Carb Choice

[Big Daddy Funk]

Thx for the help with my previous head switch thread. I have early and late model carb sets which both need rebuilding. Anyone have an idea on which is the prefered set to put on my engine?(1980 head,3H5 cams on 1979 engine with 40 over wiseco kit)

[81xsproject]

I HIGHLY recommend going with the carbs that goes with the head you are running. If you have an 80's head, run 80's carbs. In my experience of cleaning and rebuilding multiple forum member's carbs, the 70's carbs never perform as well on my 80's bike as do the 80's carbs. They still run well, but my bike just doesn't have the same snap.

[Big Daddy Funk]

Card ID

Thank you, I will go with the newer carbs if I have the correct set. I looked for an ID number and found 3U9 00 B9YI . I'm not sure that is the right number because it is hard to read. That number does not match with the numbers in the manual. Anyone familiar with these numbers? Thx Rick

[TopCatGr58]

Hey Funk,

Easy ways to tell the 80 carbs: 4 small inlet ports on the inlet bell housing; the vacuum slide needle is NOT adjustable;
the pilot/idle screw is down in a recessed well on the top front of the carbs vs. sticking outside with the spring visible;
there are only 1 set of fuel inlets on the side of the bodies, the upper vent inlets are capped off.
T.C.

[Big Daddy Funk]

And that's what I have. The numbers threw me a bit. Thanks guys !

[John]

I'm going to run counter to what Jessie said. I have an 80 engine, bored to 1179, with the stock 80 cams, but I used a set of 78 carbs, because they are a little more easily tuned than the 80-81 carbs. If you think you may need to adjust the jet needles, then it can be done with out any tricks, if you are using the older carbs. I also have a Uni air filter and Jardine pipes.
My main jets are 140, the pilots are stock, and the pilot screws are about 2 1/2 turns out. The floats are plastic, and set to the level of the 80 carbs, which is 23mm I think.

[oldyam80sg]

TomCat- what do you mean the upper vent inlets are capped off?Could you describe this ?Only one set of fuel inlets on the side of the bodies?

[81xsproject]

Randy, may be correct. My experience with them is limited because everytime I have done them, I am setting them up for someone who has a 70's bike. So, I have never taken the time to try and tune them for MY bike. However, I test them w/ my WBO2 on and didn't notice any major mixture issues, my bike just didn't have the ksame umph with the 70's carbs on. JMHO.

[Big Daddy Funk]

Both styles

I believe I will do both sets of carbs anyway, so I can try both to see if I feel any difference. It can't hurt to have a spare set ready to go. Thx Rick

[trbig]

I might also add...

With the setup you have, your compression will be less than normal. The later heads had much larger valve reliefs built into the heads for the larger valves. To offset the compression loss, the made a higher domed piston for the later models.

So.. with the setup you have, you have the lower domed pistons with the larger valve reliefed head... Not sure what this translates into as far as compression loss. It isn't huge... but it isn't the most optimal setup either.

Tod