1987 Mercruiser 454 Timing Issue

"I have an unusual timing issu

"I have an unusual timing issue with my port Mercruiser 454 engine. After setting the timing to the appropriate setting at idle, the timing reads fine until a little after 700 rpms. The timing then jumps about 10 degrees when we cross about 720 rpms. This happens every time, regardless of how slowly we bring the rpms up. Due to this jump, we get a top number of 35 degress at a little over 3000 rpms, which is not good. We have changed out the electronic module with one that we know works. The problem is still identical, even with the good electronic module. The engine is the counter-rotating of the two engines. Does anyone have any idea what could be causing this 10 degree "jump" when crossing over the 720 rpm limit?"

Joe.
This is normal. The dist

Joe.
This is normal. The distributor will advance the timing. Check the starboard side. If it is not the same this is the one with the problem.

Joe.
This is normal. The dist

Joe.
This is normal. The distributor will advance the timing. Check the starboard side. If it is not the same this is the one with the problem. Let me add if it will let me. It is a little soon for the advance although.

"Hi again ...

The starboard

"Hi again ...

The starboard engine timing is linear. It increases with rpm increase on a somewhat linear scale and tops out around 30 degrees, which is what it should do according to the spec. The electronic module increases the timing 24 degrees. The port engine, which I believe has a problem, jumps from about 8 degrees to 18 in only about 10-20 rpm increase. I can not rev the port engine between 720-1000+ rpms. It just jumps from 720 to over 1000 due to the spike (10 degree jump) in timing. Since I can not get this engine to rev at 800 or 900 rpms because of the jump in timing, I am assuming this is not normal since the other engine runs perfectly at all rpms. My Mercruiser mechanic is not sure what to think as he has never seen this problem before. We have changed the distributor cap, rotor, wires, plugs, electronic module, coil, etc. It needed a good tuneup anyway but none of these changes has led to us finding why the timing jumps. I was told that it might be a timing belt/gear issue but that was an educated guess based on all the other things we have tried. Still looking for suggestions or if someone has seen something like this before. I am wondering if it has something to do with the engine being a counter-rotating engine."

It sounds like the centrifugal

It sounds like the centrifugal advance. Check the springs and weights. Also check the distributor bearings and gear for wear. I believe the distributor rotates in the same direction on both engines because one has a cam gear and the other has a cam chain.

Thanks ...

we did check the

Thanks ...

we did check the distributor bearings and gear. That seemed fine. We will check the springs and weights next. I do believe you are correct about the distributor rotation and cam gear versus cam chain.

Thanks again ...

"Your "mechanic" chang

"Your "mechanic" changed all those $$$ parts without checking the advance weights and springs! That's the first place he should have looked. As I read all these posts, I thought this was a pure electronic distributor.

Jeff"

"I am not that familiar with t

"I am not that familiar with the distributor work that was done but there is a chance this is a pure electronic distributor, in which case it looks like I am back to square one! The only parts I have paid for are the plugs and wires. We swapped out the coil, electronic module, etc. from either the starboard engine or spare parts from other engines. Let me know if you have any other ideas. Thanks."

Sounds like one spring is brok

Sounds like one spring is broken or weak on the counter weights. This could cause the fast jump at such low rpm.

"I've fought issues like t

"I've fought issues like this on several boats over the years. Its important to understand and remember that all these igintion systems are more or less hybrids. The ignititon module is there to replace the points/breaker setup only. The only way to have a true "electronic" ignition is no distributor at all. Similar to new car setups, a coil on each plug and triggered by the computer. All distributor setups must have a mechanical way of advancing the rotor under the cap, otherwise no advance will take place. Think about the physics. An iginition module cannot magically advance the rotor under the cap. The actual advacing of the rotor is a mechanical action and something under the cap is making it happen. Weights, springs, or even a servo controlled by the module are all still mechanically actuated. That is where I would check for the problem. You may not be willing to drop this kind of money, but its a guarateed solution. MSD makes a complete self contained billet aluminum distributor with a built in multiple spark discharge (MSD box). It is totally self contained, looks great, will not rust, and has a great warranty. I've put them on 2 boats I've owned including my current one. You install it, and forget about timing issues. Its a great feeling to know that whenever a problem arises, I now know not to include timing trouble as a possible cause."

Thanks Dialed In ...

I'

Thanks Dialed In ...

I'll pass this information along and hopefully we can fix the problem soon.

Joe