petrolhead63 Posted May 13, 2016 Posted May 13, 2016 Hi, I now have a 1977 XS500, very pleased with her and can't wait to get my mot on it! It has the later type carbs I believe. looking forward to being on the forum too. Going through the usual things and got onto carbs. Firstly my balancer adaptor tubes are I think M5 thread and too small for the threaded holes. Can anybody tell me what size the hole is? Then the air/pilot screw. The book says 1 turn out on right hand, 1 and 3/8 out on the left hand. Never come across difference before? Also when I look to lightly seat then back out they each have a square lump on them stopping them screwing right in or backing out...tamper proof? I only have about 2/3 of a turn available so have initially set them at midway on each between the stops. Is this normal on this type of carb? Many thanks for any input.
blackhat250 Posted May 13, 2016 Posted May 13, 2016 Hi there. drewpy is the XS guru. .he"l keep you right.
Moderator drewpy Posted May 14, 2016 Moderator Posted May 14, 2016 the 500 was a much different beast to the 400's as it was yams first attempt at a 4 valve head. the differences in carb settings was due to the left hand cyl running hotter. On the 400 they had a different jet. Can you not fit threaded spigots on the inlets and push balancer tubes over that. find the thread size using bolts
Moderator Cynic Posted May 14, 2016 Moderator Posted May 14, 2016 Ok, obvious curiosity question, why did the left side run hotter. Not like there is any obvious difference between sides? My Suzuki had different jetting for the middle cyls for obvious reasons, they were hotter because they were in the middle.
Moderator drewpy Posted May 14, 2016 Moderator Posted May 14, 2016 34 minutes ago, Cynic said: Ok, obvious curiosity question, why did the left side run hotter. Not like there is any obvious difference between sides? My Suzuki had different jetting for the middle cyls for obvious reasons, they were hotter because they were in the middle. I've no idea, some suggested phasing differences in the crank, others the compromised airbox shape
Moderator Cynic Posted May 14, 2016 Moderator Posted May 14, 2016 Oh ok, just curious. may of been a oddball reason.
petrolhead63 Posted May 15, 2016 Author Posted May 15, 2016 Hi Drewpy, thanks for the answer as to why the different settings! I will play with the thread size as you say. I was being lazy asking if anyone knew what it was! I'm guessing maybe m6, the balancer pipes are m5.
Tommy xs Posted May 15, 2016 Posted May 15, 2016 Hi my xs400 has different jets on each, I think its something to do with the air intake although it is all one box there's more flow on one side hence different jets
petrolhead63 Posted May 16, 2016 Author Posted May 16, 2016 OK, plugs are m6 and have as you suggested sourced spigots so should be able to cobble pipes onto those. What about these pilot screws with limiters on them? this means I can't seat them then back them out, so am I right putting them to the middle of travel and then tweaking a bit to get the 3/8 turn difference between left and right? So far I notice no real difference adjusting the pilot screws within the limited range although I think they are off balance anyway. That said it runs quite well! OK, plugs are m6 and have as you suggested sourced spigots so should be able to cobble pipes onto those. What about these pilot screws with limiters on them? this means I can't seat them then back them out, so am I right putting them to the middle of travel and then tweaking a bit to get the 3/8 turn difference between left and right? So far I notice no real difference adjusting the pilot screws within the limited range although I think they are off balance anyway. That said it runs quite well!
Moderator drewpy Posted May 16, 2016 Moderator Posted May 16, 2016 carbs prob need a good clean, but if its running OK leave alone. you might be able to flick those limiters off as I think they just push on, Caveat Emptor
petrolhead63 Posted May 17, 2016 Author Posted May 17, 2016 that's interesting if they come off..the limiters. As you say though, it seems to run well, I will know for sure when its mot is done so will simply balance then and set pilot screws sensibly. My understanding is the pilot screws only really alter slow running. The tank looks new inside which is a good sign, the fuel taps too are squeaky clean.
Moderator drewpy Posted May 17, 2016 Moderator Posted May 17, 2016 pilots, alter fuel through out the range, but more so up to 3-4k when the mains start. The Pilots don't stop feeding fuel so will make a difference
petrolhead63 Posted May 19, 2016 Author Posted May 19, 2016 OK thanks, as I thought in that as revs open up the pilot has less influence. I will open a new topic on points/timing before I check that ahead of carb set up.
Moderator Cynic Posted May 20, 2016 Moderator Posted May 20, 2016 Think of a carb like a choir. One part starts (pilot jet) then the rest come in as it progresses. One duff voilc ruins the tune. 1
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