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Old July 23rd, 2014, 05:13 PM   #1
sigma44
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08 carbs on 07

direct swap?

I have read that you just have to change the choke adjustment.

I have been building bikes for about 12 years now, just gettin a 250 goin for my girl, had carb issues, Im just goin with a complete set on a bike thats being parted. I can modify whatever I need too, but just looking for confirmation.
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Old July 25th, 2014, 11:34 PM   #2
Alex
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Free bump, to hopefully get some more help with this.
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Old July 26th, 2014, 10:14 AM   #3
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Slight changes but I don't think it to be remarkable. It should hook up just fine I think. I have never tried to look at them side by side. I just know for sure that the idle adjustment line is shorter on the pregen carb and is hard mounted to the carb.
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Old January 14th, 2015, 01:35 PM   #4
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Just bumping this from the past. I'll be getting a set in the next week or so here and i'll try to remember to take some photos.
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Old January 16th, 2015, 08:18 AM   #5
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Is the jetting the same on both carbs? If it's an easy swap I might do the same or at least have it as a backup.
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Old January 16th, 2015, 04:15 PM   #6
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Last time I looked into it, IIRC, the bores are different diameter so the rubber boots won't work, the spacing between the carbs is different so modifications to the joining hardware/linkages/etc will need to be made, and the carbs were not only jetted differently than the Pregen but they're also asymmetrically jetted due to the unequal length exhaust pipes left to right on the newgen. The upshot back then was it was a lot of trouble to do when pregen carbs are still not all that hard to find. This is from memory, best thing to do is to get a set and start fiddling.
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Old January 19th, 2015, 02:43 PM   #7
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ruh row.

they look pretty similar outwardly, i'll see when they get here, worst case scenario i try to reuse as many new parts as will swap in the old bodies.
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Old January 21st, 2015, 10:22 AM   #8
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Just got them in last night, didn't have any time to do a proper tear down, but by outward appearance they are identical. As someone else mentioned, the idle adjust mechanism is very slightly different, i.e it doesn't have a bracket to hold it to the carb body.. i guess it bolts to the frame somewhere?

I'll open them up tonight and compare the jets just to make sure and blow out all the passages just to make sure, but from a very careful visual inspection they are identical.

I'll take some pictures and measure with calipers tonight just in case y'all don't believe me.
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Old January 21st, 2015, 07:46 PM   #9
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The bodies should be identical. Others have used newgen carbs on pregens or vise versa in the past. Just remember that the jets and such are different between generations. Get a good look at those parts diagrams and compare numbers to see what small carb parts are the same and which ones are different
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Old January 23rd, 2015, 09:27 AM   #10
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Just wanted to post back,

I broke down the carbs last night, they were in immaculate, most likely never disassembled shape. No crusties or anything inside. Even the mix screw adjustment plugs had never been removed. NICE!

My '00 jets were 105 mains with 38 pilots.

The 08 had 98 mains and 38 pilots.

Now my '00 bike has had a lot of mucked-up stuff done to it, including what looks like someone trying to wreck the mufflers. The 98-105 jump is pretty huge but i'd rather err on the side of being rich to start with.

I put the 105's in the '08 carbs and cleaned them up a little bit, not a full cleaning but they were super clean so I just blew out passages.

Should have some time this weekend to get the bike running.


Also found that the fairing bolt hole is punched through into the tank. I'm guessing that this was done by the previous owner, who was a f'n idiot, probably hours before i came to buy it in his attempt to loosley reassemble and make it look like the bike was more complete. He had the wrong bolt stuck in there and i had a bad feeling.

I'm going to try to cut off the bracket, braze the hole shut, and braze the bracket back on. I don't have a TIG and the tank is way too thin to weld with a MIG. ... But that is another thread.
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Old January 26th, 2015, 10:05 AM   #11
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So I finished rebuilding/reconfiguring the carbs this weekend. Didn't get a chance to put them on and fire it up, but I just wanted to update and post my findings.

The '00 carbs had a different needle and emulsion tube as well as different main jets. I'll edit this post tonight when I get home with the specific values.

The 08 carbs were identical L/R except for one thing, the needles were very very slightly different. That was the only difference i could find.

The 08 emulsion tubes only had a few small holes in them, where the '00 emulsion tubes have the more familiar pattern, i.e. sucking in more air.

The needles have a markedly different profile. The '00 needles had a sharp step in them followed by a gradual taper, whereas the '08 needles had a more gradual taper. That tells me the fuel metering in the 08 is more controlled by the needle and less dependent on 'air bleed' from the mixture screw.

The 08 mix screws were 1.5 and 2.0 turns (R/L) which also lines up with this theory.

This tells me that the 08 went to a more progressive fuel curve, perhaps to take advantage of a better (more aggressive) cam, or maybe the engineers thought it would come off idle better that way.

The differences R/L in the needle and adjustment screw could be due to the asymetrical header, or it could be a number of other reasons, coolant flow in the block, or they just made one cylinder run richer for easy starts, but left the other cylinder leaner to pass emissions... i dunno.



Either way, i opened up the pilot jets with a drill bit. They were about halfway between a 79 wire and a 78 wire, so i went up to 78. Since the mix screw adjustment people are posting is 2.5 turns, it should have some room either way to bleed in more or less air.

I also sanded the taper on the needles down slightly to fatten it up as it tips in. This should help out more off idle where it sounds like the bike needs more fuel, without making it too fat on top. I'm already concerned that the 105 jet is on the big side.
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