Thunderbolt Ignition

[NJCinMN]

I have a 1969 type II thunderbolt with single coil and pointless distributor. I was reading in some old ignition testing that a maintenance free battery is not recommended. I have a duel purpose starting/deep cycle battery. I'm wondering if that could have a major negative effect on my ignition system.

I'm asking because I'm short on rpms with a setup and prop that I think my 100 hp motor should push. It runs smooth, starts perfect, good compression, but can only get 4500 rpm with 16 ft glastron and a 17P prop (just me in the boat). Another thing that seems odd is that it idles great and all carbs are sync'd, timed right but the timing at 800 rpm is about 4 degrees BTDC ,butterflies still closed?? The initial throttle pickup is about 5-6 degrees BTDC. I read most people have to retard their timing to AFTDC to get it to idle that low. Thoughts welcomed, thanks.

 

[Point man]

Re: Thunderbolt Ignition

I'm not an expert, and I'm sure someone here is more qualified to answer, but once the motor is running it shouldn't have much effect on your engines performance unless you are running a huge bank of batteries, or a lot of electronics where you would be overloading the alternator. I have a merc 1000 with thunderbolt ignition that I run with a maintenance free battery(and the previous owner did also) no problem...until it died on me last week. but it still cranks so I think it's a fuel problem

 

[FZ1]

Re: Thunderbolt Ignition

I've got a 69 1000ss that I'm in the process of getting to run right too. Do you have the Seloc manual? Because if you do, you might be confused about the two timing marks like I was. When you are lining up the flywheel to the distributor pulley arrow, and checking TDC on #1 cylinder, you use the solid line on the side of the flywheel. This is not the timing mark. The timing mark is the three dotted line an inch or so to the left, and has a white dot of paint on the top of the flywheel just above it.

I think I may have used the wrong mark when I did my timing, and pointed my timing light at the wrong mark. I've got carbs on the bench just freshly looked over/cleaned and fuel pump rebuild kits on the way. That and retiming and link n sync again will get it going right I hope.

First time on the water i had mostly the same symptoms as you except i could only get 2000rpms or so. I don't think I had anywhere near enough advance for the motor to take the full throttle it was getting. It started and idled fine, didn't stall going into gear, but just had no power.

Hope this helps.

 

[Moody Blue]

Re: Thunderbolt Ignition

Had the same battery concerns about my 1971 Merc 800. Everyone said not to worry about it so I didn't and I've run it all summer with no ill effect. Don't fully understand the reason for the concern in the first place though.

As for the low rpm, have you checked to make sure the motor is mounted right on the boat? Antiventilation plate even with bottom of hull? Have you verified that the throttle plates in the carbs are fully opening (visual check)? What is the max advance timing set to? Should be about 21* BTDC.

I have a 12 3/4" x 17"P prop on my motor pushing a 16ft deep V fiberglass hull (heavy) and I turn 5400 with just me in the boat. Your 100 should do just as well or better.

 

[jerbear56]

Re: Batteries

Re: Batteries

Hi guys, newbie here. The reason they recommend a deep cycle battery on the older ignition systems is because the number one killer of early ignition modules is starting the motor with low voltage.

In a nutshell, the deep cycle batteries will discharge at a more even rate and give you plenty of warning, but maintenance free, such as car batteries, will go from somewhat discharged to seriously discharged in a heartbeat and can kill the module. Hope this helps!