Tips on performance mods

[cyclepro101]

Well I have finally got my ZBOX 80 (66cc) going good/fast. The problem I was having after doing all the std. mods was it was still crapping out at WOT. My problem was that I did too much work too quick and all at the same time. So to fix my problem I ordered another NT carb and bolted it on and straight away it went heaps better.
Things I did to the original carb was:
*upsize the jet to #76
*Match ported the manifold to the cyclinder
*Opened up the size of the intake port on the carb by a few mm.
*Sanded down the needle on the bottom 1/3 (that was my big mistake as it tured out)
Also I have cut off the pipe on the end cap of the muffler and screwed in a 3/4" brass socket with a barb on it and also match poted the exhuast manifold. I also run the NGK B*6** plug with a good lead and cap ans run at 1:30 semi syn. Motorex racing oil.
So when I put the std carb back on it ran better. Then I moved the needle clip up to the top slot. It ran even better with no smoke at idle. Then I changed from the #70 jet to the #76 jet and it went even better. Then I put my sports air filter on.............did not make that much diff.
But the good news is I hit 48km/h (30mph) with no trouble at all. So the only thing I dont have on this new carb is the sanded down needle. It goes way better and smoother now.
Steve

[Bones56k]

Hey cyclepro101

A bigger main jet (76) does not mean more power.

What you need to feel is on WOT if the motor is feeling like a forward backwards motion (lean) or is just not clearing out (4 stroking will not rev out properly).

Lean it needs a bigger main jet.

4 stroking is ...running rich seems like it was running crisp and responsive up to full throttle then it just seems it will not get to self destruct mode.

Self destruct is close to running right as it runs crisp from idle to about 6000rpm and then you know to not got to such a high rpm and restrain yourself.

The 66cc motor has a little more low down and midrange grunt (or torque) over the 50cc and is not so happy sounding like it will blow.

To testrun your current jetting hold the little girl flatout and hit the kill switch (then peddle home).

Pull out your spark plug and it tells you what the little girl is saying at WOT.

For spark plug readings on a rich or lean condition the posts on this forum will fill you in.

Thanks Bones

[Bikeguy Joe]

Do not removed the plug hot, the threads may come out with it.
A brown plug is good, black a little rich, white is in the danger zone, richen it up.

[Venice Motor Bikes]

Originally Posted by Bones56k

To testrun your current jetting hold the little girl flatout and hit the kill switch (then peddle home).

I just wanted to add something important to this technique... When you hit the kill switch; ALSO pull the clutch so that the engine isn't sucking raw gas into the cylinder & getting the plug wet!!!

[cyclepro101]

Thanks team. I have the clip in the top slot (leanest) now. On the second slot down she was smoking on idle and run a little ruff. Its just great to hear it rev hard (or crisp) up to near self destruct limit, but with the 36t sprocket I can hit 48km/h easy and down a little hill she will get to near 58km/h but she is screaming (not to good to often I figure).
But I will check the plug again and I may have to go back to the second slot down. The std #70 jet is no good at all compared with the #76.
I also have a SBP Tuned pipe ordered too. Hope that helps.

Steve

[Bones56k]

Hi cyclepro101

Sounds like you are on your way to making your 2 stroke running properly.

The SBP website has some really good parts to getting the china motor running to a point where it is tuned properly for your conditions.

I can not speak highly enough of the parts and delivery time SBP has to offer (even to Australia).

They have the parts .....it is just up to you to getting the motor running right with the parts available.

PS
All i could see they could do to be complete one stop website....would be supply extra Jet sizes!

Thanks bones

[Cabinfever1977]

i have a 48cc dualstart starfire gt-2 grubee from gasbike stock except cold air intake. its on a 26" swchinn delmar cruiser with a 44t sprocket. no problem going up hills.fast acceleration.I can cruise at 48kph and go up to 56kph on flat ground. i have a stock muffler and no engine mods. my c-clip is at the second from top. running reg gas and reg 2-stroke oil at 20:1.
my engine does not sceeam but i am workin on engine vibrations.

[cyclepro101]

The 48cc engines appear to be just a fast (top speed) as the 66cc ones.

[Cabinfever1977]

actually you have a 36t sprocket but i can go the same speed as you or faster and i have a 44t sprocket. do you have a 26" bike or is yours smaller.

[dvddtz]

My 48 cc has the same top speed as my 66cc,the 66 just gets there faster.