Fabricating a TPS Driver

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Written by Randy Fox (randysgym)   
Thursday, 27 August 2009

 

Background Info and Personal Notes

Variable ignition timing has been important in getting the most out of every gasoline vehicle's engine since the Ford Model 'T'. Early cars had a lever on the steering column to manipulate the timing manually. Modern fuel injected engines employ a computer chip to calculate and adjust the timing.

I initially installed a VOES system for my Mikuni HSR42 aftermarket carb. But over the first year, I noticed that many times the VOES was not advancing the ignition timing when I thought it should have. I never quite knew when my bike would act like a lion or a kitten. So when I upgraded to a Genesis, "Big Air", 48mm carb from PSIPower, Inc, I decided it was a good time to get my TPS back.

 

Since the Genesis did not provide any place to adapt an on-board TPS bracket, a stand-alone TPS module was my only option. PSIPower offers a stand-alone TPS module (PSI Genesis Big Air Accessories part# 05-009). And one big plus this unit offers is its ability to work with any carburetor. However, as of the date this article was published, their TPS module cost roughly $150. Plus, their unit uses an additional throttle cable -- either the 'push cable' or a 'splitter cable'.

 

Money aside, this last requirement was a deal breaker for me. I just wasn't interested in re-installing the archaeic 'push cable' that I had removed some years before.

 

In the end, I decided to build my own TPS module -- one that would incorporate the TPS from my stock carb, not require the throttle's 'push cable,' and would fit in the space under the tank. This article describes how I did this.

Warning: This project is among the most time consuming and exacting of any I have done on my bike. Considering the relatively small, seat-of-the-pants performance improvement it makes, most others would likely prefer to spent their time in other improvements. I am happy with my result, and would do it over again, but then, I enjoy this kind of thing.

 

Tools Needed

Angle Grinder --with cutoff wheel and grinding wheel

Electric drill (minimum) --or drill press, or machine lathe

Bench vise -- or other means to bend heavy gauge sheet metal

Pliers --for bending sheet metal, and general use

General hand tool set --screwdrivers, allen wrenches, file/s, punch, measure, etc.

Tin (sheet metal) snips --or nibbler or plasma cutter

Sandpaper --in the following grits: 50, 100, 220

Dremel, rotary type tools:

  • Dremel motor unit, or equivalent
  • Small diameter, straight-shaft, diamond cutter
  • Sanding drum
  • Cutoff wheel

4-40 tap --used to thread the set-screw hole in the pulley.

0.09" drill-bit --used to drill the set-screw hole in the pulley.

 

Materials Needed

2" x 2" x 1/4" mild steel plate (or nylon) --for making the pulley system.

2" segment of a 1/2" mild steel dowel --for the axle.

Brass/bronze round stock or bushings --This will be used to make axle bushings.

Lexan, polycarbonate, plexiglass sheet --At least 4.25" x 3.5" x 0.93". This will be for building the plates that hold the axle/pulleys in place.

8-24 x 3/4" Stand-offs --Quantity 4, for making the framework.

8-24 x 1/2" Screws --Quantity 8, for holding the plates together. I used stainless steel ones.

Thick gasket material --I used pieces of an old inner tube.

Sheet metal --Approximately 24 gauge, at least 6" x 3.5", for making spacers for the TPSensor mount and the dust cover.

6-32 x 2" Screws --Quantity 2, for mounting the TPSensor to the plates. I used stainless ones.

6-32 Washers --Quantity 2, for mounting the TPSensor to the plates. I used stainless ones.

6-32 Nuts --Quantity 2, for mounting the TPSensor to the plates. I used stainless nylock ones.

4-40 Screw --Quantity 1, for use as a set-screw to hold the pulley to the axle.

 

 
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