Topic: Turbo Charged CB550 Landspeed Project

[scottly]

Looked in the box o carb bits and found my extra needle jet is a P-zero
Which may be smaller than the carb is supposed to have.  A 568 series Y-6 is on the parts diagram.  Still haven't opened the carb to look.

  The biggest needle jet may not be a bad idea.

Don't fret about the needle jet until you get the main jet sorted. Is it as easy to change the main on the HS as it is on a VM, by removing the brass plug on the bottom of the float bowl?
Also, I found some jetting recommendations for a Harley with the same carb:
main 160-165
needle jet Y6
pilot 22.5-30
air .09

For an XR650:
main 135-137.5
needle jet Y4
pilot 22.5
air 1.2

At 10 pounds of boost your motor will be pumping over 900cc's worth of air, so keep that in mind..

[BomberMann650]

Well, i've already walked past the harley sportster setting hahaha
Could probably run the 37.5 pilot and never worry about it again.
The main is a match for the XR650 but damn if this little motor don't want some more.
Ordered a full run of needle jets and mains.  Along with the genuine deep well drain plug.
If i do have the y6 needle jet.  Then i can work through the Zed series, and if it ever needs to go all in, BB-0.  Which is basically a 3.25mm straw to hold the main.  The two dozen main jets max out at #240

I really do want a tractable midrange from the bike.  Especially if i start putting 65-70#ft of torque to the track.  The FJR in all its weight and might can easily walk out the rear wheel with that amount.  I've already been encouraged to put a harley agm battery in the swingarm as a ballast.

New jets will arrive soon enough.  Then i'll have to plan a dyno day. Might be able to tune up to 12psi without overwhelming the fuel.

Other overwinter maintenance will include rebuilding the suspension.  The old atv shock needed a refresh from the start.  And the fork seals have not appreciated being strapped down to the trailer

Nevermind the birdcage hanging out in the barn.

[BomberMann650]

Dunked the carb in fhe rust removal ultrasonic bath.  Plastic, rubber, felt and all.  Came out really neat and clean.  Hoping to avoid the wild corrosion issue from last winter.  Lubed it back up with boeshield t-9.

Confirmed the needle jet of lean size is the y-6.  Set up the 37.5 and 147 jets for now.

Still cleaning salt off of the bike.  Discovered the paint on my triple tree was failing.
I want to get some tuning done before i strip it down for deep service.

[scottly]

 Set up the 37.5 and 147 jets for now.

[LiveeviL81]

Looked in the box o carb bits and found my extra needle jet is a P-zero
Which may be smaller than the carb is supposed to have.  A 568 series Y-6 is on the parts diagram.  Still haven't opened the carb to look.

  The biggest needle jet may not be a bad idea.

Don't fret about the needle jet until you get the main jet sorted. Is it as easy to change the main on the HS as it is on a VM, by removing the brass plug on the bottom of the float bowl?
Also, I found some jetting recommendations for a Harley with the same carb:
main 160-165
needle jet Y6
pilot 22.5-30
air .09

For an XR650:
main 135-137.5
needle jet Y4
pilot 22.5
air 1.2

At 10 pounds of boost your motor will be pumping over 900cc's worth of air, so keep that in mind..

Tossing in my $.02. I have a 78 CB838A with a TD025 Drawthrough and an HSR42. I finally got WOT fueling to be a steady 13 AFR up to 12lbs of boost using these settings. May help narrow in with the slightly larger carb and slightly larger engine


main Drilled out to a .116", not sure what size that is equivalent to, but its darn near a straight bore
needle jet Y-6
pilot 10
air 1.75
Needle 98 clip 2 from bottom

There is also a threaded "main nut extender for the float bowl, apparently can change fueling a bit as well as add some more volume into the bowl.https://www.amazon.com/Mikuni-Main-Jet-Extender-Carburetors/dp/B0DWYH76LY

[BomberMann650]

LiveeviL - you rock.  Welcome to the freak show

How in the heck does an 838 need 1/3 of the pilot jet?  Pictures of intake?
Did the conversion on your drill bit size. 2.95mm so yeah, definitely close to the needle jet bore.

What did changing the air jet do for you? 

My main extender kit just arrived. 

[BomberMann650]

Well thats a bit of a let down

Extender isn't threaded for the 568 series.
Bowl cap fits 🤷🏻

Don't have a die to match either.  My kingdom for a micro threading lathe

[scottly]

Check out this tuning guide. I found something on the same site where they said you could leave the main out entirely and the bike would run fine until the throttle was WFO!!?? Note the order they recommend: idle first, then main, then mid-range.
https://mikunioz.com/tuning-tips-and-manual-downloads/?v=0b3b97fa6688

[BomberMann650]

I've definitely been working bottom up instead of top down.

Also, the Internet has die sizes in either side of the mikuni thread spec.

LiveeviL's discovery opened up the idea that the biggest main possible may be necessary

[scottly]

I don't know about the flatslides, but the VM jet sizes have nothing to do with the diameter of the hole like most other carbs. The VM 36 on my 500cc Ascot has a 220 main, but it's much smaller than 2.2mm. Maybe LiveeviL is never getting to WFO?

[BomberMann650]

They're the same big round jets betwen vm amd hs - hopefully a vm jet extension will work for my needle bore

LiveeviL's claim was that drilling the main out to 2.9mm gave him reliable 13:1 afr.
By the bore size, he had basically rigged up an extended length Y-6 needle jet.

Looking at his 025 series turbo is slightly smaller.  If i can get the bigger 4 series to liven up this little motor of mine will be fully stuffed

[scottly]

I think the jet extensions are more for dirt bikes that experience radical variations in attitude? It used to amaze me how my buddy Henry could ride his XR500 for 1/4 mile with the bike at a 45* angle.

[BomberMann650]

Whoohoo Wheelies!

Wonder if the jet extension has any effect on mixture.  Like the way float level settings do

[LiveeviL81]

LiveeviL - you rock.  Welcome to the freak show

How in the heck does an 838 need 1/3 of the pilot jet?  Pictures of intake?
Did the conversion on your drill bit size. 2.95mm so yeah, definitely close to the needle jet bore.

What did changing the air jet do for you? 

My main extender kit just arrived.

Whoops! Good catch, I looked back at my notes and I am actually running a 22.5 Pilot. Though I suspect that there is also some fuel being pulled through such a large main jet, cause I noticed I had to dial the idle mixture screw out (to lean out the mix) as I upjetted the main.

Check out this tuning guide. I found something on the same site where they said you could leave the main out entirely and the bike would run fine until the throttle was WFO!!?? Note the order they recommend: idle first, then main, then mid-range.
https://mikunioz.com/tuning-tips-and-manual-downloads/?v=0b3b97fa6688

I also have read this in Jenning's two stroke tuning guide as well. That's actually how I discovered I could jet up as large as I did. I forgot to install a jet when changing from like a 160-180, and was amazed that it was so much better once I got to WOT. Like a lightbulb went off in my head. I would recommend trying it as well.

I run the small turbo because of the torque converter on the automatic, If I had a turbo sized to spool around 5-6k rpm, I am already doing 40mph in 1st, or 80mph in second! I had a dyno session earlier this year, but a valve tappet nut came loose and started making a real racket! Never got to do a complete run, but I suspect my turbo will choke out my motor around 9kRPM.

[BomberMann650]

@LiveeviL

Mine draws some off the main during idle as well.  Discovered a plummet in afr as i turned the slide adjuster down.  Bigger pilot went in after that.

Small turbo probably will wheeze out up top.  Mine did.  Between the low a/r and limited compressor volume, redline performance wasn't there. 

[BomberMann650]

The bag o main jets arrived - 170 - 240.

The 240 takes up nearly the whole center of fhe jets core.  But its not quite as big as the needle jet orifice.
So if i were to hazard a guess, LiveeviL's .166" drilled main is somewhere in the ballpark of 280/290
May have to take a small jet and just gore it out as an experiment.
waiting on postal service to deliver the slide needles and needle jets before I bug the local tuning shop for an appointment. 

Did make a stop at the powdercoater recently.  Prices have gone up since i last had a frame done.
Small batch parts to be done in black are cheap.  Wheels are priced fairly, though the additional cost is knocking out the bearings.

I don't even know what color i would want the wheels to be!

[BomberMann650]

The last of the carby bits arrived - vm33 extender worked a treat.

And, from the list of bad ideas, comes the big bore kit.
I did the math, 63.88mm is as far as the 650 class will allow.  And obviously beyond what stock liners can take.  But i know a guy who does sleeves, really well.  So it comes down to finding a piston that can be shoehorned to fit. 
Oddly, honda grom piston could be viable.  Provided the wrist pins match.  Would be open to alternatives.  Need a flat top because turbo.  Machining 12 thou here and there expected.

If anyone knows/remembers the bore size in the top case, please comment.

[Old Scrambler]

Do the wheels AFTER you try out the largest airbox possible...........even if it has a u-shaped top. Numerous examples have gone past your tech-inspection, particularly Tom Mellor's Triumph. A BIG box provides even mixture to each valve and has minimal, if any,  reverberation to 'fight' the induction flow. With the larger jet, start out with very low boost-pressure (1-2 lbs.) and when all is good at WFO, slowly increase boost until its not so good. If the motor is still together, re-jet according to the desired AFR at or very near WFO.

Heading out to the desert for 'a while'

[scottly]

The bag o main jets arrived - 170 - 240.

The 240 takes up nearly the whole center of fhe jets core.  But its not quite as big as the needle jet orifice.
So if i were to hazard a guess, LiveeviL's .166" drilled main is somewhere in the ballpark of 280/290
May have to take a small jet and just gore it out as an experiment.

The largest main you've ever run is a 135, you have a 240 that you've yet to try, and you're thinking about drilling one out even larger? Follow the tuning guide I linked, starting with the pilot, which you can do without a dyno, then save the dyno to select the main jet for WFO. Remember that a slide carburetor's operation is dependent on the amount of the slide opening, which determines where each jet and the needle have the most influence, rather than RPM. 

[BomberMann650]

The bike idles just fine.  Did a lot of it while waiting for the green flag.
Got the dyno session scheduled. 
Road testing would be unwise.  Bike is a real handful.

[scottly]

What is the setting on the idle mix screw? How many turns out from fully seated?

[BomberMann650]

What is the setting on the idle mix screw? How many turns out from fully seated?

Generally been going with two turns out on this carb.  Prior experience with its adjustment range found its pretty small.  Very fine tuning.  More effective to just change the jet.  Going from home to the track, idle afr was on target.  Could probably go to three turns out and be fine.

What really throws off afr wideband reading at idle is when motor oil makes its way from the bearing to the compressor.  Instant 10:1 reading and a distinct odor.  Took two restrictiors to make that stop.  Its still getting oil, and hopefully the right amount of it 

[scottly]

What really throws off afr wideband reading at idle is when motor oil makes its way from the bearing to the compressor.  Instant 10:1 reading and a distinct odor.  Took two restrictiors to make that stop.  Its still getting oil, and hopefully the right amount of it 

Please give more details about this, oil shouldn't be making it's way into the intake?

[BomberMann650]

What really throws off afr wideband reading at idle is when motor oil makes its way from the bearing to the compressor.  Instant 10:1 reading and a distinct odor.  Took two restrictiors to make that stop.  Its still getting oil, and hopefully the right amount of it 

Please give more details about this, oil shouldn't be making it's way into the intake?

Its a side effect of running draw through on a journal bearing turbo.  The added vacuum pressure on the compressor can draw oil from the shaft.  The solution is to have a machine shop add an extra seal. 
Its also a side effect of having a high capacity/high pressure oil pump. When i first fired the tiny turbo, the pump was enough to push oil out both ends of the turbo shaft!  One restrictor and a little better drainage got the tiny turbo across the finish line.  The 4 series seems to have benefited from and additional restrictor on the oil feed.

Cb650 pump mod for the win everywhere else.  Crank and Rod bearings loved it!  Left side engine cover, not so much haha

[scottly]

You need a turbo with seals.
Edit: Are you absolutely certain it's oil causing the 10:1 AFR? Are you getting mass quantities of blue smoke, suitable for fogging mosquitos?