'76 cb360 cafe:ROUND 2...third times a charm!
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That's a CL motor never heard it run that Luke bought months ago. Did valve adjustment, didn't even adjust points had them removed when I painted engine and just tossed em back in, never pulled plugs. Completely from scratch harness, only verified lights worked when I built it, never checked for spark. Dead battery hooked to a jump box. Two flat slide dirt bike carbs, never even pulled bowls to check jet sizes or needle clip position. "Fuel can" is a folgers coffee can, no front wheel on a mc jack on a sketchy wooden crate, mind you I'm standing on a bar stool kicking the bike over! 7 kicks and it fires right up with no adjustments other than turning idle down a bit. Revs smooth and idles nice.
redwillissuperman
Keep it simple- engine, wheels, bars
Which flat slides? 
redwillissuperman
Keep it simple- engine, wheels, bars
Nope two. But it will idle with two. Just a big flat spot.
redwillissuperman
Keep it simple- engine, wheels, bars
One would be awesome turned out to the right side of the bike opposite the high exhaust. 
redwillissuperman
Keep it simple- engine, wheels, bars
Looks good.
Two carbs. Fit to stock carb boots. And uni filters I ordered to fit stock carbs. More fine tuning and plug checks will be had. Didn't have a big flat spot. This is slapped together to see if motor would run/check harness and charging system. Really to regain motivation to work on this thing. I'd rather be wrenching/building stunt parts for my sport bikes
Still need to get a more correct throttle cable. This one was made of a single cable and a Y splitter from a giant tote of random NOS cables. This one Has too much free play, too short and doesn't have an adjuster inline or at throttle tube. Also note there isn't a clamp on the can to the rest of the exhaust.
focusinprogress
City Limit Moto:Parts-Service-Apparel (716)8038606
It was pretty surprising how cleanly it revved and idled with absolutely no adjustments to out-of-box carbs.
For those of you saying a pair of PWK 34mm is far too large....would you elaborate why?
We don't really know flow specs on these carbs, but they were ordered based on measuring the intake size of the stock carbs so we were under the impression they're pretty close in sizes but just newer/better tech.
For those of you saying a pair of PWK 34mm is far too large....would you elaborate why?
We don't really know flow specs on these carbs, but they were ordered based on measuring the intake size of the stock carbs so we were under the impression they're pretty close in sizes but just newer/better tech.
So the stock carbs that came on the bike are CV carbs and the PWKs are slide carbs. CV carbs generally have a larger diameter because of the way they operate (throttle controls a butterfly valve and the air passing through the carb, in conjunction with a diagragm, is what causes the slides and jet needle to move). This means the throttle controls only the air and the air controls the fuel metering.
In slide carbs, the throttle cable controls both the air flow and the fuel flow. Because the air is not needed to control the fuel flow, the diameter is generally smaller.
When you use a carb whose diameter is too large, this tends to have a negative impact on throttle response. There needs to be a certain amount of restriction in the carb due to the venturi (which is what "sucks" the fuel from the bowl and into the carb). Too large a diameter and the air moves too slowly. If the air moves too slowly then the fuel metering is not precise.
In slide carbs, the throttle cable controls both the air flow and the fuel flow. Because the air is not needed to control the fuel flow, the diameter is generally smaller.
When you use a carb whose diameter is too large, this tends to have a negative impact on throttle response. There needs to be a certain amount of restriction in the carb due to the venturi (which is what "sucks" the fuel from the bowl and into the carb). Too large a diameter and the air moves too slowly. If the air moves too slowly then the fuel metering is not precise.
focusinprogress
City Limit Moto:Parts-Service-Apparel (716)8038606
very much appreciated sonreir.....we assumed jetting and needles might need tweaking, but these carbs came with extra jets and different taper needles to play with....we'll have to do plug chops and see how the bike responds overall.....for now we're super happy it just fired right up and revved decent and settled down to idle.
For what it's worth, the exact same carbs are available in 28mm, 30mm, and 32mm if these prove to run poorly. but based on initial fire up I'm not convinced they won't dial in just yet.
For what it's worth, the exact same carbs are available in 28mm, 30mm, and 32mm if these prove to run poorly. but based on initial fire up I'm not convinced they won't dial in just yet.
redwillissuperman
Keep it simple- engine, wheels, bars
Earmark the 28mm ones for later just in case. I have 32's on a built XS650 motor.
crazypj
Split personality, I fake being smart
redwillissuperman said:
VM 32's will support around 50bhp PER CYLINDER
Sonrier gave a good concise explanation of mechanical slide carb operation.
You will have to jet the mid range real rich to compensate for the low airflow around 1/3~3/4 throttle then somehow lean off top end (Suzuki had same issue several years ago on GSXR600/750)
Suzuki used solenoids to add air around 2/3~3/4 throttle.
The original Honda 3 jet carbs use a similar plan by using 'lean' jetting on primary jet then adding fuel with secondary main jet as slide lifts. It isn't as precice as electronic operation but being 'all mechanial' it removes any possibility of electrical issues
With 2 jet carbs (Mikuni VM, etc) you can only rely on needle and needle jet for mid-range operation (slide cut-away is only for initial throttle opening to around 1/3 throttle)
The Bernoulli principle shows the pressure drop as air accelerates through venturi which is what is going to draw fuel through jets, low float level, (high fuel level) will help mid range running as the pressure differential won't have to 'pull' fuel so far
focusinprogress
City Limit Moto:Parts-Service-Apparel (716)8038606
we finally put in a bit of time on this again.
last night we finally got an exhaust clamp for the muffler, proper hardware for the rotor adapter and mounted that, balanced the wheels, rebuilt the forks, installed the chain guide we grabbed on ebay, and buttoned up the front end.
I think what's left is mount the electronics tray, fill and bleed the front brake, double check all the bolts and such are tight, mount the seat (just resting on it right now), blast and powdercoat the gas cap, mount the petcock and run fuel lines, and then she can come off the table and do some test rides (once the snow melts to an acceptable level to try out the dual sport tires in lol)
last night we finally got an exhaust clamp for the muffler, proper hardware for the rotor adapter and mounted that, balanced the wheels, rebuilt the forks, installed the chain guide we grabbed on ebay, and buttoned up the front end.
I think what's left is mount the electronics tray, fill and bleed the front brake, double check all the bolts and such are tight, mount the seat (just resting on it right now), blast and powdercoat the gas cap, mount the petcock and run fuel lines, and then she can come off the table and do some test rides (once the snow melts to an acceptable level to try out the dual sport tires in lol)
Got the clutch bled and adjusted. Front brake as well. Took it for a test ride in the ice and snow, was a little sketchy. Has high idle. Checked the plugs a touch rich. Backed mixture screw out and it improved a bit. The PWKs have a 38 pilot jet, gonna go a size smaller. Haven't touched needle jet, or sync'd the carbs yet. Still need to get some nicer hardware for random things. Also still have some small exhaust leaks at the clamps to take care of as well
