454 timing issues

Need some help. I have a 1995 Mercruiser 454 with the Thunderbolt iv ignition system. First, I will set the timing at the recommended 8 degrees advanced. The engine will idle perfect at 750-800 rpm. I give it gas and it bogs down and backfires throught the carb. Nice. I then can advance the timing until the engine will accept the throttle without much hesitation. I put the timing light back on and it reads about 26 degrees advanced at idle. I rev the engine and the advance appears to be working and advances fine. So I figured if the timing really is at 26 degrees, it will struggle to roll the motor on restart. I cut it off and it fires right back up no laboring. Am I not setting the timing correctly? Could the timing mark on the balancer be off or the timing pointer be that wrong?
While I have your ear, The ignition box or module or whatever the correct name of the box that botlts to the port manifold. Mine is shaped like a box, a lot of what I see online are small modules on a triangle shaped plate. I also have a 350 in a Larson and it has the small module. What is the difference and can I use the smaller module to replace the box? I hate electronics so I would like to carry a spare with me. Thanks for all your wonderful advice!

Re: 454 timing issues

is your engine a fuel injected and if so what type of fuel injection or is it carbureted? do you have the proper service manual? what is the serial number of your engine?

Re: 454 timing issues

It is carbureted with a new Quadrajunk! I dont have the numbers off the motor in front of me. I have a couple service manuals but nothing that describes the timing reading way off but running correctly.

Re: 454 timing issues

Does your ignition module look like the one in this picture?

Re: 454 timing issues

Yes Don, that is exactly what it looks like!

Re: 454 timing issues

I was afraid of that.
That module--- amplifier was used on 81 thru 87 Thunderbolt IV ignitions, not on 95 models. Now the problem is, was the engine changed or just the module.

Now, back to your timing, if you set your timing at 8? BTDC at idle rpm, what does timing go up to at around 3000 rpm?

Re: 454 timing issues

Long story short, I bought a 1995 boat that had a Jasper rebuilt engine in it with 20 hrs on it. I believe the previous engine had a fire and the owner appears to have replaced the ignition with this older unit. I junked the boat and removed the motor and outdrive to use in my boat. Can I switch the module or what options do I have?

If I set it to 8* it will not go to 3000 rpm because it backfires.

Re: 454 timing issues

If I set it to 8* it will not go to 3000 rpm because it backfires.

Click to expand...

You should be able to slowly raise the throttle (In neutral on muffs is ok) the timing changes with rpm.

Can I switch the module or what options do I have?

Click to expand...

At this point, I don't know. What outdrive do you have on the engine?

Sounds like your whole engine/drive/boat setup is made out of whatever someone could find ( sometimes called a junkyard dog). But, even back in 81, they ran without bogging, so it should again. Just going to take a liittle figgerin' out to get it there.

Re: 454 timing issues

Yea, I tried to slowly increase the throttle but at abut 1500 it bogs out tehn backfires. everything appears to be be correct except the ignition system, so far. It has a bravo 1 outdrive. I don't suspect the amplifier as being the issue but its not ruled out. the timing mark being so far off bother me. Even though the engine runs good on the trailer after I jack the dizzy around by ear. I will pull #1 plug tomorrow to verify the mark for tdc is correct. I don't know whats going on with this thing. I will take some better nots of what its doing at waht rpm and timing.

Re: 454 timing issues

Alright Don, I pinpointed the problem. The module has to be bad. I was incorrect about the statement that I said early in posts. The timing is not advancing. So when I gas it from 8*, it runs 8* until the motor can't take the fuel and backfires. This would explain why it would take the gas when I cranked the timing. Now the question has turned to what options do I have? Can I find the older module(is it worth it?) Can I switch to the newer style module? Can I switch to a HEI unit? What is out there that won't kill my wifes wallet? haha

Re: 454 timing issues

fastimz said:

I will set the timing at the recommended 8 degrees advanced. The engine will idle perfect at 750-800 rpm.

Click to expand...

It should be 8? BTDC and idle at 600 RPM.

Re: 454 timing issues

Regardless if I set it at 600, 700, or 8000 rpm it still doesn't advance any when I give it throttle!

Re: 454 timing issues

I don't know if you can replace them with the new style or not, the one you want is for a model 330 which is a 454 Mercruiser. problem is, you may get one for an Alpha drive, and you don't want that. Let me do some checking.

Re: 454 timing issues

Did some checking, seems the old style amplifier you now have is replaced by the new style that mounts on the riser. The PN is15248A1. I found them online for $200 to over $400 one from ebay for 195 with harness and module (oem in unopened package) you get to look.
Anyway, you will also need some fiber spacers and bolts to mount it to the elbow. But that's not a big deal, hardware store items.