Old style slides new style carbs?

[Crazcnuk]

Anyone out there using the 78-79 style slides in the 80-81 style carbs?

Due to the 'death' of JD I took the SG to Ride for Sight this weekend. On the way down to Kananaskis the bike ran like crap. It 'loaded' up at speeds unfer 3500rpm, and bogged at speeds over 6500rpm.

It was also getting >30mpg.

On saturday, pulled the carbs apart, I was going to drop the floats 2mm, to see if it helped, but discovered the floats are already 2mm lower (25mm).

However, found that these carbs, even though they are Type III's (recessed mixture screws, plastic floats, etc) they have the type II slides in them.

Is there any functional difference between the older and newer slides if they mix and match them?

[3Phase]

Anyone out there using the 78-79 style slides in the 80-81 style carbs?

They won't work because the '78/'79 slides are smaller in diameter. You might be able to swap the diaphragms but I haven't torn them down that far, yet.

I think the old-style needles and emulsion tubes will swap to the newer carburetors. With the needle clip on the bottom notch the needles are almost the same length. I'm trying the swap sometime this week to see how the longer, thicker, blunt-tip needle works.


BS34II and BS34III jet needles

[Crazcnuk]

Well, they work, they fit the bores properly, or I wouldn't be riding the bike!

The major difference between the two series are that the older style have a spring that pushes the needle up, and the newer pushes the needle down.

Just don't know if this places the needles at the same height...

[3Phase]

I'm sure the old-style slides would drop right in the new-style carburetor bodies but they're not the correct size. They're smaller so they're too loose.

Here it is the other way 'round; new-style slide in old-style carburetor body:-

BS34III slide does not fit a BS32II carburetor body.

[Crazcnuk]

Well, mine fit fine.

If they were loose, at all, the bike wouldn't run at anything off idle.

Did they make some of the later model slides with the same setup as the early ones, maybe?

What I mean is, the other set of 1980SG carbs I have have a metal plate, with philips screws holding it down. Underneath is a spring, spacer, washer and clip.

These carbs, the ones I am asking about, have the circlip with a plastic 'thingy' spacer, clip, washer and a spring, in that order, like the older style.

[3Phase]

These carbs, the ones I am asking about, have the circlip with a plastic 'thingy' spacer, clip, washer and a spring, in that order, like the older style.

Yes, those are the old-style slides and the difference in diameter is not great. As you can see in the picture the old-style slide bores are slightly smaller than new-style bores.

There isn't enough vacuum at idle to lift the slides so you wouldn't notice anything until the small slides lifted faster than they should and the fuel/air mix went too rich too soon. You might be able to tune around it but... why?


NB: Old-style carburetors are BS34II, not BS32II as I wrote in the previous post but I can't edit the post to correct it.

[Crazcnuk]

The bike runs fine, up to about 180kph (haven't tried any more) . I can't see it doing that if the slides are at all loose, but hey who knows.

I don't have any other slides, and my only issue, is poor fuel economy.

I tried but can't find a diagram showing me the order of parts in the older style to see if they are together correctly.

[3Phase]

The bike runs fine, up to about 180kph (haven't tried any more).

Sounds like fun, now I want to try it! Apologies to all that were holding their breath waiting for a writeup on emergency Radio Shack diode voltage regulator/rectifier bodges. I carry a spare OEM regulator/rectifier now and carb tuning sounds like more fun (Ooh! Shiny!) at the moment.

I have a set of '79 slides and a set of '80 slides that I put '79 needles into. I was going to try just the longer, adjustable, '79 needles per Dan Hodges comment about all of the OEM needles being too short and his decision to use Dynajet needles but I might as well try the '79/'80 slides and springs along with the different emulsion tubes and main jets, too.

[Crazcnuk]

Yeah, a lot of this is just trial and error.

It just depends on the relative height if the needle in each of the slides. Obviously ANY change in the height will make a huge difference in how the bike runs.

I dropped the needles one notch, and the bike RAN a lot better, but the fuel mileage only went from 29mpg to 31mpg.

I did notice some wear on the needles, though, so that could be part of the issue as well. I should buy some new needles and tubes.

[psycoreefer]

if you find new needles and tubes somewhere post it up....

I looked all over and as far as I could find I bought the last 4 tubes on the planet, (at least for the "early" carbs). I could not find a source for new stock needles, only the K&L's which are noticeably different.

[3Phase]

if you find new needles and tubes somewhere post it up....

OEM is pretty much gone, no more, hasta la vista but he bought some crazy Canadian needles and emulsion tubes for his bike.

You can see what was uncovered about Mikuni needle jets and jet needles if you read all of Craz's thread or just have a look at post #84 to get the part numbers/sizes in
Help Find A Cure for Crazcnuk's bike?