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Post by ewasleske on May 3, 2017 10:06:14 GMT -5
I remember coming across these but can't seem to find them. Anybody know who sells them? I want to tweak the air volume going to the carb. My Keeway runs great with the snorkel out but starts really hard.
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Post by ryan_ott on May 3, 2017 10:14:40 GMT -5
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Post by ewasleske on May 3, 2017 11:09:33 GMT -5
Thanks Ryan. E Bay....duh!
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Post by ryan_ott on May 3, 2017 11:31:13 GMT -5
Before you start modding the air box do a basic carb clean and maintenance to make sure that's not the cause of the hard starting. The fuel nowadays isn't that good for small carbs. I have issues getting some stuff started if they sit with fuel in the carb for a couple weeks, it I drain after each use it will start right up. Damn fuel.
But go figure I needed fuel for my mower and didn't have any non mixed so I dumped some 20 year old Coleman camping fuel it, yup started right up.
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Post by knobby on May 3, 2017 13:35:19 GMT -5
Same here, the smaller hole of the pilot gets screwed up pretty easy, even if its only a couple weeks. Or sometimes even faster if its an old jet. With a newer jet I don't know if its the smooth surface finish, but they seem to resist clogging better. I think the ethanol scores or chemically alters the surface of the brass over time. The larger size hole on the main seems to keep that one alright even if its an older jet.
I have those uni vents if you don't want to do ebay.
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Post by ewasleske on May 3, 2017 14:14:25 GMT -5
Good God! White gas...NASA uses that stuff to launch rockets.
The scoot pops off if I loosely cover the snorkel hole.Hence my thought on airflow.
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Post by ewasleske on May 3, 2017 14:46:31 GMT -5
Ryan, you got me thinking about the gas. Perhaps my storage additive did too good of a job "cleaning " the system. Then it carries all the unwanted stuff straight to the carburetor.
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Post by FrankenMech on May 3, 2017 18:34:20 GMT -5
White gas, or camping fuel, has a very low octane number. It is good for cleaning stuff out but don't run a scoot on it.
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Post by ewasleske on May 4, 2017 12:35:48 GMT -5
Wouldn't dream of it! Too many camping stories involving white gas...
Some funny and some not too funny.
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Post by FrankenMech on May 4, 2017 17:28:48 GMT -5
If you want a good carb setup buy a 'performance' carb that is jetted for an open filter from the factory and modify it to vent the bowl into the carb intake (there is a specific way the vent must 'point'). Doing so will get you a carb that does not have to be re-jetted for each and every little airbox modification. I believe Jon at NYC scooter parts has a performance carb with a choke. Call him and ask; 212-598-0016. You will have to do your own vent modification. I also use a Vito adjustable jet for seasonal temp variations.
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Post by ewasleske on May 5, 2017 14:44:55 GMT -5
I thought that the bowl vent was for pressure equalization.
Alas, I am at the crossroads with my current set up. I haven't heard of this idea before.
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Post by FrankenMech on May 6, 2017 0:15:35 GMT -5
I thought that the bowl vent was for pressure equalization. Alas, I am at the crossroads with my current set up. I haven't heard of this idea before. It should be used for pressure equalization with the intake but it is usually just vented to atmosphere. That is the part of scoot carb design that causes major problems. Larger carbs used in autos, trucks, and other engines etc back in the dark ages b4 EFI vented the fuel bowl to the intake. Some carbs used a type of atmospheric venting of the carb fuel bowl as a type of power valve to enrich the mixture. I have no idea why scoot carbs are so backwards. Playing with jets all the time is idiotic to me. |
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Post by benji on May 6, 2017 0:37:41 GMT -5
So, does that mean the bowl vent on a scooter carb could hooked up to the intake tract with a vacuum port? That way it could equalize pressure w/o the possibility of atmospheric air entering the carb?
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Post by benji on May 6, 2017 0:39:58 GMT -5
I thought that the bowl vent was for pressure equalization. Alas, I am at the crossroads with my current set up. I haven't heard of this idea before. It should be used for pressure equalization with the intake but it is usually just vented to atmosphere. That is the part of scoot carb design that causes major problems. Larger carbs used in autos, trucks, and other engines etc back in the dark ages b4 EFI vented the fuel bowl to the intake. Some carbs used a type of atmospheric venting of the carb fuel bowl as a type of power valve to enrich the mixture. I have no idea why scoot carbs are so backwards. Playing with jets all the time is idiotic to me. I've noticed that scooter and motorcycle technology seems to stay in "classic" mode- I had a 78 xs650 special with a points ignition. I guess older tech is cheaper and simpler and easier to rebuild. |
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Post by FrankenMech on May 6, 2017 0:52:38 GMT -5
Basically yes. The shape of the vent port facing the flowing air is important. I used an existing port in my airhorn for my vent port. A piece of brass tubing cut at a 45° angle is a good shape. Face the opening towards the incoming air. There really isn't much of an exchange of air or gas, it is just a pressure signal that allows the internal carb jets to adjust fuel flow based on conditions at the carb intake. There is no need to change jets due to air filter mods, changes in the filter media like dirt loading, etc etc. Back in the age of carbs an exceptionally dirty air filter could cause problems but normal changes to the filter condition or type didn't cause problems with fuel metering.
Air flow ------>
/| <---45° cut
|| <---1/8" dia brass tube
|| <---1/8" dia brass tube
||
-to bowl vent.
Brass tubing can be purchased at hobby shops.
Tubing can be secured in a drilled hole with baking soda and super glue.
There is a .pdf file here with an explanation of how to convert points to electronic ignition using a Ford remote mount TFI module in the tech section.
There are a lot of scooter tech 'myths' passed on as gospel....
I was lucky and started working on scoots without any previous scooter tech babble clouding my mind. I was able to apply real engineering and scientific knowledge to the systems I found on the scoots. It was interesting to see how many 'myths' there were out there. It is incredibly hard to teach people when they have pre-concieved notions and don't want to learn anything different. The internet is full of 'experts' that pass on those myths as gospel even when they are false. It was much easier to teach when I faced a class full of adult students and their jobs depended on what they learned.
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