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Quick, Simple Question

3K views 17 replies 12 participants last post by  scrimmer 
#1 ·
Bike: 2005 M50
Miles: 16000

I used 87 grade fuel up to around 10,000 miles. Then I switched to 89.
At around 15,250 miles I debaffled and now I do believe it is running rich. What gives? Should I switch back to 87 and that will lessen the problem, or should I just break down and buy that PCIII?
 
#2 ·
I have a 2005 with about the same miles. I've ran 87 since I got it and it's been running rich since I got it. I've debaffled, demickeyed and did the KN Filter Mod with a small hole cut out of the front of the airbox.

From what I understand, they run rich from the dealer and will pretty much do so unless you get the PCIII. Either way, the book says 87, so I run 87. Just my 2 cents.
 
#4 ·
I've played around with the bike a good bit and I've come to think that they run a little rich at idle. I also started smelling some gas after I debaffled. Debaffling should not effect the air/fuel mixture that much but if it does it should make it a little more lean, not rich.

When I made my new air intake, I learned real quick that the bikes aren't rich while cruising or at WOT. Also, on our Fi2000 fuel processors, we have to adjust the units to add fuel during steady engine speed, like highway cruising, and WOT. However, although we can add fuel for when it's idling, I've found it runs great when adding little to no fuel at idle.
 
#5 ·
I find it funny how the owner's manual says to run only 87 in the bike while the service manual says to either run 87 or 93. I have ran both in it and honestly have not seen a difference in performance other than mileage. I seem to get a touch better mileage when I run 93, but maybe it's because my wallet is a little lighter! I also noticed a gas smell when I debaffled but it went away with about a week of riding debaffled.
 
#6 ·
Hey, thanks for the input guys. Jim, always a wealth of information! I think I'll probably just run out this tank of 89 and switch back to 87 until I can afford to snatch up a PCIII.
 
#7 ·
I think there's a lot of misinformation in this thread.

What makes you folks think that a stock VZ800 runs rich? What makes you think that changing the octane rating of your fuel changes the air to fuel ratio entering your cylinders?

Leaving the octane issue aside, the issue of the stock VZ800 running rich is a bit more complicated than the blanket statement "they run rich from the factory" would suggest.

The truth is the VZ800 runs rich at certain RPM and throttle combinations, but it runs lean at others. The complete story is contained in the graph below. The green areas are where the bike runs lean, and the blue areas are where it runs rich. The darkness of the shade indicates how lean or rich it runs at a given RPM-throttle combination.





Now I agree that my position is based on an analysis of one power commander map--but at least the data in that map are objective. The discussion so far in this thread has been, for the most part, purely speculative.
 
#8 ·
Nico, is that map before or after you adjusted the fuel settings with the PCIII? If its after I don't really see how it would apply. If its before then I think its great for this thread. As for the octane level I agree with you, I don't know what would make the air/fuel ratio any different regardless of octane. I know mine runs a little rich and every once in awhile I get a backfire, but besides scaring the people around me nothing bad really happens and its something I've learned to live with (at least until I decide wether or not I want to depair!)
 
#9 ·
Before. That map shows the adjustments that the power commander makes to the stock fuel-air mixture at any RPM-throttle combination. For instance, when I twist the grip 20% of the way and the engine is at 4250 RPM, the power commander is adding 22% more fuel to the mixture than stock. This suggests that the stock mixture at that particular throttle-RPM combination is 22% too lean. You an interpret the rest of the graph the same way.
 
#10 ·
Octane rating shows the fuel's resistance to pre-detonation. Period. If the bike does not knock and ping on 87, then 89 is a total waste of money, and the mixture can not be leaned out or richened by changing the octane rating of the gas.

Most bikes come from the factory on the edge of too lean, to help meet EPA emissions standards.

Pulling the baffles screwed up the mixture. An engine is basically an air pump- 14.7 parts clean air and 1 part gas in, heat and dirty air out. When you modify the exhaust you change the amount of air the motor can pump. Unless you remap the FI unit or change to an aftermarket one from Cobra or Power Commander, you have not adjusted the amount of fuel available to mix with the air. On some bikes exhaust mods make the motor lean, on others it makes it rich, depending on the intake system, the fuel processor, emissions control equipment, and other factors. And sometimes the exhaust mods will cause the bike to run lean at idle or steady throttle and rich on hard acceleration, or rich at idle and lean on acceleration. I can put the exact same pipes on two identical bikes, yet end up with different jetting to make then run right. That's why remapping a FI unit or rejetting a carb correctly is so hard, more of an art form than a science.

As an example, when I changed exhaust on my Harley the idle/ closed throttle circuit was WAY too lean, steady throttle was fine, and hard acceleration/ high speed was just a touch lean.

Backfiring is a sign the mixture is off. It is NOT always a sign your mixture is rich. A bike that is running lean will backfire because the mixture is so lean it does not ignite. The unburned mixture gets into the exhaust, where it does ignite, causing a backfire. A bike that is too rich will also backfire, also because of the unburned fuel in the exhaust, or sometimes because the extra fuel momentarily fouls the plug, causing it to not fire, dumping the unburned fuel into the exhaust.
If you backfire on hard acceleration you are probably too rich on the main circuit of the carb or power band of the FI map, if get poor performance under hard acceleration you are probably too lean. If you backfire on deceleration, at idle, or at steady, part throttle, then the idle circuit of the carb or idle band of the FI map is too lean. If you backfire while holding a steady speed, the middle circuit or middle part of the FI map could be either lean OR rich.

Have a headache yet? LOL!

So the short version is don’t assume that the bike is running rich because it is backfiring. If could be lean.
 
#12 ·
Your awesome chart does match what I see with the Fi2000 in that the middle rpms and WOT throttle need fuel added much more than at idle or under 2000 rpms. Each time I look at your charts I learn something more.

I do have a question about your graph, Nico. When is the bike ever at 100% throttle and at only 1000 rpms? It might be for a millisecond if starting from a stopped position. Just wondering how the PCIII figures that out. Great info.
 
#17 ·
You're right, a warm properly tuned VZ800 idles around 1100 RPM. So unless your idle speed is low, I can't envision any situation where you'd be at 1000 RPM with full throttle. That particular combo is on the map because the map needs to cover all combinations of throttle and RPM.

But suppose you're drag racing. You'd start out idling (approx 1100 RPM). The power commander is making no adjustments to the mixture because throttle is at 0. The very next instant you'd be at full throttle and RPMs would quickly increase from 1100. So you would be at 1100 RPM and 100% throttle, albeit just for an instant.

This is how I believe the PC works: X times every second (I don't have any idea what X is; though I'd be fascinated to know) the PC samples your throttle position and your RPM. It takes that combo, say 20% and 2500 RPM, and looks it up in the map (see pic below). The value at the intersection of 20% and 2500 RPM is 5. So the PC adds 5% more fuel to the mixture. The PC is constantly repeating this procedure, hundereds, possibly thousands of times every second.

I'm sure X is fast enough to handle cruising and typical driving. But at full throttle and in low gears (where RPM changes rapidly), hopefully X is way faster than the rate of change in RPM, or the PC's adjustments will lag (the adjustments will come too late). But PCs are really made for bikes whose RPMs are changing A LOT faster than ours ever will, so I'm confident that the PC can optimize our mixtures even at full throttle.

 
#13 ·
For those of you contemplating de-pairing, but don't want to bother with the whole removal, just remove your air filter cover and plug up the pair valve intake hole in there. I used a flat head screw as close to the right diameter as possible, and duct tape (yes, it does fix everything) Same effect as de-pair, no hassle. And, it definitely helped partial throttle response after I debaffled.
 
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