1995 7.4 Thunderbolt starting

[tango13]

Hi all,

I recently just changed boats and am getting accustomed to the 7.4/Bravo 1 with the Thunderbolt ignition system. The engine has 23 hours on it, as the shortblock was replaced a couple years ago by a very reputable marine shop (new engine is a 7.4 bored 0.030 over, with a non-stock cam and internals , estimated about ~425ish hp). Engine is has the stock Carter AFB and factory mechanical fuel system.

This might be a dumb question, but how "good" should this motor fire up in general? My previous ski boat had a carbed (Q-Jet) 260hp 5.7, w/ the pertonix ignitor kit, and it fired up absolutely perfect - literally just had to bump the starter after it was warmed up. I find this 7.4 wants to turn over a little more after it gets to temp. I guess I expect it to run as good with the Thunderbolt ignition, but I have no experience with this system.

I expect the ignition system aside from the module (plugs/wires/ cap&rotor) are in acceptable shape post-engine replacement. But before I start going down rabbit holes, I was hoping to know how these motors are expected to regularly start. I realize there are ALOT of variables that can affect this, just looking for some general info.

Boat is a 1995 Cougar Sport Skier 20.5

Thanks

 

[ScottinAZ]

just like with everything else, some can and will be a bit more recalcitrant than others. If it becomes an issue, or gets progressively worse, then is when I would start looking at the electrical side of the house. Make sure ALL connectors are clean and tight, ensure that you have good grounds throughout the boat, and that your switch isnt causing issues due to internal corrosion. (not saying it is, but that is a set of contacts that you CANT clean). As long as the electrical side is kept in good order, it makes troubleshooting any other issues that much easier.

conversely, you dont say what style of fuel delivery you have, carburetor or fuel injected. that can also make a difference in how easily the engine kicks to life, especially if injected and the fuel pressure at the rail is dropping off when the engine is shut down (takes a second or so to build pressure), unlike a carbureted system where the fuel in the float bowl is ready to go when you hit the key

 

[tango13]

just like with everything else, some can and will be a bit more recalcitrant than others. If it becomes an issue, or gets progressively worse, then is when I would start looking at the electrical side of the house. Make sure ALL connectors are clean and tight, ensure that you have good grounds throughout the boat, and that your switch isnt causing issues due to internal corrosion. (not saying it is, but that is a set of contacts that you CANT clean). As long as the electrical side is kept in good order, it makes troubleshooting any other issues that much easier.

conversely, you dont say what style of fuel delivery you have, carburetor or fuel injected. that can also make a difference in how easily the engine kicks to life, especially if injected and the fuel pressure at the rail is dropping off when the engine is shut down (takes a second or so to build pressure), unlike a carbureted system where the fuel in the float bowl is ready to go when you hit the key

Thanks, I did update my boat and included that its a carbed engine with a mechanical fuel pump system.

 

[Bondo]

Ayuh,..... The weber/ merc carbs can, 'n do leak internally, try startin' it at Wot next time, to see whether it's floodin' out, when ya shut it off,...

 

[todhunter]

Ayuh,..... The weber/ merc carbs can, 'n do leak internally, try startin' it at Wot next time, to see whether it's floodin' out, when ya shut it off,...

Help learn a guy something who has little carb experience...

Is the thought here to give it as much air as possible to start on the extra fuel that's in there from the flooded shut-off? The accelerator pump adding a squirt of fuel doesn't make it just that much more rich? And, is the idea to see if it starts at WOT, and then if it does, immediately pull it back down towards idle?

 

[Bondo]

Help learn a guy something who has little carb experience...

Is the thought here to give it as much air as possible to start on the extra fuel that's in there from the flooded shut-off? The accelerator pump adding a squirt of fuel doesn't make it just that much more rich? And, is the idea to see if it starts at WOT, and then if it does, immediately pull it back down towards idle?

Ayuh,..... I was taught, if ya suspect, or prove a carbed motor is flooded,...
Wot will clear it,....

If the Op's is leakin', not only will he have flooded restarts, after sittin' a week or so, he'll experience long grinds, 'n hard starts, as the fuel pump, refills the carb,.....

 

[tango13]

Ayuh,..... I was taught, if ya suspect, or prove a carbed motor is flooded,...
Wot will clear it,....

If the Op's is leakin', not only will he have flooded restarts, after sittin' a week or so, he'll experience long grinds, 'n hard starts, as the fuel pump, refills the carb,.....

Thanks for clarifying. And that actually makes a lot of sense - when I looked at the boat before buying, the previous owner couldn’t get it started and we figured it was flooded. He had ran it earlier that day on the muffs. I wonder if the carb is infact leaking…

 

[ScottinAZ]

Thanks for clarifying. And that actually makes a lot of sense - when I looked at the boat before buying, the previous owner couldn’t get it started and we figured it was flooded. He had ran it earlier that day on the muffs. I wonder if the carb is infact leaking…

its possible. QuadraBogs have a couple known leak points, but the Carter AFB's usually are pretty good about not leaking. Check your float height to make sure it isnt overflowing, but I cannot for the life of me remember if there are any welch plugs in the bottom that would leak. a porous casting is a possibility, but I dont recall the Carters being known for this either.

 

[achris]

... the stock Carter AFB ...

Well known for being 'dribblers'.

I had one on a previous engine. I did a bunch of test, which included having the carb in a vice on the bench with the top off and the fuel bowls filled. I blew air down one of the primary venturis and got a nice stream of fuel/air. I could see the fuel level in that bowl dropping, so all working as it should. I then refilled that bowl and left the carb overnight. Next morning that bowl was empty (the other one was still full) and all the fuel was on the paper I'd left under the carb... That was my final proof that these carb DO leak, and it's just a design flaw. The internal passages are so small that the fuel continues to flow due to capillary action. There's not a lot you can do about it, but knowing it happens means you can try to work around it.

First start of the day will be difficult because the carb is empty, which means you'll need to crank it a while for the pump to pick up fuel and fill the carb. Being a mechanical pump means there's not a lot you can do to avoid that, but you could put an outboard engine fuel primer in the incoming fuel line. Just give the primer a couple of squeezes before the first start and the carb will be filled. The other consequence is that when you shut off for more than about 15 minutes, the engine will be flooded. An open throttle will help clear the flood, but be ready to pull the throttle back as soon as the engine catches (or it'll rev to kingdom come).

Hope this helps.

 

[ScottinAZ]

Well known for being 'dribblers'.

I had one on a previous engine. I did a bunch of test, which included having the carb in a vice on the bench with the top off and the fuel bowls filled. I blew air down one of the primary venturis and got a nice stream of fuel/air. I could see the fuel level in that bowl dropping, so all working as it should. I then refilled that bowl and left the carb overnight. Next morning that bowl was empty (the other one was still full) and all the fuel was on the paper I'd left under the carb... That was my final proof that these carb DO leak, and it's just a design flaw. The internal passages are so small that the fuel continues to flow due to capillary action. There's not a lot you can do about it, but knowing it happens means you can try to work around it.

First start of the day will be difficult because the carb is empty, which means you'll need to crank it a while for the pump to pick up fuel and fill the carb. Being a mechanical pump means there's not a lot you can do to avoid that, but you could put an outboard engine fuel primer in the incoming fuel line. Just give the primer a couple of squeezes before the first start and the carb will be filled. The other consequence is that when you shut off for more than about 15 minutes, the engine will be flooded. An open throttle will help clear the flood, but be ready to pull the throttle back as soon as the engine catches (or it'll rev to kingdom come).

Hope this helps.

Put one on an old El Camino I had when I was younger. Never had issues with it, unlike the Q-Jet it replaced..... But, like any mass produced piece, there are good and bad ones. I WILL say, they are much easier to change jets and metering rods on than the alternatives!!!

 

[nola mike]

Being a mechanical pump means there's not a lot you can do to avoid that, but you could put an outboard engine fuel primer in the incoming fuel line.

I've been thinking about installing a momentary switch at the helm to activate the FP relay. Obviously won't work with a mechanical pump...