4.3 TB carb. Lossing fire

[philbullet]

Hello all. It's been a while sence I've been on here with a busy life but boating and fishing goes on.
I also have gotten really busy with a side hobby make Boat covers and motor cover,( upholstery work) it's been crazy.
anyway!
I have been having a lil trouble with my 21' chris craft with the 4.3 TB carb.
seems after running for a while I'll loose fire to the plugs but the coil is still putting out fire so I'm thinking it the distributor module.
Not sure if I can change just the module or I'll have to change the whole Distributor.
any thought on this?
Also it seems to crank right up after cooling off and even after sitting for months so its acting up after a good long warm up.
thanks

 

[alldodge]

having a lil trouble with my 21' chris craft with the 4.3 TB carb.
seems after running for a while I'll loose fire to the plugs but the coil is still putting out fire so I'm thinking it the distributor module.

Don't understand what a TB carb is?
List the boat is a 1981 model so should have points distributor. If the coil is producing fire (spark) then its not the module or the points. It would be the distributor cap, rotor, wires or plugs

 

[philbullet]

Nah ,I changed to a 1993 v6. Thunder bolt.
I might be wrong about the TB but it has the counter balance shaft and a 4.3 vortex

 

[alldodge]

With a TB (Thunderbolt) ignition and if you have spark at the coil, then its not the distributor pickup module, its one of the other items listed above.

This is TB injection

 

[Walt T]

Sounds like vapor lock to me. Go to pure-gas.org and find a station nearest you with non ethanol fuel in your state. Use that gas only from now on. I bet the hot no start goes away. It's a cheap and easy fix that's worth a try. Non ethanol fuel is usually more expensive.

 

[philbullet]

Oh well ,its not a TB then. Lol
4 barrel carb.
I really cant get get the numbers off motor because I'm away from at work.
And no it not the fuel ,I loose fire to the plugs after a while of running for a while.

 

[alldodge]

That's different
Your loosing spark at the plugs. Start by disconnecting tachometer wire from coil

When you loose spark run through this troubleshooting chart

 

[philbullet]

Ok thanks, I snap shot the diagram and next time I'm home I'll try all that.

 

[achris]

1993 was before any injection so it's either a 2bbl or 4bbl carb. That year would also make it Thunderbolt IV... If you have spark from the coil, forget that chart, it's only for diagnosing a 'no spark' condition...

Spark from the coil but not at the spark plugs can only be the leads, the cap, or the rotor... If they are all still original, I'd start by replacing them. The cap and rotor will have to be genuine, the leads can be any good quality aftermarket 8mm silicone...

Chris....

 

[philbullet]

1993 was before any injection so it's either a 2bbl or 4bbl carb. That year would also make it Thunderbolt IV... If you have spark from the coil, forget that chart, it's only for diagnosing a 'no spark' condition...

Spark from the coil but not at the spark plugs can only be the leads, the cap, or the rotor... If they are all still original, I'd start by replacing them. The cap and rotor will have to be genuine, the leads can be any good quality aftermarket 8mm silicone...

Chris....

No the cap and rotor have been changed before. Not original.
this was a total rebuild a few years ago.
and yes a Thunder bolt 4.
and yes,after running for a while the coil will still spark but not at plugs.
eveything under distributor cap look good and clean that's why I was thinking the module but I dont think just that can be changed.
may have to change the whole distributor?

 

[alldodge]

may have to change the whole distributor?

No

The components in the distributor control the spark. The mechanical parts of the distributor have no effect so long as the internal are not damaged.

Need to find out if you have a fuel issue or a spark issue. Right now from your comments. it is uncertain which is the issue

 

[philbullet]

No fuel isues, I already said It looses fire after running for a while. It's been checked and proved many times.
but thanks, we'll get it figured out when able to.

 

[achris]

If you are still getting spark from the coil it CAN NOT be the sensor or the module... It can ONLY be the leads, cap or rotor... NOTHING ELSE!

 

[QBhoy]

Mmm not sure ACChris. Not often I would disagree with yourself, but I would be thinking it’s the module (I call it the ignition sensor)
if there is power and spark at the coil and diz and leads are good, then if the module or wire from ignition are faulty....then it wouldn’t spark at plugs surely.

 

[achris]

Mmm not sure ACChris. Not often I would disagree with yourself, but I would be thinking it’s the module (I call it the ignition sensor)
if there is power and spark at the coil and diz and leads are good, then if the module or wire from ignition are faulty....then it wouldn’t spark at plugs surely.

He's getting spark at the coil. That eliminates the sensor in the distributor and the ignition module/amplifier. The ONLY things that can stop a spark existent at the coil, getting to the spark plugs are leads, cap or rotor...

Chris....

 

[QBhoy]

Chris I’ll take your word on this, but my thinking doesn’t agree totally. He could have power at the coil and nothing coming out the diz if the module was faulty.
I think on a working engine, if you disconnect the ignition feed from ignition to module, you might find that there will be power at the coil but no spark put the diz.

 

[achris]

Chris I’ll take your word on this, but my thinking doesn’t agree totally. He could have power at the coil and nothing coming out the diz if the module was faulty.
I think on a working engine, if you disconnect the ignition feed from ignition to module, you might find that there will be power at the coil but no spark put the diz.

:facepalm:

Re-read the original post (actually, I'll quote it and underline the important part that everybody seems to have missed)....

...seems after running for a while I'll loose fire to the plugs but the coil is still putting out fire ...

So, as I have already stated, three times, if he has spark at the coil and not at the plugs, it CAN NOT be the module .... It can ONLY be the leads, cap or rotor....

Chris.......

 

[Scott Danforth]

I agree with Chris with one additional potential. if there is spark at the coil. only the cap/rotor/wires are between the coil tower and the plugs. so somewhere there is a potential breakdown in one of those items.

The other potential issue is worn distributor bushings could have the shaft slopping around enough to be unable for the gap to jump to the cap. however you would see carbon tracing inside the cap and the shaft would be wobbly when you grab it.

if there is spark at the coil, then the dizzy pickup / amplifier is doing its job triggering the charging/discharging of the coil. so it CAN NOT be the module

 

[achris]

...The other potential issue is worn distributor bushings could have the shaft slopping around enough to be unable for the gap to jump to the cap. however you would see carbon tracing inside the cap and the shaft would be wobbly when you grab it....

If that was the case, it wouldn't run for 20 minutes and stop...

I believe the problem is a cracked cap or rotor, and the crack opens up (when heated) and shorts the spark to ground.... If he replaces the cap and rotor, I believe the problem will be resolved.

Chris.........

 

[Scott Danforth]

it may if the oil viscosity was thick enough to help hold the shaft straight-ish.

however a cracked rotor or cap would be the likely culprit

either way, the cap should be pulled and the problem will be evident by looking and grabbing the shaft and wiggling.