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I just picked up a 78 xs and put a 4 into 1 header and a set of pod filters. I have the low speed and th main jet set up right but the needles are on the second notch from the bottom. It studders around 5000 to 6800 rpm and comes back to life after 7000 rpm. Just looking for an opinion on whether to go up or down on the needle adjustment.
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What size jets are you running and what color are your plugs? The stumble might not even be from the needle height, might be timing or something else..?'79 XS11 F
Stock except K&N
'79 XS11 SF
Stock, no title.
'84 Chevy K-10 "Big Blue"
GM 350, Muncie SM465, NP208, GM 10 Bolt with 3.42gears turnin 31x10.5 Baja Claws
"What they do have is an implacable, unrelenting presence and movement that bespeaks massive power lurking behind paint and chrome. They don't wail like a screeching ninja, the don't rumble like a harley. They just growl like a spactic, stressed out badger waiting to rip your face off and eat your soul." Trainzz~RIP~ -
If everything else (timing, advance mechanism, correct plugs, etc.) is in order, try tuning fyour carbs from the top down.
1. High RPM - find the best main jet.
2. Mid RPM - find the best needle position.
3. low RPM - get the best float height adjustment.
4. Idle RPM - adjust idle mixture screws.
FactoryPro.com has a good procedure for this on their website. It is a bit of a pain to do but it works.Mike Giroir
79 XS-1100 Special
Once you un-can a can of worms, the only way to re-can them is with a bigger can.Comment
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He was having a problem trying to post so he sent me this above message...Originally posted by noflyzone View Post
I would think you are at a good starting point, but according to this you should be running 147.5 mains so you might be running a little lean on the top side. The best way to tell is to do a throttle chop at WOT and read the plugs. If they are white or really light brown then your lean and need to drop the needle clip one spot and test again. If your dont have much experience with reading plugs search in the maintenance section on how to read plugs and search throttle chop to lear how to do that properly. Some one else will chime in on the jetting but I think that youe not too far off. GL and welcome to the form.Last edited by WMarshy; 04-29-2010, 06:15 AM.'79 XS11 F
Stock except K&N
'79 XS11 SF
Stock, no title.
'84 Chevy K-10 "Big Blue"
GM 350, Muncie SM465, NP208, GM 10 Bolt with 3.42gears turnin 31x10.5 Baja Claws
"What they do have is an implacable, unrelenting presence and movement that bespeaks massive power lurking behind paint and chrome. They don't wail like a screeching ninja, the don't rumble like a harley. They just growl like a spactic, stressed out badger waiting to rip your face off and eat your soul." Trainzz~RIP~Comment
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Way too big. I would bring those mains down to at least 145's and those pilots down to 45's. I have never seen or heard of anyone needing to go beyond a 45 pilot.'81 XS1100 SH
Melted to the ground during The Valley Fire
Sep. 12th 2015
RIPComment
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Apparently he's having troubles posting in topics... IDK what to tell him. Any suggestions guys? Here is what he sent me...
Originally posted by noflyzone View Post'79 XS11 F
Stock except K&N
'79 XS11 SF
Stock, no title.
'84 Chevy K-10 "Big Blue"
GM 350, Muncie SM465, NP208, GM 10 Bolt with 3.42gears turnin 31x10.5 Baja Claws
"What they do have is an implacable, unrelenting presence and movement that bespeaks massive power lurking behind paint and chrome. They don't wail like a screeching ninja, the don't rumble like a harley. They just growl like a spactic, stressed out badger waiting to rip your face off and eat your soul." Trainzz~RIP~Comment
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I think it is way overfueling in the midrange, since this is the place where all 4-1's die. Drop your needle so it opens as late as possible and see what happens. If it gets better, you might need a longer taper needle to slow the midrange mix a little. I think your main jet is also too big making the problem even worse.
At 5-7K you are actually fueling twice due to resonance frequencies being wrong, so you are running doubly rich at that speed anyway. Remember that a 4-1 is a high RPM pipe, and sucks in the mid range (although it can suck less
) Coupled with the fast open needle and the large main jet, the engine is drowning. Once over 7, you are using enough fuel for it to come out of it, and are gaining the advantages of the scavenging.
Healthy is merely the slowest rate at which you can die
Some people will tell you that slow is good - and it may be, on some days - but I am here to tell you that fast is better. I’ve always believed this, in spite of the trouble it’s caused me. Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba….Hunter S. ThompsonComment
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