Finally got up above freezing here for a few days so I took the bike out for a short ride on Saturday. Temperature was in the mid to upper 40's and the bike ran fabulously. In fact, the mild to moderate decel/downshift popping I was used to during the warmer weather was completely gone. What does this say about how I might want to try adjusting things when the weather does warm up? Is it even worth mucking around with things as the bike runs great and pulls hard despite the decel popping even when it's warm out. I understand that cooler air is denser air so there's more oxygen in the cylinders (and possibly more complete combustion). Does this possibly point to a rich(er) condition in the warm weather, leaving some unburned gas which is igniting in my exhaust on decel? I know that for most the condition is the other way around (lean pop) but I'm just trying to understand why the bike does not pop at all when it's cool/cold out.
As always, thanks for any and all feedback,
Charlie
Well I would have to say this kinda looks like a rich condition unburnt fuel in the pipes burning off and causing the popping. So in the cold weather as you stated it leaned it out causing it to run better ie less popping and better running in the cold.
So I would say you are right on in your observation!!!
Thanks Allen. If that's the case, I wonder if turning in my idle mixture screw will make any difference at all. Guess I'll have to try it a quarter turn at a time to see if it has any affect once the popping comes back.
It would not hurt maybe a 1/4 turn in to lean it out on the low end which is where it is because it happens when you let off the gas so the idle circut is the one feeding the fuel!!
I have never heard of unburnt fuel burning off in the exhaust and causing popping. Not saying it aint so. My experience has been that popping on decel was a lean condition with the pilot jets.
http://mysite.verizon.net/vzesx5ly/myroadstar/id31.html
Not an expert so to say but he explains it good..
This part says alot
First, when you close the throttle, you are also closing the throttle plates. This reduces the air and fuel flowing into the motor, and increases the vacuum (lowers the pressure). This results in less air and fuel in the cylinder during the power stroke, which in turn results in a lower pressure in the combustion chamber. Remember I said earlier, that the A/F mix burns faster in proportion to the pressure applied? Well, when we reduce pressure this way, the mix burns slower. This results in two things happening.
1. The lower burning fuel generates less heat, and the cooling effect of the non-burning fuel tends to "quench" the flame front, or slow it down even further. Because the mix is burning much slower, the exhaust valve can open before all the fuel is consumed, and the unburnt fuel is ejected into the exhaust.
2. The engine designers, in order to promote smoother idling and better combustion, retard the spark when the throttle is shut, and this results in the mix being lit later.
So, now we end up with unburnt fuel in the exhaust, and burning fuel being ejected into the exhaust, and bang! Backfire. In addition, Honda has added a device called a "programmed air injection valve" (Pair Valve) that actually injects some fresh air into the exhaust to help this process along – since fully burning the fuel results in cleaner exhaust. So the backfiring is not only a normal part of the engines operation, it's also intentionally amplified by Honda! Of course, normally, that massive bazooka pipe Honda hangs on your bike hides most of the noise, but it's there, even when you can't hear it.
So the bottom line, is: That backfiring is perfectly normal and expected. If you've just got get rid of it, that's up to you. You're entitled to set your motor up the way you want, and your goals are your goals. But don't refer to it as "fixing" the popping. Rather, the correct way to think of it is "de-tuning a bit to get rid of the popping".
I believe that even a lean pop is basically the result of combustion outside of the cylinders. Take a look at this post:
http://www.allthingsmoto.com/forums/f-13/deceleration-popping-explained-10/
I'm just trying to understand why it's not there when it's cold out and whether or not I should do anything about it or just leave everything alone. From all I've read, it's really not an issue either way but if a small adjustment of my pilot screws will help alleviate the issue, then I'm game to give it a try.
interesting reading, both things. My take after reading them both is that the popping might have gotten better in the cold air for just that reason. cooler air.
QuoteThe exhaust gas temperature of a lean engine is substantially higher than one that is running on the rich side ( an EGT probe will show this). Therefore, the high EGT serves to heat the pipe more and the gases themselves become a much better source of re-ignition. By richening things up, you are cooling down the exhaust temp and therefore reducing potential re-ignition sources.
So, since the ambient air is cooler the exhaust itself would be cooler. Again, I am clueless and just trying to understand and learn. :-)
In trimming the mixture on a light aircraft engine, you are trained to "lean it out" (with a mixture control on the dash) until it begins to pop or stumble, then increase the gasoline input until it smooths out.
That's unless you have an EGT (Exhaust Gas Temperature gage) and platinum plugs and valves. If you run the engine at the maximum EGT, you will definitely burn stuff up. With an EGT gage, and if you have platinum plugs and valves so they don't burn up, then you can get better efficiency by leaning it past the maximum exhaust temperature, and cool the engine with excess air instead of excess fuel. The first time you run an engine this way, it make you nervous as a cat in a room full of rocking chairs, because it runs really rough and sounds as if it will croak at any moment. But it works.
So our bike engines have to be cooled with excess fuel -- we have no choice. When you run it leaner, it may be more efficient, but you may be pushing the rough running regime.
All I know is that both my bikes came to me with aftermarket pipes and both had midrange performance issues, and both popped on deceleration. I went through the same carb exercise on both, as detailed by Greg on the web site, and simultaneously switched to K&N filters. Both dropped in gas mileage a few mpg -- from 52-53 down to 42-50 around Austin. They both pull strong through the entire rpm range. It is not necessary to wind them up to 8 or 9 grand to get them to move on out. To me, this is a reasonable trade. I don't ride at 80-90 mph, however. Except on rare occasions, such as racing a thunderstorm to get to shelter, I obey the speed limits. So, as they say in the commercials "your mileage may vary"... :cool: :cool:
Quote from: lragan on January 19, 2010, 09:30:17 PM... nervous as a cat in a room full of rocking chairs...
(http://i43.tinypic.com/6htelf.jpg)
Quote from: DG on January 19, 2010, 08:32:22 PM
So, since the ambient air is cooler the exhaust itself would be cooler. Again, I am clueless and just trying to understand and learn. :-)
Never thought about it that way (always looking for the more complicated solution I guess) but it certainly makes sense too. There's more than one way to look at any problem and I definitely appreciate all the feedback.