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Timing Puzzle

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jefmar View Drop Down
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    Posted: March-12-2006 at 6:16pm
I recently bought my '89 Nautique with PCM/Ford 351. It has low hours - 380 hrs - the previous owner was adamant that the hours are original. It was running rough with a high idle when I bought it.. but that is fixed now. I have one remaining problem – when the timing is set per specifications (10 degrees btc) it stumbles/coughs under heavy acceleration in the water. I played with the timing by trial and error with the boat in the water and found that if the timing is retarded to 18 degrees btc it does not stumble; however, at 18 degrees btc the starter is slow to crank the engine. The starter cranks the engine normally at 10 degrees btc. I have a new carb and no vacuum leaks and noticed that the idle is not totally consistent (it varies from 600-800RPM) between heavy acceleration attempts. I am guessing that something is causing my timing to change. Or the distributor is not advancing correctly under power. But, the spring mechanism inside the distributor seems to move okay and the springs are functional. I also guessed that my timing chain/sprockets are loose/sloppy. Or the distributer is not set correctly...

The boat is running well but I do not feel comfortable advancing the timing so far that it affects how quickly the starter cranks the engine.

Here is my diagnostic results and what I have changed so far:

-Fuel pressure: 4 psi
-Fuel flow: did not measure it carefully but half filled a soda can with about 10 revolutions of the engine.
-Vacuum: Steady 19"Hg at idle. I had some leaks but fixed them.
-Compression: looks great (120-135 psi)
-New Holley 4160 marine carb for 351 (Holley part number HLY-0-80319-1)
-Cleaned spark arrestor
-New electronic ignition conversion (GLM Part number 72540) in the original Prestolite distributor
-New distributor cap, rotor, spark plugs, spark plug wires
-New coil
-New gas filter/oil water separator
-New PCV valve

Before I tear into the timing chain or buy a new distributor, does anyone have a suggestion of what the problem is??   What would you try first??
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JEFF KOSTIS View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JEFF KOSTIS Quote  Post ReplyReply Direct Link To This Post Posted: March-12-2006 at 6:34pm
   If you had to set the timing to 18 btc, then you are advancing it. Did you try putting the timing light on it and start at idle and increase rpm as see what it is?? This will either prove correct or incorrect advance.
                                Jeff...
                            
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jefmar View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-12-2006 at 7:21pm
Thanks Jeff. You are right, I advanced rather than retarded the timing. I wish I would have thought of checking the mechanical advance when I had it in the water earlier today. I will check it later this week.. It looks like I should be at about 32 degrees btc at 3000RPM from other posts... does that sound right?
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JEFF KOSTIS View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JEFF KOSTIS Quote  Post ReplyReply Direct Link To This Post Posted: March-12-2006 at 7:35pm
    I would try it at different rpms and take note of it so you can see a rough curve. Im not sure on the exact degrees for the rpm, and I forgot, you might have trouble with a generic timing light as the markings on the engine usually dont go that high. You can get a rough idea to see if it advances at all.
                                 Jeff..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick Quote  Post ReplyReply Direct Link To This Post Posted: March-12-2006 at 9:10pm
This is a long shot but make sure 2 spark plug wires aren't crossed.check that the firing order is correct. If 2 of the wires are wrong you get a rough idle hard start and depending on the order advancing the timing can make it better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64 Skier Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 1:00am
Couple of questions? Does she knock with that much retardation? Initial timing is "recommended" at 10-12 degrees but the only way to time the engine is in the boat running and listening to the engine as you further retard. This is also the only way to get full power. For some reason I hvae 3 timing lights...they all read different but within about 2 degrees.

Before you time her on the lake...measure full advance and make a simple plot of timing versus rpm up to 3000 RPM. Springs get old and I've seen some "jump" which causes a stumble simlar to a carb with a weak accelerator pump.

Time the engine with the fuel you plan on running. The gas we purchase on the lake is somewhat less quality than what I buy at the pump. This also made a difference in my boat. When I was tuning I had a fresh tank of premium. When pulling skiers in the spring she'll have an old tank with "Stabil" so I save the timing check for later.

What cured the rough high idle?
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79nautique View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 6:29am
Remember you have to set the timing first then adjust the carb's idle and idle mixture screws and not the other way around. Get the timing at 8-12 btc then adjust the idle, then fine tune the carb using the vacumm gauge to adjust the idle mixture screws and idle screw.

Make sure that the wires aren't crossed like rick suggested as well. Set the base timing then see what it is at 3000rpm and that will tell what the full advance is.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 882001 Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 7:04am
^^^^ well said 79^^^^
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 9:39am
Thank you for the input

Jeff, Rick & 79 - I will check the spark plug wiring, reset the timing to around 10 btc at idle, adjust idle mixture and idle screws using the vacuum gage, and note the timing curve... later this week.

64 skier - there is no knock when the timing is set at 10 or 18 btc at idle. The rough, high idle was mostly caused by a vacuum leak in the hose to the pcv valve.. a tune up helped too.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 10:11am
Be sure that the idle is at around 600-800 rpm before you set the timing, or you will get false reading because you will start to engauge the mechanical advance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JEFF KOSTIS Quote  Post ReplyReply Direct Link To This Post Posted: March-13-2006 at 8:22pm
    All are possibilities. If timing is OK, check the PCV valve. It may be sticking and causing a leak and unstable idle. If you put your finger over the end of the PCV valve at idle, you should hear it "click" and suck your finger in. When you pull off your finger, it should "click" again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-14-2006 at 7:27am
79.. Thanks for the tip.

Thanks Jeff. I forgot to mention that I have a new PCV valve. It was changed when I fixed the vacuum leak. The new one seems to function correctly.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-26-2006 at 8:33pm
Sorry for the slow troubleshooting. Finally had a chance this weekend..

I checked the spark plug wiring, reset the timing to around 10 btc at idle, adjust idle mixture and idle screws, and noted the following timing curve:

600 RPM – 10 degrees
1000RPM – 10
1500RPM – 12
2000RPM – 18
2500RPM – 20
3000RPM – 22

What do you think?

I also noticed that spark plug wiring order is correct for LH rotation but based on the schematic in the repair manual the wires appeared rotated clockwise one position (i.e.; the front is no. 6 rather than no. 2).   Does this mean anything?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 64 Skier Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 12:05am
You got me stumped on the wiring. I'd have to see an engine in front of me to understand.

However, you should have 10 more degrees of advance. The new electronic ignition in the old Distributor is OK, but it sounds like the advance is not working properly. Take it apart and look at the springs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 7:01am
It sounds like you are referancing where the wire is on the cap relative to the diagram in the manual and if so don't it's meaningless. All you have to worry about is the order and not location.

You need to check and make sure that the base plate for the mechancal advance is moving freely and not gumed up before you start changing the advance springs to get a little more top end advance on the timing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 7:29am
Thank you for the input

64 skier - I took it apart a couple weeks ago.. the springs are functional.

79 - the mechanical advance inside the distributor seems to move okay; however, there is very light corrosion on the metal parts..

Do you think it is worth the effort to disassemble and lubricate the mechanical advance or would you buy a new distributor?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 8:20am
I would clean and lube the plate and change the springs to correct the problem with the advance. Your springs seem to be to stiff and not allowing enough advance. It's an electronic ign already and not a points dist correct?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 9:10am
Yes. It has new electronic ignition conversion (GLM Part number 72540) in the original Prestolite distributor. Where do you purchase distributor springs?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 9:36am
any auto parts house
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-27-2006 at 9:41am
Thanks 79, I'll give it a shot
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SS-201 Quote  Post ReplyReply Direct Link To This Post Posted: March-28-2006 at 3:45am
Take a timing light set to 32-34 total at 2500 -3000 rpm.If this solves the problem, forget about the inital, its only a starting point. Of course too much advance will detonate or buck at start.The chain retards it self from use, the advance springs lose their tension. If its hesitates from here then you need to check the chain and dist.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-28-2006 at 6:53am
79 - I went to a couple autoparts stores and neither had springs. I lubicated the assembly and tried adjusting the advance ajusting brackets in the distributor. I bent the brackets to engage the springs harder and I had no advance at higher RPMs. I bent the brackets the other way such that the springs were loose when starting and I get the same curve as before. I'm thinking I need a new distributor or something else is wrong. Do you agree? I noticed in your other posts that you suggested a new prestolite distributor on ebay.. Do you think that my electronic ignition conversion kit would fit in those ebay Prestolite distributors? I'm also considering Mallory.

SS-201 - I have essentially done that already. I'm only getting 12 degrees max advance so when I had the timing 18 btc at 600RPM, It was around 30 btc (18+12) at 3000RPM. You mention the chain..

79 & SS-201 - Do you think the timing chain could have something to do with this? I'm only getting 12 degrees advance max.. I possibly could pull my distributor and have a shop measure how much advance I should see in the boat. If the shop measures 25-30 degrees max advance then the distributor is okay.. and possibly the timing chain is to blame.. Does that make sense? Or should I just buck up and buy a distributor?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-28-2006 at 8:16am
The timing chain isn't the issue, it will retard the timing a little, but it won't change as it runs. Don't under stand what bracket you bent but you should have bent anything, maybe a new dist wouldn't be a bad idea, mallory YLM-554-CV or a YLU-554-CV
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: March-28-2006 at 9:16am
Thanks 79, The PCM repair manual labels the posts that hold the springs as "advance adjusting brackets". I bent them a little to put more/less spring pressure at rest.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HOLESHOT Quote  Post ReplyReply Direct Link To This Post Posted: March-30-2006 at 10:24am
jeg or sumitt will have the springs
IF IT HAS A SPARKPLUG I CAN FIX IT
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: April-22-2006 at 11:55pm
I bought and installed a new old stock prestolite distributor off ebay. Here is a link to the completed auction.

.Purchased Distributor

Unfortunately it did not solve the problem. At 10 btc initial it still stumbles in the water out of the hole. At 20 btc initial it runs very strong at any RPM but starting it is a little difficult as it requires pumping the throttle to get it started. Setting it back to 10 btc, it starts perfectly. Here is the rough timing curve measured:

700RPM - 10 degrees
1500RPM - 20 degrees
2000RPM - 22 degrees
3000RPM - 22 degrees

I am thinking that Mallory MAA-YLM554CV will provide the advance curve (and adjustability) that I am looking for but it seems strange that two distributors have the same problem and something else might be going on.. Any suggestions before I spend more money and buy the Mallory?? Thank you for your help.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: April-23-2006 at 12:37am
well first your timing should be around 8 btdc and the max needs to be 30-32, so you have a mechanical advance problem of some kind, stiff/strong springs or sticky components limiting advancement of the base plate.

Your stumble out of the hole isn't the timing at all, it's the accel pump on the carb or the carb it's self.

If you can't adjust the dist you have, a new one isn't going to make matters better, do your self a favor and save your money and pay someone to fix your problems that knows how to do it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefmar Quote  Post ReplyReply Direct Link To This Post Posted: April-23-2006 at 9:43am
Thanks for your input 79 but I will not give up and take it to a mechanic yet. I just purchased and installed a new carb; nothing changed when it was installed. If the accelerator pump is to blame, then the old carb and the new carb both had accelerator pump issues.. this is doubtfull. Changing springs in the Prestolite distributor is easy but finding springs for it is not.





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jim_In_Houston Quote  Post ReplyReply Direct Link To This Post Posted: April-25-2006 at 10:01am
Jefmar,

Your initial timing needs to be around 8 to 10 degrees BTDC. Lower timing advances like this makes the engine easier to start. (I used to drive around in a Ford Model A that had a spark advance control lever (before these modern days of automatic advance) attached to the steering column. You had to retard the spark a lot just to get the engine started - then the faster you wanted to go the more you would advance the spark.) At higher RPMs the timing has to (of course) be advanced. Every engine and installation is a little different and the best timing depends on your choice of fuel and your engine.

Typically, a good total advance is somewhere around 32 to 34 degrees coming in somewhere around 2500 to 3000 RPMs. 30 degrees may work well for you but it should not be less than 26 to 28 degrees.

Your total full advance is presently too low and it is coming in too soon.

You are going to have to struggle with getting your advance curve to these values.

It sounds like money is no problem for you.

My advice is to get a new Mallory distributor and sell you other distributors on Ebay. Be sure to get a marine distributor NOT an automotive distributor. (Or less thee suffer the wrath of 79).

(For peace of mind be sure to accurately describe your old distributors on Ebay.)

BTW, I struggled with my timing a lot until I discovered my engine was a reverse rotation engine and the previous owner had installed a standard automotive balancer. I was setting my timing at 25 to 30 degrees ATDC and couldn't figure out why my boat ran so crappy. (I bet I am not the only one to do that.)

-jim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: April-25-2006 at 10:46am
I guess I've never seen a carb that you could take out of the box, bolt on to the engine and only have to adjust the idle, very foolish thinking to me. I've always had to inspect and adjust the linkage, idle air screws, float levels, idle and the throw of the accelarator pump. So If your saying that it runs fine at 20 degrees of timing and comes out of the hole without stumbling as well then something is way off or you have a bad harmonic blancer giving you a false timing reading but I doubt it since it doesn't crank right, so I'll assume that you still have the stumble at 20 degrees of timing and the stumble coming out of the hole is caused by accel pump being out of adjustment 9 out 10 times. The pumps not bad, it's just squirting too much or too little gas, to soon or too late causing a stumble.
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