Lean condition on long deceleration

[ccdhowell]

When motoring fast down a dirt road on my Tecate and I let off and pull the clutch in to coast to a stop or slow turn, my engine really leans out. The revs increase pretty high anyway, I figure it's creating a lean condition by closing the carb up and coasting. Is there any way to minimize the affect of this lean condition? I mean should I go up on the pilot jet or something like that?

Give me some ideas, if you have them. Trike runs great all the time, plug is good, throttle responce is good, I think I'm jetted near perfect so I don't think it's the basic jetting, just an induced lean condition.

Chris

[Rustytinhorn]

The tecades a 2 stroke, isn't it?
I was thinking about this the other day while riding. The usual trail I ride is all uphill one way and all downhill the other way. (Several miles) So going uphill I am giving my wheeler lots of gas so it is also getting lots of oil at high rpm's. But when using the engine brake going downhill, I am not giving it any gas, therefore it is only getting a minimum amount of oil compared to the high rpm's its operating at. Any comments on this?

Anyway to answer your question, Go ahead and try a larger pilot, and if it brings bad results then put the smaller one back in.
Maybe is just needs the idle turned down. When a bike is cold started it usually needs assistance to stay running until it gets up to operating temperature, then it will idle by itself without dying. If you cold start yours and it idles just fine right off the bat, then chances are your idle will be a little too high when it reaches operating temperature and will need adjustments.

So now that I wrote a book on this, maybe I should ask if this "lean condition" only occures when coasting downhill? Using engine braking or with the clutch pulled in?

Then again, I have a dirtbike that when the choke is on the idle increases and when its off it idles back down. HUH?

[tecat-z]

Chris, raise your needle! You're lean in the middle. You can sieze you ride this way. i've done it. R's should drop right away and not be eratic at all when clutch is pulled in on deceleration. Be sure clutch is disengaging all the way as well. Ed

[Billy Golightly]

I'd agree, the needle is on the lean side and possibly the pilot. Be very careful, especially since its doing it even though the clutch is pulled in. If you had been letting off the throttle and downshifting to stop/slow yourself down it woulda already seized.

[Jason Hall]

What size pilot & main Is In It now? Could It be sucking air from a base gasket, Intake boot crank seal? I had my 310 jetted to a leaking base gasket, what I mean Is I had to jet way up on the main to make up for the leaking base gasket. I finally realized what was happening when It finally revved out of control after running It real hard for a long period & It was HOT.

[ccdhowell]

I was thinking along the lines of changing the pilot a little bigger and lowering the jet needle one position to see if things got better. I though I had this carb really sorted out, took it for about a 2 mile run, uphill some on the out leg and coming back in, on the downhill side, I discovered this decelerating lean condition. Jason, I have a 52 pilot and 172 main, middle clip on the jet needle.

And Ed, you're right on target about the clutch. I bought some fancy Royal Purple synthetic trans oil to try, shifts really well now, but the friction coeficient is all wrong on this oil, it grabs the clutches too much. Now it won't kick over while in gear and I can't locate neutral while the trike is running, the clutches are trying to grab even when the clutch is pulled in all the way. Yeah it is a new cable and is adjusted all the way in, clutch plates are coming as far apart as this machine will allow them. I know its this fancy fluid, it only started it when I put it in. I'm going to the cycle shop this weekend to get some Gear Saver, that's what I shoulda bought the first time.

I find this most interesting about the carb. I ran it and changed jets(main and pilot) jet needle position and mixture screw for the better part of two riding days and thought I was close to spot on. Good plug color and strongperformance throughout the rpm range, all on level ground. It wasn't until I went for this last high-speed run, right before I called it quits, that the lean condition surfaced. Of course I'd never done a longish downhill coast before. Looks like I'll have to add this as a test for carb jetting in the future.

Thanks for all your help guys...and Billy don't scare me like that, I do sometimes downshift to decelerate. Guess I dodged the bullet for now.

Chris

[Billy Golightly]

Yeah Chris...thats a 4 stroke habit. I still do it occasionally but catch myself most of the time. A 2 stroke receives ALL of its lubrication from the fuel, and most of its cooling capacity. What happens when you cut off the throttle, you turn off the fuel, consequently part of the cooling and the lubrication. What happens when you downshift? The engine speeds up. Higher engine speeds + less lubrication=not good for piston and cylinder longevity. It does not take long, especially when the engine is already hot, for that to end up being more then it can handle.

[Jason Hall]

Wow I would say your pilot Is big enough. I usually run 42-45 pilots In my R's. Not sure what pilot you Tecate guys are using. Maybe you just need to bump the main up to a 175-178 If It only happened after the long top end run.