rockstar38

I recently got a set of thunderbolts off of my buddies boat that he didn’t need anymore. I have pretty fresh 454's on my Cig.

I replaced the caps, rotors, and wires, and modules that I got from him on both motors. I had a weird points/electric setup on there when I bought the boat. At the same time I replaced my Rochester carbs with the Holley’s he gave me.

So after have all kinds of issues everyone suggested it was the cards so I put the old carbs back on and I still have the same problems so that just leaves the problem in the thunderbolts.

What both motors are doing sound like a timing issue. They spit and pops and just sound like hell. Then when you get the timing set to where they sound normal they won’t rev without big back fires.

Should I just give up on them and look into MSD's or is this something that you guys have seen before?

BenPerfected

They should work. Have you checked the timing at full advance? If you haven't, hold the RPM at 3000 and adjust to 34-36 degrees. It should now idle decent regardless of the Merc advance box. Is the valve train stock?

rockstar38

Yeah we timed it at 3000.

Everything on the motors are stock and they have about 25 hours on them.

Griff

I thought only one engine was running poorly now????

rockstar38

Well thats what the guy I had look at it told me. But once I went to run it I couldnt even get it to rev correctly. It would spit and then all the power would kick in around 2000 rpms and it would run decent.

Mbam

How old are the original engines to start with? Did they come with point ignitions (like the old 400 or 370)?

Check for a resistance wire built into the harness for the + coil connection. You can ground the - terminal to put a load on it then measure what you have on the + side. Should be 10-12 with the engine not running. If it is down near 6 you have a resistance wire.

rdoactive

Did you remove the ballast resistor/resistor wire used with the points ignition?

Griff

You definately don't need to look into MSD's. The TB IV's are are simple and very reliable. The same cannot be said for MSD's.

I never thought about something in the old wiring. Thats a good bet.

SB

MBAM/rdoactive gave you great advice. Modern electronic distributors need full voltage. Without it, the engines will run like poop. Points use reduced voltage - no good for your TBIV.

Also, not all TBIV advance curves stop at 3000rpm. I've seen one stop at 4200rpm. Way to find out is keep reving motor until you see the advance stop then go a few hundred rpm higher to make sure it has stopped. This is where to set total.