Idle issue 4.3 mercruiser LX

[garthwjensen]

I have a 4.3 LX thunderbolt IV carburated engine. The first time i took boat out it ran ok. The second time after I had tightened belt for alternator I guess to tight the alternator seized up and smelled rubber burning turned off engine was something broke loose in alternator so belts started spinning the voltage jumped up and then went flat. I got boat started to limp back to dock. I replaced alternator but now rpm on start up is 2200 not safe for engaging gears. I checked linkage and it is OK. checked by disconnecting and engine still high rev. sprayed carb cleaner around carb to check for vacuum leak seems ok. Idle set screw is OK and throttle bottoms out like it should on idle set screw. adjusting set screw little to no effect. Cannot figure out what is causing high idle. (Timing? ) Some other electrical thing that went wonky when alternator spike happened? I just do not know where to go from here engine starts and seems to run smooth just cannot get RPM down to Idle speed. Please help with suggestions

 

[alldodge]

Guessing same motor S/N 0D817803 as mentioned about replacing the ALT and using a solar charger?

Check the butterfly plates in the carb and see if the screws holding them in place are loose. Could be the plate(s) are offset and won't let it close

 

[garthwjensen]

I will check after work. I did notice that the two butterfly valves have a small gap on one side is there not supposed to be any gap at all and yes same person about the overcharge situation.

 

[alldodge]

both sides should be the same and next to no gap. The idle adjustment screw adjust the gap

 

[garthwjensen]

Guessing same motor S/N 0D817803 as mentioned about replacing the ALT and using a solar charger?

Check the butterfly plates in the carb and see if the screws holding them in place are loose. Could be the plate(s) are offset and won't let it close

Thanks for advice I will verify I noticed that there is a gap on the rear side of butterfly valves, You can watch the fuel coming in to the carb at the gap. I hope that is all the problem and easily correctible. I have been scratching my head for last couple of days trying to figure it out.

 

[Scott06]

Thanks for advice I will verify I noticed that there is a gap on the rear side of butterfly valves, You can watch the fuel coming in to the carb at the gap. I hope that is all the problem and easily correctible. I have been scratching my head for last couple of days trying to figure it out.

sounds like the carb bowl is overflowing. That would be the result of a non functional needle and seat/ float or too high of a fuel pressure

 

[garthwjensen]

sounds like the carb bowl is overflowing. That would be the result of a non functional needle and seat/ float or too high of a fuel pressure

The butterflies as I look down into the carb are closing well. I was looking at the ones on the top back of carb that had the gap at first. If it is carb bowl overflowing does that mean a carb rebuild is in order. How do I change fuel pressure?

 

[alldodge]

If it's flooding then rebuild time

No way to adjust pressure

 

[garthwjensen]

Here is a picture of looking down into carb. If I need to rebuild is there a rebuild kit I can purchase? If so please advise which one and again thanks for advice.

 

[alldodge]

That's a weber carb and it will have a number stamped on the side of it. I would contact Mike's carbs and get a kit there. Could order the Merc rebuild using 8M0120196 but Merc just adds cost

 

[stresspoint]

if there was nothing wrong with the carb prior to the alternator having a blow out "" then leaver the carb alone"", a power spike will not affect the carb.

the ignition advance built in / programed into the distributor module may have changed somehow and is advancing the ignition causing high idle when the alternator / VR spiked the system " don't ask me how ' as i am just guessing here , i do know those modules are very delicate little jiggers so a voltage spike could have messed it up. .

 

[garthwjensen]

if there was nothing wrong with the carb prior to the alternator having a blow out "" then leaver the carb alone"", a power spike will not affect the carb.

the ignition advance built in / programed into the distributor module may have changed somehow and is advancing the ignition causing high idle when the alternator / VR spiked the system " don't ask me how ' as i am just guessing here , i do know those modules are very delicate little jiggers so a voltage spike could have messed it up. .

I think that may be what happened is there a part number for the distributor module ?

if there was nothing wrong with the carb prior to the alternator having a blow out "" then leaver the carb alone"", a power spike will not affect the carb.

the ignition advance built in / programed into the distributor module may have changed somehow and is advancing the ignition causing high idle when the alternator / VR spiked the system " don't ask me how ' as i am just guessing here , i do know those modules are very delicate little jiggers so a voltage spike could have messed it up. .

Is this the part we are talking about? see picture

 

[garthwjensen]

if there was nothing wrong with the carb prior to the alternator having a blow out "" then leaver the carb alone"", a power spike will not affect the carb.

the ignition advance built in / programed into the distributor module may have changed somehow and is advancing the ignition causing high idle when the alternator / VR spiked the system " don't ask me how ' as i am just guessing here , i do know those modules are very delicate little jiggers so a voltage spike could have messed it up. .

I think that may be what happened is there a part number for the distributor module ?

 

[nola mike]

I think that may be what happened is there a part number for the distributor module ?

Is this the part we are talking about? see picture

No, that's the sensor. Module is NLA. A voltage spike wouldn't magically reprogram the module, it would fry it. And the idle isn't set by the module. Timing is, which affects idle. You can check timing. But at 2200 rpm you likely have air getting into the engine, either past the butterflies or leaking somewhere.

EDIT: Rereading, are you saying that your secondary butterflies have a gap, AND you have fuel dribbling at idle? If so, that's your problem(s)

 

[garthwjensen]

No, that's the sensor. Module is NLA. A voltage spike wouldn't magically reprogram the module, it would fry it. And the idle isn't set by the module. Timing is, which affects idle. You can check timing. But at 2200 rpm you likely have air getting into the engine, either past the butterflies or leaking somewhere.

EDIT: Rereading, are you saying that your secondary butterflies have a gap, AND you have fuel dribbling at idle? If so, that's your problem(s)

If you look at picture above the gap is on the butterflies up top not the ones on the choke side of carb. What does NLA mean is that the name of the part

 

[stresspoint]

No, that's the sensor. Module is NLA. A voltage spike wouldn't magically reprogram the module, it would fry it. And the idle isn't set by the module. Timing is, which affects idle. You can check timing. But at 2200 rpm you likely have air getting into the engine, either past the butterflies or leaking somewhere.

EDIT: Rereading, are you saying that your secondary butterflies have a gap, AND you have fuel dribbling at idle? If so, that's your problem(s)

a voltage spike would not re set the carb to a different idle , so IMO , and guessing here , it has to be something electrical , distributors don't move themselves either , so the only other way the timing could have only been changed enough to raise the idle is electronically.
something weird is going on here with the OPs motor after a spike so my thought is>
the module adjusts the timing as the engine needs so "my guess" is and a long shot , that instead of frying ,as it normally would , its somehow blown the advance /retard circuit or whatever makes the magic happen in the module instead.

this is just speculation because unless someone has mechanically altered the carb adjustment , adjusted the timing by turning the distributor there is no other way the idle can go to the moon.

thinking ( add scratch head here ) an easy check for the OP would be to hook a timing light up and see where the timing is at ?.possibly mechanically hold the butterflies shut to stop too much air going in however doing that could cause lean burn , not a good thing if timing is off the dial to the advance side, so keep that to a minimum.
if it is hanging @ full advance may be try hooking the jump lead and cranking the dizzy till it hits the timing back to 8 degrees and see if the idle comes down.

 

[garthwjensen]

If you look at picture above the gap is on the butterflies up top not the ones on the choke side of carb. What does NLA mean is that the name of the part

does it mean not listed anymore

 

[garthwjensen]

does it mean not listed anymore

Also could the timing belt have shifted when the alternator seized?

 

[stresspoint]

If you look at picture above the gap is on the butterflies up top not the ones on the choke side of carb. What does NLA mean is that the name of the part

no longer available , belt does not have any affect on timing .

 

[Scott06]

did you verify the timing has indeed moved with a timing light? easy to check and also check if it is advancing with rpms like it should