HARRISONMIRAGE

IS IT POSSIBLE IF TOO HOT OF PLUG IS USED FOR THE PLUGS TO LOOK LEAN EVEN IF THE CARB IS JETTED RICH.I'VE JUST BEEN BREAKING IN MY FRESHLY REBUILT RELATIVLY STOCK 454.FOR THE FIRST 10 HOURS I KEPT THE RPM IN THE 3000-3500 RPM RANGE.THE PLUGS APEARED TO BE JETTED PERFECT IN THIS RANGE.THIS WEEKEND I STARTED RUNNING THE ENGINE HARDER AND OBSERVING THE PLUG COLOUR IT APEARED TO BE RUNNING LEAN.I RICHENED UP THE PRIMARYS AND SECONDARYS UNTIL I RAN OUT OF JETS AND THE PLUGS STILL APPEARED LEAN.JETTED THIS RICH I WAS GETTING LOTS OF CARBON OUT THE EXHAUST TIPS.I AM SUSPECTING TOO HOT OF PLUG AS AFTER ABOUT 30 SECONDS OF FULL THROTLE OPPERATION (5300 RPM)I START TO GET A BIT OF A MISS WHICH I THINK IS PREIGNITION.THE THINGS THAT CHANGED WITH THE REBUILD ARE .030 LARGER BORES, A SLIGHTLY LARGER CAM 224/230 AT .050, AND THE ADDITION OF STAINLESS MARINE EXHAUST MANIFOLDS.THIS MOTOR HAS GM VORTEC HEADS.LAST YEAR I WAS USING ACMR43LTS PLUGS BUT I CHANGED TO ACR42LTSM PLUGS BECAUSE I FIGURED A COOLER PLUG WOULD BE GOOD INSURANCE.DURRING THE REBUILD IT WAS NOTICED SOME OF THE INTAKE VAVES WERE TULIPPING DUE TO PREIGNITION.I THINK THAT HAPPENED TRYING TOO LARGE OF PROP WITH TOO LOW OF OCTANE FUEL.I DO NOT KNOW WHAT THE M IN THE R42LTSM CHANGES IN THE PLUG CONFIGURATION.AC DELCO INFO ONLY SAYS THAT IT IS A SPECIAL DESIGN ELECTRODE.IS IT POSSIBLE THIS PLUG IS HOTTER.IT DOES HAVE MORE OF A REACH THAN THE REGULAR EXTENED REACH PLUG.SOME OF MY ENGINE SPECS ARE 9:1 COMMPRESION (APROX 180 PSI CRANKING PRESSURE),LARGE OVAL PORT VORTECH HEADS,AIR GAP MANIFOLD,224/230 DURATION CAM,750 CFM EDDELBROCK CARB ,AND STAINLESS MARINE MANIFOLDS.THE CARB JETTING NOW IS .116 PRIMARY WITH A .037 POWER STEP AND A.113 SECONDARY.THIS SETTING PUKES CARBON ALL OVER THE TRANSOM BUT LEAVES THE PLUGS LOOKING LEAN.LAST YEAR I WAS JETTED WITH 107 PRIMARY AND 104 SECONDARY.ANY HELP APRECIATED.

WETTE VETTE

Where is your timing set at and what type of fuel are you using? As far as the plugs are concerned the 42's should be colder than the 43's. In my opinion the 43's are the right plug for your motor. Be sure to check your timing at higher rpm to be sure it isn't over advancing. Check it at 3000 and at 3500 to see if it is all in. You may want to try a different carb and check to see that your fuel pressure is good at wot. You may be running out of gas at top end which would cause the lean condition even though you are jetted rich. If you are running an inline fuel filter be sure it isn't plugged. Let us know what you find.

HARRISONMIRAGE

INITIAL TIMING IS 4 AND TOTAL IS 28.I'M USING 92 OCTANE FUEL.I PLAN ON CHECKING THE FUEL PRESSURE.

blue thunder

Isn't a base timing of 4 degrees retarded (no offense )? I run my 454 mags at 8 degrees per the merc book and have surmized from this board that 8-10 is a good range. BBC are very sensitive to slight timing variation. Doesn't explain anything on your lean condition, but just a thought.

BT

JohnJan

Tuliped valves is from excessive heat in the chamber causing the metal to soften. Either from running lean or from detonation.

A coupla things come to mind. You're timing is WAYYYY off. Set the initial timing so that you get about 34-36 degrees total by 2500 RPM. Vette is correct, make sure it doesn't advence any further at higher RPM's.

The temperature of the plug refers to it's ability to dissipate heat, not to make heat as is often thought. Go to an MR43T as a base plug.

Put your carb back stock (the way it came from Edelbrock) and it should run well that way. Checking the fuel pressure is also key. Make sure there's 5 to 6 PSI at the carb under ALL conditions.

formula233

The low timing advance will really show it's effect at higher rpm. That sounds like your initial proublem when you increased your rpm range. You seem to have a flow proublem in the fuel which a pressure gage should expose. You might end up using a carry on outboard style tank to diagnose it if it isn't your fuel pump. The AC MR42LTS is a plug for Vortech motors. It should only be used with a breakerless ignition system with the full 12 volts on the coil and should be gapped at .045". Good Luck with the tuning!

formula233

What failed on your previous motor? Might it of carried over to these proublems. Are you using the same fuel pump? There might also be some air leaks in you fuel delivery system or in the pickup tube in the tank.

jpclear

I would say JohnJan has it pretty much right. I'd be a bit leary of setting things as high as 36 deg./2500 rpm though. Could be getting pretty close to the big "D". most marine electronic advances aren't all the way there till 3000+ so I would start with 34 deg. at 3200 and bump a little (like only 1 deg.) at a time till it gets you no more R's and then go back to your last setting. then let your initial advance lie where it falls. Check it out, record it, and use it for further reference so that you can check/reset timing without going through that whole testing thing again. Takes some testing and a helper with the hatch off but you will be rewarded in the long run. Enjoy. --- Jer

HARRISONMIRAGE

THANKS FOR THE INPUT.I HAVE RIGGED MY FUEL LINE FOR A PRESSURE GAUGE WICH I HOPE TO TEST TOMMOROW EVENING.I THINK I MIGHT HAVE FOUND MY PROBLEM.I TOOK THE CARB APPART FOR A QUICK CLEANING AND ONE OF THE NEEDLE SEAT SCREENS WAS PARTIALY PLUGGED.I WILL LET YOU KNOW HOW I MADE OUT.MY PREIGNITION LAST SEASON I THINK WAS FROM ONE ISOLATED EXPERIANCE WITH A PROP THAT WAS TOO LARGE AND LOW OCTANE FUEL.I AM USING 92 OCTANE ALL THE TIME NOW.ANY RECOMENDATIONS AS TOO MAX RPM TOO RUN.I WAS A LITTLE SCARED OF LOADING THE MOTOR UP LAST YEAR AFTER MY NEAR MELTDOWN EXPERIANCE SO I KEPT HER SPINNING UP AROUND 5200.WITH THIS YEARS MODS IT SEEMS TO HIT 5400 PRETTY FAST.MY BOAT IS A 24 DEGREE HULL,25'7'' LONG AND WEIGHS ABOUT 5000# LOADED WITH FUEL.I'M RUNNING A 21''MIRAGE PLUS AND WAS PLANNING TO JUMP UP TO A 23''MIRAGE PLUS WICH I HOPE WILL SPIN AT ABOUT 5000 RPM.AS TO LAST YEARS BREAK DOWN IT WAS DUE TO A BROKEN OIL PICKUP TUBE. I ATTACHED A PICTURE OF MY MODIFIED PICKUP.

excaleagle42

your setup is almost identical to mine, even the same jetting. the only differences are you have vortec heads and i have hi po gm rectangular ports. i run my timing at 10* initial and use AC MR43T's. you may find the motor likes 8*,10* or even 12* initial better than 4*. you may be getting close to the limit at 10* but should be ok with 92 gas. i would check under your rotor and make sure your stop posts on the centrifical weights didn't break off causing you to over advance at high RPM's. crap stuck in the needle and seat definately won't help either. i like between 5100 and 5250 WOT.