Carburettor Plug and Jet change (on 49cc china motor) Observations

[MattK]

I Replaced stock items with Runtong (RACING CARBURETOR 2 STROKE MOTORIZED PUSH BIKE 49/66/70/80cc Engine KIT AU).
So; My first run, I have to say I was not impressed at all. Mid to full throttle doesn't exist. The engine peeks at half throttle and after that all you get is a muffled change in engine noise and no power increase.
I then replaced the Runtong jet (I'm Guessing 0.70mm) with the stock (I'm Guessing 0.6-0.65mm) jet. Basically the stock jet has a smaller hole. My Iridium spark plug arrived; NGK - Iridium IX Spark Plug (BPR7HIX) so I also put that in. I now have a full range in the throttle. I have Significantly more power. I clocked my speed at 45 km/h and also notice better response to hills.
Summary; In case anyone wants to know. If you put one of these kits on, you will probably need to change the jet to the stock jet depending on your motor size. The new plug works a treat and as other people have mentioned the stock one is crap. I now have no fuel leaks and in general better designed carburettor that doesn't fall off while riding. My stock cable fit, all I had to do was change the adjustment pipe over from the stock carburettor. Was it all worth it for the power increase; Only just, the biggest thing I noticed was that it maintained speed better going uphill and ran slightly smoother. 46 km/h is fast enough for me. Cheers

My next move is to to mod the exhaust.

DSCN0386

• MattK
• May 7, 2018

NGK

DSCN0385

• MattK
• May 7, 2018

Runtong

DSCN0376

• MattK
• May 7, 2018

Bike

DSCN0370

• MattK
• May 7, 2018

Speed

 

[MattK]

I've used this bike quite a bit lately and have to say that mods were totally worth while

 

[Tyler6357]

Definitely! I did the same thing. It's totally worth it to get an expansion pipe too!

 

[Inf3ct3d89]

So I just need to put a different plug in?

 

[MattK]

So I just need to put a different plug in?

I would Change the carby(You must put original jet in the new carby otherwise you'll be very disappointed), change the plug and also from what I have heard and read the exhaust pipe. Also I'm starting to think that the timing is more crucial than anything I have changed. I like the thread on adjustable CDI timing.

 

[Venice Motor Bikes]

I've found that the stock carb can actually work as well (if not better) than almost all of the 'high performance' carbs.
No matter what carb you choose?, you're gonna have to re-jet it for the best performance.

 

[MattK]

I've found that the stock carb can actually work as well (if not better) than almost all of the 'high performance' carbs.
No matter what carb you choose?, you're gonna have to re-jet it for the best performance.

I have to agree the stock carby is pretty good performance wise. I changed it mainly because it kept falling off with vibration and also it leaked "like a drunk in the cold night air."

 

[Inf3ct3d89]

I would Change the carby(You must put original jet in the new carby otherwise you'll be very disappointed), change the plug and also from what I have heard and read the exhaust pipe. Also I'm starting to think that the timing is more crucial than anything I have changed. I like the thread on adjustable CDI timing.

The old jet is too long

 

[MattK]

The old jet is too long

Mine came apart long brass hex with the jet screwed into the end?

 

[Inf3ct3d89]

They don't call it a bag of smarts for a reason lol, it looked fused in

 

[MattK]

They don't call it a bag of smarts for a reason lol, it looked fused in

I actually opened the original carby, had a look like you did then shook my head thinking that wont fit. Reassembled it and put it away for a day or so. I read someones post and had another look. Its in 2 pieces. LOL

 

[Venice Motor Bikes]

I changed it mainly because it kept falling off with vibration and also it leaked "like a drunk in the cold night air."

It should never fall off if it's installed properly... Make sure it's pushed onto the manifold completely, & torque the clamp bolt as much as you can. You can also drill the holes in the carb clamp a little bigger & use a better bolt.

They also shouldn't leak (if everything is as it should be).

& last, if your engine is vibrating so bad that the carb is coming off?, you should look into mounting it a little better so you don't have problems with the engine mount bolts eventually breaking.

 

[MattK]

It should never fall off if it's installed properly... Make sure it's pushed onto the manifold completely, & torque the clamp bolt as much as you can. You can also drill the holes in the carb clamp a little bigger & use a better bolt.

They also shouldn't leak (if everything is as it should be).

& last, if your engine is vibrating so bad that the carb is coming off?, you should look into mounting it a little better so you don't have problems with the engine mount bolts eventually breaking.

I also didn't like the stock air filter (Piece of **** really) and so all these factors including the prospect of going faster helped me make the decision to change carb. I eventually got the stock carb to stay on but it always still leaked. New carb is so much better.

 

[Tyler6357]

I use Runtong ones also, better air filter and I think they are easier to tune.