Tuning Diagnostic Help needed

[Chrisingippy]

Hi Guys,

I'm looking for some input on tuning issues I'm having please.
Its a 66cc New build with stock NT carb.

I ran it with 16:1 mix for a tank but found it was just making a mess as well as smoking like crazy and not running too well with 4 stroking at anything other than full throttle so for the second tank I've changed it to 20:1.
I've read a lot of threads here including the tuning basics and as a result sealed an inlet leak at the carb to manifold joint and lowered the needle, using the top clip position.

Spark plug went from sooty black (presumably the 16:1 mix) to a nice tan biscuit colour everywhere except the edge of the plug and a few threads which i'm putting down to residual soot from the first tank.

The bike on initial take off seems to hesitate/struggle a little sometimes surge a little and this continues anywhere in the mid throttle range. If I go full throttle, it takes off, runs nice and evenly and happily pulls under load and/or up hills and runs up to 40kph on the flat. It just doesn't like lower speeds/mid range.
It also takes a little more effort to start (like about 2-3 seconds) where previously it would burst to life instantly and actually run at a high idle for about 30 seconds or so, then settle (this was before I changed the needle and vacuum leak).

Closing the choke anymore than half kills the engine (it easily starts without choke) and there's no sign of a vacuum leak anymore.

I cant put my finger on what is going on.

Your thoughts please...

Cheers
Chris

 

[DAMIEN1307]

The 1 thing i would do right off the bat is to replace that Chinese Z4C or Z8C junk spark plug with a much higher quality NGK B6HS which runs much smoother and also make sure it is gapped, (NEVER trust pre-gapped plugs), to 0.025, (25 thousandths),...now take it for another spin and see if it settles in a little...remember that your still into your breakin period and things take a while to settle in a little...DAMIEN

 

[Chrisingippy]

The 1 thing i would do right off the bat is to replace that Chinese Z4C or Z8C junk spark plug with a much higher quality NGK B6HS which runs much smoother and also make sure it is gapped, (NEVER trust pre-gapped plugs), to 0.025, (25 thousandths),...now take it for another spin and see if it settles in a little...remember that your still into your breakin period and things take a while to settle in a little...DAMIEN

Will do Damien thanks. Are the stock plugs that bad?
I'll report back when done.

 

[Chainlube]

Play with the clip on the needle, one position can make a big difference.

 

[GreasyChris]

16:1 and 20:1 is way to much oil. 32:1 is fine for break in. You're bike will run much better on a 32:1 ratio and then rejet your carb until the 4 stroking goes away.

 

[Axl Myk]

I went to 32:1, a .65 jet, and lowered the needle. Before that I was using 20:1 and getting oil all over my shoes.
I dumped all the fuel in my lawn tractor tank and mixed up a new batch. Runs great now.

 

[wolframore]

Experiment with different oils, some leave more deposits and ash than others.

 

[Chrisingippy]

Hey Guys, thought I'd report back..
New NGK plug, changed mix to 32:1.
Its less smokey (oil smoke) as you'd expect, but still runs the same. Its clearly too rich at idle, you can see the black smoke on the concrete as it idles.
My needle is a 4 position needle and its second from the top. I'm thinking it needs a jet change as the new plug was quite sooted after only a short run. It still runs smoothly and evenly firing at full throttle and or under load climbing a hill...

Thoughts?
Cheers
Chris

 

[DAMIEN1307]

My needle is a 4 position needle and its second from the top.

At this point if it seems to rich, place the needle valve "C" clip on the very top notch which will be its leanest...take for a good ride, (not just a short run),...you need to run out the residual oil still clinging inside the engine from the 16:1 you were running and then see if it is still too rich......also remember that if its still new with still less than 150 miles on it, things will still need some time to settle in...DAMIEN

Ps...You did of course check the spark plug gap and made sure it is at 25 thousands?

 

[Chrisingippy]

At this point if it seems to rich, place the needle valve "C" clip on the very top notch which will be its leanest...take for a good ride, (not just a short run),...you need to run out the residual oil still clinging inside the engine from the 16:1 you were running and then see if it is still too rich......also remember that if its still new with still less than 150 miles on it, things will still need some time to settle in...DAMIEN

Ps...You did of course check the spark plug gap and made sure it is at 25 thousands?

I did.. and it was..
Ill try the clip and report back..