Question maybe one of you know or know someone that is really knowledgeable

I measured CO on idle.
Front Cylinder 4.1
Rear cylinder 1.6

Rear cylinder backfires on deceleration too.

Setup just new (70miles)
Big Bore 108 10.5:1
Mikuni HSR 45
Dyna 3000 28b
Hypercharger Pro R
Nemesis S&S Super E manifold
Jardine Exhausts

The heads and manifold have been slightly hand ported without flow bench.

What other causes than flow can there be.
Do any of you have suggestions where to start looking.

Which intake should I open up more if it is flow front or back?

What RPM did you test at? Di you go through a range of RPM's and measure at a few different points? Also what did you use to measure the CO?

3.5 to 4.0 is ideal for Road Stars, but you will find that this moves dramatically as you progress through different RPM ranges, and some areas just can't be ideal no matter what you do. You need a read on idle (Pilot Circuit), mid way through the throttle range (needle circuit) and perhaps somewhat higher, although the WOT test will be your best barometer on the main.

Gram

I measured only at idle as the engine is newly rebuild with big bore pistons.

The rear cylinder backfires on decelleration.
The front doesn't.

Please advice what can be wrong.

John

Do a real good leak test on your manifold, use water in a squirt bottle (set spray to be a stream). Spray the water all around the mating surface where the manifold meets the head. If you have a vacuum nipple installed on the manifold, do the same there (or stick a rubber cap on it to eliminate it all together).

Your bike should be running while you are checking, if you find a leak you should notice a change in your idle when the leaking area is wetted down. You can also use wd40, but you may have some cleanup work to do afterwards.

Also, check the carb to manifold seating to be sure its good.

Start with this stuff, they are the most common causes of rear lean cylinders. Nemesis manifolds can be a little tricky to get on and sealed real well, since they don't flex like the stock ones do. If you find a leak, take your manifold off and check your o-rings real well. If they are good, reinstall using a cross tightening sequence on all four bolts.

Gram

You need to be sure you are getting a true reading from EACH cylinder. The AIS ports will be the best place to get an exhaust gas sample from. The outlet end of exhaust pipes may not be accurate, especially if you have any type of crossover in your exhaust system.

I used silicone engine sealer to mount the manifold.

I have no AIS port available anymore.