Idle issue 4.3 mercruiser LX

[Scott06]

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

the carter AFB/ Weber/ Edlebrock carbs have a weighted air valve on the secondary's. the throttle plates are below this and should be fully shut. The air valve essential operates as a vacuum secondary to open more as the engine demands more airflow regardless of where the secondary throttle plate is. This allows the same carb to be used on multiple engine displacements

If you see fuel seeping below the air valve at idle it is likely coming off the boosters or out of the float bowls. Usually this would cause a rich idle and staff out vs increasing the idle rpm.

You checked the throttle cable is adjusted so the carb can fully return onto the idle speed screw ?

 

[alldodge]

There is a lot of "IF's" going on in the thread and need to no what is and is not happening

IF the carb is flooding it needs rebuilt, if not then it probably doesn't

Motor lowest RPM is at 2200, cable has been removed from the carb and even when pushing the carb throttle plates closed it still will not idle down.
IF this is the case something is bent/warped in the crab throttle plates or control. Carb needs to come off to find out what the issue is. The pic of the carb from on top does not clearly show they are fully closed

IF the timing is stuck somehow full advance then this would be a problem but don't see how this will make it idle this high by it self. Check timing to see what shows and try to bring it back down to 8* BTDC

 

[garthwjensen]

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

I have not just because I thought RPM was too high to check could i do any harm just by manually adjusting distributor without a timing light?
When I move throttle forward RPM goes up but then stays high for a while I have shut off the engine while at 2200 rpm several time as i have tried a couple of solutions.

 

[garthwjensen]

the carter AFB/ Weber/ Edlebrock carbs have a weighted air valve on the secondary's. the throttle plates are below this and should be fully shut. The air valve essential operates as a vacuum secondary to open more as the engine demands more airflow regardless of where the secondary throttle plate is. This allows the same carb to be used on multiple engine displacements

If you see fuel seeping below the air valve at idle it is likely coming off the boosters or out of the float bowls. Usually this would cause a rich idle and staff out vs increasing the idle rpm.

You checked the throttle cable is adjusted so the carb can fully return onto the idle speed screw ?

Yes I checked that

 

[garthwjensen]

I have not just because I thought RPM was too high to check could i do any harm just by manually adjusting distributor without a timing light?
When I move throttle forward RPM goes up but then stays high for a while I have shut off the engine while at 2200 rpm several time as i have tried a couple of solutions.

Also I should get an inductive type timing light the one i have is ancient and you connect it to plug

 

[garthwjensen]

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

I know the outside belts have no effect on timing but because the motor was still running could the added friction caused something to happen to the actual timing belt or chain

 

[alldodge]

Also I should get an inductive type timing light the one i have is ancient and you connect it to plug

Inductive pickup is the way to go, but don't need the advance type

 

[Scott06]

I know the outside belts have no effect on timing but because the motor was still running could the added friction caused something to happen to the actual timing belt or chain

no

 

[garthwjensen]

Yes I checked that

 

[garthwjensen]

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 I bought this distributor assembly 805185A27 of it was the part with distributor would that be the right one

 

[alldodge]

If I bought this distributor assembly 805185A27 of it was the part with distributor would that be the right one

Don't do that, the motor runs so its not the distributor

 

[garthwjensen]

Must be carb issue time to rebuild? Which kit should I get?

 

[nola mike]

If you see fuel seeping below the air valve at idle it is likely coming off the boosters or out of the float bowls. Usually this would cause a rich idle and staff out vs increasing the idle rpm.

Yup, but if his secondaries aren't closing completely then now you have extra air + extra fuel. Also, none of this has anything to do with the alternator. It's a 30 year old boat. My boat has been acting perfectly for exactly 10 minutes out of the last 5 years.

 

[garthwjensen]

Had motor rebuilt like 5 years ago and has been trouble free till now

 

[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

post 10

 

[garthwjensen]

Maybe the carb just acted up at same time as alternator issue just by coincidence!

 

[Scott06]

Yup My boat has been acting perfectly for exactly 10 minutes out of the last 5 years.

you should find a new mechanic , your current one must drink too much beer on the job …

 

[nola mike]

you should find a new mechanic , your current one must drink too much beer on the job …

I should have kept my mouth shut. Running perfectly, then my windshield hinge broke, then my oil pressure gauge started acting up, pulled the cannon plug and f'd it up, so now no power to the helm. My current mechanic stays plenty busy, but what do you mean by "too much"? He thinks he drinks a perfect amount.

 

[garthwjensen]

Is there a less expensive rebuild kit like at Napa for 8M0120196 merc part? Please help