Help with tuning a rough running 1976 Mercruiser 233 (Ford 351W)

[Lancer76]

1976 Lancer with Mercruiser 233, S/N 4518524. I purchased this boat last year and tracked down a cooling problem, which I resolved. It was running great until I decided this year the the dwell angle was a bit too large. Well, I adjusted the points and the timing to 10* BTDC, but I had a heck of a time starting the engine when it was fully warmed. Even worse was getting into gear from neutral - it will die. The battery and starter are fine and the boat cranks well. I can start it, but I have to have the throttle opened a bit and when I back it down to put in to gear, it dies. Also, I noticed today that when under way, the motor ran a little rough, as if a cylinder was missing. However, no apparent backfires. Did not have this issue prior to my messing around to 'improve' the situation.

As I said, I have checked the point gap and the timing. I have also changed the fuel/water filter (not the one on the carb though). I also checked that all pistons were firing - I did this with my timing light, so it's possible that I have a cracked plug insulator.

My plan is to pull all the plugs and check them. I will also check compression. I will change the points as well.

I am wondering about rebuilding the carb. It is new to me, and it sat for a while before I got the boat. The carb is a Rochester '2 Jet'. It is stamped on the top with "CM' or "GM'. Looking at my Selco guide, it looks similar to what is referred to as the Rochester 2GC (i.e. two idle adjustment needles). At a minimum, I will replace the filter in that carb.

Am I going down the right road? Would you suggest something different? Is the carb a 2GC? And can you point me toward a better manual online. the Selco is OK, but I wouldn't mind a second source. Thanks a lot.

 

[Bt Doctur]

what did you gap the points at

 

[Lancer76]

Points gapped at 0.018". Well that was the final gap. I set the gap with 0.02 and tightened, which closed to 0.018". My manual says 0.016 to 0.019".

 

[Lancer76]

When the boat ran well, the dwell was 41* which was outside the 28-31* range. So in that circumstance the point gap was a bit tight. Should I shoot for that again? Of course, my dwell meter has since gone on the fritz. I will be getting a replacement in tomorrow.

 

[kenny nunez]

The Rochester is an easy rebuild. If there is any calcium deposit in the float bowl from water a diluted solution of Muratic acid will remove the calcium. Otherwise carburetor spray cleaner and compressed air should take care of it.
Easiest way to get the dwell perfect is to remove the spark plugs and remove the coil wire from the distributor cap and ground it, set the dwell while spinning the engine with the starter.

 

[Benny67]

It's an old motor. I'd suggest a compression test to see the general condition of the motor itself

 

[jones01m]

Lancer, for around $135 you can get Pertronix II and the Flamethrower II .6 ohm coil and never have to worry about wearing pioints, gaps, dwell, etc. For sure you will be happy with the conversion. I put a set in my 1963 thunderbird about 6 years ago. I drive it all the time, she starts right up, and I have not removed the distributor cap in all of those six years.

 

[Benny67]

Lancer, for around $135 you can get Pertronix II and the Flamethrower II .6 ohm coil and never have to worry about wearing pioints, gaps, dwell, etc. For sure you will be happy with the conversion. I put a set in my 1963 thunderbird about 6 years ago. I drive it all the time, she starts right up, and I have not removed the distributor cap in all of those six years.

Agreed....replacing points with the pertronix setup in my opinion is the cats ass..

a lot of people here don't like the pertronix set up because points are like $5 and the pertronix costs $80

My opinion is that you buy it once, set it and forget it.

Outfitted both my 180s 3 years ago and never looked back

 

[Lancer76]

I am.leaving on a lake camping trip in 2 days and I couldn't get the petronix shipped quickly enough, so I went the cheaper route and installed new points. I also checked the plugs - they all looked great. However, one plug boot was torn. I replaced the torn boot with a $2 NAPA replacement boot.

Measured compression as well, on a cold engine with full throttle. Readings in PSIG were

130 135
130 122
130 130
127. 127

Not sure if those are all good or low, but glad they are generally consistent.

Finally, picked up a new dwell meter and set gap to 29.5*. Set timing to 10* BTDC. Runs like a champ on the hose. Hopefully this will carry through on the water. Just in case I am packing a carb rebuild kit for the camping trip.

Thanks all! Great help here.