High RPM issues

[Shadowbird]

O.K. 1973 Mercruiser 888 has new wires, plugs, cap, rotor, rebuilt carb, and new points. All are set to specs. Timing is perfect at idle. Motor runs great until 2000 rpm and then the tach is all over the place cuts out and sounds horrible. If I go wide open throttle it will die. When I replaced the plugs all were oily, fouled and black. The motor was rebuilt 20 hours ago (Ford 302). Any ideas???
Thank you,
Travis

 

[JoJoBetsy]

Re: High RPM issues

Any black smoke when running? Have you done a compression check to see if the rings have seated (20 hours...should be)? With those plugs looking like they did, sounds like oil is getting into the cylinders by way of bad rings or valve guides. What do the plugs look like now?

I'm a Seaman App though, wait for the big guns to chime in.

 

[Shadowbird]

Re: High RPM issues

No black smoke. I was running rich before I did all the above. I had bad wires cap, carb...everything. Haven't done a compression check yet, guess that's next. I also changed the water/fuel seperator. Maybe I should check the fuel pump as well? Thanks.

 

[searay3]

Re: High RPM issues

With the tach going all over the place, it is telling you there is something amiss in the ignition/electrical. Do you have a manual? Coil been replaced? Points and such can be bad out of the box, although rare. I would start there. Age of wiring (harness) is also of concern. Run a wire (with resistor) from the batt to the coil + and see if it acts up. Have to test under load, on the water. Help narrow it down to a coil breaking down under load or a wiring/component issue. To kill it you'll have to pull the wire from the coil. Were the same symptoms there prior to the rebuild?

 

[Shadowbird]

Re: High RPM issues

I just looked at the coil and it seems pretty corroded on the inside. Can I clean this or just replace? The harness looks original and beat up.
Thanks again

 

[searay3]

Re: High RPM issues

Replace the coil. Cheap part. Try that and see before you start diggin in too deep. Coils can act up or fail with some strange and inconsistent symptoms. Just make sure it is the right type. As old as the harness is, I'll bet the resistor is either in the coil or seperate from the harness. Easy check: remove the + side coil wire and measure it with a meter, key on. If around 7volts the wire has the resistance, if 12, you'll need the coil with the internal resistor or put a ballast resistor in line on the + side. Remember also there is one wire that goes to the starter solenoid for a 12 volt shot to the coil while cranking. Do not put a resistor on that line.

 

[Kevin70]

Re: High RPM issues

Have you checked the timing advance cogs to make sure they are moving freely and springing back like thier suppose to?

 

[Shadowbird]

Re: High RPM issues

Allright, just installed a new coil. Didn't help. As I reach around 2000 rpm, with the timing light on #1 I can clearly see some missing going on. Now I'm thinking bad wire or contact somewhere.
Thanks for all your help

 

[Don S]

Re: High RPM issues

When you installed the points, did you install the spring on the points? There is a C shaped spring that follows the shape of the copper strip. Without it, the points will float at around 1500 to 2000 rpm and start missing.

 

[ron7000]

Re: High RPM issues

being a 1973 motor I would have gotten a whole new distributor. and went electronic and done the rebuild right. Your old one may be on it's death bed. I would've done the same with the carb. On a fresh motor, ignition and carburetor are the two things you want 100% so the motor will run with no problems and seat the piston rings and also allow for cam break-in.
Having oily plugs may be a sign the rings aren't sealing due to a poor rebuild, which is not uncommon. Hopefully it's not that, and mostly caused by a 30+ year old ignition that isn't lighting all cylinders. Get it fixed, and change your oil because most likely it's diluted with fuel which isn't the best thing for wearing in a new motor (it'll really wear in).

 

[Shadowbird]

Re: High RPM issues

When you installed the points, did you install the spring on the points? There is a C shaped spring that follows the shape of the copper strip. Without it, the points will float at around 1500 to 2000 rpm and start missing.

This round goes to the Admiral! You were right, I completley omitted the spring. Running like a champ now.

Thank you!!!!!!

 

[Don S]

Re: High RPM issues

Send me the money you saved by not taking it to a Merc Tech