For those of us that think we know what we are doing and that our opinions should have merit.
My dyno testing and resulting AFR charts has proven that this article needs to be memorized. While I will not test the way the article describes – because I have a dyno shop around the corner – this knowledge should be CVK "101" for every one of our members - especially us loud "old dogs" that think we know..

Edit: This is CV performance tuning - Not CV problem troubleshooting. If your bike runs perfectly well, this article could unlock potential. If your bike is not running correctly, you need troubleshooting.

CV Carb Tuning Procedures

 

You seriously need to get over yourself.

 

Pretty much reads like what we did with regular slide carbs when flat tracking and off roading in the 70s.

Jet fat, big main, then drop down until clean. No way we wanted remotely lean since it is wide open peak rpm on the straights... no place to run lean and stick a piston... two strokes, y'know.

Needle adjustment until clean and decent transitions.

Float was something we'd look at, setting as factory, but in some cases had to raise them. In a side note, I had a TM125 that would only get 1/2 hour per tank of gas when I first got it. Then one of the guys noticed when the bike was running that gas was dribbling out the overflow hose. Never saw it because I always shut off the petcock when stopped. Reset the float and it would run a couple hours. Amazing what paying attention can do.

Pilot/idle mix screw, once we grew enough brain to realize it was important, was the difference between a good starting bike that would actually idle in spite of reputation. Seems a lot of people thought Bultacos and Maicos wouldn't idle and start decently - change the pilot and adjust it by idle drop - half the number of turns from one extreme to the other - and the bikes would fire nicely and act like they'd idle all day long.

Still, a nice on-line document for a person new to carbs.

 

"Pilot/idle mix screw, once we grew enough brain to realize it was important,"

LMAO..

What's sad is how true that is to my experience.. Decades of open class bikes that didn't idle well and didn't carb cleanly off idle - We all figured it was the nature of the beast and came with the territory...

 

The reason for this thread is because time and time again, the information on that link has proved to be dead-on. They say it is not based on any one elses work or knowledge but comes directly from years of tuning - and a lot of trail and error..

My last dyno chart shows clearly that the #136 main jet install affected the AFR over the entire RPM range. All AFR lean-outs, that had previously plagued my power production, were gone.

I went on a mission to find out how and why this happened. Once again, it was this article and these people that knew this would happen.. Quote "REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting." A small sentence in a large article that proves to me with finality that these people have the CVK fully understood.

All members can be set free to find power in a professionally guided manner. What I had trouble with, in the article, was keeping in mind that you are tuning circuits while at WOT.


Poor me,, I put my trust in the DJ kit - that they had worked out all the trial and error for me - only to find nothing but lean AFR's killing my power... With the #136 main jet, I have only now achieved step #1.. Step #2 - I guess lets try 5N as 4N didn't go rich enough...

 

Yeah, we only considered wide open.

Similar issue with the Bultaco clutches, they were known for dragging something fierce. Then I learned to true the clutch. They had six nuts on studs. If you adjusted them so the clutch pressure plate ran true when disengaged (handle tied to the bar for adjustment) the clutch worked like a Japanese bike clutch did. Guys were in shock because I could put either my Sherpa S or Sherpa T in gear then back to neutral, no drag no fuss. Only took a bit of looking and thinking to figure out why it didn't run true.

My friend bought a Maico 250 that, like most, didn't idle decently. He got a proper pilot jet (leaner) and we adjusted the mix - Maico Magic! It idled nicely, Bing and all.

 

I've got some of that, but a lot of what I've learned has also been from others' experiences I've seen, been a part of, or read about.

Thing is some riders want plug and play, it ain't always that simple when some of us are in damp warm, some in cold dry, some vary from either extreme. Still, getting in the ball park is about 80% of the work. One jet size, a half turn of a screw, or a slot on the needle is good.

I do find that one sentence interesting. What if the float is low enough the main sucks lean? The float should be set at factory recommended height to start. Maybe they take that for granted.

 

There is some useful info but I'm confused about setting float level AFTER picking the correct main jet. Fuel level should have an effect on all of the carb circuits-a higher level will require less vacuum signal to pull fuel through the jet so I'd think that it's important to set that first.
But that could be my basic understanding of carb operation shining through...

 

You guys hit on a very important point.
This is CV performance tuning - not CV problem troubleshooting.

If your float level is non-standard, your jets jacked with, pilot system running a muck, or any other problem that causes aberrant operation - you need troubleshooting.

If your bike runs just fine - It's right off the showroom or, otherwise, is carbureting perfectly well - this article is for you.

 

I think the article was better than most any of the Mikuni stuff they put out. Never hurts to try to give people reasons and explanations. I appreciate your posting it.