jetting?? warmed up 2.7L high end missfire

[nabilious]

So before it blew up on me, the engine was perfectly dialed. Idle jets are 52's and mains are 140. After a complete rebuild its up and running with a couple exceptions. The only thing I changed was add a Mod-S cam in place of the regular S cam. the car has 36/35mm ports, S dizzy, ect. Now as I'm breaking it in, I'm noticing a couple of things that I'm having trouble eradicating. If I get after it in 2nd gear, 3rd, or any others, after the tack swings past 5.5k there is a slight miss as it winds out. The jetting was spot on before the rebuild, with the exception of the Mod-S cam. Could that mean its a little lean on top? baaaaaataaaaaataaaaaaaataaaataa. is what is sounds like, the 'T's' are the light miss. It use to be really crisp so maybe the little extra cam is enough to cause it to be lean? I have the timing set at 34 degrees @ 6k rpms and I've adjusted the valves ect.

One last issue, while trying to balance the carbs left to right, I cant seem to get rid of this wobbly engine note from 2.5k to 3.1k ...Whomp whomp whomp kinda sounding loopsidedness....if that makes sense.
Any pointers would be appreciated, Its so close to being right and my rebuild (my first went really well!) I'll include pics when I download them later.
Cheers,
Nabil
__________________

[Steve@Rennsport]

Nabil,

Need more information,.....

Air corrector jets?
Emulsion tubes?
Main venturies?
Tall manifolds?
Compression ratio?

JMHO, but 140 MJ's are too small for a 2.7.

[nabilious]

Thanks Steve, I tend to agree, It worked before but it used to be real 'crisp'. couldn't have gone any leaner I'm sure. With the new Mod-S cam it probably only made the leanness more acute.

The emulsion tubes are what ever they would be with S cams (what was in there before)
the Air correction jet is 170
Idle jets 52
Main jets 140
chocks are 34mm
and yes, it has the tall manifolds. (does that effect jetting much?)
thanks,
Nabil

[nabilious]

It also has the tall venturis (stick up in the air horns)
and the Comp Ratio is 8.6

[Steve@Rennsport]

Originally Posted by nabilious

Thanks Steve, I tend to agree, It worked before but it used to be real 'crisp'. couldn't have gone any leaner I'm sure. With the new Mod-S cam it probably only made the leanness more acute.

The emulsion tubes are what ever they would be with S cams (what was in there before)
the Air correction jet is 170
Idle jets 52
Main jets 140
chocks are 34mm
and yes, it has the tall manifolds. (does that effect jetting much?)
thanks,
Nabil

Thank you; that REALLY helps. One cannot troubleshoot anything without all pertinent data.

You did make sure that your idle jets and passages are not blocked????? (VERY common)

Emulsion tubes are critical as they are generally matched to the camshaft's intake vacuum characteristics. S cams use F3's but you need to know exactly what you have without guesswork. These sit under the air correctors and can be fished out using a round wooden toothpick.

Assuming there are no vacuum leaks anywhere, I'd be using 145's to 150's (MJ). I would also be using 36mm main venturies since you have the tall aux ones.

I'm also assuming that every component in your ignition system is in perfect working order.

[nabilious]

Thanks So much Steve.
Very helpful. I figured they were a size too small on the mains. I didn't realize that I could go ot 36's one the chocks due to the tall aux. vents. Also very good to know. I'll continue to dial this thang in. Half of the fun has been the 'testing'....:-))