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Post by william on May 3, 2012 6:42:41 GMT -5
I've recently discovered that you can't run a 49cc 2T engine without the airbox installed. I'm still not quite sure why but I believe that it has something to do with airflow through the carburator. The Yamaha CA50 Riva that I salvaged from the junk yard and am trying to restore doesn't have an airbox so I have to make something work. I did manage to get ahold of the airbox body, but nothing else. So I made a cover for the body and connected it to the carb with some parts I found while browsing the local hardware store.
My question is: How important is the the size of the adapter from the airbox body to the carb? Was it designed to have a certain diameter to allow, or restrict, airflow to the carburator?
And also: How important, again for airflow purposes, is the material used for the air filter?
My whole point is, does the airbox do more than just filter the air or are there other things to consider when adapting an airbox to fit this engine? Am I getting the proper airflow to keep everything in balance?
Much obliged for any replies...
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Post by bullet on May 3, 2012 7:28:49 GMT -5
A carb. likes still air to draw from and IMO that's an important part of an air box. I would never run without some kind of filter. I used some foam from an air conditioner filter wrapped around a cone filter in an air box until I found the correct part on one of my project bikes. Also to keep the fuel mixture right it should be a tight fit to the carb. If your jetted right for a filter and air box any major leakage of air between the air box and carb. will lean out the mixture. Home improvement stores carry a variety of different types and sizes of hoses and clamps. Get creative. You don't have to have an air tight seal just one that does a good job from the filter to the air box to the carb.
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Post by sentinex on May 3, 2012 15:26:17 GMT -5
I've recently discovered that you can't run a 49cc 2T engine without the airbox installed. I'm still not quite sure why but I believe that it has something to do with airflow through the carburator. The Yamaha CA50 Riva that I salvaged from the junk yard and am trying to restore doesn't have an airbox so I have to make something work. I did manage to get ahold of the airbox body, but nothing else. So I made a cover for the body and connected it to the carb with some parts I found while browsing the local hardware store. My question is: How important is the the size of the adapter from the airbox body to the carb? Was it designed to have a certain diameter to allow, or restrict, airflow to the carburator? And also: How important, again for airflow purposes, is the material used for the air filter? My whole point is, does the airbox do more than just filter the air or are there other things to consider when adapting an airbox to fit this engine? Am I getting the proper airflow to keep everything in balance? Much obliged for any replies... From what I understand the airbox is designed with the carburetor and jets on it in mind. I read in many forums and threads that if you change the airbox you might have to re jet your carburetor, is the same if you change your exhaust. Changing the airbox might increase or decrease the airflow making the system run lean or to rich. Hope it helps. |
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Post by 90GTVert on May 3, 2012 15:36:24 GMT -5
You can run without an airbox, but the carb has to be tuned for it. With stock jetting it's generally not gonna work out well, as you have seen. Bullet and sentinex made a lot of good points. You can get UNI air filter sheets and cut your own for your custom airbox. It'll be less restrictive than what's stock in most, so you still might have to do some tuning. Unless you get a spot on stock setup, it might need tuning. I have played around with my stock airboxes enough to see that even reasonably small changes can result in needing an upjet. The airboxes on the most common jog style 2T scoots have a snorkel inlet. I removed that and went from a 78 main jet to an 85. I then opened the hole where the snorkel was up a little more and added filter vents to the airbox and had to move to a 90 main. An open UNI filter needed a 100 main jet. All the details on all of that are in the Project 90 thread in the Tech Library if you're interested or want to see pics of exactly what was done. Point being, they can be pretty sensitive to change.
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Post by william on May 4, 2012 7:24:41 GMT -5
I'm certain that I have an airtight seal on both the carb to airbox and cover to airbox, and being that the airbox body is stock, I would think I should be ok with the set up I have. The air inlet holes of the airbox, however, are facing the front of the scooter and being that I don't have any side covers for the scooter I might have at least some air being forced into the airbox by the forward speed of the scooter. Might that be a problem? I can experiment with different materials for the airbox filter and use the one that gives the best performance, but how will I know if I need a different carb jet? Is there a surefire method to tell that I need a different jet?
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Post by 90GTVert on May 4, 2012 10:07:44 GMT -5
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