how much vacuume is an 80 special supposed to have at idle, right now i have about -9psi but im curious if it should be more. I have pod filters and a 4-1 exhaust with no muffler(straight pipe). Also jets are at 122.5-127.5-127.5-122.5 and im running lean on 2-3-4 should i bump uo jet sizes again or are these in the ball park. Finally at idle i have gas leaking from #4 carb i have reset the floats 3 times to stop this to no avail. Oh and this is what the bike looks like now that i finished my suzuki 1000 fork swap[IMG][/IMG]
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vacuume at idle, and yet another jet question
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You need to take those carbs apart again and actually clean them. If there is gas leaking then the floats are not sealing. Either the needle and seat can seat for some reason, the o-ring around the seat is leaking, or some other unknown reason. There is something wrong there that needs to be cleaned out. Those jets should be way big enough (if not too big) for that.
Second, good luck with the straight pipes....no one has ever really gotten that to work. These engines need back pressure to run right and that maybe be the cause of the problems.Nathan
KD9ARL
μολὼν λαβέ
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 Roosevelt
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Originally posted by natemoen View PostYou need to take those carbs apart again and actually clean them. If there is gas leaking then the floats are not sealing. Either the needle and seat can seat for some reason, the o-ring around the seat is leaking, or some other unknown reason. There is something wrong there that needs to be cleaned out. Those jets should be way big enough (if not too big) for that.
Second, good luck with the straight pipes....no one has ever really gotten that to work. These engines need back pressure to run right and that maybe be the cause of the problems.
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I don't know the actual number for how much vacuum shoud be measured at the vacuum ports on the intake boots, but if you're sucking fuel at the venturi level and the vacuum advance is working, I'd say you don't have to worry about vacuum. As far as #4 leaking, I'd check the vave seat/pin to make sure there's not some dirt or perhaps a damaged tip that's letting gas get past it when it should be seated and stopping the flow. Some guys have said that in some instances the float bowl gasket may be a bit large, preventing the bowl from sealing properly. That's at least a coule things you can check.Can't beat the smell of gas & oil
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Originally posted by Lonerider62 View PostI don't know the actual number for how much vacuum shoud be measured at the vacuum ports on the intake boots, but if you're sucking fuel at the venturi level and the vacuum advance is working, I'd say you don't have to worry about vacuum. As far as #4 leaking, I'd check the vave seat/pin to make sure there's not some dirt or perhaps a damaged tip that's letting gas get past it when it should be seated and stopping the flow. Some guys have said that in some instances the float bowl gasket may be a bit large, preventing the bowl from sealing properly. That's at least a coule things you can check.
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8-9 inches of mercury would be right in the ballpark; you'll see some variation due to gauge calibration and idle speed....Fast, Cheap, Reliable... Pick any two
'78E original owner - resto project
'78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
'82 XJ rebuild project
'80SG restified, red SOLD
'79F parts...
'81H more parts...
Other current bikes:
'93 XL1200 Anniversary Sportster 85RWHP
'86 XL883/1200 Chopper
'82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
Cage: '13 Mustang GT/CS with a few 'custom' touches
Yep, can't leave nuthin' alone...
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Originally posted by crazy steve View Post8-9 inches of mercury would be right in the ballpark; you'll see some variation due to gauge calibration and idle speed....Last edited by motoman; 04-03-2012, 10:31 PM.81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
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Originally posted by motoman View PostNot even close...........should be 14-17in. of mercury depending on calibration.if your down to 9in. your idle mix is way too lean...Fast, Cheap, Reliable... Pick any two
'78E original owner - resto project
'78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
'82 XJ rebuild project
'80SG restified, red SOLD
'79F parts...
'81H more parts...
Other current bikes:
'93 XL1200 Anniversary Sportster 85RWHP
'86 XL883/1200 Chopper
'82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
Cage: '13 Mustang GT/CS with a few 'custom' touches
Yep, can't leave nuthin' alone...
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Originally posted by crazy steve View PostInteresting.... I saw 8.5-9 on the SG I did, and that's with all OEM parts (exhaust/airbox/jetting/etc) and settings. That was the 'sweet spot', and turning the idle screws either way from that only dropped the vacuum...81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
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ok, i am running 9 PSI on my guage, converts to 18.4 in/HG. so i am good there and also going back through the manual i downloaded it is saying the main jets should be 137.5. before the new jets were installed the jets were 110-115-115-110 which i believe would have been very lean. where would the new jets leave.. 122.5-127.5-127.5-122.5 and yes the drain bolts are on the bottom
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The 137.5 jets are for the '78-79 carbs; if that's the ones you have, you should be somewhere around 142 with pods and a 4-1. Not having a muffler is going to give you fits for tuning, as these just don't tune well without backpressure.
If you have the '80-82 type carbs, you should be close.Fast, Cheap, Reliable... Pick any two
'78E original owner - resto project
'78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
'82 XJ rebuild project
'80SG restified, red SOLD
'79F parts...
'81H more parts...
Other current bikes:
'93 XL1200 Anniversary Sportster 85RWHP
'86 XL883/1200 Chopper
'82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
Cage: '13 Mustang GT/CS with a few 'custom' touches
Yep, can't leave nuthin' alone...
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Originally posted by Justindrider View Postok, i am running 9 PSI on my guage, converts to 18.4 in/HG. so i am good there and also going back through the manual i downloaded it is saying the main jets should be 137.5. before the new jets were installed the jets were 110-115-115-110 which i believe would have been very lean. where would the new jets leave.. 122.5-127.5-127.5-122.5 and yes the drain bolts are on the bottom81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
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White mean lean.Nathan
KD9ARL
μολὼν λαβέ
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 Roosevelt
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