Carb Problems

[twmiller]

I have a 1980 XS1100 Special not a Midnight Special I am having carb problems. I replaced the stock air box with k&n filters I decided to put larger main jets in the carbs so it would run better. Yamaha calls for the carbs to have 120 jets for 1&4 and 125 for 2&3 I put in 122.5 for 1&4 and 127.5 for 2&3 the jets I took out of the carbs were 110s someone else had put those jets in the carbs before I bought the bike. The bike runs very good it idles great and has great throttle response but when I get up past 80 mph it runs like its starving for fuel but it doesn’t miss or run bad. I would greatly appreciate any help anyone can give me.

Thank You
Todd Miller

[TopCatGr58]

Hey TWMiller,

Despite what the manuals say, many folks have found that their jets were 110's all across, instead of the various sizes for the inner vs. outer cylinders!

But still, the size of jets you chose should not cause a problem with your Indy Filters. Have you checked your float heights? Running at high speed/rpms, you could be emptying the bowls faster than they can fill? Put your petcocks on PRIME and try it. IF you are able to run to top end without that fading feeling, then you're NOW getting enough fuel, and your octopus could be at fault. At higher rpms, the vacuum pressure being applied to the octopus can actually be less than at lower rpms, and could be partially closing restricting fuel flow and allowing the bowls to empty faster than being able to fill?

Also, are you sure you used K&N brand, or just that STYLE? It has been reported that folks have gotten some air restriction from an inner lip on the filter partially blocking the inlet bell ports!?

Try it WITHOUT the filters on as another test! IF it runs better, then you'll need to make some mods to how they are mounted!?
T.C.