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Scooters - 50cc => zx50 => Topic started by: gsx600racer on April 28, 2015, 08:08:39 PM

Title: BBC kit initial tuning
Post by: gsx600racer on April 28, 2015, 08:08:39 PM

I'v installed a Malossi 70cc kit. The kit claimed you could maintain the stock exhaust, carb and airbox.

I have ran one tank(fill) on break-in so far. I am trying to get it tuned in but having some dificulty gettting it to run decent.

At idle at a dead stop to around 20mph(1/2 to 3/4 throttle take off) it runs great.
Then at 20+ and pushing it to full throttle it stumbles over its self and acts like its going to stall.(I can not tell if it is starving for fuel or if its something else)

I am running stock carb(jetted at 96) and stock exhaust. I'v removed the stock air box and using a performance air filter. I'v installed the carbon reed that came with the kit. I am still running the oil injector pump and adding extra oil to fuel. I have also raised the needle in the carb. I had the top of the cylinder machined to bring the squish band in @ .04 inch.(i think .024-.031 inch was recommended). I chamfered all the cylinder ports

I have recheck the compression(180 psi). The spark plug looks decent(brownish but not sooted up). I have a camera to view inside of engine, there is a little carbon build up on top of the piston(on both side transfer port locations). I jetted back to #92 and its still having the same trouble

My goal was to gain more low end torque(climb hills better)hence keeping stock carb and exhaust. I am considering going back to the stock reeds too.

Looking for advice in which direction to go in.

Title: Re: BBC kit initial tuning
Post by: leo.portner on April 28, 2015, 08:47:22 PM

Go back to stock aor box and filter you have too much air coming in on the stock carb! Is it a 19 mm carb?

Title: Re: BBC kit initial tuning
Post by: gsx600racer on May 04, 2015, 06:10:05 PM

Thanks, leo. I have tried with and without air box and it runs the same. The carb is stock and I believe it is 14mm according to the manual.

I am looking at aftermarket exhaust and carb, any suggestions ?

Title: Re: BBC kit initial tuning
Post by: BettinANDlosing on May 04, 2015, 06:11:56 PM

Quote from: gsx600racer on May 04, 2015, 06:10:05 PM

Thanks, leo. I have tried with and without air box and it runs the same. The carb is stock and I believe it is 14mm according to the manual.

I am looking at aftermarket exhaust and carb, any suggestions ?

96 is too rich, like LEO said you need to tune your bike with the stock Airbox. It will always run like crap with a pod filter. Go to an #85 and put the stock airbox back on, then do some plug chops. These bikes are SUPER picky once you get that stock airbox off.

Title: Re: BBC kit initial tuning
Post by: gsx600racer on May 05, 2015, 12:26:18 AM

Thanks Bettin,

I will try smaller jetting and put the stock airbox back on. Also will go thru carb and clean as well.

Before the BBC(stock cyl), the main jet was #90 and it ran good before the swap. It did have a little carbon build up on the piston and head.(pics attached)