Topic: Jetting size question

[pjlogue]

I am trying to get my jetting right.  I rebuilt my '76 750K last year and I cleaned the carbs well.  Ultra sonic cleaned bodies and emulsifier tubes and made sure carb internal passages were clean.  I put in new primary and secondary Klein jets 105/40 and fuel inlet valves and seats.  Float heights were adjusted by float height then clear tube with carbs level, front to back and side to side.  I am running really rich at idle and 55-60 mph.  Plugs (ceramic, tip and center electrode)  I have new rubber carb boots and they are leak proof.

What is the 40 stand for on the slow jet?  Is it a diameter or flow rate?  I am using ethanol free 91 octane and use 10 milliliters of Acetone to 5 gal of gas.  The Acetone acts as a surfactant to the gas and allows smaller mist droplets.  I suspect that it is causing the engine to run rich.  I have #38 Klein slow jets but before I install them I am wondering if I'm missing something.  Any ideas as to why stock carbs with stock Klein brass and new Honda air filter and stock exhaust would run rich?  (I'm at ~400 ft. above sea level so it isn't high altitude induced richness)

Thanks for any ideas you folks might have.

-P.

[BomberMann650]

Never heard of adding acetone to gas.

What makes you think its over rich?  Plug chops?  Poor Fuel mileage?

[jonda500]

The jet numbers indicate the hole diameter in hundredths of a millimetre, e.g. #40 = .4mm, #105 = 1.05mm
John

[pjlogue]

The jet numbers indicate the hole diameter in hundredths of a millimetre, e.g. #40 = .4mm, #105 = 1.05mm
John

Ah, thanks!

-P.

[pjlogue]

Never heard of adding acetone to gas.

What makes you think its over rich?  Plug chops?  Poor Fuel mileage?

Mileage is low and with a plug chop the plugs are black as coal at idle and sustained 55 mph riding.

The Acetone helps the fuel atomize better.  It acts as a surfactant to reduce the surface tension of the gas.  I have used it in my cars for the past 15 years.  For a feedback injection system it increases the gas mileage ~5-15%.  Since it allows better atomization of the fuel droplets you get a more complete burn of the fuel.  This gives better mileage, cleaner combustion chambers and fuel system.  The Acetone works best in non-ethanol gas but does work in 10% ethanol gas to a lesser degree.  Feedback carburation is where you see the mileage increase because the pulse width of the injection time is adjusted by the PCM from the O2 sensor ratio in the exhaust.  With a normal carb you have to adjust the jets.  That's what I'm trying to do. 

-P.

[jonda500]

I actually have the same unanswerable question! Why did my all stock set up cb500 with new boots, rebuilt carbs & genuine keihin jets run rich at 0 to 1/8 throttle until I changed the slow jets from #40 to #35? (even without acetone in the fuel!) All I know is the bike is perfectly rideable ever since - around town it performs flawlessly but it hesitates slightly if I close and re-open the throttle at highway speeds (60+) - I can live with that, with the 'correct' size jets in it it really wasn't usable except for maybe on a race track where you could live without a working slow speed circuit.
If I were you, I'd go ahead and try the #38's!
John