High humidity = really bad running

Do you even know what octane is? Doesn't sound like it.

 

Your damm right I know what octane is and I bet I have studied more on that subject then most. I am a previous NHRA national record holder, I built all my own engines and when I destroyed one, I did a failure analysis and corrective action,so not braging but I really do know volumes on the subject of engine operation. Anyway when I post on a thread I do so to share my knowledge to help my brother biker be more astute in that subject of discussion. If I can save one or two guys from frying an engine , it makes me happy!

 

Apples and oranges. Highly tuned bikes with performance mods are pretty fragile, while street bikes are built more robust so they don't need all that tinkering, and they can run on a wider variety of fuels.

You need enough octane to prevent predetonation. Any more than that is wasted.

Maybe you have a tiger in your tank that can eat that extra octane, since you've been modding the bike. But most of us don't, so all it does is lighten our wallet.

 

Guys... Thanks for all the posts. I've been away for a while and now that I'm back and I think I'm going to try at least removing the O2 eliminators and then replace the fuel regulator with the stock one I got from the previous owner.

One thing I've discovered is that it make sure I rev it up above the 7K zone once in a while (I'm not ham fisted by any means) that the engine tends to run better more often.

Thanks again everyone!

 

EVT is absoultely right.:wink:
Standard air is 0.075 lb/cuft. Look at the X axis on the graph (zero humidity) and dry bulb temp = 68 deg F. Specific volume = 13.3 cuft/lb which is the inverse of 0.075 lb/cuft. Again, standard atmosphere.

Now look at 80% relative humidity at 90 degrees F. The specific volume there is about 14.4 cuft/lb or 0.069 lb/cuft.

The combustion air your bike is pulling in is 8% less dense at those conditions than standard. Here's more... that doesn't include elevation or system losses (pressure drop across box inlet/filter/inlet horns), which causes even more rarefaction.

When you have a closed loop = (MAF, air temp sensor and O2 sensor) like a modern car, it matches the fuel to burn properly with the given amount of oxygen available. Other, simpler, sytems may use an O2 sensor alone to indicate the post-burn excess oxygen levels and trim the fuel input.

You're former owner's mod is taking away the ability for the bike to realize it's running rich or lean, given the atmosphere around it. He should retire his tools and read some books before picking them up again. At the conditions you describe, you were running quite rich. Check your plugs for fowling and hope you didn't fowl your cat.

Don't worry about the gas. Get your O2 sensor in, and if you desire more stoichiometric combustion than the stock map gives you, bite the bullet and get a power commander.

Something elegant in the simplicity of carbs, eh?:first: Although tuning is far harder.:frown:

 

Hot Love

all the thermodynamic engineers are getting a chubby, he said "stoichiometric combustion" :smile:

 

Hey Vlad; I like the chart where did you get it? I am going to try and gain an understanding of this after which I should have some questions. eddie

 

Well, that explains why mine was running poorly Sat. nite (havent taken it out since) really warm (around 90F) and the humidity factor was unreal (for the prairies anyways)

The engine was slightly surging, gas mileage sucked and not sure if it was related, but vibration was felt at the grips and footpegs at a higher rpm.

My O2 sensor is gonna be hooked back up before I venture out again.

 

I pulled it off the web. They are easy to find. Look for "psychrometric charts" and you can't miss. There's some decent resources out there to explain thier use too.
HVAC, industrial ventilation, fan, and blower references will certainly have them. I had hoards of this stuff at work until my last office burned down.:frown: I'm rebuilding my library.:smile:

Two good resources for understanding the application of the charts and fan equations are New York Blower and Chicago Blower. NYB has a series called "Engineering Letters" that does a good job of explaining the affects of altitude, moisture, rarefaction, temperature. Chicago Blower has "Fan Courses", kind of a rip-off of NYBs idea, but they do a better job with charting inlet rarefaction in fans. If you can look a bit convincing that you may be in the position to purchase an indusrtial fan, all of this great info is free.eace:

Got questions? I'll be hanging around this site for the forseeable future.

Enjoy!:bounce:

 

Hey Vlad; Thanks for your response,from back in my drag racing days, I knew that high temps combined with high humidity really rob horsepower.I printed your chart,seems like I can study something on paper better than on a screen. I would like your opinion on something, from my experience smaller engines seem to be more effected by the high humidity ,high heat condition ,
where as the larger cubic inch cars although effected, they were not
subject to as much of a decrease in power.Any comment and do any of those tables(charts) show that? eddie

 

These charts won't show that. Smaller displacement engines put out their power by increased RPMs. The incresed RPM dictates moving intake gasses faster, which "stretches" or rarefies the gas. Rarefaction is a system effect and will happen to all gasses, hot/cold/dry/wet.
It's the same stuff that applies to port/polished intakes, free flowing air filters, smaller valve stems, larger intakes, etc. The easier the gasses can travel the less they stretch, maintaining density for more oxygen & fuel on intake strokes, an subsequntly more power when burned.
Go too far with it and you can have mixing problems. If the gasses move too slow the fuel can drop out of the stream or just distribute poorly in the cylinder.

Back to work....

 

One other question....I've done all the "mods" to my VFR, (pair removal, eliminate O2's, de-snorkel and flapper) and found that my fast idle is no more.
Even after I put two of them back to the original state (hooked up O2's, snorkel) still no fast idle.

I'm not too worried about it but is it the flapper mod that has eliminated this?
Or is it something else?

Again, no big deal but I am kinda curious.

 

Yosh, Speaking of modified air boxes, I am sure there has been tons of discussion on this subject , however can you supply me with what the elementry mods should be to improve air flow to the engine. I already have a K&N air filter . Thanks eddie

 

true and yosh, any differences in the way your bikes have been running since last week?

 

Eddie, here is a link to some "budget" mods I performed.
http://www.vfrdiscussion.com/forum/index.php?showtopic=15783

Lance, I removed the resistors and hooked up my O2 sensors recently and of course now the humidity has subsided quite substantially so as of now, my bike runs pretty good.

 

Wow! Great stuff! I plugged in my O2 sensors and so far smooth running (and it's been in the 90's with 90% humidity! ) The bike does have the 4-4.5K lagging problem but I just keep myself out of that range. I have the PC on my Christmas list... so if anyone is looking to give an early Christmas present :wink: