Quick question YX160, runs good but small bog at times.....

[DHXrider]

Back story:

genuine VM26 on a YX160 with low compression and starting to smoke, with this carb on that particular engine ran fine and hard even with low compression, no bog, fairly easy starts etc. no issues, ran it for a whole summer !!!! I know, should have changed the rings and valves but too lazy....

details: #20 pilot, #180Main, middle clip, float height-->floats parallel with bowl bottom. Air screw 2.5 turns out.

Recent story:

So obviously rebuilding that engine this year. I have another bike but it had a POS molkt on it that worked up until now when apparently it just died. SOOOOOOO, took the genuine VM26 off of the other bike (from the bike mentioned above in the backstory) and put it on this new bike with the same engine YX160. This engine has good compression, no leaks, no smoking etc. Basically the bike runs great, about as good as the other bike but when rolling through the throttle, the mid feels ever so slightly flat, also, after heavy bumps, hills or long stretches of idle, it will bog when cracking the throttle. Not sure if this means too much gas or two little. As a note, I have the air screw out 2.75 turns vs. 2.5 turns. Seems like the further I turn it out, the less instances of bog but it's still there.

Curious to hear feedback, I'm thinking either it's float level or jetting but I really hesitate to play with jetting considering this combo worked perfectly on the previous engine and I have tried playing with jetting before and have always come back to #20pilot and #180main.

 

[headsmess]

lift the needle a notch or two.

 

[DHXrider]

Will try, and report back thanks.

 

[ilikemotorbikessoverymuch]

Hahah wow. Mate i just bought a reign with a yx160 and molkt. Had a couple of hours from previous owner. Clean as! Did this exact thing. ****ed around with the carb for the last couple weeks. Just bought and put on the mikuni 26mm yesterday. Does the exact same thing. Got a thread going which you can see in the recent threads at top right if forum. "Help Yx160 problems"

Now i know its not the carb im thinking and have been told to check valve clearances.

Ill let you know how i go this morning mate. Also let me know if you work anything out.

Cheers

 

[my67xr]

So which Mikuni is on it now, an VM26-606, spiggot mount ?

That is very lean on the mixture screw.
Have you tried lowering the slide in the carby by turning out the idle speed screw.
When the slide is adjusted too high it will let too much fuel into the engine and need's the mixture screw to be turned out further than normal
Mixture's will need to be readjusted once the slide is lowered

The best position for the mixture screw is between 1.5 and 2 turn's out, any further either way and you need to rejet it


If lowering the slide doesn't help, i would be dropping the pilot jet 1 or 2 size's try a #17.5 or a #15
I think you may be trying to compensate for rich mix's (too big jetting) by has the mixture screw set at 3.5-2.75 turn's out
As you know it'll need to mixture screw to be readjusted once the pilot has been changed
If that doesn't help then the only other thing to

 

[ilikemotorbikessoverymuch]

Its valve clearances mate. Just set mine and runs nice now!

 

[my67xr]

The engine has just been rebuilt, i doubt the valve's would need adjusting just yet.
Low compression doesn't cause the engine to bog

 

[DHXrider]

just to reply to my67xr about my original post.

just to clarify, I've taken the carb off the engine with low compression and put it on a new engine with good compression. I'm rebuilding the ORIGINAL engine.

Yes, it's a VM26 with spigot mount. Like you're saying all things point to the pilot being too large if I'm having to go 2.5-2.75 turns out but it's weird because this setup ran perfect on that original engine that I'm building now. I remember testing different pilots back when I was seting up the Vm26 on that motor for the first time and I always came back to the #20 pilot. I guess the only way to find out will be to bite the bullet and try it out, I'll report back what happens, I'll try the pilot first, then if nothing, I adjust the needle.

 

[DHXrider]

Ok, so problem fixed, I put in a 17.5 pilot and about 1.5 turns out and that seemed to do it.....
thanks guys.