shudder at 4000 rpm

[underdog57]

how many turns are your idle mix screws ??
By the way they are really easy to break off , so might take them out and look at the tips ....once the tip breaks off it runs funny , not ha ha ..

I have the air box on(not drilled) and 4 into 1 headers . Am using stock jets ...I could bump the mains , but it will go to 8500 pretty
quick till you get to 4rth and fifth 110 MPH . So mains are not that criticle unless your racing a crotch rocket...
27MM float ...
79 carbs that have the screw in float needle seat ...
Same as yours ??

I had that stumble under load about 4500 RPM . its totaly gone now ... I changed nothing but float level and idle mix ...
Its not perfect , as I find idle mix tricky to notice a change in rpm .
Been watching the plugs color ...

might also check that all your jets and cap screws(tower) are all seated ...Found a loose one myself ...


One more thing is the needle jets . the long jet that goes in the emulsion tube . What does it look like??shiny silver is bad , gold is good ...

I have another set of carbs that run great eccept the one that has a pitted needle jet .. Coincidence I think not...

I found it helpfull when setting the float to rotate the carbs so the tang on the floats settles . Did have it not giving me repeat
float heights , with out doing that ...

Mine is running pretty good , now and I had the carbs off dozens of times wondering what the ....starts with F ...

Let us know how it goes ....
Sorry for being longwinded , but I've seen a lot of differance with idle mix adjustment . Mine is out 1 turn now ...

Bob

[scott0757]

These jet sizes seem huge to me. The post is old, but I figured I toss in my two cents.

I have a '80 XS1100SG which now had 7500 miles on it. When I got it, all four main jets were 110s. After reading this site, it appeared the OEM set-up would be 110's on 1 & 4 and 120's on 2 &3 (to help them run a bit cooler. I then update my exhaust to MAC 4-2 pipes sop I went with 120's on 1 &4 and 125's in 2 & 3. My carbs had the idle mixture screws capped so I pulled the plugs so I could get to them. I still have the OEM airbox. My thought is your carbs are jetted way too rich.

It runs well, but has a slight hesitation as I transition to the mains, after which it flies. Still checking things out..Will have to look at the wires by the timing advance unit as suggested. May opt for the pods some day.

Large backfires when slowing typically indicates a lean mixture in the pilot setting, so open the screws a 1/2 turn or so. Mine our out about 2 turns right now. and I only get the normal burble.

If you got it figured out, fill us in!

[raqumup]

its at the shop now

i took it to a new local shop, a friend recomended it and the owner is working on it for me. i don't have a jet kit to tune it so i finaly broke down and i a going to pay someone to tune it for me. he said that he does not know how it started but he said he is mentioned alot on this sight for knowing how to fix these bikes. his name is rick, he used to own fast lane cycles in chantilly VA. well he just opened his new shop R and R cycles in sterling VA. i hope he can fix my bike. the other reason i broke down and am paying someone is the summer is comming to an end and i have not ridden it sence the middle of lats summer and man do i have the itch. i will let you know the outcome and what jets he ended up putting in and any other info that might help someone else. later

[Meatloaf]

Yikes. Been through EXACTLY what you're going through on my own '78E. Just ended up thowing good money after bad trying not to miss the season. Spent $2800 fixing up a bike that cost me $1000 to buy (in my own defense an all stock 78E with only 15,000 miles on it...) before I saw the light and told the mechanics to get lost.

Eventually did it myself. One way to protect your season is to scrounge a set of spare carbs. Better running ones stay on bike, worse one's are used for teardowns.

I'm still running rich, but it's very drivable. What I learned is that you just can't own one of these bikes if you don't do the work yourself.