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351 PCM Prestolite Points Timing

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64stang View Drop Down
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    Posted: June-25-2012 at 9:39pm
Hi

I have a 1990 Ski Nautique with a PCM 351 with a Prestolite mechanical advance distributor with points. It started running really rough and would not idle, so I replaced the points, condensor, coil, plug wires and plugs. Before I replaced the points I checked the point gap and it was between .018 and .020. I did not remove the distributor and installed the new points and set them to .018 when wide open on the cam lobe. Book states .018, I believe that would also be at the top of the cam lobe. It will not start at this setting, but will fire just when I turn the key off. I opened the gap to .027 and it starts and runs at all speeds very well. There might be the slightest miss at 700 rpm, but not much. I have a cheap timing light and took it out on the lake and could not see the marks on the pully even if I shaded the motor. But it was bright sun?

My question is, why will it not start at .018 gap and why does it start so well at .027?

Thanks for the help in advance.

I do love my boat and do not want to damage anything with this setting.

Mark
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: June-26-2012 at 1:30am
The timing must be way off & the extra wide gap may be compensating. Check the springs on the advance weights - may 1 is broken. Other than that, find a dwell meter to check points adjustment. Also get that timing checked out. Are you sure you are triggering the timing light from #1 cyl (Starbvoard front wire)?
“Beer is proof that God loves us and wants us to be happy.”

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64stang Quote  Post ReplyReply Direct Link To This Post Posted: June-26-2012 at 10:23pm
Thank you for helping me SNobsessed. I double checked the gap and it runs best at .030. Springs and advance works as it should. I was using the timing light from #1 but it was a cheap light and I could not see in the sunlight, even in shade. I ordered a electronic ignition conversion set and it will be in on Thursday, so I am hanging fire on the points. But I was thinking, could it be that the new coil I installed is not producing enough spark? I installed the type that does not need the external resistor. I can not see one on my 1990. If the boat does have an external resistor somewhere, could that be causing my coil to only develop enough power if the gap is .030?

Thanks again for all the great information and help.

Mark
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1989SN2001 Quote  Post ReplyReply Direct Link To This Post Posted: June-26-2012 at 11:38pm
I too had problems with my points this past weekend. Boat ran fine in the morning and got harder and harder to start as the day went on, finally, around 3pm it quit completely, no spark. Checked the points, and they were garbage. Didn't close flat, not even close to concentric, and dirty/burned/cratered. Couldn't even get them running for more than 10 seconds after cleaning them with sandpaper.

Tonight, new set of points, new cap, new rotor, old condenser, gapped at .019 when on the high point of the lobe. I also closed the spark plug gap from about .045 (bad advice from a friend) to .031-ish. Initial timing set with a light at 10* at about 750RPM. Did not check the dwell. It started and idled better than it ever has before. No pumps of the throttle, no giving it a little throttle to keep it running til its warm, just turn the key and its purring.

However, when I bring the RPMs up to 3000-3200 with zero load, timing only advances to about 25*. Guess my mechanical advance isn't working 100% correctly? This should be hitting 32-36* total advance by 3000RPM, right? I'm probably missing out on some top end power because of this as well, no?

Does anyone have a link to a writeup on how to rebuild the mechanical advance unit? Or just a basic explanation? I had the points plate out tonight and looked at the advance mechanism, it seemed to rotate freely, but I'm not really familiar with how things are supposed to work in there.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 10:50am
TJ - Your measured timing @ 3000 is about right for the stock distributor. Customized dizzys will hit max advance at 3K, but they didn't come from PCM that way. I sent my dizzy to a shop to have it recurved. They installed lighter springs & also extended the groove in the nylon guide plate.

Mark - The coil won't affect where the points are to be gapped. You definitely have a problem somewhere. .030 is way to much gap.

What kit did you buy? I hope it wasn't a Petronix, they are junk.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64stang Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 11:20am
I got my kit from the local auto parts store, did not see the Petronix name, but it was called an "ignitor", they had Ignitor, Ignitor II and III, but I just got the Ignitor, it was the only one they could get and cost twice as much as the internet Petronix ones. What brands should I be looking for?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1989SN2001 Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 12:28pm
Mark, the Ignitor is the Petronix. If you paid twice as much as they're charging on the internet for it, take it back. Its junk, and its expensive junk.

Chris, thanks. I'm glad I didn't tear into my dizzy last night thinking something was wrong. Do you have any more information on what the curve for a factory dizzy should look like? I didn't want to rev above 3200 or so in the driveway, but I guess I could have a buddy drive it on the lake at 4600 and see where my total advance is getting. Seems kind of dangerous running 42mph with the motorbox off using a timing light...maybe I won't do that.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 1:03pm
A quick rev in neutral (on the hose or at the dock) to verify total advance is appropriate.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nautiqueseventy Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 5:55pm
You need a dwell meter as the point gap changes so does the timing and if you don't have the dwell correct it will never run right. You will never be able to guess the high side of the cam lobe in the distributor. Borrow a Meter or buy one set the dwell to spec then set the timing
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 8:04pm
TJ - I think OEM was 18* advance at 4000 RPM. I too was hesitant to hold at 4000 in driveway. Just blip the throttle to see that it advancing at a steady rate & call it good.
“Beer is proof that God loves us and wants us to be happy.”

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64stang Quote  Post ReplyReply Direct Link To This Post Posted: June-27-2012 at 8:36pm
Thanks for all the help, I like the electronic ignition conversion idea, is there a good brand or are they all bad?

Mark
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: June-28-2012 at 1:17am
Best plan is to get a DUI or Mallory distributor. Next step down is a Mallory conversion.
“Beer is proof that God loves us and wants us to be happy.”

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64stang Quote  Post ReplyReply Direct Link To This Post Posted: June-30-2012 at 9:15pm
Thanks for all the help. Because I already ordered the Ignitor conversion I installed it, and it ran OK. But my problem was attempting to static time the motor, it did not work, and I was using an Ebay timing light. First I got rid of the Ebay timing light and got a good one and found I could set the points. The points were great and idle was even and acceleration was very strong. Now the Pertronix points Idle a little faster and require adjustment, and do NOT start as well as the points. For some reason the motor must turn over several times before the ignition seems to start, then it is OK, but because it must cycle fist it seems to start a little flooded with the petronix unit. Probably going back to points.

If I had chucked the ebay timing light right off the bat, everything would have been much better.

If I have any other information about the pertronix conversion I will revisit this post.

Mark
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