Why is it?

[planedick]

3-phase gave me a new set of later model carbs for my E model and the jets are only 110's all the way across, the bike runs a little richer than the old carbs with the 137.5's. The performance is better because the old carbs with the 137.5's were too lean. WTF

[dbeardslee]

The early model carbs drew all their gas from the main tunnel, so the mains fed the pilots and needed to be larger to accommodate the pilots. On the later model carbs the pilots draw directly from the bowl via the open pilot tunnel, so they didn't need the bigger mains.

[planedick]

Then

"So I see", said the blind man.

[3Phase]

Planedick, I'm killing some time up here in Vancouver so here you go! You need some '78/'79 slide needles and, possibly, larger main jets. Try it first with just the needles; clips in the stock #3 position and go from there. With the 110 main jets it should be pretty well set for cruising around town and short bursts of speed.

Besides the separate idle and main fuel circuits, I think a lot of the late-model carbs use slightly smaller main jets than optimum (110 vs 115/120 or larger) along with the smaller slide needles.

With the short, sharp, needles the smaller main jets start supplying fuel a little sooner. The engine runs well, then leans out as the RPMs pick up, the needles max out and the smaller main won't supply any more fuel. The engine can rev to redline in the garage but under load it might be a little anemic at higher speeds.

Ultimately, it depends on how fast you want to go for how long carrying how much weight and how much fuel you're willing to burn. Within reason:

Smaller main jets use less fuel, run the engine hotter and provide less power;
Larger main jets use more fuel, run the engine cooler and provide more power.

Short, sharp slide needles fuel midrange and top end sooner then max out;
Long, blunt slide needles fuel midrange and top end more slowly and take more time to max out.

The float levels can help dial it all in when you're finished jetting -- happy tuning!

[planedick]

Actually...

I'm very happy with the way it runs. It will now do 130 in 5th even with the 750 final. Faster requires shifting to 4th and it will climb some more. Good cold idle at 500, warmed up idle 1100, smooth axcel at any rpm. Very happy.

[3Phase]

I'm very happy with the way it runs.

That's great, me too!

I can't say how fast my bike runs; still out on the road and too many miles left to go before I get home.