Question for you late carb gurus

[BA80]

I know some of the later carbs have a rubber plug over the pilot jet and some don't. Question is, how do you tell which take the plug and which don't?

I'm putting Doc's carbs together and there are plugs in the parts but looking at the carbs there is no feed to the pilots. Seems that if they take plugs there would have to be a feed port from the main well and these don't have one.

[GLoweVA]

You got it right. If there's no crossover hole from the main to the pilot then no plugs.
If you did plug it up, then the pilot circuit would get no fuel and you'd know it real quick.

Vice versa works too, If you do have the crossove hole and leave the plugs out, then the pilot circuit gets way too much fuel and you'll know that too. BTDT.

[BA80]

Thanks George. That's what I thought but I wanted to be sure. I've never used the lat carbs because I always thought the early ones better because of being more adjustable.

[motoman]

Thanks George. That's what I thought but I wanted to be sure. I've never used the lat carbs because I always thought the early ones better because of being more adjustable.

Actually having seperate fuel feeds, not being combined the later carbs are more adjustable for each circuit.

[BA80]

Actually having seperate fuel feeds, not being combined the later carbs are more adjustable for each circuit.

But, no adjustment on the slide needles and the idle mixture screws are a p.i.t.a. to get to.

[motoman]

But, no adjustment on the slide needles and the idle mixture screws are a p.i.t.a. to get to.

metering rod slots......gotta give ya that one........idle mix screws, not so much since hopefully the tank is off for a sync anyways if the mixture screw settings are changed with the 'lean drop' method.......if your hearing is up to snuff.

[BA80]

I don't need to take the tank off. I can see the screws and adjust them with my 1970's 90º adjusting tool.

The only thing I don't like is the bowl vent tubes going to the air box, adds to the clutter in there, and the idle can be a bitch to adjust.

[natemoen]

Flat blade screwdriver makes adjusting idle a snap

[Rasputin]

One thing I have found to be common on all my carbs (which I think most are original) is the small tit located in the later fuel bowl and its absence from the earlier fuel bowls. It is located in a place which would hold in a rubber plug when the bowl was installed. Here are a couple of pics to show you the tit I speak of. I may be wrong but all of the carbs I own with rubber plugs have this small tit in the fuel bowl.

[BA80]

One thing I have found to be common on all my carbs (which I think most are original) is the small tit located in the later fuel bowl and its absence from the earlier fuel bowls. It is located in a place which would hold in a rubber plug when the bowl was installed. Here are a couple of pics to show you the tit I speak of. I may be wrong but all of the carbs I own with rubber plugs have this small tit in the fuel bowl.

Hmm.....Interesting. I've not heard of that before. Thanks Doug.

[motoman]

good 'catch' there Doug! Myself, never messed with the early model XS carbs, but in a nutshell I can see where they would be more 'forgiving' to deal with feeding from both circuits. I can say, if you make so much as a minute change in the later carbs and they don't like it, they will definitely let you know. IMO, maybe not so much from the early carbs, just from the fact they share circuits to a certain extent.

[petejw]

hey greg,
the later carbs on the rh bikes (aus)
had adjustable slide needles that u could
use with the later special carbs,
the later carbs are also better designed to run pods
and the mixture screw tips dont break off either. :-)

[BA80]

Gotta give you the idle mix screw tips. Those are weak and suck.

[mikubuilder]

yeah, that little tit will prevent you from swapping bowls into earlier carbs, plus brass tube doesn't line up right

[natemoen]

yeah, that little tit will prevent you from swapping bowls into earlier carbs

Most of the later carbs don't even use that rubber plug so that usually is not an Issue, only the first part of the '80 model year used that plug.

The brass tube IS the true issue.