It has stormed here all weekend but we did get about a 2 hour break today.

New cap and rotor (Sierra from parts house) swapped the original mercury coil on it. Fired up but sounded like it has a misfire that would dissappear over about 1200 rpm. Gonna bring my timing light home tomorrow and check base timing. The pickup in the dizzy looked brand new. Checked with the previous owner and he said he put it in when the engine went in. (Less than 50 hrs) I doubt it could be bad already? I did however ;upon reading the box the msd marine rated coil came in, discover that the msd says it needs an 8 ohm resistor in line with it. That is why I put the oem coil back on. Let it run at 1200rpm for 5 mins or so. The rain returned so it got covers back up.

The ballast resistor is only used on points ignitions because the points would burn up if supplied with a full 12 volts. When hooked up to an electronic system, the coil can be wired just like the factory Merc unit.

I thought so but wasn't certain. I try not to play with this distributor junk. I prefer 18 to 1 compression and direct injection lol.
So im almost to the point of calling it quits on this thing. If I put another distributor in here where do I need to set the weights for the advance curve?

Just talked to an engine builder/long time big block hot rodder friend of mine. Laid out the build of the engine to him. He recommended if I do go with a regular hei with weights to simply put a curve kit in it with soft springs so it comes in quickly and will get to ~24° around 3800rpm. He said don't really worry about what the initial timing at idle is as long as it gets to 24 at 3800. Although initial timing should be around 10 or so.

Does this sound right to you guys that play with marine engines?

I'm sorry but I refuse to waste any more money on the thunderbolt system. I'm sure its a good thing when it works like you all say. Simply put, mine still is not working and I will not spend another dime trying to make it work.

32 all in. some guys go more but I think they really watch their gas.

Great! Sounds good. I have my timing light and will get a timing tape to poke in the ballancer this evening.

The v8 24 module provides 24 degrees of advance plus the 8 initial gives 32. Most run 34ish but at 24 total it isn't enough and will leave power on the table and be inefficient. Not sure why he would say that unless you misunderstood him.

I did misunderstand. I asked again. He said between 34-38 with that camshaft would be good but need a hotter fuel and colder plug. So around 32-34?

I run 34* timing with 8.8 compression, rectangle heads, 134561 cam, and 5lbs boost.

I went by a fiends hot rod shop to get some timing tape and weight kit for the dizzy. Got home to find the balancer has the timing numbers laser etched into it...
Only $3 wasted. I hate ups right now! The plug wires have been sitting at there facility 3 miles from my house since Saturday! Maybe tomorrow I can get them, put the dizzy in, set timing, and call it done!

It'll also burn up the exhaust valves and cook the cylinder walls and rings. 24 degrees total is great way to ruin your engine.

Set it to 32-34 total. If it audibly pings on regular fuel at 34 degrees, back it off.

Honestly, I believe that you're about to go way over your head with this thing. The stock Thunderbolt ignition with the 24 degree module should work fine with your engine. If it's messing up, either a component has gone bad (and you need to properly troubleshoot it using Mercury's diagnostic procedures) or you have a bad ground, these things are basically bulletproof in their operation especially the version you have.

If you are bound and determined to get rid of the Mercurry system, buy a GM Voyager Marine ignition kit. It uses a Delco small cap distributor, and comes with everything needed to install it. It has a preprogrammed module that works well on a stock or mild perf big block. Install it, set the timing at 32 degrees at 3k rpm and be done with it. Cost is about $350.

But I seriously doubt that there is anything wrong with your TB-IV. Sorry if I sound so militant on this point, but I've worked on a lot of these systems; they really are the last thing to go bad, and engineering something "better" usually ends up really messing up a good engine.

I have followed the little trouble shooting guide. It has power where it is supposed to. Every ground has been cleaned. The ony thing left I have to suspect is the v8 24 module. The price of a new one is outrageous. I see where Mr gary offered to let me try his for troubleshooting. That is awful nice of him and I appreciate it but if that does help then that means I have to buy one. Hei distributors work every day in vehicles. Worst case in a year if it farts out, another $50 and we go again.

1) I totally agree with TomZ
2) Modules can be had here for $100 easily, this is where I got my spare, (different curve & advance)
3) I believe when you are done chasing your tail on the ignition you will be back in the carb and fix the problem.

A carburetor will not cause a direct misfire on 3 cylinders under 1000rpm then mysteriously disappear above 1000 rpm. This is 100% a firing issue. The carburetor bowls are holding fuel. Every gasket, accelerator pump, power valve, needle and seat are new. I've buit enough carburetors to know that it is not a carburetor problem.

I am not saying the tb iv is a bad thing. I'm just saying it is apparently bad on mine and the price of a module is the price of 2 heI distributors.

Now I am confused. Post #111, idle to 3,200 OK. Post #149, OK until you hit secondaries (2,500) then busting up. Now Post # 214 running on 5 cylinders <1,000 then clears up.

Try Gary's module. If it works, you'll know that's the issue. If not, then the ignition isn't the problem. All it'll cost you is the shipping.

Guys sell this stuff in the Swap Shop all the time. If you post something in the wanted section, I'm sure you'll get some quick hits.

And don't discount the carb issue. I've witnessed plenty that have acted relatively the same way. Just saying. Do you have another carburetor to try just to see how she idles?

Heck, you pay round trip shipping and I can send you module (V8-20), distributor w/module, wires, and coil. Sorry I sold my last Q-jet I was keeping for troubleshooting purposes.

It has progressively gotten worse gary. Earlier in the thread (2 weeks ago) it was just in the secondarys. As time has gone on (3 water tests) it has gotten worse. I can watch the carburetor spraying fuel. I am more than confident it is not a fuel issue. It is something in the ignition system that is either breaking down or is failing under a load requiring more fire.

It is more than likely the module. That I all I can see it to be by the little procedue mercury has. I might look at the sea ray and see what modules it has if it has any.

Just a stray thought, how are the batteries and charging system. Not just voltage but load test.

TB-IV modules don't really fail this way. They generally just die unless there's corrosion problem causing a jump across terminals in the boot (that's what happened with my V6 module). I have seen the system drop random cylinders, but only on a TB-V (a system that's prone to problems... Merc's fix is to replace with a TB-IV or aftermarket). TB-IV's are stupid reliable.

You have cylinders dropping off under 1k rpm. Are they the same cylinders or is it random? Have you changed plugs? Could any be fuel fouled? What about water intrusion? Any exhaust issues that could be drowning out cylinders at low rpm? What camshaft is in the engine?

Sorry... grasping at straws to help you out here.

Batteries brand new. Load test with 350 amps bounce back to 12.4v. Alt charging around 13.8

Tom to answer your questions. Yes sir the plugs are new. It sounds like 2 or 3 cylinders are picking up and dropping sporadically as it is at idle up to around 950-1000 once above that you can't really hear or feel any vibration. The exhaust seems tight no signs or exhaust leaks. The cam shaft is a stock 450hp 454. I will check the modules in the parts boat this evening. It is very possible this one died when water was spraying on it due to the lack of speedometer fitting.

Thank you guys again for all of your help!

Watch the exhaust at the stern while idling. If its sputtering on one side only, could be a riser gasket.

It feels like both sides if you put your hands on the risers. It's odd. Almost feels like when a plug wire is breaking down.

I might have missed this so I'll ask, what generation is this block?
If it's a roller cam in a general 6 block you may have an issue with the distributor gear. I put my thunderbolt distributor in my gen 6 and found it was wearing out my distributor gear. The roller cam gear is hardened so it tears up the stock gear on the distributor. I had to buy the composite gear to run on the distributor to prevent metal shavings in the oil. This most likely isn't your problem, but I know my brother in law and I messed either the tb vi for days and swore it was a module when really it was the gear was missing a tooth.

This is a normal flat tappet cam shaft in a gen iv block. Just has roller rockers. Good suggestion though.

What's a "stock 450 HP" cam? Do you mean the factory Merc 365 (454 Magnum Cam)?

The reason I ask... if the cam has too much overlap, it will start sucking water into to the cylinders. That's why I was asking about the exhaust too. If you have some exhaust mist coming through, you could be knocking out cylinders that way. Just a suggestion.

Do you have the cam card handy? I'm curious as to what's in there.

Merc did make a 450hp. It was a carbed merc hp500 except 454 cubes.

The man that built the engine is going to look in his file cabinet tomorrow and get me the cam card.

Today afyee work (5:30 almost dark) my work partner towed one trailer while I pulled the other and we swapped it onto the other trailer.

The HP450 used a hydraulic roller cam.

GM V8 454 cid (7.4L) Gen V.
Sterndrive Models (LH rotation), 4 bolt mains, flat lifters.
7.4L XW 1992-1996, 1XW, start Gen V, no mechanical
fuel pump pad on cylinder block, GM
4-bbl intake.
14 (356)
7.4LX MPI UC 1996, MerCruiser MPI intake. 14 (356)
7.4L PT Bravo 3 UW 1993, cast pistons, start GM hi-rise intake. 14 (356)
7.4L PT Bravo 3 UB 1993-1994, start forged pistons. 14 (356)
7.4L PT Bravo 3 XX 1994-1996, start new design cast pistons. 14 (356)
454 Mag XA 1992-1996, 2XA, start Gen V, no mechanical
fuel pump pad on cylinder block, GM
hi-rise intake.
14 (356)
454 Mag XAA 1995, GM hi-rise intake. 14 (356)
454 Mag MPI UA 1994-1996, MerCruiser MPI intake. 14 (356)
Ski Models (LH rotation), 4 bolt mains, flat lifters.
454 Mag MPI UA 1994-1996, no mechanical fuel pump pad
on cylinder block, MerCruiser MPI intake.
14 (356)
Inboard Models (LH rotation), 4 bolt mains, flat lifters.
7.4L XY 1992, 2XY, start Gen V, no mechanical
fuel pump pad on cylinder block, GM hirise
intake.
14 (356)
7.4L MPI UD 1995-1996, MerCruiser MPI intake. 14 (356)
Mercury Racing built Sterndrive Models (LH rotation).
HP425 UA 1993. GM hi-rise intake, 4 bolt mains. 14 (356)
HP450 UA 1995. 14 (356)
HP525 SC UA 1993-1996, supercharged. 14 (356)

Don't remember any pics on motor/bilge

See this thread...

http://www.offshoreonly.com/forums/g...454-450hp.html

Ok fellers. I have the cam specs for you.
It is a custom grind cam that the engine builder has made in oregon. He says is similar to a 1970 chevelle 454 450hp factory cam.

Intake duration 224
Exhaust duration 232

Lift intake 527
Lift exhaust 553

Center line 110
Exhaust 118

He said he has built hundreds of engines using this cam shaft. They pull great around 5k-5500

His recommended timing is 34-36 all in.

Hunter, what kind of exhaust is on the engine, and specifically, how far away does the water enter the exhaust?

The cam you have is more than likely a Speed-Pro piece. Running the numbers on it, overlap comes in at 75 degrees which is a lot. I'll bet it's sucking in water at idle. Try kicking up the idle to about 900 RPM and see how it acts.

It has imco thumper power aluminum manifolds and risers. I will adjust idle up and see how she does. Thanks for the tip tom.

Hunter, that exhaust is really meant as a replacement for Merc's heavy, iron system (the riser is similar to the ones made by Marine Power). Your cam has more overlap than a Mercuiser HP420 (an engine famous for sucking water). The HP420 was eventually equipped with a Gil system that used a long riser to mix water farther downstream. Bumping the idle might help it, but you have to keep the idle acceptable so that the drive shifts properly.

Play with the idle speed to see how she does.

Ten4. Thank you for the info! Itll be a few days before I can do anything. It's cold and raining here now.