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The 80-81 bowls will swap. The choke tube is in the same place. If you have 137.5 mains and it runs fine check your emulsion tubes. If you have 78-79 emulsion tubes you will need 137.5 mains.
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79 F full cruiser, stainless brake lines, spade fuses, Accel coils, modded air box w/larger velocity stacks, 750 FD.
79 SF parts bike. -
It has always been my theory that the older carbs had the 137.5 main jets to provide enough fuel for both the main and the pilot circuit. While I know the emulsions and needles are different, they are also different from the 80-81 models. The 78-79 carbs also use a much lower float setting.
so I guess I question the thought that simply changing the emulsion tubes and needles would change the mains that drastically.
I do agree that 80-81 bowls swap easily. The 78-79 bowls will not fit the 80-81 carbs and vice-versa due to the location of the tube mentioned.Life is what happens while your planning everything else!
When your work speaks for itself, don't interrupt.
81 XS1100 Special - Humpty Dumpty
80 XS1100 Special - Project Resurrection
Previously owned
93 GSX600F
80 XS1100 Special - Ruby
81 XS1100 Special
81 CB750 C
80 CB750 C
78 XS750Comment
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I know it's been common theory that the mains are different due to feeding the pilots or not. But think about it. How much gas goes through the pilots, it's an air fuel mixture, 12-14% gas. There is no way that little bit makes up for the difference from 110 to 137.5 mains or even 120 to 137.5 , yes it does affect it. Now look at the emulsion tubes. How many holes are in the 80-81 tubes compared to the 78-79 tubes. As you know these are air holes. This is a major difference. And yes there are other factors. Your profile says you're an engineer. Do the math. If your math says I'm full of beans I will believe you. I'm saying the emulsion tubes have a lot more to do with it then the pilots being fed through the mains. 78-79 tubes with 80-81 mains will not run worth a dang and vs/vs.79 F full cruiser, stainless brake lines, spade fuses, Accel coils, modded air box w/larger velocity stacks, 750 FD.
79 SF parts bike.Comment
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Well since the main jets are submerged in fuel I would have to diagree with you, there isn't air going through the main jets, just fuel.Nathan
KD9ARL
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1978 XS1100E
K&N Filter
#45 pilot Jet, #137.5 Main Jet
OEM Exhaust
ATK Fork Brace
LED Dash lights
Ammeter, Oil Pressure, Oil Temp, and Volt Meters
Green Monster Coils
SS Brake Lines
Vision 550 Auto Tensioner
In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.
Theodore RooseveltComment
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You are right, only gas goes through the main jets. I didn't say air goes through them. I said air fuel mixture goes through the pilot jets, that tiny little hole on the upper end.79 F full cruiser, stainless brake lines, spade fuses, Accel coils, modded air box w/larger velocity stacks, 750 FD.
79 SF parts bike.Comment
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Yep Engineer, yesterday I could not spell it...today IR one. Mechanical at that, but it has been years since I delved into stoichiometery. And the discussion is not worth the effort of the math involved that would not resolve it.
I have no problem with you having your theory and me having mine.
Life is what happens while your planning everything else!
When your work speaks for itself, don't interrupt.
81 XS1100 Special - Humpty Dumpty
80 XS1100 Special - Project Resurrection
Previously owned
93 GSX600F
80 XS1100 Special - Ruby
81 XS1100 Special
81 CB750 C
80 CB750 C
78 XS750Comment
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Thanks for the input, fellas. I have a set of 110 mains and 42.5 pilots arriving. I'm going to go back to stock. It works fine on Court's identical bike, and should be fine for mine. He has commented on how pristine my carbs are, and I'm looking forward to getting them back on the bike, and carrying on with the resto.
Phil1980 XS1100SGComment
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