5.7L 88-95 ignition question

[Speakrdude]

Is there much (performance) difference between the older, "distributor mounted" ignition amplifier vs the Thunderbolt IV, mounted on the exhaust elbow?
The reason I ask is, on an 88 Sea Ray 300DA I've rebuilt, the engines and drives were changed out with 94 models, but they simply swapped the ignition parts over.
(so newer engines, older ignition.)
If the engines aren't started weekly, they become real dogs to start. One of them, if you pump the throttle (12 times) it will finally start but will smoke (black rolling smoke) like a freight train!
I realize I've flooded it, but that seems to be what it takes to get it started. Yes, chokes are working.
The other engine, takes as many pumps and as much time to start but doesn't smoke as much.
Other engines I've had, in the 90's that had the Thunderbolt IV ignition, never really seems to be a doggy.
Your thoughts?

 

[Bt Doctur]

If you pump more than 3 or 4 times, something else is wrong.The chokes should be set to with 1/8 inch closed, cold.They should fully open in about 2 minutes if electrically heated. TB V is dist mounted, TB IV is riser mounted

 

[thumpar]

I don't think the ignition has anything to do with your starting issues. It is probably something with the carb or fuel supply.

 

[Speakrdude]

Really! So these are TB 5's?

 

[Speakrdude]

I've read up a little now. Both of these, I'm talking about are TB IV's.
Any preference between the two?

 

[wrench 3]

Strictly a personal opinion, but I've found the TB IV to be more reliable. The modules are so reliable that the aftermarket industry doesn't even make a replacement for them.
If you're running Rochester Quadrajet carbs, they have the float valve in the bottom of the float bowl. If they sit for a week or so, the fuel drains back into the fuel tank and you have to pump it back up and fill the carb before it will start.

 

[Speakrdude]

Good winter weekend project. Off she comes. Time to (un) divorce the choke. Going electric. (Some of you will get that one)

 

[NHGuy]

Those carbs vent to atmosphere, the fuel in the bowls evaporates in a week or a few days. If you put a shot of gasoline or a burst of carb cleaner to it before you crank, it will probably give you a quick cold start.
Then if it runs enough the fuel pump will catch up with the engine's needs, if not you can still give it a pump or 3 after that and it will probably start right back up. It should never need 12 pumps unless there's no choke at all or a carb problem. If I haven't run mine for a week I crank it for 2 or 3 cycles of a few seconds each, that brings some fuel into the bowl. Then a couple of pumps and it will start nicely.
If your chokes are closed they should open a little bit when the engines start, and then more as the engines warm.
And if the engines run well when they are warm the ignition is probably OK.

 

[Scott Danforth]

you do not have an ignition issue, you have a fuel delivery and/or a carb problem

I used to run a truck in winter without a choke and never had to pump it 12 times. pump once, and kept the foot on the throttle until the motor warmed up.

 

[Speakrdude]

Pulled the carb today. Full of crap. Old smelly, typical.

 

[NHGuy]

I must be an old carb too!

 

[achris]

Is there much (performance) difference between the older, "distributor mounted" ignition amplifier vs the Thunderbolt IV, mounted on the exhaust elbow?

None whatsoever. It's the same electronics mounted in a different package. Just check you have the right curve. Some of the earlier V8s used 22 degrees, some used 24 degrees and some even used 20 degrees.

Best source of info on TB IV modules are the Merc service bulletins. 95-11 is the most comprehensive.

Chris.........

Really! So these are TB 5's?

No, TB IV was distributor mounted from about 1988 to 1995. TB V was introduced around 95....