Carb Jetting and tuning Questions

[Special K]

I rebuilt a BBC last year for my 18' Tahiti. Had it out at the lake a few times before the end of the season, but it wouldn't seem to run right. Under hard acceleration, it would sound like the engine was 'popping'/backfiring out the exhaust...leaning out, possibly?
Here's my setup:
-454, 0.060 over
-10.0 CR
-Victor Jr.
-Holley 850 DP
-HEI Ignition
-Solid Cam, 108', 0.560/0.560 lift, 250'/250' dur @ 0.050"
-OT headers
The carb came w/ #78 jets in it. Should I change them out for larger? Any size suggestions?
Also, how many degrees advance should I be looking for?
Thanks for any help...
-K-

[HalletDave]

Special K,
I am no expert on this stuff, but, 78 sounds a little on the lean side to me.
It may take some time for someone with more knowledge than I have to give you advise, so...
You may want to send a PM to HotCrusader, Dennis Moore or Infomaniac just for starters.
There are many people on the forum that can give you more detailed info for your set up than I can.
Good luck.

[Hotcrusader76]

What's your fuel pressure at?
What's your initial and total timing at?
What's the condition of your fuel line and or complete fuel system? IE have you replaced your fuel filter, how long ago did the carburetor get a refresh, type of fuel pump...etc etc....
Carburetor.....float level wrong? causes? faulty float, stuck needle/seat, something lodged inside your holley jet...sometimes a piece of silicon/teflon from shade-tree fixes to the fuel line, working it's way up to the carburetor.
Sometimes a pop or bucking bronco kicks out the pipes are timing event related along with fuel pressure concerns. Otherwise consider working your way from the bottom up to the carburetor...leaving the carburetor as the last thing you check...
Answer the above questions and I'm sure many of us on the boards here could find the "diagnose your cancer over the phone":D

[fourspeednup]

Hotcrusader is for sure the expert here but since this is ***boat, I'll put in my $.02;)
78's both primary/secondary?
I've always jetted mine fatter on the secondary side
78's primary
85's secondary
Give's decent cruise and when you get into it flat hauls azz:cool:

[Hotcrusader76]

The jetting concerns aren't to critical at this point. He very well could have something wrong down stream and adding more jet could just worsen the equation right now.
But I do agree, the jetting out back needs to be a little thicker with a venturi that size.

[fourspeednup]

Originally posted by Hotcrusader76
The jetting concerns aren't to critical at this point. He very well could have something wrong down stream and adding more jet could just worsen the equation right now.
But I do agree, the jetting out back needs to be a little thicker with a venturi that size.
Aha! A problem with the fuel delivery system would be UP stream!;)
I see what your saying... fatter jetting might compensate for another problem:cool:

[Moneypitt]

Popping in the exhaust means it didn't pop in the cylinder. Usually an ignition problem.......Moneypitt

[Special K]

Originally posted by Hotcrusader76
What's your fuel pressure at?
What's your initial and total timing at?
What's the condition of your fuel line and or complete fuel system? IE have you replaced your fuel filter, how long ago did the carburetor get a refresh, type of fuel pump...etc etc....
Carburetor.....float level wrong? causes? faulty float, stuck needle/seat, something lodged inside your holley jet...sometimes a piece of silicon/teflon from shade-tree fixes to the fuel line, working it's way up to the carburetor.
Sometimes a pop or bucking bronco kicks out the pipes are timing event related along with fuel pressure concerns. Otherwise consider working your way from the bottom up to the carburetor...leaving the carburetor as the last thing you check...
Answer the above questions and I'm sure many of us on the boards here could find the "diagnose your cancer over the phone":D
Hotcrusader:
Sorry, I don't know what my fuel pressure is at; I've always been driving the boat. I'm using a Holley mechanical fuel pump; It looks fairly new. Carb is brand new.
Timing is initially 8-10' advanced, with a total advance of 30-34'.
Your comment about something lodged in the jet got me thinking. The gas tanks had a lot of flaked off cork from the fuel sender gaskets in them. Most of it had gotten trapped in the fuel filter, but I'm sure a piece could have easily gotten to the carb. Both tanks are out right now, and I'm fixing that problem.
Does that provide any more insight?
Thanks

[Hotcrusader76]

Yupp:D
Something down stream as predicted:D