Carburetor mounting angle?

S

SuedePflow

New Member
Hey all. I'm new to the forum and in the process of building my first motored bicycle.

I'm using one of the common 50cc kits off eBay, but I'm putting it on a BMX bike. Due to the size and shape of the frame, I'm mounting the motor under the seat, above the rear tire as apposed to in the middle of the bike. The easiest/bet way to fit the motor there, the intake side leans back instead of forward like normal.

My question is in regard to the angle in which the carburetor sits. Is this angle critical? Will I have problems with the intake side of the motor leaned back? Any info on the subject is appreciated.
 
Welcome you'll get a lot of help here!

However you do it the carb needs to sit pretty near level
if not dead level.
However there are different ways to mount the carb
you can even make a specialty pipe for it, if need be.
 
Thanks for the post.

My next question was going to be about the manifold itself. So it is a viable option to re-work the manifold so that the carburetor itself sits at the proper angle? And there won't be any issues with the angle of entry of fuel and air into the head?

I'm a pretty decent metal worker and welder, so if that's all it took to make this work, then that's the route I'll go.
 
SuedePflow said:
Thanks for the post.

My next question was going to be about the manifold itself. So it is a viable option to re-work the manifold so that the carburetor itself sits at the proper angle? And there won't be any issues with the angle of entry of fuel and air into the head?

I'm a pretty decent metal worker and welder, so if that's all it took to make this work, then that's the route I'll go.
Click to expand...

Not only is it an option, but at about 6 inches it vaporizes the gas better.

but be prepared to tune it, what type of carb just the standard nt
or a cns?
 
I'm not sure which carb I have, but here's a pic of it below.

What is involved in tuning one of these?


$T2eC16d,!wsE9suwywewBQ-qGQccpg~~60_12.JPG
 
That is a speed carb and I've never used one, it's similar to an nt I believe
as I understand it here are the difs, the nt you tune by the c clip on needle
and jet size, the cns has a hidden air mixture screw and that one
I'm not sure, but someone will chirp in later in the day

hope that helps, Oh do a google above on speed carb you will find out all about it.
http://motorbicycling.com/showthread.php?t=37986
here you go
 
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We could probably tell you more if we could see a photo of the engine/carburetor installed on the bike. The angle isn't too critical. It can slant forward or rearward slightly and even from side to side, slightly. It is a float operatated carb so you must keep float level in mind. If possible show us the installation and we'll try to offer more definitive advice.

Altering the intake manifold either to change the angle or length will not effect the fuel charge entering the engine that much. Of course we don't expect you to mount the carb on the handlebars or over the rear wheel so when I say "altering" I don't mean extremes. :)

Tom
 
SuedePflow said:
I reworked the intake manifold yesterday and the carb now sits level. Thanks for the info, guys.


20130615_204435_zps242d3f00.jpg


20130615_204833_zpsc4afa5b8.jpg
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NIce work, very clever.
Since the motor has no oil in it you could run the thing upside down if you wanted to, but the carbs float bowl is gravity based with direct air venting so if it's not level fuel will go out somewhere.

The big question now is what are you going to do with the exhaust as the port looks to be right up against the bottom of your seat?
 
KCvale said:
NIce work, very clever.
Since the motor has no oil in it you could run the thing upside down if you wanted to, but the carbs float bowl is gravity based with direct air venting so if it's not level fuel will go out somewhere.

The big question now is what are you going to do with the exhaust as the port looks to be right up against the bottom of your seat?
Click to expand...

AWESOME CLEVER:Maybe there is more room then it looks in the picture but a hot spark as well.
 
The seat isn't in position in that pic. It's loose and falling backward. When in place, there's actually a good amount of space there. I also plan to header wrap the exhaust pipe to help prevent my rearend from getting too toasty.
 
All welding is now done and fuel cell is mounted. Waiting for handlebar grips and the longer throttle cable to come in the mail. Meanwhile, I'm stripping and painting the frame. Still need to figure out what I'm going to do for a clutch disengagement lever. I'll be welding up an exhaust on Friday or Saturday.

Having fun with this so far. :-)
 
Very cool original use of a chinagirl. Been wondering if something like this would work on a bmx I recently was given... very interesting.
 
You might want to think about something to deflect air into the cooling fins the head might have an issue with airflow over the head a little flap hanging from your seat angled towards your engine might help
 
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