carb problem? starves when accelerating By dubyajayes (Read 2,023 times)

[steven]

Jun 28, 2015 16:07:23 GMT -6 Alleyoop said:

Most folks believe that the Fuel/Air mixture screw is only for idle but the Pilot Jet passage is always having gas sucked out of it along with the main jet. There is no CUT OFF from the pilot jet it is an open passage and the screw if its a CV CARB cuts off SOME of the fuel passage when turned clockwise having the screw tip go more into the passage. As a matter of fact if you look by the butterfly and open it a little you will see about 4 tiny fuel outlets, the back outlets are ALWAYS open those the screw does nothing to them because the passage for those outlets is BEFORE the fuel Ratio Screw. The Fuel Ratio screw controls only the front outlets not the ones further back.
So contrary to what most folks believe sorry to say but they are wrong.
Here is a chart of when things get going on a carb.
Alleyoop

I believe that chart is over-stating the impact the air/fuel screw has on the performance at WOT. I just screwed mine in all the way, and took it on a ride. Then backed it completely out, to where it was removed, and took it on a ride. It obviously made a difference at idle, but if there was a difference in performance under throttle, it was not noticeable. No difference in top speed. Maybe mine is a rare case.

[Alleyoop]

All I was saying is that the Fuel Ratio Mixture screw feeds fuel all through the throttle range. Granted it feeds less fuel as the butterfly is opened as the chart shows but never the less fuel is always being sucked out of it as well as the Pilot Jet Outlets further back that are always open and there is NO control to shut them off as you can see by this cutaway of a carb. When you up the IDLE, you are actually opening the butterfly uncovering the Fuel Outlets further back so that more fuel is sucked in.

If you ever had a motor make a BRAT sound at high speed it is telling you it need just a little more food in the way of fuel. So to feed the animal so as NOT make that sound all you do is richen up the Fuel Mixture and the motor will not make that sound anymore.

As far as noticing any difference you would have to have very good ears and feel for your scooter and motor to notice anything, pretty hard with the wind and the noise. If you slap on a free flow muffler the only thing anyone will notice is how loud it is but in reality the motor will gain a couple rpms and due to that a bit of mph more maybe 1/2mph which is not noticeable. But one cannot tell any difference with all the noise and wind going on, but for many a loud muffler means more speed anyway(HAHA).
Alleyoop

THIS CUTAWAY DEPICTION OF A CARB SHOWS WHAT I MEANT:

[olblindman]

Thanks. I have ordered the tach, and will install as soon as possible. As a point of reference, what sort of r.p.m.s should I be seeing at WOT?
This forum, and you, have been very helpful to me. I really appreciate it. Scooters and motorcycles
are 'new' to me......I have always been a sports car sorta guy.

Thanks again!