still lean...

[lykos23]

So today I FINALLY got my UNI filter! So I drove a few miles WOT (even though I know I shouldn't) and cut the killswitch and pulled into my drive way; essentially the whole plug chop process, with a BRAND NEW spark plug and freshly changed 92 jet. And this is what I got:



It doesn't look quite as white as last time, but it's definitely still white.


Gonna try #95 next...

[techie610]

Give it a hotter coil?..

[lykos23]

Originally Posted by techie610

Give it a hotter coil?..

For real?! I thought that was for rich conditions??? I'm already running an orange one... D:

[lykos23]

The tip is still white with a #95 jet but now there is the slightest of brownish tint to it. I think I'm getting closer. (This is with a BRAND NEW spark plug, mind you. Not the last sparkplug I used.)



Do y'all think I should go to #98?

[techie610]

Originally Posted by lykos23

For real?! I thought that was for rich conditions??? I'm already running an orange one... D:

My apologies.. Your correct.
Ugh. been a long day. lol

[lykos23]

Originally Posted by techie610

My apologies.. Your correct.
Ugh. been a long day. lol

No worries, lol. It's just that everything I knew about scooters was turned on its head for just a little while as I pondered your comment, haha.

[lykos23]

For the sake of science I did another plug chop, but running for a few more miles this time.

I think #95 might be the one!

[qwertydude]

You should take a GPS and measure the top speed on a level road with no wind you get with the various jets. One or two of them among your 92, 95 and 98 ought to give you a better top speed which will tell you what range you ought to be going for.

And the 38 pilot can be washing the plug clean. Are you able to adjust the idle mixture screw using the idle drop method? If not then you're too rich on the pilot jet and would be better off switching back to the 34. If your pilot jet is flooding your cylinder with gas at idle it can throw a proper plug chop off.

Because by the looks of it the 95 or 92 are actually closer to the jets you want. In fact it looks like the 95 you're getting carbon build up on the metal edges. On mine when I have them tuned perfect metal has no carbon build up and looks like a dull even brown no black spots or build up.

[lykos23]

Originally Posted by qwertydude

You should take a GPS and measure the top speed on a level road with no wind you get with the various jets. One or two of them among your 92, 95 and 98 ought to give you a better top speed which will tell you what range you ought to be going for.

And the 38 pilot can be washing the plug clean. Are you able to adjust the idle mixture screw using the idle drop method? If not then you're too rich on the pilot jet and would be better off switching back to the 34. If your pilot jet is flooding your cylinder with gas at idle it can throw a proper plug chop off.

Because by the looks of it the 95 or 92 are actually closer to the jets you want. In fact it looks like the 95 you're getting carbon build up on the metal edges. On mine when I have them tuned perfect metal has no carbon build up and looks like a dull even brown no black spots or build up.

So far my highest speed I've ever attained on the scooter is 58mph with the 95 jet and my performance seems great. There was the slightest popping with the 92, but no more with the 95. I think the 95 might be the one. I also think I was too anxious and didn't go for a long enough drive for the first plug chops - I mean you can still see the result, but it's not that clear on the picture.

My stock idle jet wouldn't come down from revs. No matter what a/f setting I had it on it just wouldn't come down after giving it throttle. It was hard to start, and it sometimes died at stops. So someone on the forum suggested I try the 38 pilot jet and I got it from AbsolutelyScooters and all my problems were solved. Now I can actually adjust my a/f setting. I'm a bit confused as to what size the stock is. Is the stock 32, 33, or 34? Because the stock for 150cc scooters is 35, correct?

[qwertydude]

Stock size is 34, it's possible you got a bad stock jet. You should definitely try a new 34 pilot jet.

And also when plug chopping the engine needs to be fully warmed up and up to temperature, usually 15 minutes of riding.

[buford1488]

95....but to me thats reall clean....not that bad...but thats just my opinion.....

[blueboy5000]

That's still very lean. You could try covering a bit of the air filter with some e-tape. I've found that a cone-style paper filter on my 90cc BBK 139 w 95 jet works best 3/4 covered with e-tape.

[lykos23]

Originally Posted by qwertydude

Stock size is 34, it's possible you got a bad stock jet. You should definitely try a new 34 pilot jet.

And also when plug chopping the engine needs to be fully warmed up and up to temperature, usually 15 minutes of riding.

Is there any reason to avoid a larger idle jet? I'll order up a #35 from absolutelyscooters and see what happens since that's what they have in stock and they're the first ones I found that offer the extended length idle jet for easier starts. But I still don't understand the reasoning if my current setup seems fine, is there some chance I'm running too rich at 1/8 throttle?

The first few plug chops consisted of a five minute warm up in idle and a ten minute drive at WOT. The last plug chop was a longer drive because my mother asked me to go to the store for her - I got much better results with the longer drive, that's for sure. Sadly it just so happens that a lot of roads were flooded around town so I was confined to a small strip of road on 120 since my speeds are too high to do WOT around the neighborhood anymore.

Originally Posted by buford1488

95....but to me thats reall clean....not that bad...but thats just my opinion.....

Clean, or lean? It may just be your opinion, but I value your opinion Buford.

Originally Posted by blueboy5000

That's still very lean. You could try covering a bit of the air filter with some e-tape. I've found that a cone-style paper filter on my 90cc BBK 139 w 95 jet works best 3/4 covered with e-tape.

You think so? I've been running a restricted free flow filter for months now because I didn't have the proper jets. Millsc says I shouldn't have to go over 95 with jets and I'm trying to get the best performance possible - won't the restriction hinder that? I mean... the tip of my spark plug is white from my hotter coil, but the base is coffee colored - isn't that what I'm looking for?


In any case I'm ecstatic that I can almost hit 60mph now. I'll try a smaller idle jet for some reason, but otherwise I'm liking my setup so far.


Thanks for the input, Y'all!

[qwertydude]

Originally Posted by lykos23

Is there any reason to avoid a larger idle jet? I'll order up a #35 from absolutelyscooters and see what happens since that's what they have in stock and they're the first ones I found that offer the extended length idle jet for easier starts. But I still don't understand the reasoning if my current setup seems fine, is there some chance I'm running too rich at 1/8 throttle?

The first few plug chops consisted of a five minute warm up in idle and a ten minute drive at WOT. The last plug chop was a longer drive because my mother asked me to go to the store for her - I got much better results with the longer drive, that's for sure. Sadly it just so happens that a lot of roads were flooded around town so I was confined to a small strip of road on 120 since my speeds are too high to do WOT around the neighborhood anymore.


Clean, or lean? It may just be your opinion, but I value your opinion Buford.



You think so? I've been running a restricted free flow filter for months now because I didn't have the proper jets. Millsc says I shouldn't have to go over 95 with jets and I'm trying to get the best performance possible - won't the restriction hinder that? I mean... the tip of my spark plug is white from my hotter coil, but the base is coffee colored - isn't that what I'm looking for?


In any case I'm ecstatic that I can almost hit 60mph now. I'll try a smaller idle jet for some reason, but otherwise I'm liking my setup so far.


Thanks for the input, Y'all!

There reason you don't want to run too big a pilot is it masks the symptoms of a lean top end. This is a dangerous situation because your plug may look well and good on a plug chop but you're in reality running lean on the top end. That's why a plug chop isn't the only tool to use when determining correct jetting. The top speed method works especially well for scooters especially well because on most bikes you won't be able to reach top speed in order to determine correct jetting.

It's a simple fact that the correct jetting gives you the most power so hence the jetting which gives you the highest top speed is the correct jetting. From there you work your way down, and experiment with needle height and then finally mixture screw. I don't know why it keeps getting posted over and over again if you're lean on the top end just turn the mixture screw. That's absolutely 100% bad advice as it doesn't solve your problem and only makes you foul spark plugs and again on a plug chop hides the true reading.

[blueboy5000]

Originally Posted by qwertydude

There reason you don't want to run too big a pilot is it masks the symptoms of a lean top end. This is a dangerous situation because your plug may look well and good on a plug chop but you're in reality running lean on the top end. That's why a plug chop isn't the only tool to use when determining correct jetting. The top speed method works especially well for scooters especially well because on most bikes you won't be able to reach top speed in order to determine correct jetting.

It's a simple fact that the correct jetting gives you the most power so hence the jetting which gives you the highest top speed is the correct jetting. From there you work your way down, and experiment with needle height and then finally mixture screw. I don't know why it keeps getting posted over and over again if you're lean on the top end just turn the mixture screw. That's absolutely 100% bad advice as it doesn't solve your problem and only makes you foul spark plugs and again on a plug chop hides the true reading.

On my three 139 bikes, all of them are properly upjetted, and NONE of them have had a thing done to the idle jets (which are all #34 stock jets). I agree that there should be no reason to switch to a bigger idle jet. Properly adjusting the needle and switching to a larger main jet should solve your mixture problems.

That said, I run a 95in a 83cc BBK, and I probably could get away with a 88 to 90 mainjet. My current 95 and tape-restricted air-filter proves that the 95 is too big.

I am going to suggest you adjust the needle to a richer position.