Question about "base" carb mixture and idle adjusting?

[rhillman75]

I rebuilt my 96 Mercarb 2 Barrel on my 96 Mercruiser 4.3 LX Gen + with the Thunderbolt IV ignition this evening due to it being gummed up. I know you have to set the timing in "base" mode by grounding the purple/white wire before turning the motor on to set timing, but do you still need to do the "base" sequnece again in mixture/idle adjustment. I honestly did it both ways in the water and I can't really tell a difference. In the water with the Quicksilver 3000 side commander in forward gear at the "detent" notch it reads about 625 rpm on the shop tach, but it also reads the same in the driveway on the "muffs". I am still playing with it to get as close to 99.9% as possible but without really knowing if it needs "base" mode or not (considering I don't really notice a difference) is it needed. I do have a "slight" clunk in forward and reverse when it engages the drive but I hear that is normal.

 

[franktrav]

Re: Question about "base" carb mixture and idle adjusting?

you must have thunderbolt V....IV does not have a pup. wire to ground for base mode
tV has a idle speed spark control that will adjust the timing in an effort to keep idle speed within specs.....if that wire is not grounded
i would definately set the idle speed in base mode,,,,while its there mite as well adjust idle mixture too...per the manual
like you ...i noticed little difference either way

 

[rhillman75]

Re: Question about "base" carb mixture and idle adjusting?

Well I'd hate to tell you this... but it DOES have a purple/white wire that has a female bullet connector on it just to the left of the carb as you are looking at the motor that is in the factory harness and the manual states that is what it is and the plastic cover states that it is a Thunderbolt IV Ignition.

 

[franktrav]

Re: Question about "base" carb mixture and idle adjusting?

sorry,,,, but there is no "base mode" for a thunderbolt 4 ignition.....only t5
perhaps your cover is marked incorrectly...or just an extra wire in harness
goodluck setting your idle tho

 

[John_S]

Re: Question about "base" carb mixture and idle adjusting?

Probably wrong cover. Switched by prior owner? See your other thread.