IGNITION TIMING

[270 laser]

I have a pair of 350 magnums in my boat, one pulls 5150rpm the other pulls 5000rpm. The week motor doesnt feel as snappy either. I turned up the timing on both motors to 34 degrees. It helped both engines but one is still weeker than the other. I turned up the timing to 36 degrees on the week motor, now they are within 50rpm. after doing a plug check, I noticed very slight electrode erosion on the strong motor & sharp edges on the week motor. Can the tdc mark (timing) on the harmonic balancers be off this far? I know that the balancer did not spin. Should I just keep bumping the timing on the week motor until theyre even? the strong motor turns over hard at 15degrees initial timing. The week motor turns over hard at 19degrees initial timing. These are thunderbolt IV ignitions that say 24 degrees advance on the modules, however I am only getting 18 degrees at full advance on both motors. Thanks

[270 laser]

Sorry, I meant to say Im only getting 18 degrees of advance at final timing. 14/32.

[gnarley]

I don't know what to say about your ignition but you could have a tolerance stack-up meaning that every part that is in the TDC measurement or only one is out of spec & throwing TDC out by a small amount. Think that if the crank, each gear, cam, balancer & marks were each off by say .4 degrees the total would be 2 degrees or more. This isn't likely but it is possible. As far as tuning twins goes someone should be able to recommend what works best.

[BOFH]

This may seem simple but... Have you checked your timing mark? First, find true TDC. This can be done with a pointer dial gage and you only have to pull the number one spark.
Next, check the distributors. Do they both have the same advance, and is it comming in at the same rate?
After all this, keep in mind that twins NEVER pull the same. Never. Not ever. Nope. It don't happen. :-) They will almost never be more than 200 apart, (if they are, worry!) but the real test is when they are matched about 200 RPM before max on the slow one, hor far apart are the throttles? What is the vacume reading when the engines are synced just under top? If that is way of, you have something to tune.

[270 laser]

Thanks for the advice. Could this be a carburetion or fuel pressure problem? Motors are stock and have weber 4 barrels, 1993

[The Raven]

Hi Buddy
Sorry it took a while to get back to you. But my contact at Merc. is out on vacation.
[ ref. cam size]
Both your engines are standard rotation?? yes!! you have alpha drives ? Yes! Both are standard rotation !! Alpha Never made a GOOD counter rotator!
Now Start with one change and try it out. Example. Swap carbs from one engine to the other.. Yours are the old Carter AFBs. You did a fuel presure check ofcourse!! And you checked both Fuel Pick ups in the gas tank? right! Now if that works, you can jump To Switch Props. Yup it can make a Diff. Do you have Mech. Trim indicators ? if one is out further than the other >> bingo!!! The Merc. guages aren't worth shit.
Then jump to the Ignition system. Swap coils, then then caps, rotors, Reluctors with the pick ups. Then control Modules. The Merc ThunderBolt Ingnition system is very much like the system made by Ford. so If you Know a Ford Mech. ask!!!
If all else and you have done the timming with a good DIAL BACK light. it might be internal. Valve adjust. ETC.
What ever else, Don't give up The Mouse Motors will always be the best!! Remeber you are looking for low end and MID range power.
best of luck
The Raven.
PS
I own 4 mouse motors and one HUGE "V" ten"