Mercruiser 233 mis-firing at throtle up

Long time reader first time poster.

I have a 1976 Chris Craft Lancer I am restoring to its previous glory. I inherited the boat from my father in law who was the original owner. The problem I am having is that it starts to mis-fire at higher RPMS (>2K RPM). It starts and idles great but starts to mis-fire past about 1/4 to 1/2 throttle. To date I have 1) rebuilt the carburetor 2) replaced points, condenser, plugs, plug wires (set dwell and timing aslo) 3) replaced fuel pump and filter/separator 4) replaced gas three times 5) had carb shop check carb- no issues. 5) tested with new coil and external ballast (mine has the resistor wire set up) All to no avail.

I'm at a loss. It's been suggested to replace the points with an electronic ignition set-up. Any thoughts or suggestions are greatly appreciated.

Re: Mercruiser 233 mis-firing at throtle up

Have you check the fuel filter(s) for debris?
If the fuel system is trustworthy the ignition might not be not advancing the timing as you bring up rpms. Does this motor have a mechanical advance system in the distributor? If so you might want to test it for timing as the revs go up. I don't know the exact advance start & finish point but you can expect on it starting around 1000 to 1400 rpms and being fully advanced by around 2800. If the timing does not advance with rpms in those ranges check out the distributor advance system.

Re: Mercruiser 233 mis-firing at throtle up

NHGuy - The fuel is debris free post filter. I've pumped a couple gallons throught the filter and it is nice and clear. The distributor is a prestolite with mecahnical advance. It advances about 10 degrees during throttle up (timed to 10degree BTDC per manual then advances to 10degrees at highrer revs. How much should it advance? The advance feels a slightly sticky but does advance. I've heard theories that the riveted wire junction in the distributor may be arching or grounding out. Does this theory have merit?

Re: Mercruiser 233 mis-firing at throtle up

I believe it should be advancing the timing more than that. I would check to make sure the counterweights/springs are functioning properly in the dizzy.

Edit: By 2000rpm you should be around 19deg and at 3000rpm you should be around 22deg. So total timing should be 29 and 32 respectively.

Re: Mercruiser 233 mis-firing at throtle up

Have you replaced the distributor cap / rotar?

Re: Mercruiser 233 mis-firing at throtle up

I checked counterweights last night and they are moving freely. They fully extend and retract. There are two springs, what would call a primary and a secondary. The secondary only engages slightly before the weight travel maxes out. The cap and rotor are new. As for the advancing I will have to confirm the RPM before the mis-fire but when it starts to mis-fire the timing reads at the 20-25 degree mark. The riveted post, where the condesor, points and distributor wire connect to each other and it appears to be in good shape, no rust or artifacts which may cause a short.

Per the issue of not advancing enough - Assuming the weights are not fully extending, would slightly advancing the timing test this theory?

Could a partially plugged exhaust create these symptoms? been reading about plugged risers and fear I am turning into a hypochondriac.

Re: Mercruiser 233 mis-firing at throtle up

You could try manually advancing the ignition, but I'd just get a Pertronix Ignitor II and call it done. No more rivet grounding issues, no dwell, no gap, just set the base timing and be done with it, lol. I doubt the exhaust would be causing a problem at 2K rpms.