Timing Puzzle

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??

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?

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.

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.

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.

    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.
                               Jeff...

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?

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.

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?

any auto parts house

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.

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

jeg or sumitt will have the springs

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.

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