Carb Floats and jets

[CUBuffs]

I got the carbs off on my 1980 Special and popped open the float bowls. The floats are plastic, are they stock or have they been changed?

Also, how can I determine if the carbs have been rejetted? The bike came with 4 into 1 exhaust but the pipes have turned black so I would like to make sure that the jets are what they need to be. Thanks.

[fxrer]

Nope, plastic floats are OE for 1980. Go to tech tips and read about carb rebuild. Also, there are literally hundreds of posts on carbs & jetting from the knowledgeable folks on this forum.

Stock main jets for your ’80 SG are 110 for cyls 1 & 4, 120 for 2 & 3. Pilot jet is 42.5. Air jet - pilot- is 180.

If you unscrew the jets, you will see the sizes stamped on the jets, and be able to compare to original.

I’d recommend doing a thorough search for “carb”, “jets”, etc. This topic has been covered extensively!

[CUBuffs]

Well I haven't looked at my pilot jets yet but the main jets were all 110's. If you put 4 into 1 headers on these bikes shouldn't the Original jets be replaced with larger jets?

[skids]

Well, its like this: I put 4-1 Jardines on but a 78E and an 81H (4 years difference from purchases). Both have 78E carbs on them. Both have K&N filters in OEM boxes. One has 132 mains (78E) and One has 145 mains... and the latter one needs to go even larger! Don't ask me why they are so different!!!

Originally posted by CUBuffs
Well I haven't looked at my pilot jets yet but the main jets were all 110's. If you put 4 into 1 headers on these bikes shouldn't the Original jets be replaced with larger jets?

[81xsproject]

Don't the 80's have bigger valves? Maybe that is why they need bigger jets? I don't know, wild guess.

[CUBuffs]

I found Denny's jetting recommendations

http://www.xs11.com/forum/showthread.php?&threadid=382

and have some questions:

1. I have a 4 into 1 exhaust does it matter who the manufacturer is and if so how can I tell who it is?

2. My stock airbox has a hole in the bottom but is that normal or has it been drilled out?

3. Also, if I have a K&N filter in my stock airbox then I need to adjust the jet size?

Thanks.

[pggg]

Originally posted by skids
Well, its like this: I put 4-1 Jardines on but a 78E and an 81H (4 years difference from purchases). Both have 78E carbs on them. Both have K&N filters in OEM boxes. One has 132 mains (78E) and One has 145 mains... and the latter one needs to go even larger! Don't ask me why they are so different!!!

Skids, maybe 210 pilot airs in one and 180's in the other?

[fxrer]

A great source of info can be found in the “Articles”, left column. If you read the first test report, from Cycle 1978, you can learn some of the Yamaha design philosophy that went into the first XS (E). Then other test reports for subsequent years describe the changes, in valves, carbs, timing, etc, and the reason behind those changes.

It answers many questions about differences between models, what will fit and what won’t. Why the jets were changed from 1979 to 1980, e.g.

If you haven’t read them you should take time to do so. Very enlightening

[Ken Talbot]

Originally posted by CUBuffs
2. My stock airbox has a hole in the bottom but is that normal or has it been drilled out?

The stock airbox has one small drain hole in the bottom. It should have a square rubber block over it with a bit of filter material that will allow moisture or extra element oil to drain yet still keep bugs out.

[skids]

Nope. Both sets have 78E carbs with stock pilot air jets: 210's.

Originally posted by pggg


Skids, maybe 210 pilot airs in one and 180's in the other?

[TopCatGr58]

Hey CUBUffs,

Doesn't matter what brand of pipes, just that you HAVE aftermarket pipes vs. OEM. Secondly, the K&N filter does breath a bit better than the OEM, so with both breathing mods, you may need to go up 2 to 3 sizes. The 110's are common on the specials in 80-81.

Skids, the 78 engine has a higher compression ratio of 9.2:1, the 81 is rated at only 9.0:1. The 78 has smaller valves, the 81 larger, but less lift or duration. Wonder if the reduced compression means it needs more fuel to make the same amount of power!? Or... the larger valves means it can breath better, and needs more fuel to mix with it!?
T.C.

[pggg]

About the airbox, this thing here is liable to have 27 years worth of built up gunk inside. Cleaned mine out for the first time ever. The amount of sticky soapy garbage in there was incredible. Can't be good. Swished it all out with a flexy wire and heaps of petrol.

[skids]

Well, here is another strange thing...The 81 routinely gets 38+ mpg on the interstate at 65 mph, the 78 is lucky to get 35. I know the float settings have a lot to do with things, but I think the floats on the 81 are set a bit higher!

Originally posted by TopCatGr58
Skids, the 78 engine has a higher compression ratio of 9.2:1, the 81 is rated at only 9.0:1. The 78 has smaller valves, the 81 larger, but less lift or duration. Wonder if the reduced compression means it needs more fuel to make the same amount of power!? Or... the larger valves means it can breath better, and needs more fuel to mix with it!?
T.C.

[CUBuffs]

Hey TopCat,

Thanks for the info. I don't think my air filter is a K&N so it looks like I only need to account for the after-market pipes.