The original pipes were 4 into 4, and quite high pressure. This helped Honda meet hydrocarbon emission requirements, as it withholds some gasses to be burned again on the next firing. The goal was for a “lean burn” motor which was all the rage back then. Anyway, the reburned gasses addition meant less fuel was needed from the carbs to idle and get engine pickup from throttle. It also meant that this motor runs hotter than prior carb Style models, as a hotter engine also is better at a complete burn cycle efficiency. (EPA goal). Because of all this an exhaust change to a low back pressure exhaust makes stock carb tuning too lean , resulting in an even hotter running engine, and poor response to throttle twist. Note that these mechanical slide carbs were never expected to perform with a full open throttle whack, as they have no accelerator pump, as the 750’s did in this era. So, the sudden inrush of air with no additional fuel makes the engine wheeze and die instead of pick up and give power. The stock configuration would pick up properly with up to one half throttle twist and as the engine picked up, you could progressively add more throttle.
For these reasons when you put a 4 to 1 on this bike, ALL the fuel metering jets in the carb need to become larger, with the possible exception of the pilots. The main jet needs increasing, and the jet needles need to be raised to get the mixture back close to what the stock configuration of the bike had with original exhaust.
Lastly, the filter box had a cover and curved horn like the F models had, but with an additional plate restrictor to narrow the inlet. This has the effect of raising the vacuum level in the carb throat, and causes more fuel flow through all the fuel metering orifices in the carb. So, when you remove that cover, guess what? With less fuel flow, the carb delivers less fuel, and the engine goes leaner for that change, too. Your rag is just a restrictor to get a deeper vacuum in the carbthroat, which enriches the fuel mix. But, you may think about calibrating your rag to maintain consistent mixture authority in the future, if you aren’t up to doing a proper carb rejet to compensate for the changes you made to the bike. Oh, and that rag will also choke of max air flow to diminish power in the high rpm band of operation, making the bike slower. This motor likes and needs rpm to give any sort of spirited performance. It won’t fall far behind 750s if allowed to rev, as it is a lighter and more nibble bike.
Cheers!
