Mercruiser 233HP Won't Start

[DMK2]

I have a 1975 Trojan with a twin Mercruiser 233HP 351 Ford Engines with Prestolite electronic ignition. Before I pulled the boat for the winter, I was experiencing starting problems with my starboard engine. I would have to keep the starter engaged and pump the throttle until the engine eventually started. Once started the engine would begin missing when throttled up beyond 2000RPM. Once I pulled the boat I can't get the engine started to winterize it. I have tried the following lengthy diagnostics:

Replaced: Spark plugs (set@ .30), wires, distributor cap, rotor, coil and gas filter and water separator. Fuel pump was replaced 5 years ago. I rebuilt the carb and had the same problem. I swapped the port carb with the rebuilt and had the same problem. I ran a portable tank with fresh gas and had the same problem. Looking into the barrels of the carb, I can see I am getting gas while engaging the throttle.

I checked the timing by aligning the timing marks at 10 degrees BTC with #1 cylinder in the up position and the rotor aligns with #1 position on the cap. I removed the spark plugs, turned the engine over and all spark plugs were firing. Because the engine would occasionally backfire while trying to start, I loosened the distributor and tried to start it in different positions but no luck.
I tripple checked the wiring to insure the wires are correct according to the firing order 18456273 (RH Rotation). I swapped the electronic control unit with the port unit and no change.

I performed a compression test and got the following results which I don't think would impact starting:

Cyl Dry Wet
1 125 140
2 120 135
3 140 150
4 130 140
5 135 145
6 135 145
7 135 145
8 140 150

The only thing that I am thinking now is that I may have a vacuum leak that is preventing enough gas to be sucked into the cylinders but I don't know how to test for this without the engine running.

I have reached the end of my rope and would welcome any suggestions.

 

[Alpheus]

Re: Mercruiser 233HP Won't Start

Swap distributors with other engine and give that a shot. Buddy of mine had same problems you just described and replaced everything you just described. Turned out that the fly weights on his distributor were corroded and the springs were shot and Would not run over 1800 rpm without cracking and popping. He put a new distributor in and it runs perfect.

 

[haulnazz15]

Re: Mercruiser 233HP Won't Start

Yup, that would be my suggestion as well. Petronix makes the Ignitor II that should be a good replacement if the Prestolite unit is bad.

 

[DMK2]

Re: Mercruiser 233HP Won't Start- SOLVED

Re: Mercruiser 233HP Won't Start- SOLVED

I finally solved the problem after a lengthy and expensive diagnostic effort. The problem turned out to be a bad resistor wire between the electric choke and the coil. The new coil was only getting around 4.5 volts instead of the required 9.5 volts. Although there was spark at the plugs, it was apparently too week to fire. It would occasionally fire causing a backfire which mimimicked bad timing. Vintage Mercruiser owners should take note of this, because it was a very frustrating problem to solve.

 

[ErieRon]

Re: Mercruiser 233HP Won't Start

That resistor wire seems to be quite a mystery to many. I converted mine to the Pertronix set-up and have never been happier. I actually had a "cut the resistor wire" party. I literally just cut it in half and capped it off. Life is good.

 

[Don S]

Re: Mercruiser 233HP Won't Start

I converted mine to the Pertronix set-up and have never been happier. I actually had a "cut the resistor wire" party. I literally just cut it in half and capped it off. Life is good.

That's strange, most of the Pertronix I have run into say to keep the resistor/resistor wire in place to prevent over voltage to the Pertronix unit. Maybe you have something different.

I finally solved the problem after a lengthy and expensive diagnostic effort.

Can we assume that you replaced a lot of parts hoping to fix the problem without actually doing some voltage and resistance tests with a VOM meter?
Those meters will show if there are corroded terminals or open wires.
But if you changed a lot of parts and it didn't fix it, yeah, that gets expensive.

 

[ErieRon]

Re: Mercruiser 233HP Won't Start

That's strange, most of the Pertronix I have run into say to keep the resistor/resistor wire in place to prevent over voltage to the Pertronix unit. Maybe you have something different.


Actually, I was real confused about it, so I called Pertronix (several times) and that's what they told me to do. Doesn't mean it's right I suppose, but that's what I did. Never had any trouble with it though.

I installed the;

45,000 VOLT FLAME-THROWER II (0.6 OHM) BLACK, and IGNITOR II DELCO 4 CYL CW