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Archive through March 17, 2020Missionbolts30 03-17-20  01:11 pm
         

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Mnscrounger
Posted on Tuesday, March 17, 2020 - 01:20 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Oh, after all the poking around the carb will DEFINITELY need more tuning. But I'm beginning to entertain the possibility it is not the primary problem.
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Mnscrounger
Posted on Sunday, May 31, 2020 - 08:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I finally had a chance to get back to investigating.
In my last post, I mentioned I was entertaining the thought it might not be carb but ignition. I popped the timing cover off to see if the ignition module TDC indicator was failing to light. (It seems to be working fine, but my screwing with it will mean I need to reset the timing now too.) So, back to the carb.
This time while running, I had the airbox cover off again, and was investigating all the little bits in the slide and needle area. I noticed as the revs went up, the slide would rise, and the needle seat would hop out of its recess and the stumbling would start. If I held the needle seat down in the carburetor body with a screwdriver, it would rev much higher without much stumble. I know I am not the first person into this carb, and I've never seen a CV 40 before this one, so I don't know how it's "supposed" to be. I am wondering if I am missing something, (a spring or clip),that is supposed to hold that needle seat down? Is it supposed to be a press fit and not even come out of the carb body? I will attach a pic or two later so you can see what I mean.
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Mnscrounger
Posted on Sunday, May 31, 2020 - 09:29 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)







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Missionbolts
Posted on Monday, June 01, 2020 - 12:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Well that's not supposed to move around like that!

If I remember rightly, that piece is held upwards from below by a brass tube that is threaded into the bottom of the carb

That tube must not be all the way up where it would clamp the jet into place?

In the book, the piece you see moving around is the 'needle jet' and that is held by a long skinny brass 'jet holder', but it's also got a lot of tiny holes down it's length, which feed air into the center in order to mix with fuel being drawn up through the center of that tube. Most everyone else calls that an 'emulsion tube' as that's it's primary purpose

Breaking the fuel down into smaller droplets before getting tumbled out into the main airflow through the center of the carb helps a little bit

The main fuel jet is a smaller bit of brass which screws into the bottom of the 'jet holder'

You have to take the float bowl off in order to check all this out

The book doesn't show any o-ring or other seals in relation to the jet

There might be just a chance that somebody has over-tightened the 'jet holder' & broken off a small lip that keeps the 'needle jet' from moving upwards
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Mnscrounger
Posted on Monday, June 01, 2020 - 11:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Thank you, is that you referenced that retains this part possibly known as an "emulsion tube"? If so the CV performance website mentioned it mates to the end of the emulsion tube. I don't remember seeing that emulsion tube when inspecting all the little passages. I wonder if there is even one in the bike... I'll have to go back into the carb, but for under 20 bucks total, I think its worth a trip to the HD dealer for them before I start taking the carb off again.
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Missionbolts
Posted on Monday, June 01, 2020 - 01:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

The world-class name for that is indeed 'emulsion tube', because that's what it's design is primarily focused on. It has a series of very small holes along it's length to introduce air to the fuel that is being drawn up through the center of this tube. That method of using an array of mixing jets helps to break the fuel down into smaller droplets just before it tumbles out of the top of the needle jet and into the main airflow running through the carb

Holding the 'needle jet' is a secondary function, and from certain points of view, a completely useless feature because it's much more cost effective to make the top of the emulsion tube function as the 'needle jet'

Combing those two features will reduce the machining required on the carb body, as it then becomes unnecessary to have a step holding a separate part tightly against the end of the emulsion tube. A plain & simple hole will work just fine and with increased reliability. A simple o-ring can seal the top of thew hole & maching an o-ring groove into the emulsion tube is very straight-forward, adding almost nothing to the production costs. This design approach makes it a lot easier to clean the carb by only having one single piece instead of two

Pics will make it easier to explain. I just now photographed the two pages that I'm looking at. I'll use 'hotlink for forums' at https://postimages.org/ and just simply paste that here, without using this forums 'link' feature





Part number 3 is what you have seen moving around. #4 is what holds it in place & #5 is the main fuel jet which meters fuel flowing into the center of the emulsion tube

One of the two small holes at the very front of the carb's mouth is where the air comes from to supply the emulsion tube. So that's one of the small passages to keep clean. It's best to blow that out with the emulsion tube removed, otherwise you might be blasting crud into the holes on the emulsion tube and making it stop working properly
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Mnscrounger
Posted on Monday, June 08, 2020 - 10:51 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I figured it would be something simple the PO had screwed up.
The needle jet was installed incorrectly, floating in the venturi of the carb. ( see pictures above) The person who "serviced" the carb before me did not pay attention that the needle jet dropped in the hole UNDER the emulsion tube, before the tube is installed. Me being timid, I simply kept repeating the mistake, because I didn't know any better. When the throttle opened and the vacuum came on the needle jet would jump out of the hole and do a pole dance on the needle. With a wide open needle jet port, the gas would flood the motor until the vacuum dropped and all returned back to idle conditions.
Its still WAY out of tune because I've fiddled with nearly everything that can be fiddled with, and the cold start is almost impossible, but it runs well enough for me to putt around town Friday and prove everything works, except the riding position. (IIRC, I heard Tootall once use the term " monkey humping a football" to describe his position on some bikes. This one feels like that.)
A lot will be changed over for trail use now that it runs.

1.figure out new controls and get rid of the stock pegs.
2. Go back to the stock forks and triples so the XB wheels and forks can go onto the S3 someday.
3. remove the airbox and go to a carb brace and low profile filter. I need room for my knees
4. Fab up a proper off road style spring and ball jointed exhaust that doesn't require bungee cords. (That's when the real tune will be worth the time.)
5. chain conversion to gear it WAYY down for backwoods trails.
6. 19"F and 18"R kawi cast wheels to give it that XR look, and more ground clearance

Missionbolts, (and Gearhead) : Thank you guys for your patience and teachings. If we ever cross paths, I owe you a beverage of your choice.
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Missionbolts
Posted on Monday, June 08, 2020 - 12:03 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Oh good! So the hole for the emulsion tube wasn't broken, just misunderstood

Sounds like you can finally do a proper tuneup

I would not recommend the stock forks for trail use, they bottom out really easy

I'm running a dual-sport front tire, front & rear. Shinko SR244 in the 3.00-16 size. On pavement handling is perfectly adequate, as I regularly grind my footpegs in 3rd gear on this tire. Even in 1st gear, when I'm in parking lots, it's really effortless to drag the pegs. So the turning raduis can be pretty short. I find it's better to start slow into a hard bank, then roll on the throttle. Seems to 'steady out', plus giving it more gas will pick the peg back up off the pavement when I grind it too hard. Cruising has much lower rolling resistance than the OEM tire, but also is noisy from the huge air pockets in the tread

On badly rutted forest roads, the traction is great, but I have to go really slow because I'm bottoming out on everything. There's a huge dent in the bottom of my muffler and the welds on the pipe up where it bolts to the head broke twice due to bottoming out, 5 or 6 times just because the rubber isolator holding the muffler to the bottom of the engine is just too darn soft! The entire exhaust bounces around enough to tweak the pipe where it bolts to the head. I've had those two nuts fly off on several occasions, usually out on the highway. So I've been safety-wiring those. But one of the studs stripped from the stress, so now that nut is welded on with the other nut safety-wired

I've changed the fork oil to a heavier weight. I'm thinking about going heavier still. I might just add 20cc's of Power Punch on each side, just for the heck of it

The 'monkey hump' riding position isn't that bad once you get used to letting your arms relax during hard & fast maneuvers, because you're using your legs to keep control over the bike

Dodging potholes on forest roads is super sweet with the Blast. Effortless and with great precision. Better than a modern CR can do

I've broken the drive belt from riding in deep snow. So I would be concerned about getting any sort of debris in between the belt and the rear sprocket. That snow got packed right in front where the belt runs under the sprocket, then it broke free and ran under the sprocket. Belt snapped so easy I didn't even feel it happening. There was an icey chunk of packed snow still stuck in the grooves on the belt when I looked at it, right where it broke

That airbox does get annoying! Pushes right into my leg unless I keep scooted way forward on the seat. And the filter is installed backwards, which is also really annoying, because it's more difficult to look at how clean it might be when all the dirt is being trapped on the inside of the filter where you can't see it easily

I would consider a custom intake that would re-orient the carb so it's more tucked in & not sticking out like some kind of 1970's chopper

But at that point, I would also be thinking about putting in a Keihin CV with a cable-operated cold-start and an ignition that doesn't need the TPS signal

The rear turn signals need to get replaced with something more flush-mounted. I broke mine off when I had to dodge an oncoming truck by darting in through a thicket of alder saplings on the side of the road

Replacing the muffler with a skidplate and something really skinny like one of those Supertrapp style mufflers will help the ground clearance

I'm still thinking about doing something dumb like hanging a muffler right in front of the engine, just outside of where the front tire swings
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Mnscrounger
Posted on Tuesday, June 23, 2020 - 01:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Well, one more tweak of the enrichener, and a couple degrees more retard on the timing, and it runs well enough to get me to work. No major grinding, clunking, or smoke. It looks cute with the XB wheels, ZTL brake and race bars.( like a seven year old running around in a superhero cape.) The makeover into a dirt cheap dual sport can now begin.this thread ends, and the build thread will begin in the custom section of the Thumper forum.
Thanks to you guys for the advice and technical help.




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Gearheaderiko
Posted on Wednesday, June 24, 2020 - 06:27 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Nice job on the wheel conversion and exhaust. Looks factory.
I’d love to see the shock mounting and what shock you used.

Yep, looks really good :-)
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Mnscrounger
Posted on Thursday, June 25, 2020 - 11:20 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I didn't do it. This is pretty much the way I bought it. The exception being it had a punched Sportster can for a "muffler". I wanted to make sure it had no major running issues before I started any work on customizing, so I bought the Supertrapp on CL and temporarily bungeed it on to get rough tuning. It also came with most of the parts to put it back to stock, a few XB parts, some big twin front pulleys, and a rough but complete set of red bodywork.
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