Carb adjustment

[JNorris630]

I have 1978 xs1100 and it runs great below 4000 rpm but misses bad above that. I thought about adjusting the needle position inside the carbs. I have straight exhaust and pod carb filters. I went up to 140 jets and runs great below 4000. No poppng and idles great. Synced carbs and replaced all jets.

[natemoen]

Are the carbs clean? Did you remove the emulsion tubes and clean them? Do you have the vacuum advance hooked up to the port on the #2 carb and NOT hooked to an intake boot?

[bikerphil]

One size up on the main jets (stock is 137.5) is probably not enough, might need to go higher with pods and no back pressure exhaust.

[JNorris630]

Main jets

Sorry.....I went back and looked at my order and I have 145 main jets.

[JNorris630]

Fyi

Emulsion tubes are clean, vaccum hose is on #2 carb port, not the intake connecting boot

[JNorris630]

Clean

Carbs are clean

[bikerphil]

Does it run so bad at 4k+ RPM that it feels like 2 cylinders are cutting out? It may be bad pickup coil wires. The vacuum advance moves the ignition wires causing them to flex. They can appear fine but are really broken inside. JAT

[JNorris630]

Progress

I first thought it was the carbs but after reading your responses I deceided to check the firing. I am just working on this in my spare time. Sorry its taking so long to post. Since it runs fine below 4000 rpms I started looking for a way to check the spark plug voltage at low and high rpm. I found a nice little tester http://www.amazon.com/Thexton-404-Ad.../dp/B0002STSBM. I got mine at autozone for 6.99. I hooked it to number 4 cylinder and had a nice long arc all the way up to 5000 rpm and then it went completely away. My next test will be to check the other cylinders and wiring around the vac advance. I will get the manual and try to check all primary voltages. I suspect ignitor circuit or coils. Let me know if anyone has any ideas. I appreciate your feedback.

[JNorris630]

update

I checked all four cylinders and the spark goes away on all. The only thing I saw common with all cylinders was the CDI. I bought one off ebay and still have the same problem. I have the pickup coils off now repairing bare spots on the wiring. I do not believe this is the problem. I will check the high voltage coils tonight and I am going to jump the lean angle switch.

[3Phase]

J, just unplug the tipover switch to take it out of the circuit, do not put a jumper on it.

The switch works by shorting one specific wire from the TCI to ground and that kills the ignition. If you put a jumper on it you will be doing the same thing the tipover switch does when the bike tips over and the engine will not start.