points on my 1989 5.0 OMC Cobra. I set the idle and it sits withing the 550 to 600 RPM range and runs pretty smooth. I set the point gap as specified in the manual but when I take the dwell reading I am getting around twenty degrees. The manual says it should be 29 degrees plus or minus two. What would this indicate? I know that the dwell and point gap have an inverse relationship so I guess what this reading means is that the point gap should be decreased. The points were replaced last year. Would this cause it to break up at higher rpms? Thanks for any input.

 

[ziggy]

Re: Low Dwell Reading

i got points on my rig. i don't even bother with point gap. i just set the dwell to desired spec.

my guess is your just feeling the gap poorly with the feeler gauge. which wouldn't be hard to do since points are springy. + ya gotta be on the high side or the distributor cam. which isn't always easy to do.

set your dwell. then if ya have to, go check the gap. my guess would be that if your in dwell spec. the gap will also be correct. imho. i'd believe dwell over gap.

 

[wrosales]

Re: Low Dwell Reading

What kind of problems would arise from a low dwell reading?

 

[miller1starr]

Re: Low Dwell Reading

I have a '88 5.0 OMC cobra. I have same problem with low dwell (can only achieve dwell reading of 20 when gap is set at exactly at .017 (versus 29 spec dwell). I spent 2 hours moving the gap around to try and even get close to the 29 dwell-not possible. Seems to run great at .017 gap and not good when I go away from the .017. Have 2 dwell meters and both the same. Only thing I can come up with is that there is a secondary wire connected to the coil to points connection that I believe is the (modified from orginal) motor interupter for shifting and that is somehow modifying the dwell angle. I am going to disconnect secondary wire and see if the dwell changes.

 

[mkast]

Re: Low Dwell Reading

Only thing I can come up with is that there is a secondary wire connected to the coil to points connection that I believe is the (modified from orginal) motor interupter for shifting and that is somehow modifying the dwell angle. I am going to disconnect secondary wire and see if the dwell changes.

Dwell Angle: The dwell angle is the number of degrees of rotation of the cam/distributor during which the points are closed. During each rotation of the cam/distributor, the points must open and close once for each cylinder. The points must stay closed long enough to allow the coil primary current to reach an acceptable value, and open long enough to discharge and produce a spark.

That "wire" won't affect the degrees of rotation. Start looking for worn distributor parts.

 

[Don S]

Re: Low Dwell Reading

miller1starr

http://forums.iboats.com/showthread.php?t=462748

 

[HorizonblueDK]

Re: Low Dwell Reading

Just a comment about ignition with points. To me, it's a pre-historic system that only should be taken out of an engine and never be installed again.

I have replaced a couple of points with electronic kit. The kits where you only replace the points, and keeps the original distributor works fine. There are also kits, where you replace the whole distributor with a new one that has electronic advance, instead of mechanical.

You don't get a horsepower increase of 20% and a 30% lower fuel consumption, but the engine will have a great idle, start up right away, and never need setting the timing. A steady idle is indeed what we need on our marine engines, and especially on engines with ignition cut-out for gearshifting.

Install an electronic kit, and you don't have to worry about dwell, points gap etc.

 

[Lou C]

Re: Low Dwell Reading

I don't have the same disdain for points, all our cars had them before 1974 or so and changing points, condenser and plugs was more or less a yearly ritual. The cars started about as reliably as they do now but they needed maintenance. The issue is that some of the electronic conversions don't work that well with the OMC ESA, which has to function in order for you to shift out of gear. With the points it works fine, at least on mine. With so many things on the boat needing regular maintenance, changing the points/condenser is no big deal, and there is no electronic mystery box to fail that can't be bought anywhere but the internet on a holiday weekend! Carry a set of points n condenser on board with a feeler gauge and a screwdriver and you're back in business.

BTW I have never had trouble getting the right dwell from setting the gap, if you set the gap just right, the dwell will be to the lower end of the range, as the rubbing block wears it will still be correct....dwell and gap are inversely related....

 

[Joshua Nichols]

Re: Low Dwell Reading

I don't have the same disdain for points, all our cars had them before 1974 or so and changing points, condenser and plugs was more or less a yearly ritual. The cars started about as reliably as they do now but they needed maintenance. The issue is that some of the electronic conversions don't work that well with the OMC ESA, which has to function in order for you to shift out of gear. With the points it works fine, at least on mine. With so many things on the boat needing regular maintenance, changing the points/condenser is no big deal, and there is no electronic mystery box to fail that can't be bought anywhere but the internet on a holiday weekend! Carry a set of points n condenser on board with a feeler gauge and a screwdriver and you're back in business.

BTW I have never had trouble getting the right dwell from setting the gap, if you set the gap just right, the dwell will be to the lower end of the range, as the rubbing block wears it will still be correct....dwell and gap are inversely related....

Amen brother..
I can buy A LOT of point sets for the price of that electronic unit and a new esa set up.. I can install a set PDQ.. A bit tougher on the gm only cause its in the back and in the dark.. Still pretty gravy.. If I hated maintenance I would bought something with a yamaha outboard..

Is this a old tread that got hijacked?