5.7 L Thunderbolt troubles
 

1994 Mercruiser 5.7 L Thunderbolt (Quadrajunk) SN 0f067387 Alpha 1 Gen 2
w/279 hours...New plugs, wires, rotor and cap @ 269 hours.
Boat would run fine at all speeds most of the time BUT sometimes after
coming off a WOT run engine would not run below 1200 rpm. Stumbles, etc as
if it was starved for fuel. Makes it interesting trying to dock. Had to baby
Mercotrol to get it to stay running at that speed. Any speed above that runs
fine.
First time it happened I suspected bad fuel (boat had set for sometime with
1/4 tank). Added 6 cans of B12 (50 gal tank) 6 cans dry gas, sprayed carb
down with carb cleaner (lots of gunk) and changed the Merc fuel filter water
separator. Opened primary mixture screws to 2 turns (was @ 1 1/2)and all
seemed better.
Boat ran fine for next 5 hours, but did have a wandering idle and has always
been hard to start from cold.
Now, on last trip, same thing happened again.
Drug it home,put muffs on, fires right up. No problem.
Let it warm up and try to restart. No start.
Check fuel- yep, accel pump squirts it out. Check for 12v at both sides of
coil. Got that. Pull distributor cap and check rotor and inside of
cap...looks like new. No spark though, verified with timing light.
Check for loose wires, blown fuses, etc...none found.
Now....do you think the 2 events are related?
I would think that if the Thunderbolt went south it would be an all or
nothing event, not a random loss of low speed.
Ideas, men, ideas.

--
"Only the dead have seen the end of war" Plato

5.7 L Thunderbolt troubles
 

I would check the coil for failing when hot, the control box for the ignition
system, and a loose wiring connection in the ignition system.

1994 Mercruiser 5.7 L Thunderbolt (Quadrajunk) SN 0f067387 Alpha 1 Gen 2
w/279 hours...New plugs, wires, rotor and cap @ 269 hours.
Boat would run fine at all speeds most of the time BUT sometimes after
coming off a WOT run engine would not run below 1200 rpm. Stumbles, etc as
if it was starved for fuel. Makes it interesting trying to dock. Had to baby
Mercotrol to get it to stay running at that speed. Any speed above that runs
fine.
First time it happened I suspected bad fuel (boat had set for sometime with
1/4 tank). Added 6 cans of B12 (50 gal tank) 6 cans dry gas, sprayed carb
down with carb cleaner (lots of gunk) and changed the Merc fuel filter water
separator. Opened primary mixture screws to 2 turns (was @ 1 1/2)and all
seemed better.
Boat ran fine for next 5 hours, but did have a wandering idle and has always
been hard to start from cold.
Now, on last trip, same thing happened again.
Drug it home,put muffs on, fires right up. No problem.
Let it warm up and try to restart. No start.
Check fuel- yep, accel pump squirts it out. Check for 12v at both sides of
coil. Got that. Pull distributor cap and check rotor and inside of
cap...looks like new. No spark though, verified with timing light.
Check for loose wires, blown fuses, etc...none found.
Now....do you think the 2 events are related?
I would think that if the Thunderbolt went south it would be an all or
nothing event, not a random loss of low speed.
Ideas, men, ideas.

--
"Only the dead have seen the end of war" Plato

5.7 L Thunderbolt troubles
 

I'd replace the ignition pickup unit inside the distributor. I think the
part is only 60 bucks or so. When mine went bad I lost power and ran very
rough at idle. I also thought (and everyone else told me) that it was bad
fuel.


"Kenneth670" wrote in message
...
I would check the coil for failing when hot, the control box for the
ignition
system, and a loose wiring connection in the ignition system.

1994 Mercruiser 5.7 L Thunderbolt (Quadrajunk) SN 0f067387 Alpha 1 Gen 2
w/279 hours...New plugs, wires, rotor and cap @ 269 hours.
Boat would run fine at all speeds most of the time BUT sometimes after
coming off a WOT run engine would not run below 1200 rpm. Stumbles, etc
as
if it was starved for fuel. Makes it interesting trying to dock. Had to
baby
Mercotrol to get it to stay running at that speed. Any speed above that
runs
fine.
First time it happened I suspected bad fuel (boat had set for sometime
with
1/4 tank). Added 6 cans of B12 (50 gal tank) 6 cans dry gas, sprayed carb
down with carb cleaner (lots of gunk) and changed the Merc fuel filter
water
separator. Opened primary mixture screws to 2 turns (was @ 1 1/2)and all
seemed better.
Boat ran fine for next 5 hours, but did have a wandering idle and has
always
been hard to start from cold.
Now, on last trip, same thing happened again.
Drug it home,put muffs on, fires right up. No problem.
Let it warm up and try to restart. No start.
Check fuel- yep, accel pump squirts it out. Check for 12v at both sides
of
coil. Got that. Pull distributor cap and check rotor and inside of
cap...looks like new. No spark though, verified with timing light.
Check for loose wires, blown fuses, etc...none found.
Now....do you think the 2 events are related?
I would think that if the Thunderbolt went south it would be an all or
nothing event, not a random loss of low speed.
Ideas, men, ideas.

--
"Only the dead have seen the end of war" Plato

5.7 L Thunderbolt troubles
 

I know somebody who has one of these beasties and had
a similar problem - turned out it was loose sparkplugs.

No joke.

Thunderbolt ignitions are easy to replace though, so try that.
You might want to just check through the engine though just
to make sure - do some compression checks and stuff. A
cracked head could cause a problem like this.

Later,

Tom
"Steve Arnold" wrote in message
news:Vh%Va.48497$AD3.46058@lakeread04...
I'd replace the ignition pickup unit inside the distributor. I think the
part is only 60 bucks or so. When mine went bad I lost power and ran very
rough at idle. I also thought (and everyone else told me) that it was bad
fuel.


"Kenneth670" wrote in message
...
I would check the coil for failing when hot, the control box for the
ignition
system, and a loose wiring connection in the ignition system.

1994 Mercruiser 5.7 L Thunderbolt (Quadrajunk) SN 0f067387 Alpha 1 Gen
2
w/279 hours...New plugs, wires, rotor and cap @ 269 hours.
Boat would run fine at all speeds most of the time BUT sometimes after
coming off a WOT run engine would not run below 1200 rpm. Stumbles, etc
as
if it was starved for fuel. Makes it interesting trying to dock. Had to
baby
Mercotrol to get it to stay running at that speed. Any speed above that
runs
fine.
First time it happened I suspected bad fuel (boat had set for sometime
with
1/4 tank). Added 6 cans of B12 (50 gal tank) 6 cans dry gas, sprayed
carb
down with carb cleaner (lots of gunk) and changed the Merc fuel filter
water
separator. Opened primary mixture screws to 2 turns (was @ 1 1/2)and
all
seemed better.
Boat ran fine for next 5 hours, but did have a wandering idle and has
always
been hard to start from cold.
Now, on last trip, same thing happened again.
Drug it home,put muffs on, fires right up. No problem.
Let it warm up and try to restart. No start.
Check fuel- yep, accel pump squirts it out. Check for 12v at both sides
of
coil. Got that. Pull distributor cap and check rotor and inside of
cap...looks like new. No spark though, verified with timing light.
Check for loose wires, blown fuses, etc...none found.
Now....do you think the 2 events are related?
I would think that if the Thunderbolt went south it would be an all or
nothing event, not a random loss of low speed.
Ideas, men, ideas.

--
"Only the dead have seen the end of war" Plato

5.7 L Thunderbolt troubles
 

"Rural Knight" wrote in message .net...
I know somebody who has one of these beasties and had
a similar problem - turned out it was loose sparkplugs.

No joke.

Thunderbolt ignitions are easy to replace though, so try that.
You might want to just check through the engine though just
to make sure - do some compression checks and stuff. A
cracked head could cause a problem like this.

Later,

Tom
"Steve Arnold" wrote in message
news:Vh%Va.48497$AD3.46058@lakeread04...
I'd replace the ignition pickup unit inside the distributor. I think the
part is only 60 bucks or so. When mine went bad I lost power and ran very
rough at idle. I also thought (and everyone else told me) that it was bad
fuel.


"Kenneth670" wrote in message
...
I would check the coil for failing when hot, the control box for the
ignition
system, and a loose wiring connection in the ignition system.

1994 Mercruiser 5.7 L Thunderbolt (Quadrajunk) SN 0f067387 Alpha 1 Gen
2
w/279 hours...New plugs, wires, rotor and cap @ 269 hours.
Boat would run fine at all speeds most of the time BUT sometimes after
coming off a WOT run engine would not run below 1200 rpm. Stumbles, etc
as
if it was starved for fuel. Makes it interesting trying to dock. Had to
baby
Mercotrol to get it to stay running at that speed. Any speed above that
runs
fine.
First time it happened I suspected bad fuel (boat had set for sometime
with
1/4 tank). Added 6 cans of B12 (50 gal tank) 6 cans dry gas, sprayed
carb
down with carb cleaner (lots of gunk) and changed the Merc fuel filter
water
separator. Opened primary mixture screws to 2 turns (was @ 1 1/2)and
all
seemed better.
Boat ran fine for next 5 hours, but did have a wandering idle and has
always
been hard to start from cold.
Now, on last trip, same thing happened again.
Drug it home,put muffs on, fires right up. No problem.
Let it warm up and try to restart. No start.
Check fuel- yep, accel pump squirts it out. Check for 12v at both sides
of
coil. Got that. Pull distributor cap and check rotor and inside of
cap...looks like new. No spark though, verified with timing light.
Check for loose wires, blown fuses, etc...none found.
Now....do you think the 2 events are related?
I would think that if the Thunderbolt went south it would be an all or
nothing event, not a random loss of low speed.
Ideas, men, ideas.

--
"Only the dead have seen the end of war" Plato





Is the carb a 2, or 4 barrel? If it's a 4 barrel the secondaries can
stick open, or closed, if their dirty, it's real common. You have to
take the flame arrester off the carb, and, with the engine off, push
the throttle to wide open, see if the secondaries move freely. If the
secondaries stick open the idle speed will come up, depending on how
much it's open. If it's open a lot it will be difficult to restart the
engine, too much air. If they stick closed the engine lacks power,
whick isn't your problem.