CL450 Racer - Prepping For Loring 2015 Part 2

After waiting on parts for a few weeks, over the weekend I finished wiring and installing the PAMCO ignition system. 

The installation first involved attaching connectors to the wires and covering them with heat shrink tubing (to both protect and stress-relieve them). Next, I made a small bracket to attach the Electronic Advance Module, sealed the module with liquid electrical tape to keep out moisture, and zip-tied everything in place. After this, all that was left was to time the ignition with the help of my friend and a Timing Strobe.

In addition, rather than apply the race registration numbers to the tank, I fabricated some brackets and installed number boards under the seat. Now all I need is warm weather!

PAMCO Ignition Installed

Air Intake Cover with appropriate warning

Number Board Bracket

Ignition Advance Module Bracket

Sealing the Advance Module from Moisture

Mounting the Advance Module Under the Seat

Wiring Harness Adapter for the Electronic Ignition

Ready For Testing and Tuning....once the snow melts.

CL450 Racer - Installing an Air/Fuel Ratio Gauge - Part 4

Here is a quick video of the operation of the Innovate Air/Fuel sensor. The response time is excellent, and I have ordered a miniature data logger so that I can record the results from my rides to analyze later.

CL450 Racer - Installing an Air/Fuel Ratio Gauge - Part 2

Now that the gauge housing was complete, it was time to mount it to the bike. I made a simple steel bracket that attaches beneath the handlebar mounting bolts, and installed longer assembly screws in the gauge housing that doubled as mounting screws.

CL450 Racer - Installing an Air/Fuel Ratio Gauge - Part 1

The standard low-cost method for tuning a carburetor is by performing a "plug chop". This is a process where a fresh set of spark plugs is installed in the engine, the vehicle is driven at a specific throttle opening for a few miles, and then the motor is quickly shut down and the plugs are removed and inspected. By checking the relative condition of the spark plugs, such as the location of carbon deposits, the color of the ceramic insulator, and the color of the exposed metal parts, it is possible to determine the relative tune of the engine. 

Carburetors are surprisingly complex components, and are equipped with multiple jets to provide even fueling to the engine at all throttle openings and load conditions. Every jet has to be independently tuned, so it is important to maintain a steady engine speed/load in order to perform the plug readings. Acceleration and speed changes will vary the fuel circuits and jets that are used. To determine the state of tune of a specific jet, the engine must be started, maintained at the desired speed, and then quickly shut down (ideally by pulling in the clutch, killing the engine, and coasting to a halt).

The phrase "plug chop" refers to the practice of cutting down the side of the plugs so the entire ceramic insulator can be inspected. If the plug ceramic is black, the engine is running rich. Likewise, if the ceramic is white, then it is running lean. Carburetor jets should be swapped until the plug is a brownish/tan color through the entire load range.

However, this process is tedious, wasteful (you go through ALOT of plugs), and not particularly exact. It is especially time-consuming if you are maintaining a race bike, and need to tune the carbs for a variety of air filter, muffler, temperature, and air pressure variations. Rather than do things the old fashioned way, I decided to purchase an on-board Air/Fuel Ratio sensor and gauge from Innovate Motorsports.

Special Delivery!

Laying out the equipment

Panel-mount gauge

This kit includes a high-resolution wideband O2 sensor which permanently mounts to an exhaust header. Based on the composition of the exhaust gases, the sensor calculates the ratio of fuel to air in the carburetor, and displays it on an numerical LED screen. The ideal stoichiometric ratio for a gasoline engine is 14.7 parts air to 1 part gasoline. Any more than this, and the engine is running lean. Lower, and it is running rich.

The biggest problem with this kit is it is meant for automotive use, so there are no mounting kits available for powersports applications. Normally this would mount to a hole in a dashboard, so the first step was to make a robust aluminum housing to mount to the motorcycle.

Raw material

Rough Cut

Shaping on the lathe

Test Fit

Marking out the shape of the back plate

Boring the back plate

Shaping the back plate

The raw material for the gauge pod

Drilling the bottom pkate

Drilling the gauge pod body

Tapping the holes

Hogging out clearance for the wires

Finished with Stainless Hardware

The final product

In the next installment, I'll focus on mounting the gauge and the O2 sensor bung.

Carburetor Modification Part 4

One of the benefits of installing the smaller Scrambler tank is, since it is physically smaller and sits higher on the frame, I can now perform all the carburetor tuning without having to disconnect hoses or prop the tank up. Following the results from the last round of carb testing, I determined that the idle/slow jetting is slightly rich (fixed by adjusting the air screw), the midrange is too lean, and the top-end of the bike still surges and stumbles.

Much more room now with the small tank

 I solved the midrange problem by installing the next higher-size needle jet (P-6). For the top end, rather than change the jetting, I reinstalled the sheetmetal baffles in the float bowls and lowered the float height. Both of these steps will lean out the mixture (and make the carburetors stop leaking fuel!)

The shakedown ride I took following these changes was encouraging. It now idles perfectly and accelerates strongly right off the line. There is still some stumble at full throttle, but it can now cruise at 60-65mph with no hesitation. I'm sure the correct setting is within reach, but I'll have to wait for warmer weather to really open it up and test it. The current carburetor settings are:

Mikuni VM26-8074

Main Jet: 130
Pilot Jet: 35
Needle Jet: P-6
Needle: 5F21
Air Jet: 2.0
Slide: 2.0
Float Valve: 2.5
Air Jet Turns: 2
Needle Notch: Center
Float Height: Approx 17mm

Hard at work with a cup of hot tea

CL450 Racer - Installing the Original Tank

When I purchased the hulk that would form the basis of my 450cc land speed racer, it was incomplete and didn't come with a gas tank.

Among other things

I had a larger CB500T gas tank installed on its original motor-less chassis, so I swapped it onto the new frame and modified the mounting points to suit. That tank served me well, until I stumbled on an original CL450 "Scrambler" tank on Craigslist.

That seat came from a junkyard and is WAAAY worse than it looks.

The inside is surprisingly clean

I was browsing for a donor tank to put onto the rolling chassis I assembled in my previous post, but the opportunity was too good to pass up. I decided to refurbish the scrambler tank, put it on its correct chassis, and return the 500T tank to its original home.

CL450 with the 500T tank

Lean and mean with its original sheetmetal

The scrambler tank weighs 5 pounds less than the 500T tank, and holds around 1 gallon less of fuel, so now the bike handles brilliantly :-D . Next up is to refurbish that seat, so I can actually use this machine regularly on the road.

Carburetor Modification Part 3

Jetting a non-standard carburetor for an engine, especially when no one has tried the combination before, is an extremely time-consuming process of trial and error. I reasoned that the original jetting would be a close match, or at least a decent starting point, because the three carbs had previously been mounted to a Triumph Trident, with each feeding a 250cc cylinder. What I didn't take into account though, was the possibility that the previous owner may have jetted it TOTALLY WRONG.

This is becoming an annoyingly familiar sight...

 Mikuni carbs have three main fuel circuits: the pilot circuit for 0 to 1/4 throttle, the midrange circuit for 1/4 to 3/4 throttle, and the main circuit for 3/4 to full. After weeks of fiddling, testing, and tinkering, I have determined that the pilot circuit was JUST ABOUT right, the midrange was extremely lean, and the main was extremely rich. In fact, the disparity between midrange and main was so large, that it created the illusion that it was jetted correctly, but had an air leak/low range stumble. The rich main supplemented the lean midrange and they compensated for each other, while causing poor power and a tendency to stall at low throttle.

Needle Jet Swap

Seriously, I've had enough of propping the tank up...

I think I'm pretty close to getting it dialed in mostly right, and will post the final settings when I have them. Though, I think I should bring it in to a tuning shop and have them doublecheck it...and also rebuild the brakes....possibly replace the clutch plates...sooner or later it will be "done"!

Carburetor Modification Part 2

Once the carburetor diameters were modified on the lathe, I boiled them for half an hour to leach out any remaining salt from the various passages. I bought a cheap pot from Wally World, filled it with water, and let it sit at a rolling boil:

Someday, I may actually cook FOOD on this stove...

I then blew the passages out with compressed air, and a bit of carb cleaner to purge any moisture.

A few years ago I bought a pair of grimy velocity stacks at a swap meet for a fiver, but never really knew what to do with them. I tried them out on my gutted mikunis, and found that they just happened to fit nearly perfectly. I just needed to file off some burrs and smooth out the casting, give the bellmouths a thorough scrubbing, and clamp them on.

Taking Shape

After that, it was relatively straightforward to clean and reassemble the rest of the carbs. I have no clue which jets to use, so I'll just keep using the ones that the carbs came with to get started. They were previously installed on a Triumph Trident 750, so they should be relatively close to the correct tuning for a 250cc piston each.

Clean and ready for installation

The only other major modification I made was to the float bowl screws. It is difficult to remove the bowl with a screwdriver when the carbs are installed, so I replaced them with a combination of spacers and thumbscrews:

Now the bowl can be easily dropped by hand, in order to adjust the jetting while in place.