Weber Geometry at Full Throttle

rhk109 · 05-01-2006, 11:18 AM

I was fiddling around with my full throttle stop when I noticed that the right bank is wide open the left bank has another 5 to 10 degrees of rotation before it is wide open. Both banks are even on the STE at idle up through 3000 RPM.

Any cause for concern?

Mike Bonkalski · 05-01-2006, 11:27 AM

You need to adjust your linkage so both sets of throttle plates are perpendicular at full throttle.

rhk109 · 05-01-2006, 11:36 AM

Quote:

Originally posted by Mike Bonkalski
You need to adjust your linkage so both sets of throttle plates are perpendicular at full throttle.

Easier said than done... I tried with little success. Is there a trick? What part of the linkage should be adjusted to achieve this? Should the press rods be equal length?

smdubovsky · 05-01-2006, 11:58 AM

http://www.pmocarb.com/installation.htm

Graphic #4 is what you need. You have to move the pivot rod points up/down and fore/aft, get mirror angles, etc.

Mike Bonkalski · 05-01-2006, 12:00 PM

Check out this link on the PMO site:

http://www.pmocarb.com/Images/Instructions-4.gif

There are also some decent detailed instructions on setup and balancing. It's a good place to start.

rhk109 · 05-01-2006, 12:16 PM

Thanks, but I already have all the PMO info. I was hoping for a magic bullet. I guess I'll start over from scratch.

Does anyone have a method or tool for ensuring that the W & X angles are equal? It's pretty hard to tell just by eyeballing them.

Mike Bonkalski · 05-02-2006, 06:08 AM

You can make the measurements with a plumb bob, straight edge to follow the line of the linkage, a protractor and a ruler.

It's helpful to have an extra set of hands around when doing all of this.

rhk109 · 05-02-2006, 06:34 AM

I eyeballed it! The anal-rentative engineer in me was hung up on keeping the press rods the same length. Once I got over it and set the geometry and individually adjusted the press rods she came right in. Balanced all the way up to 4000 rpm. Both throttle plates are vertical at full throttle.

However, I did notice something strange. When I pressed the pedal to the floor boards I didn't get all the way to full throttle at the carbs. So I reached in and pushed on the pivot arm at the front of the engine and the carbs opened up fully and stayed there when I let go of the pivot arm. I then released the pedal and took the return springs off the carbs. This time when I pressed the pedal to the floor the carbs opened fully. I then released the pedal, put the springs back on and pressed the pedal to the floor. Sure enough, the carbs did NOT open fully.

Is there something in the linkage/cable that can stretch?

smdubovsky · 05-02-2006, 07:39 AM

Not really stretch, but there is a little slop in all the linkage that the springs will 'find'. Cent remember if there is a throttle stop on the board under the pedal - like the clutch stop (Its been a LONG time). If not, there is probably enough free play at the top of the pedal that you can shorten the rod that goes from the bellcrank on the back of the enginte to the weber crossbar. Will move the pedal higher so that 'mashed to the floor' gives you a little more travel.

SMD

Boele · Boele's Garage

Quote:

Originally Posted by smdubovsky

http://www.pmocarb.com/installation.htm

Graphic #4 is what you need. You have to move the pivot rod points up/down and fore/aft, get mirror angles, etc.

Does anyone know if these manuals are still available somewhere? I face difficulties with mounting the PMO linkage. The provided installation manual looks like an old scool copyprinter version that is very poorly readable..