Pods are on my 73 750 engine. Carbs were supposedly cleaned and calibrated when I bought it. It runs rough, won't idle below 1600, and when I goose the throttle to accelerate it just wants to die at 4000 rpm.
First, tell us that you have done the entire tune-up checklist and the air filter is new or so clean that it behaves as new. Then balance the carbs. If troubles still persist, then address carb mixtures.
1 - I have been told that the vacuum which exists with the airbox is necessary to make the carbs work properly. Pods just can't achieve the vacuum. Yet I constantly see guys running 4 into 1 exhaust, pods, etc. and they keep saying everything works fine. Other guys seem to be readjusting their carbs constantly. So, is it possible to say once and for all that the airbox should not be replaced?
Of course not. However, if you expect the factory settings for the carbs to work as delivered from Honda, then yes, the stock airbox, filter, and exhaust are the proper combination.
A filter that changes restrictive properties, effects the carb throat pressures relative to the surrounding barometric pressure. The differential pressure is what pushes or draws the fuel from the metering devices in the carburettors. More restriction draws more fuel through the jets for any given RPM or throttle setting. Restriction varies with filter material, amount of foreign debris trapped by the filter, and the turbulence signature relative to the velocity of air moving through it. The latter can be a non-linear relationship with velocity.
2 - Currently have 110s on the carbs, was told to go to 120s. But I just got thru a long discussion with a guy who does mostly old British bikes. He went into a long diatribe about gas not being the same as it was 30 years, what with all the detergents, etc, etc. He said he recently had a problem with an old bike where he ended up going down to 95s. His rational was sound, but I am not 100% convinced. Is there anyone out there running main jets less than 100s?
Unless you are using fuel blended with alcohol, it has the same energy content it always did. Detergents are added to keep the fuel injector nozzles clean, as well as the entire fuel system. The octane rating only changes the flame front travel speed.
For the home mechanic/motorcycle modifier who does not have access to a Dynomometer and exhaust sniffing equipment, learning to read the spark plug deposits is essential toward rational and straightforward adjustments to the carburetor's multiple metering systems. A track and a stopwatch are also helpful for peak tuning. Some knowledge about how your carbs work and what metering system is dominant at a given throttle setting is also helpful in minimizing the carb adjustment flail after changing your bike's looks with intake and exhaust changes from stock.
I don't believe in all the "rules of thumb" for carb jetting. Component characteristics vary among manufacturers. The way to tell what your bike in its current configuration needs, is to read the spark plugs and note the conditions and throttle settings under which the plugs were operated. Then address that aspect of the carb that governs those conditions and adjust accordingly.
The old brit bikes don't acheive the high RPMs the Honda fours do. The main jet is set for wide open throttle and lots of air velocity through the carbs. Velocities the old brit bikes can acheive only very breifly before shedding important internal bits. Your midrange issues will likely be addressed with throttle valve (Needle jet) changes, and your idle issues with either air bleed screw or slow jet changes (or both).
Learn to read plugs here:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.htmlHere is a chart as to what to adjust in the carb. Good luck!
