2. I set the floats at 14.5MM. I actually set them 0.1-0.2MM higher (allow a little more fuel) b/c I did not want the bowls to empty with the larger jets. Supposedly, the 1977 carbs were set at 14.5MM and the 78 were set at 12.5MM (even though the Honda manual I have states 14.5MM for both years). I have a 77 engine with 78 carbs and since they came close to 14.5MM out of the box (off of ebay), I set them to 14.5MM. I have not clear tubed and will after reading the suggestions but I am definitely not overflowing the bowls (or the overflow tubes) and don't think I need fuel at WOT because the bike pulls and pulls. I think the clear tube suggests fuel be ~1-2MM below the bowl and carb body connection point?
With intake and exhaust mods, the stock setting are mostly meaningless for your application.
Sock filters will negate any possible benefit of V stacks even if they are properly aerodynamic. Because the sock will introduce turbulence at the stack lip entrance, which is exactly what the lip and stack is trying to prevent.
Mostly what you are trying to compensate for is the massive increase in throat pressure shortening the intake duct instigates. Each jet flows relative to the pressure differential across it. It's throat pressure vs the atmospheric pressure supplied at the bowl vents. Shortening the duct brings the carb jet outlets closer to the atmospheric source, reducing the fuel jets volumetric contribution. Since there is no mention of changing the engine's volumetric efficiency, cc changes, or valve timing, the engine will suck nearly the same volume of air it did before duct changes. The result: nearly the same O2 supply, but less fuel to pair with it.
The stock settings in every throttle position will be wrong, and almost certainly lean.
Raising fuel level in the carb bowls, is probably the first step in adjustment compensation. The closer the fuel is to the jet exit point (carb throat) the less energy or force is required to lift it. 14.5mm is fine for the stock bike, to enrich the entire carb operational range, go higher in bowl fuel level. The limit, of course is the overflow stand pipe inside the carb bowl. For initial test and try method (vs dyno), go to 12.5mm float height, or as near the seam as you can with the clear tube measurement.
3. The carbs changed for the 550 in 77 and changed from a fuel air screw to fuel metering. On the 1978 carbs, inward is to lean outward is to richen. My tests of inward to lean played out based on how the bike responded when I turned them to only 1/2 out from fully closed (choke helped smooth out the throttle response, popping on decel, etc.).
When slides are opened, the carb throat is exposed to whatever atmospheric pressure is present at the inlet. Since it is closer to atmospheric than when slide are near closed, the pressure rises, and reduces fuel flow from ALL the metering devices, yet more air is now available to the engine cylinder. In short, the mixture goes too lean to support powerful combustion.
The carbs really should have accelerator pumps, like those found on the 750 and 650 machines with PD carbs, to allow very lean idle mixtures. It doesn't, so the idle must be set over rich as a compromise, and get descent throttle response. The idle mixture should be set so that the throttle can be snapped to the 1/2 travel position, while the bike is under load at idle. I do this while rolling in top gear (5th). The engine should pick up reliably to demand without wheeze or stumble. Won't be quick due to gearing and lack of torque. But, the provided mixture supports reliable combustion. If you can go more than half throttle, then you risk a too rich idle mixture fouling spark plug electrode insulators and shunting spark energy away from the spark gap.
This adjustment I do last in the carb rejet process, as the leakage from the main and throttle valve paths do contribute some to the idle mixtures.
4. Needle setting is stock. Messing with the needle on the 78's is a pain. Only messing with those after main and pilots are as close as possible (and may not even touch them until a dyno tells me too). Raising the notch drops the needle and makes it more lean, not rich, right?
Raising the needle allows more flow from the throttle valve jet orifice. Hard to believe the stock setting is an anywhere near proper for an altered inlet duct.
I'd likely start with raising it one notch, (lower clip position from top of needle). I don't care if it is a pain. It controls mixtures from 1/8 to 3/4 throttle positions. It is totally dominant for most all street driving. It is the second fine tune adjustment in the process of carb rejetting. First being the main.
5. As far as main jet, I read you can tune by taking it to the drag strip and keep upping the main until HP falls off at WOT. I upped to 122 and the bike pulled better than ever. So I think I am really close with the 122. The bike also doesn't gurgle rich so its not way off.
Yes, the drag strip is a good place to determine main jet (Dyno better). This is where you can set the max fuel flow the carb will ever deliver and the main jet is the most dominant provider. Fuel requirements vary with the engine load. It needs less fuel to operate at 9200 rpm with no load than it does with full load. Drag race with pilot aboard and hold throttle wide open while shifting through gears. Max engine load will occur at about 90 MPH when air resistance requires the most horsepower to overcome. Hold for a few seconds, hit kill switch and pull in the clutch. When stopped, pull out the spark plugs and read the deposits of a mixture indication when the engine was at full power. If white, up the jet size. If black deposits on the spark plug electrode insulator, then reduce the main jet size. Stop adjusting when you get light tan on the insulator. And move on to slide needle position adjustment for the same color.
You can use spark plugs for testing that have white insulator deposits (clean). Sooted and/ or any prior operation deposits will require cleaning or renewal, to perform rejet mixture analysis.
Any idea on why the idle dies out after running for a bit? Any other reasons than fouled plugs or heat?
Yes. Too lean mixtures starve the engine progressively. The RPM will gradually increase until the engine simply doesn't have enough fuel to support combustion.
Too rich mixtures will generally slow down gradually, until again there is too much fuel for available oxygen to ignite.
The engine cylinders do not scavenge 100% during run operation, particularly at idle due to cam/valve timing optimized for higher RPMs. Residues left behind in cylinder contribute to idle efficiency. Too lean delivery uses up any residues. Too rich creates build up. This latter is why so many "customized" harley riders must continually blip their throttle to keep the engine running. (Or, they just crave attention using 2 year old behavior.)
Good luck on your fun adventure.
Cheers,
