Sumo Throttle Travel

[Ranger Bob]

Standard Sierra pedal box connected to Holley Carb on Rover V8. The amount of pedal travel seems excessive. I can extend my leg fully and still not get full throttle. What have I done wrong?

[Miket]

Originally Posted by Ranger Bob

Standard Sierra pedal box connected to Holley Carb on Rover V8. The amount of pedal travel seems excessive. I can extend my leg fully and still not get full throttle. What have I done wrong?

Push your seat further forward. :thumb:

[andywsussex]

I'm afraid I don't know what the normal setup is for a Sumo - or whether the Sierra box should give the correct travel - but if you're not reaching full throttle your lever ratios aren't correct.

To get the full throttle range the arc lengths need to be the same. This is determined at the carb end by the angle through which the throttle arm at the carb moves and the length of the lever (from hinge to cable connection); at the pedal end you need to decide what angle you want to move the pedal (which at the moment is obviously too large) and then work out the lever length (pedal hinge to cable attachment) you thus require.

Arc Length = 2 x Pi x (Lever Length) x (Angle through which it moves) / 360.

Work this out for the carb (you can approximate it using a ruler - you won't be far off as the angles tend to be small.

Then use:

Pedal Lever Length = (360 * (Arc Length at Carb)) / (2 x Pi x (Angle you want the pedal to move through))

If anything, I'd make the angle the pedal moves through (in the calc.) a touch less than you want, because in reality the cable will probably stretch and they'll probably be a bit more travel needed because the outer cable will most likely not be fixed rigidly all the way along. Again, you can guesstimate the lever length by putting a ruler against the mounted pedal and seeing where along the lever a full sweep of the pedal corresponds to the length you measured at the carb.

A bit of a geeky method of working out something that actually ends up pretty simple.

Andy

[Paul B]

Basically, you need to move the cable attachment point, on the carb, closer to the pivot point such that you will not need to pull so much cable to get the full angular movement of the throttle linkage.

Simple to say but you may need to fabricate a new cable attachment bracket.

Paul

[Almac]

......or you could weld an extension onto the top of the pedal to increase the pivot ratio in favour of cable travel. I extended my mine by about 50mm and it seems to have made all the difference. As a result, the cable now passes throught the bulkhead about 20mm below the top.

Alan