Zuma 50 w/BBK - switch back to stock airbox from freeflow?

[robthegob]

I recently picked up a 2008 Yamaha 50 that had been modded with a cast iron BBK, a Tecnigas Next-R, an Arreche carb(?) and an open air filter. It was tuned by a professional shop - with a dyno. I'm very new to 2T engines.

It actually runs quite well. Peak speed & power is pretty impressive.

But I have a few complaints:

1) It's unbearably loud. I repacked the pipe, but it seemed to make little difference.

2) It has very little throttle response off idle. The throttle is almost "digital" in nature - off or on. At WOT it goes well. At part throttle, it has very little power.

3) Poor mileage. I suspect it's running quite rich. Not really worried about this - but longer range would be nice.

I want to use it (with my wife on the back!) when out camping. My main requirements: reliability and ease of ridability.

So - I saw lots of discussion here regarding using the stock air box (which I have). I thought this might reduce sound volume a bit and also maybe give me a smoother throttle response. But I'm sure it will make it even MORE rich.

I'm not sure what jets are in the carb - I don't have a lot of documentation for the initial mods. But I may throw the air box back on and see how it runs and sounds.

Am I heading in the right direction?

Thank!

[2TDave]

If it's tuned for the open filter it would need a smaller main jet. You could try it since it'll just run crappy if that's the case. Open filters are loud. You'll need to find out what main jet is in there. A guess would be around 5-10% smaller.

[robthegob]

I tried just installing the stock air box and not changing anything else. It was definitely quieter, but it sure ran like crap!

Worse than I was expecting... I could barely make it back up my driveway - it can pull wheelies normally!

So - for now. the open filter is back on...

[90GTVert]

:welcome2:


The open filter and airbox have very different jetting requirements, so if you switch to the airbox you will need to use a main jet something like 10% smaller as Dave suggested. Otherwise it will run very rich with the airbox on the tune intended for the pod filter. Adjustments to the needle settings and idle mixture settings may also be required for it to run as it should. I suggest picking up a selection of main jets to tune the carb with if you plan to use the stock airbox.

If the carb is stock, PFS sells a Mikuni main jet kit that should work for you.

I have a set of 4 vids that go over carb operation for Minarellis that may be of use. This is 1 of 4, links to the rest are in the vid or on the same page.
www.youtube.com/watch?v=UipC6DLD-EE