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VortecCPI

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Re: Blue Header
Reply #15 - 05/31/19 at 15:24:06

justin_o_guy2 wrote on 05/31/19 at 11:36:00:

If that's true, something is in need of correction. Even the crappiest lawnmower I've had didn't require that kinda pampering. I start it on cooler days with full choke and ride away. I drop the choke to first adjustment after a couple of miles, and then no choke in a couple more. Is the idle set high enough? That's only determinable once it's at full operating temperature.

True but please note I wrote "Properly-jetted". Utility engines such as those found in lawnmowers do not have to meet the same EPA standards as motorcycles nor do they have to compete for MPG numbers.

When I got my brand new 2019 Honda CRF230F it would not run unless it had been warmed up for about 10 minutes. If I shut it off and it sat for more than a few minutes it needed partial choke again. Now with proper jetting it only needs choke and warmup for a few minutes.

In the old days we had systems such as EFE (Early Fuel Evaporation) and CCS (Controlled Combustion System) to help carbs and engines during warmup periods. If an engine comes off choke very fast and does not exhibit a lean condition during warmup it is jetted too rich.

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Re: Blue Header
Reply #16 - 06/01/19 at 03:55:40

[quote author=6E574A4C5D5B7B6871380 link=1559102549/15#15 date=1559341446]justin_o_guy2 wrote on 05/31/19 at 11:36:00:

True but please note I wrote "Properly-jetted". Utility engines such as those found in lawnmowers do not have to meet the same EPA standards as motorcycles nor do they have to compete for MPG numbers.

When I got my brand new 2019 Honda CRF230F it would not run unless it had been warmed up for about 10 minutes. If I shut it off and it sat for more than a few minutes it needed partial choke again. Now with proper jetting it only needs choke and warmup for a few minutes.

In the old days we had systems such as EFE (Early Fuel Evaporation) and CCS (Controlled Combustion System) to help carbs and engines during warmup periods. If an engine comes off choke very fast and does not exhibit a lean condition during warmup it is jetted too rich.

I think there is some "room" for "opinion" about what "proper" jetting. An air/fuel ration of 14.7:1 is good for economy - the ratio for maximum power is around 12.5:1. An engine that is jetted within this range will run pretty smooth - and this spread is why a primitive carb can be made to run well........there is some wiggle room

Some of the new engines are running far leaner than that to help reduce emissions and satisfy the EPA......and if these engines have carbs and chokes - they are engines that are really finicky and require long warmup. In my opinion these engines are legal in the eyes of the EPA - BUT - they are not jetted "properly. I agree with VorteCPI and any engine that needs to sit in the driveway and idle for 5-10 minutes before you can add throttle and ride away is not jetted properly and it needs some larger jets!

There are "lean burn" engines that run fuel/air ratios as high as 65:1 - those do require fuel injection and computers to make them run properly....it would be impossible to get them to run with a carb.
https://en.wikipedia.org/wiki/Lean-burn

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VortecCPI

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Re: Blue Header
Reply #17 - 06/01/19 at 05:41:39

We must also take into consideration other practical aspects. If we are trying to win a dyno war we can jet lean and mean but that will never work for daily duty. In many cases tuners jet rich, especially on the slow/pilot, (and/or needle) to assist in keeping the engine cool during high-load part-throttle conditions. This is especially true for air-cooled dirt bikes in the SW and Baja areas.

Ambient air temperature and humidity also come into play and are even more critical as our engines are air-cooled and head temperatures vary wildly. There is no "right" or "proper" jetting that covers all circumstances. Even the idle mixture screw must be changed from summer to fall/spring. For my CRF230 about 1/2 turn in summer and about 1-1/2 turns in fall/spring.

My wife's 2012 LS650 was so lean it was annoying to ride. Small throttle inputs resulted in little or no response from the engine so you had to use large inputs to manage wind and uphills. Now the carb responds to the smallest of inputs and it is a joy to ride. Adding the extra slide hole was the icing on the cake.

So... Just to be clear... When I write "properly jetted" is simply means what works best for the current situation at the time.

With a carbureted air-cooled engine jetting is nothing but a compromise...

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Re: Blue Header
Reply #18 - 06/01/19 at 22:09:34

Guys, this has provided me with an overload of information. Much of it useful and informative. Thanks again to everyone who contributed. The main thing was, what to make of a bike with less thn 50 miles with a blued header like this? The significant point being that the bike was probably started and allowed to run regularly while sitting on the kickstand to keep it operatinal and to be aware of the consequentise of that. Again, Thanks to everyone.

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