Ordered smartcarbs

[Luther]

Paul, can you tell us what size airjets? Yamaha was on the right path giving it separate low and high speed air bleeds even if it took Rick 30 years to figure out how to make them adjustable and useable. When I was last talking to Rick he was very wound up trying to explain it all but I was bogged down with life and didn't take it all in. I told him to come 100 miles out of his way to his mom's in Dallas to show me what he was doing so I could make the fixture he wanted to make it easier. Rick was very stubborn and I rode several bikes there before he had a solid grasp on all this so I have no doubt stock carbs can perform as good as any. Better Rick would say. In the Ivan's needle kit Ivan says he got no difference on the dyno with or without airbox. I don't know how that can be as its the big stumbling point and what Rick was trying to fix. I can say that the way my bike is now with the TM28's it makes no difference with or without airbox.

So in the last couple years I tried using and tuning around the 1.1 stock carb air bleeds in my TM28's instead of 1.8 they came with. It runs best it ever has but I need to go to the track to see how wide open running is.

The factories have spent years developing 4t motors to run flawless idle to wfo. RZ500 does an amazing job of doing the same. Its also amazing how bad they can run if the slightest bit off. I hope the smartcarb can make tuning easier

[lost1750GTV]

"People actually cruising"
If that was a consideration I'd have a different bike.
Rztoms dyno compares show the stock filter/airbox are a weak link (with pipes) without removing the elbows.
"Make tuning easier" - as the carbs don't have to come off for anything, I'd say thats without question.
There's plenty of room for adjusting the height of the rod without taking anything apart, so then the question is if one of the dozen or so available is right for a particular build.
They seem to have it well sorted for current (and older) 2 stroke dirtbikes, so it would seem its just a case of matching per cylinder output and power curves to one of them for rod selection.
So I look at it that I might spend the same amount of time doing the actual tuning, but no time spent in the associated carb removal/reassembly tasks. With the external adjustments, having the carbs "outside" should make even rod replacement quick clean simple.

[rz500guytexas]

Next time I am doing carb work will look. I wish he would have taken offers from some people on design of the carb work. Maybe it was his way of keeping us customers. My issue with the 500s was the surging at a steady 3500 to 4500 rpm. Above , below, or giving it gas was fine. Never checked but his mods were also oval bore. He said that way the slide stayed matched to the carb. If correct it made for an equivalent 29 to 30 mm carb. There are two air jets in the front because he drilled the brass ball out and tapped it for the other jet. There is also some passage he drilled out that i believe connected to the float bowl or choke circuit. My TZR250 that I am working on has 6 air jets that are connected to two electric solenoids. The solenoids work with the controller and depending on rpm open and close passages to allow better throttle response at low speed. Modifying the 500 carbs was a difficult process due to different jigs so he tried to do a large batch at a time. It was not a cheap mod but works for me. Would be interesting to see what others think about the mod if they have them on their bikes. Some might not even know with the way these bike swap hands.

And a whole entire subject from Rick was his second radiator. An entire different discussion

[hailwood1965]

Has anyone seen the inside of these smart carbs to try to understand how they work? I looked on the USPTO site last night and found nothing ...

[lost1750GTV]

Plenty of youtube vids with them apart, and air/fuel flow diagrams etc on their website.
I have been out of town so asked them to hold my shipment.
Maybe best overview is their "lectron vs smartcarb" summary, as it explains how the lectron works and how this is different, diagrams etc

[lost1750GTV]

Have them now, just double checking float heights in the warm kitchen using isopropyl alchohol,which for some reason we seem to have lots of.
For anybody checking these on the internet, these smaller ones have a conventional pivot float mount, not the center pin used on the larger ones.
In any event, when tilted nothing comes out anywhere, which was one of my reasons for purchase. Sealed float bowl with check valves.

[lost1750GTV]

Above freezing today so had a chance to remove tank and loosen off old carbs - and I can confirm what Bill Wilson already knew, these carbs seem to fit without any clearance issues.
Not much for progress, but a little bit on decent days might have it complete come spring. Yes, I could do more but frozen wrench/cold hands can lead to a lot of dropped stuff and sloppy work - and I do that at the best of times.
And there is always something else needing attention.

[lost1750GTV]

Cancel the above " fit without any clearance issues".
That was a quick check. Old carbs still hanging, sliding one new one roughly in place. Supposed to get really cold again, so got the old ones completely removed - and it seems I do have issues on both sides. So if anyone is thinking of these. Hold off for now.

[tacky1]

I know I had to space out the upper cylinder manifolds to get the 34s to fit, Are you having probs on the uppers..

[lost1750GTV]

On the right the lower carb choke hits the up cylinder.
On the left the lower choke hits the other carb - so perhaps shorter plungers, or trimming will resolve.
The only "expected" issue was accessing them would maybe be a pita and probably different filters needed to access, so maybe they made a slight parts change since Bill did his test fit.

[lost1750GTV]

Haven't been supplied with parts number for choke assembly to see if a shorter one is out there, so am cutting the shafts so that they can not only be installed, but actually used. Offered solution was disappointing (bill & sc), "you probably won't usually need to use a choke" or something. Right rear cylinder base may also need some filing to get that one on.
Realized the "test fit" was done without chokes installed, so it was a known issue(forgotten?), but referred to as an "access to choke is difficult", again to paraphrase. Access is different than dont fit without removing two.
Bill "proactively" advised sc to drill for a vacuum petcock line, which I didn't ask for because I've done the luther mod. Any opinions on best aluminum patch epoxy that's impervious to gasoline?
I didn't realize you could get fuel inlet to left or right side of carb - they shipped 2 of each, but it looks like a 3/1 may be better for reaching the shortened and difficult to access chokes.
Weather and other stuff have made this a little slow to sort out.

[Smoker]

Well, I'm guessing you're not going to be pulling the choke levers on all 4 carbs to start the bike. Maybe you could cap off a couple, and convert the hand pull chokes to cable pull chokes (for more clearance).

There are several different kits for the PWK 28 carbs. If it will give you more clearance, maybe you could use or modify a set for the smartcarbs.

[lost1750GTV]

Thanks Smoker
These are mikuni chokes, but yeah, I checked different levers etc for access before ordering - and looked at smaller overall length ones after realizing it was more than access.
Of course without the part # to cross reference it was just "looks like might maybe".
So I have cut two shafts as necessary; the longer one may get the also shortened knob reattached. The shorter one that had cylinder clearance needs something thinner, maybe a lever, maybe a safety wire pull. Havent had to file the cylinder base to get it installed, with choke pulled, but access to pull it is the trick now.

[lost1750GTV]

My makeshift test choke for bottom right functions - with a thin blade screwdriver to push it out, and no air cleaners inhibiting access. But just enough room to click open, without any filing of the cylinder base
SC is sending me another choke to cut down, and now that I know the clearances involved, am going to try and fashion a brass lever, threaded onto the shortened shaft.
Noticed that the mikuni spigots are flat/grooved/flat where they fit into the rubber boots. The SC are the opposite, so may use cloth tape to lessen one/both of the grooves. Not so much concerned about air leaks, but damaging the boots when tightened. Perhaps just paranoia.

[lost1750GTV]

Thought I'd give an update - slow progress as there's been a lot of snow to shovel the past couple months, and hands get cold in the garage pretty quick even on warmer days.
But:
Used striker plates from a door lockset to fashion levers for lower carbs. Left side the shaft needs less trimming, so a trimmed knob holds it in place. The right side is a "just fits" when choke is open. I cut a groove on the shaft for a safety wire retainer "clip". Should be inconvenient but accessible if necessary.
I have Bill Wilsons K&N air cleaner kit, and figured a way to attach, using trimmed flexible rubber plumbing drain couplers. The 1 1/2" size fits over the carb, through the air cleaner plate, protruding into the "air box". Then the 2" size is cut pretty much the width of a hose clamp, to sleeve over the inside and outside of the smaller rubber coupling, so the mounting plate (that was screwed onto the stock mounting plate) is sandwiched between these two pieces.
This should work with bigger mikuni or keihin as well, although individual ones might be preferable if you don't have the big oval setup already.
I also have Bills petcock relocating bracket, I cut off the part for the stock choke and the lower brace to get some room for hoses, and bent the bracket about 45 degrees- edit final about 25 degrees.
The reason is clearance, the metering rod adjusters are on the top of the carbs so want to access them easily for fine tuning - this means running the fuel lines behind the carbs.
With two left 2 right fuel taps on the carbs, both lines(on each side) are to the outside of the carbs. This would have had a crimped fuel line for the front left without the petcock trim and bend. My lines are a little long now, but fitting and I can figure how much to trim each to tidy it up.
Also got Bills cable set up, which he slightly adapted from his mikuni set up. To avoid sharp bends on the front left carb, the cables are long and then looped around, so its a little busy looking from above. I mentioned to him that relocating his very nice cable adapter farther forward, maybe in front of the steering looked like it would work better. This should eliminate the loops, but would require a shorter cablefrom the twist grip and a longer ( or extension of) the oil cable. Maybe when he has time and scraps he can experiment and see.
One other bit, Bills hoses use 1/4 and 3/8 sizes, standard is 8 and 10 mm, so a bit bigger and smaller, but I guess it hasn't caused flow issues with bigger mikunis. I used heavier reinforced rubber lines to reduce the chance of kinking the thin wall clear hoses that came with the kit - I had kept the stock hoses on before so didn't notice this.
This would have been pretty quick work for someone else with a warm and well equipped shop, but I should be done soon enough.
Another nice feature of the carbs is the floats have a screw valve and a spigot for checking the floats using the tube method. But I did check them indoors with alchohol; you remove the float bowl and measure the height of the fuel with it off - which is nicer than peering at a closing point on the valve.