1989 omc 4.3 timing procedure

[Dad85]

I have a 1989 omc 4.3 with points can anyone tell me what the procedure is for setting ignition timing I had to remove distributor to replace head gaskets.

 

[Bt Doctur]

If you have rep[laced the dist correctly its just point and shoot with a points system

 

[Dad85]

It says six degrees before top dead center but at what rpm is that set at

 

[Bondo]

Ayuh,..... At idle,......

Welcome Aboard,.....

 

[Dad85]

So if I set it at 6 degrees at idle do I need to worry about checking the advance

 

[Scott Danforth]

you need to worry about setting the gap first, then adjust timing at idle.

 

[Lou C]

First you have to get the distributor installed properly.

 

[Scott Danforth]

First you have to get the distributor installed properly.

correct, with plugs out, crank motor with finger over #1 hole. when finger pops off, that is near TDC of #1. drop in dizzy with rotor pointed to #1 tower location.

next spin motor to get oil pump drive to seat, then loosely clamp dizzy

set points to proper gap, check with dwell meter

then fire up motor (with muffs) and set timing, lock down dizzy

 

[Lou C]

[No message]

 

[Dad85]

I have done all of that I have rebuilt many gm motors just not familiar with mechanical advance. I have distributor all in and oil pump aligned just did not know if it was like a 2 stroke outboard were you have to also set advance. I do however have to set points but I did take it out to the lake today and it has ignition ping at full throttle goes away at 3/4 throttle and can only get 3000 rpm out of it.

 

[Bondo]

and it has ignition ping at full throttle

Ayuh,..... Welcome Aboard,..... Detonation can burn holes in yer pistons in very short minutes,.....

A lean condition, or advanced timin' cause it, a lean condition the most common, especially with today's ethanol fuels,....

 

[Lou C]

Well if you have an advance timing light you can put the boat in the water and run the engine up to 3200 rpm and check it, should not be more that 22* total if I recall right. Make sure the advance weights are not sticking there is a wick you can oil to lube it. If necessary you can remove the point plate and make sure the springs are retracting the weights.

 

[Dad85]

Ok I will check the weights I do not have a advance timing light. What is the rpm this motor should be running at wot 4,500 to 4,800?

 

[Bondo]

What is the rpm this motor should be running at wot 4,500 to 4,800?

Ayuh,......

 

[Lou C]

I went back and looked in my OMC shop manual for the '88 4.3....
base timing is 6*BTDC at idle rpm (600) and at 3200 rpm, full centrifugal advance is supposed to add 12* more, for a total of 18*. Not sure why but the 4.3s are not set to take as much advance as the 5.0 (22* total) or the 5.7 (29*total). I checked mine on the water so I could run it that high and it was right on the money. With the Advance light set at 18* it hit the mark at TDC which is as it should be. If your advance weight springs are retracting like they should and timing is set right then your pinging is likely due to a lean fuel mix or carbon build up. What did the cyl heads and piston tops look like when you changed the head gaskets? Where the heads ever decked? If so how much was taken off? That can sometimes raise the effective compression ratio. You should get at least 4600 rpm at WOT, the 4bbl models were rated at 4600-4800. Is the boat propped correctly? Mine came with a 14.5x19 and it was too much pitch, only got 4200 rpm. I had to go to a 15x17 for acceptable performance and max rpm. I have a 15.5x15 on it now, to get it a bit closer.

Lastly no matter what the boat companies say, I always used 93 octane and never had ping or run on problems. When I took the heads off to repair my blown HGs last summer, there was no sign of detonation or valve burning. Just an even build up of carbon.

 

[Dad85]

I bought this boat for 200 bucks knowing it had engine problems owner said over past few years it became slower and slower before it did not even have enough power to get up out of the water he said it has low compression on one cylinder so I brought it home figuring a bad head gasket or valves I ran it found had a bad miss and if you gave it just throttle not in gear it would die then found water in oil pulled the plugs #5 poured out water pulled intake and r.s head found bad head gasket replaced just one head gasket and intake gaskets just to see if the motor would run not knowing how much water he ran through it. Did not do any work to head. Did not want to put 200 bucks I to each head to find out lower end is bad I will redo both heads this winter. Changed the oil and took it to the lake boat comes up out of the water pretty well then found preignition issue does seem to have a bit of a miss at idle. The Pistons and heads were clean just very mild black soot spark plugs all white. The gaskets were not originals so not sure if heads have been decked and it is a 14.5 19 prop it is in a 17ft StarCraft and I always run 92 octane iam going out tomorrow to check timing,points and advance weights I will then post what I figure out.

 

[Lou C]

Plugs all white suggests lean fuel mix which can definitely cause pinging. You want light brown or grey.

 

[Dad85]

I will pull them again and check them. Does the omc repair manual have all the specs and how to rebuild the carb it has been a long time since I rebuilt a carb.

 

[Lou C]

The factory shop manual does....

 

[Dad85]

Do you by chance have a part number or something so I can look on eBay for one