vacuume at idle, and yet another jet question

[Justindrider]

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]

[natemoen]

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.

[Justindrider]

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.

ive heard about the probs with the pod filters and hi flo exhaust. as far as carb cleaning goes i will go back through and check the needle tips because i have a feeling the rubber has a groove in it and isnt allowing the full closure. thanks for the quik reply

[Lonerider62]

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.

[Justindrider]

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.

yep i got them synced but still a rough idle, i made my own guage from the tech forum

[crazy steve]

8-9 inches of mercury would be right in the ballpark; you'll see some variation due to gauge calibration and idle speed....

[Justindrider]

8-9 inches of mercury would be right in the ballpark; you'll see some variation due to gauge calibration and idle speed....

awesome!!! now on to more carb work...

[motoman]

8-9 inches of mercury would be right in the ballpark; you'll see some variation due to gauge calibration and idle speed....

Not even close...........should be 14-17in. of mercury depending on calibration.if your down to 9in. your idle mix is way too lean. If coming up on the idle mix makes plugs start showing rich, then your float levels are too high. I just went through all this the past two days to get my Venturer back correct. Same late model carbs. Your intake and exhaust set-up are gonna keep you from getting idle circuit and correct fuel levels matched correctly. IMO, you'll hole a piston before getting it right. Those float levels, if the 81 carbs with the drain bleeder screws on the bowls need to be checked with the bike on the centerstand, PERFECTLY level across the carbs. The 23mm float setting will get you in the ballpark, but that setting is for 80 carbs ONLY, and is a bit high for the 81 carbs. The 3mm+-1mm fuel levels is what you want. It will like the +1 better....while running with hose attached held up beside bowl to see fuel levels. Thos fuel levels have to be identical across all bowls. If off a half a millimeter between any two, it can be compensated with the idle mix screws, to a degree. Actually not much room for error, or you'll be cussin' the carbs till the cows come home. Be patient and anal, and the carbs willbe happy. Again, pods and open exhaust ARE gonna be your worst nightmare and no matter what you may believe,even by the seat of your pants it will NEVER run like an XS11 should. Maybe a little rough expressing, but that's the bottom line.......looked back and being that's an 80, and if the carbs are 80 with the bolt drain in bottom of bowl, 23mm is the float setting, but IMO, 24mm would be the better option with an initial 2.5-3 turns out from lightly seated mix screws and fine tune from there.

[crazy steve]

Not even close...........should be 14-17in. of mercury depending on calibration.if your down to 9in. your idle mix is way too lean...

Interesting.... 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...

[motoman]

Interesting.... 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...

Interesting......if I back my idle mix screws out from the sweet spot, it will pull 18in. of mercury, but obviously way too rich at 4 turns out. as i found out just messin' with the idea. In this case, the sweet spot is 3/8 turn out from a ever so slight change in sound at idle which puts them at 2 3/8 out from seated. Results may vary dependant on actual fuel levels in bowls at idle.

[Justindrider]

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

[crazy steve]

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.

[motoman]

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

With that last statement and the pic., I'd say you have the original carbs. 110's across ARE stock for that year carbs and also the 81Special carbs. IMO, your leanin' out the idle circuit too much to compensate for the rich main circuit when runnin in the mains. At this point, again, IMHO, your 2-3 steps too rich in the mains, even with the intake/exhaust set-up(or lack of) your scoot has.

[Justindrider]

so the plugs being white could be due to the floats not being set right not the jets? and in that case i should be around 115-120-120-115?

[natemoen]

White mean lean.