I need a little help...(the wife says “more than a little!”)
I changed the exhaust and the intake to let this big single breath a little better, and to climb out of the 25 horsepower hole it was in. But, it is no where close to passing emissions testing any more.
I had re jetted the carb to go up to a 155 main and a 55 pilot from 142 and 52.5.
I run a longshot straight pipe with Diamond Jim's baffle mounted at the end of the pipe.
It was actually fun to ride!
The emissions test said that Hydrocarbons were at half the allowable limit of 1800 with a reading of 513. Carbon Monoxide, on the other hand, was 10.13 with a limit of 5.5!!!
A local bike shop suggested that the straight pipe was not creating enough back pressure. They said that the failed CO reading was most likely due to raw gas being pumped through the system.
I reduced the main down to 150 and put the original pilot of 52.5 back in. With the original pilot back in the bike cracks and pops with every up shift and down shift. but feels strong through 85MPH.
I also plugged the baffle with Rock Wool to the point where it is hard to hold an idle. The baffle is a tight fit and designed so that all exhaust is forced through the baffle.
Absolute top speed (WOT) is 67mph!
The bike still failed with readings of 705 Hydrocarbons and 9.52 Carbon Monoxide.

I realize that it is a “Big Single” but I shouldn't have to choke it down to the point where your average 250cc will out run it, just to pass an emission test.
I hate the thought of doing an annual re-jet just to pass emissions ( in the only county in the country that still smog test bikes).

Any ideas or suggestions that don't include putting it back in stock condition?

Turn up the idle speed... ... try to go up about 200 rpm...

CalisOsin wrote on 08/06/10 at 12:15:43:


Ha Ha Ha...I just noticed you are also from Maricopa...What are the odds!

From my emissions training days, HC are usually from ignition or misfire problems ie unburned fuel going out the exhaust.  CO is from mixture levels, your high numbers indicate too rich idle mixture, as suggested turn in the idle mixture screw until just before lean misfire. Won't be the smoothest idle but should pass. cruise (2500 RPM) will also benefit from this as there is no load so the needle is low in the jet. Also as suggested having the idle at the high end of the allowed range will helps. Max

JohnBoy wrote on 08/06/10 at 19:24:20:

sounds like your idle mixture jet is a size too big.

BuckRYCA wrote on 08/07/10 at 16:26:43:

Buck, the bike after I worked on it, is definitely not slower than stock!
In stock form it cranks out about 26HP so does my 250 Honda. In the 1960's the 500 and 650 British bikes ruled the isle of Mann. All I want is to have it run at it's full potential. Is it louder...yes! Does it pollute more...yes! Does that bother me...not in the least. The day it passes emissions is the day I start putting it back the way I had it. Now If I had access to a dyno that would make life easier, in the mean time I will work with what I got.

Yes the jet sizes are marked on the face or side of the jet.
Find a magnifying glass, you will need it.