Tuesday, December 15, 2015
I finally received my wheelset from Britain yesterday so i of course had to take some pictures. Sadly I have not ordered tires yet along with lots of other parts that are in process still.
Here I am, working on bicycles, and I am trying to cut corners and be a tight-ass(read- cheap!). Mind you I am not talking about a $10,000 carbon framed triathlon machine here: I am talking about a $180, 8 year old, Norco Evolution Trials bike! These bikes use off-the-shelf mountain bike parts for the most part so even "high-end" parts for these things are not expensive.
So the background for this particular adventure in cheapness is as follows: I bought a different Trials frame and started buying parts to put it together. In the process I got a bunch of used parts that were cosmetically worse than I had hoped for so I thought to myself, "Self, why dont you try your hand at customizing the Norco and maybe make a better trials bike out of that at the same time?"
Now my friend Bryan, who is the whole fault I got into bike trials thought this was a bad idea...but thats okay. You need to live dangerously sometimes.
Some of the parts I ended up buying were; a Hope Mono Trials front brake, which needed a caliper rebuild. An Echo TR rear 135mm hub with a sprocket still threaded on. A set of ZETA 170mm FFW crankarms.
The Hope brake was cosmetically poor, but looked to be complete. I ordered up a seal kit and piston cap tool from across the pond. These went together very well thanks to the fact that the brake setup was a vintage piece so it did not require some foolishy complex system to bleed the brake lines.
Next were the crankarms. For the most part these were okay arms but the removal threads on the right side were a bit buggered up. solution? Take the tool steel crank remover tool and put a 1/2" impact on it, run it in. TADA!: new threads.
The rear hub was now in the crosshairs. The problem was that the cog/sprocket was still threaded on to the hub so that I could not lace a wheel to it and turn the cog off. I tried some simple grabbing and vice-ing with no luck other than gouging the crap out of the flanges. :(
This led me to the machine shop for an afternoon after i came up with a rough design. To the Right is the end product of that session. It looks fine and dandy but there is a flaw: Using the ParkTools chain whip didn't touch the darn thing at all. It simply flexed all over and made me angry at it. Heat didn't help, chemicals didn't help. I was at wits end.
I felt like I was close but i was missing some key component. I went over and spent some time browsing OTN for some inspiration. This led me to a thread about removing freewheels from crankarms. While not exactly the same it gave me the missing link:
Saturday, October 31, 2015
Who knows what a trials bicycle is? I think not too many people!
Thanks to my friend Brian I now own not just a MotoTrials but also two Trials bicycles!
The first bike I bought was a Norco Evolve. It is from about 2007 and I think a pretty decent frame for general use. I have put a new front rim and converted to a front disc brake, and that is about it so far!
The second bike is more of a project really. A ZOO! Pitbull frame and some parts. I happened across this gem on eBay and it turned out to be a local seller so I messaged him and a week later I had the frame, a front fork, stem, handlebars and some worn out tires. Score!!
I have done some riding with Brian and some cats from Minneapolis and I feel like I am doing okay, skills wise. I have to say that riding Trials is very enjoyable from both a personal fulfillment aspect and as a great training tool for general bike skills both Moto and Pedal.
Sunday, June 21, 2015
Main jet 107.5(or 110)
This is good. A number that both makes sense and is definitely doable
Idle Mixing Jet 17.5
Here is where things don't make sense. More research and reading shows that this is actually correct- it simply is not referring to the pilot jet like I had thought; there is an actual idle mix jet under the diaphragm!
Another good. My carbs have this needle in them! yay.
Air Screw 2 turns
When I took the carbs apart they had the air screw out about 3 1/2 turns. This didn't make much sense to me but i had read in the "social wisdom" about people suggesting such settings.
Float Height ??
Amazingly I could not locate a specification for this in the manual!
The BST Bible on ADV Rider says float is set by aligning the seam on the float with the base of the carb. GSTwins says float height is 14.6mm, which appears to agree with the Bible thread. BMW funduro appears to say 14.6mm float height. Suzuki DR manual says 14.7mm
So with all of this information I seem to have the basics for setting up a good baseline carb, with
According to user andysrage on apriliaforums.com the factory idle jet is a 37.5, with 4.5(!?!?) turns out on the idle air screw.
Saturday, June 20, 2015
So here I am with this Aprilia Pegaso: One cylinder with two carburetors, what the hell were they thinking!? Right after I acquired the bike I stripped it down to the carbs to have a look. This isn't the worst job in the world, contrary to what a lot of people on the forums claim.
What I found when I first pulled them off is that they were very clean inside and somebody had already installed the "euro" 110 main jets. Unfortunately the bike feels very "chug-y" at the lower RPMs, which is exactly where I like to keep the revs when slowly navigating a tough section of rutted gravel or dirt road. So I need to play with carbs again!
The up-side to this situation is that the Aprilia Pegaso uses a pair of BST-33 Mikuni carbs.
These are nearly identical to the pair of carbs that were used on the old Suzuki GS500. This means I am fairly comfortable opening them up and how they operate. I also know that replacement parts are readily available, I even have a tray of jets and parts from my time with the GS. Now my browsing of the forums revealed a few major issues with the "social wisdom" contained: Factory float height, factory jet sizes, and factory air screw settings.
I browsed the Aprilia forums and found very little useful information.
I then did an internet search which resulted in a few good items, namely the BST Bible thread on ADV Forums. This is a great source of photos, but all of the information is specific to the KTM LC4 engine platform.
I also had a few good sources from the GS days like: Float height
After running the bike a few days and having poor luck with the lower RPM I decided to get my baseline straight and figure things out a little better! As with all carb work it is critical that you establish that the engine is running as well as it should for the mileage: This means tune-up time!
-Replace spark plug with new, also buy a handful of the same plug for tuning work later. NGK's are usually $2/ea for basic copper plugs. Dont spend money on fancy plugs until you know the bike is tuned to a decent range.
-Check compression! Ideally you will do a leak-down test, but a simple compression test works in a pinch. You should really test it with the engine both cold, and hot. Sadly testing hot is not very friendly to aluminum heads so use your best judgment there! Cylinder Leak-down Tester
-Check timing if possible. Some newer bike you really cant, but most you should be able to at least put a timing light on it.
-Adjust valves if necessary.
-Use fresh premium fuel.
Okay, now pull the carbs off the bike and disassemble.
Make sure the float bowls are clear of gunk and debris.
Spray carb cleaner through the jets: If no fluid comes out of the throat of the carb somewhere the jet is probably clogged. Get out the fine wires and start unclogging! Dont stop till you get good squirts coming through.
Now comes an area where we need some technical information.
I happen to get a CD of the factory manual for the Pegaso when I bought it. If you don't have a service manual for your bike; buy one. Even if it is the PDF scan for 99 cents off ebay its still better than nothing as it will have the correct torques and such for other work!
Here is what the Aprilia manual tells me:
Carb type - Mikuni BST33
Idle speed - 1400rpm
Main jet - 107.5 (USA) 110 (Austria and Switzerland)
Needle - 5E 76 -2
Spray nozzle - 0 - 2
Idle mix jet - 17.5
By-pass - Dia 0.8mm
Idle mix outlet - Dia 0.8mm
Valve seating - Dia 2.3mm
Starting jet - 65
Idle air jet - Dia 1.5mm
Air screw - 2 turns
Accel cabel adjustment - 2mm
Okay, so that is a lot of numbers and things. Lets break them down a little.
The carbs are Mikuni brand, model BST, with a throat diameter of approximately 33mm.
Correct idle speed of the bike is 1400RPM when everything is happy. If it doesn't run at this speed then something is wrong.
Main jet is the orifice at the bottom of the Needle that controls fueling at most accels and higher load. Needle controls how the fuel flows from the main jet and the spray nozzle/emulsion tube into the engine. It basically constricts flow the further engaged it is.
Spray nozzle is the factories name for an emulsion tube; a term that fat American's might more readily recognize.
Idle mix jet is the jet that controls idle air/fuel mixture, also known as a pilot jet or slow jet. Unfortunately this number does not seem to jive with reality and definitely not with the "social wisdom."
The next 5 lines I will skip here.
Air screw adjustment is critical for a good idle. The approach is to carefully turn the screw all the way until it seats, then turn this number of complete revolutions out.
Accel cable adjustment is simply that you want a certain amount of slack in the throttle cables so that when everything gets hot it does not pull the throttle plate open unintentionally. SO, lets talk quickly about carburetor theory of operation:
Also important is float height. Float height will affect overall richness of mixture, to the point that if the floats are too high you can get fuel just flowing out of the inlet of the carb.
Here is the stock BMW funduro information sourced from the ChainGang:
- 1996 Onward Models:
- Main Fuel Jets #132.5
- Pilot Jets #41.3 (Idle Air Jets)
- Needles 5E94, 4th Clip from Top (Blunt End)
- Carb Venturi (Emulsion Tube) 584□□-2. The first "□" stands for a rectangle with a small square inside, the second "□" stands for a small rectangle. Thanks to Marty #436)
- Float Height 14.6mm from the Gasket Surface
- Idle Mix Screws backed out 3.5 turns from LIGHTLY seated (all the way in).