Use of Choke /Jetting

[Houndog]

I have done alot of searching and reading on jetting and have played around with it on my '95 200 which has 1/2 of the air box removed, and a FMF Rev pipe (k-30). Right now I have a 158 main, 45 pilot, AS 2 to 2 1/2 and a 1174 in the middle position at 17meters above sea level. The top end was done this winter, compression is 190. Overall the bike runs great with a slight bog if at low speed in 2nd or so when the throttle is rolled hard from closed to open. When it's 'on the pipe' it will lift the front wheel in at least 3 gears with just the throttle.

A couple of things that seem not right, one is that I don't have to use the choke to start it, normally it just takes a couple of kicks to start. I tried a 42 pilot which seemed to work OK but I was a bit fearful of running lean and the crackling sound that I had become used to was gone, just hearing the motor without crackling when I let off the gas seemed weird. Kind of sounds like a 'ting ting ting...' make sense?

This is my 1st dirt bike and I am now getting comfortable enough to pay attention to how it works. When I bought this last fall I was just happy to have it run and me stay on it, but am becoming a bit fussier now.

Any comments?

 

[CaptainObvious]

Well, lets think it through.

What does the choke do? It richens the air/fuel mixture to facilitate cold starting. If you don’t need the choke your mixture is too rich.

That “crackling sound” (a.k.a. burbling or 4-stroking) is also indicative of a rich mixture.

The “bog” you mention could be from rich jetting if is a “bog”. If it’s a “booooowaaaag” or burp it is lean, but given the other two items you mention, and your current jetting, it’s safe to call it a bog.

OK, all symptoms lead to a rich mixture. So what do we do? One thing at a time, that’s what we do.

Let’s start low and work high. Put that 42 pilot back in and tune your airscrew so that you have good throttle response with a LOADED engine from a near standstill. If the airscrew is still 2 or more turns out, go to a 40. This throttle response should affect up to ¼ throttle.

After changing the pilot, recheck the needle. “Ting, ting, ting”. Ahh, there’s the sound that we want. If you are still getting the “crackling sound” raise the clip up one position. Recheck and adjust as necessary. The “crackling sound” should be gone from ¼ to ¾ throttle.

Now onto the main jet. Get yourself a new plug (or 2) and check how your plug looks after a good 1 minute run at WOT in 3rd gear or higher (again were are looking for some load on the bike). Check the condition of the plug. Is it wet? Is it dark? If yes, go to a leaner (lower numerically) main jet. Also, remember you want “Ting, ting, ting”, not that “crackling sound”. Repeat until you get a dry plug that looks like your morning coffee with lots of half-n-half.

Most of jetting is seat of the pants. And, unless you are always riding flat-out, don’t worry if the main is a little on the rich side. Most of us ride our bikes on the needle.

And as always, check the faq for further, better defined, information.

 

[Houndog]

Thanks for your reply RV6,

I tried the 42 pilot last night, it seemed fine except for (still) a slight bog when going from idle to full throttle while going slow in 2nd gear. I went for a trail ride with my wife last night (her on a quad) and checked the plug a couple of times, it was tan looking and I figured it was ok. I adjusted the needle from the 3rd from top to 2nd (seem to feel better at 3rd) and then back to 3rd. A/S was 2 turns out.

Tonight I decided to try the sand pit where some of the local MX'ers practice. Because of the sand I was on the throttle most of the time and it seemed like my biggest problem was lack of skill. I checked the plug (new) after a few laps and was surprised to find that it was very white compared to tan near the electrode but had a dark ring near the base (previous plug chop showed a bit rich if anything). A couple of the MX guys looked at it and thought it was normal so I kept riding, but still wondering if I was on the edge... Below is a pic of the plug after the run in the pit, is this normal or should I be concerned? Thanks for your help.

This is not a plug chop, I have about an hour on this one.

PIC

 

[canyncarvr]

Been here?

Take specific note of this.

Adjust the air screw to get rid of that bog you're referring to. It will be in some from the initial hi-idle setting. I don't read that you did much with it.

It doesn't take much to make a big difference. Keep your adjustments to 1/16 turn once you get in the ballpark.