Emission Issues, Carburetor Questions, And More - Tech Q&A

Emission Issues

Q I purchased my '01 Road Star Silverado in Maryland, took it to California and now live in Arizona. I've been in the Tucson area for about a year, and all of a sudden DOT wants me to get my bike checked for emissions before I license it for a second year. So I rode it down to the emission check station only to find out that it failed the carbon monoxide part of the test. I passed the hydrocarbon section with no problem, which is somewhat surprising because I removed the air-induction system years ago. I would prefer to make adjustments to the bike myself to correct this problem, but I don't have a good understanding of what causes too much carbon monoxide. I've done the standard stuff we all do to our bikes-rejetting, exhausts, airbox, electrical upgrade, and so on. Any suggestions you might have would be appreciated.
Jerry Allen
Via e-mail

A _First the basics: High carbon monoxide (CO) levels are caused by anything that makes the engine run rich, and as a rule of thumb they go up as the unburned hydrocarbon level (HC) goes down. This is because CO is a byproduct of combustion, while HCs are unburned fuel particles. HC levels rise when there's a misfire and the engine skips a combustion cycle. When that happens, raw, partially burned fuel comes out of the tail pipe, but because combustion is incomplete no CO is produced. To get through emissions I'd get the bike good and hot, then lean out the pilot-screw adjustment until the bike develops a lean miss at idle. Then enrich the mixture slightly until the miss disappears. That should put both HC and CO levels within tolerance.

The greater issue is that this type of testing is going to become more prevalent as time goes by, and as the rules become more stringent it's going to take more than a tweak of the pilot screw or some tap dancing on the fuel module to get through emissions. My recommendation? Hang onto those old pipes and emission parts; you never know when you'll need to reinstall them._

Carb Conundrum
Q I'm considering the purchase of a carburetor-equipped '06 yamaha, but I'm not really sure it's the way to go. I'm partial to EFI, in part because I feel EFI-equipped bikes are more reliable and more powerful. what's your view? will a carbureted cycle cause more problems? Thanks.John Blazys
Via e-mail

A Like you, I've grown to really like EFI systems. In the main, EFI-equipped bikes rarely suffer from hardstarting or idle issues and work well over a wide range of riding situations. They are also easily remapped to deal with things like aftermarket exhausts and air filter kits and are for the most part bulletproof. On the other hand most carburetors work well, are dead reliable and are easy to rejet should you want to swap pipes or fine-tune them. So bottom line, if a given bike were available with either EFI or a carburetor I'd always opt for the EFI version, but I wouldn't pass on a bike I liked solely because it came only in a carbureted version.

Octane Opinions
Q It was interesting to read your opinions on grades of gas ("Hit or Myth," Oct. '07). My brand-new '07 Kawasaki Vulcan Nomad has had premium (93 octane) in it per the manufacturer's recommendation. I know you said running 89 octane would be OK and I'm going to try it on my next fill-up, but what about running 110 octane Turbo Blue? I have a riding buddy with an H-D Ultra who swears by it, running a gallon or two every couple of months or so. He says it helps clean gunk out of the engine because it burns so hot. I tried it (one gallon in a 5.3-gallon tank) and really did not notice any difference.

Also, I've had my Cobra pipes on for more than three months now, and they're brown instead of black. I asked my dealer service guy, and he said that's the opti-mum color. Not gray for lean or black for too rich-what do you think? Thanks.
Via e-mail

_Please don't read more into my comments on octane than are there. What I said was, "you can run the lowest octane you can find that doesn't detonate." you can certainly try the 89 octane, but if you experience knock or ping (detonation) you'll need to return to high-test. As for your buddy's Turbo Blue, all gasoline has the same approximate caloric value-19,000 BTUs per liter-meaning the 110 won't run any hotter than 89 octane, so his theory doesn't hold water. Ironically, though, if you run low-octane fuel that causes detonation, the pistons will have a nice, clean, freshly scoured look to them, especially around the hole that burns through the center.

Regarding your other question, I don't put much stock in the color of the pipe because there are too many variables. For instance, fluffy black soot in the pipe indicates a rich mixture, but a little bit of black may just mean you're spending too much time trolling around town at low speed. I know one guy who claims any color in a pipe means it's too rich-his tips are actually rusty and his bikes make great power (but are very high-maintenance). A better indication as to the quality of the mixture would be the color and condition of the spark plugs and how the bike runs. Off the record, though, I'd be happy with any tailpipe tip color that was between gray and brown._

Reach Mark at zimmemr@aol.com