jetting

[rubyasaurus]

New guy here, hello I’m Tim
dont want to whip a dead horse here but but I have a 1979 xs 1100 special that I have owned for 16 years, the last time it was on the road I drove it to Atlantic city (12 years ago) and my buddy rear ended me, right up the ol tail pipe, hehe, seriously (to avoid a mail truck, he was on a seca 400), that was the end of the stock exhaust, I put on a Hindle 4-1 exhaust and haven’t driven it since. Now I am going to put on pods, (and carb boots, new seat, paint and polish etc, what the heck happened to the price of bike insurance).

I wish to avoid buying 5 different sets of main jets, or damaging my engine, my confusion stems from the variation there seems to be from this and different web sites about the size of stock main jets for this bike, anywhere from 115 to 137 how can this be? Would I be silly to try the 125s that are in there to begin with? With new 4-1 exhaust, and pods. How far should I go before checking the plugs? It takes me a week to get a set of jets, any suggestions?
ps. I live 550ft above sea level (simcoe ontario), please give me your opinion on the two (best guess) sizes of main to order, Im going to up size the pilots by one any way.

[MrOzz]

Welcome to CH11.


Check out this post on jetting tips.

http://www.xs11.com/forum/showthread.php?t=382

[tinman905]

Hey Tim welcome ,

I am not sure if this will help but I was running 120's mains with a 4 into 2 and K&N in the filter box and it was running perfect. I check my plugs often and colour was right on . I am about 1700ft above sea level here also about 1400ft above Toronto.

Take your bike somewhere where you can run it hard for a few km and then shut it off without slowing down , stop the bike (make sure you pull the clutch before you shut it down). Take the plugs out and check the colour. Something I learned from a fellow XS'er . 125's doesn't seem too far off to start with.

[bikerphil]

my confusion stems from the variation there seems to be from this and different web sites about the size of stock main jets for this bike, anywhere from 115 to 137 how can this be?

The 78-79 carbs run a much bigger main jet size (ex. 137.5) as compared to the 80-81 carbs which run smaller mains (ex.115).

[81xsproject]

4-1 and pods for your XJ... 117.5 mains and 45 pilots. Just make sure you are getting them from a reputable source. Mikesxs, CRC, JetsRus, Z1E all carry quality jets. However, JetsRus carries genuine Mikuni.

[paulbaut]

how i wish we all have a single carb for our XS...removing and installing and even synching those 4 carbs really is tedious especially when u experiment in changing those main jet upto its desired size....and sometimes there are overflow issues especially when it was then stucked up....anyway,thats the way it is for 4carb setup like ours.hehe....by the way its a great idea to start with a 125..enjoy tinkering your carbs then.

[bikerphil]

I have a 1979 xs 1100 special

137.5 main and 42.5 pilot are stock jet sizes for this bike. Go up according to the jetting guide posted above. Better make sure you have the original carbs or if they've been replaced with the later type before ordering any jets. Early carbs have the idle mixture screws either exposed or under a plastic cap. Later carbs have the screw down in a tunnel, though it might be covered with a metal plug. Also, Mikuni jets and Dyno's use a different numbering system, although both will fit. I'd go with the genuine Mikuni's. JMHO

[tinman905]

I know we shouldn't assume but he has said he has been using 125 mains that would make one to believe he has later model carbs .He will have to clear that up to get the correct advice .

137.5 main and 42.5 pilot are stock jet sizes for this bike. Go up according to the jetting guide posted above.

[dbeardslee]

Tim - welcome to ch11. I've got a '79 with 4/1 and pods. 147.5 mains and 45 pilots with the floats set at 25.5mm does the trick for me.

[rubyasaurus]

thanks everyone

I think the carbs came orig. with the bike, here are some pics,
http://i783.photobucket.com/albums/y...s/DSC04799.jpg
http://i783.photobucket.com/albums/y...s/DSC04804.jpg
http://i783.photobucket.com/albums/y...s/DSC04794.jpg
http://i783.photobucket.com/albums/y...saurus/330.jpg

I guess I will get at least 3 sets, link me up with an online store with good jets at a good price?

Thanks
Tim

[bikerphil]

Yep, those are the early type BS-34 II carbs (78-79). Don't know why there were 125 mains in there, unless they were Dynojet which uses different numbering system. I'd follow Dbeardslee's setup if you're running pods and a 4-1 exhaust. Get genuine Mikuni though, you can't go wrong. I don't know if 550ft. above sea level would affect jetting , I doubt it.

For the mains, you need large round type, for the pilots you need BS30/96 type. Here's one source that carrys them at minimal cost. They are sold in pairs, you'll need 2 pr. of each.

http://www.mikesxs.net/products-4.html?category_id=x

[dbeardslee]

I'm like 440 ft. above sea level - I don't think that little bit of altitude would make much difference. I second Phil on Mikes XS. They've got the best price on genuine miks that I've seen. If you haven't got the pods yet, it's a good place to get them as well. Just to be on the safe side, you might want to verify that your carbs are 78/79 variety. If there's two sets of T's on the carbs - one set for gas, one for vents - then they're the 78/79's. If there is only a lower set of T's then they're later model carbs and you'll probably have to open them up to tell what kind of jets you need. Some of the later model carbs use a plug over the pilot jet tunnel, some don't (depending on year), and it makes a difference in how to jet.

Then he looks at the pictures. Forget what I just said. By the pics they're '78/79's.

[rubyasaurus]

thanks for the ID gentleman

one last question (probably), do I put larger mains in 2 and 3, than 1 and 4. or the same all the way across?

Thanks again
Tim

anybody got a mouse trap
http://i783.photobucket.com/albums/y...s/DSC04806.jpg

[bikerphil]

Same all the way across. If you are changing your pilot jets too, make sure you use a screwdriver that fits properly, or you'll be drilling and using EZ outs. Soak 'em with PB Blaster first. Do you know what size pilots you're running now?

[rubyasaurus]

thats great advice on removing the pilots, I wish I had read it a couple hours sooner, I might need an easy out for one of them now, the rest are soaking in releasall. Ill grind down a flat head and make a custom fit for the rest.

Thanks again
Tim