WOT less than 3k

[tonyiiiafl]

I had that issue, and it turned out be a soft camshaft, lobes were worn.

[waybomb]

Hook up a vacuum gage to manifold vacuum.
Tell me what the needle is doing at idle, and the level of vacuum at idle.

[Capn Crunch]

Qr Bbpost Hook up a vacuum gage to manifold vacuum.
Tell me what the needle is doing at idle, and the level of vacuum at idle.

I can't until Tuesday, Mechanic has Quadra-Jet pulled, in a tank soaking and destined for a rebuild kit Monday... reinstalling Tuesday.

[Capn Crunch]

Qr Bbpost I had that issue, and it turned out be a soft camshaft, lobes were worn.

Man I hope that's not contagious...

[Capn Crunch]

Update 2018-09-19:

Mechanic brought his mentor... proceeded with re-checking timing, this time @ idle and @ 3k to prove advance working - check!
Mentor then pulled each plug wire one at a time while running and found #4 not getting spark. We never found a break in the wire but after disconnecting and reconnecting wires and pulling left bank off the wire holder mounted on block the motor sounded like a race engine compared to previously. We then sea trialed her - hit 4100 right away, he trimmed motor out to see 4500rpm... and hit 29 mph!!! Woot Woot!!

Thanks all for your suggestions... extremely happy that it turned out to be something minor... and got new electronic advance, carb rebuild and fresh tune-up gratis to boot!!

Mark

[AaHubb]

Hey that's great news Mark. See ya on the river.
..Aaron

[Capn Crunch]

Well now I guess my ignorance is going to shine once again... went to buy new plug wires this morning only to be told there's 12 or more different versions of wires... person then made her best guess and pulled out wires that were labeled exclusively for EFI systems.
So my question is just how much different would wires be across all the different versions of a Mercruiser Thunderbolt 5.7L carbed engine?
Ok, 2 questions... where do you all go online to get parts like this?

Thanks again to all for keeping me on the straight and narrow...


Mark

[bud37]

Heh Mark....try Mercury website and there is a parts drop down where you can choose your engine type and serial number range etc and then pick thru what parts you want and get the numbers ....that is what I do, at least that way you will be armed with some info when you go to get the parts.

[Capn Crunch]

Qr Bbpost Heh Mark....try Mercury website and there is a parts drop down where you can choose your engine type and serial number range etc and then pick thru what parts you want and get the numbers ....that is what I do, at least that way you will be armed with some info when you go to get the parts.

Thanks bud37... after arming yourself do you shop online or locally for tune-up parts? If online, where do you normally shop?

[tomschauer]

Mark, as Bud says, take your year and serial number to the mercury parts look up.
Wires can have different ends for standard ignition / newer electronic ignition, also the plug boots may be straight or 90 degrees and the wire sets will be different lengths for different applications.

I usually shop online, as no one near me stocks the marine part numbers even after x ref.