The answer to my problems?

[CodyLane]

So I bought a '78 xs11 over a year ago for $750. It's been my daily driver since. When I first bought it, it was very weak and would barely get over 70mph. After cleaning out the carbs my performance was drastically improved and I was satisfied for a while. As of late I've been wondering more and more why I only get 25 mpg and don't seem to have the power other riders of the same bike do. Upon investigation I found a wire holding the vacuum advance unit up. I took it off, bought a timing light and tried to time it. Everything seemed to be in order but the bike ran like hell. No power, like driving a scooter. After clawing through the ever helpful forums on this site I discovered that my 78 has a 4R0 engine. I never knew! This 4R0 engine has the 4R0 vacuum advance without the mechanical advance. BUT it still has the 2H7 TCI. I ordered the 2H7 advance setup off of Ebay and am anxiously awaiting it's arrival. Perhaps this is the reason why this bike has been impossible to tune?

[skids]

4R0 vacuum advance without the mechanical advance. BUT it still has the 2H7 TCI. I ordered the 2H7 advance setup off of Ebay and am anxiously awaiting it's arrival. Perhaps this is the reason why this bike has been impossible to tune?

I am surprised it ran at all! I tried that once and I got xtra loud back fires.
The pickup coils and the ignition box need to match and the later model (81) does not have the ballast resistor. Also I think it had different plug wire coils.

[CodyLane]

I'm really suprised that it runs as well as it does given the Frankenbike setup it currently has. I seriously think that the wire holding the vacuum advance up is the keystone to my current performance. The pickup coils may be from the 78 but I'm not sure. I'll have to see if maybe the ballast resistor is still on the bike. I've got a bunch of parts being delivered right now. Hopefully I'll be able to piece together a working (better working) setup. Due to a new job and a big salary increase my XS is finally getting the love it needs.

[mxmikie]

i have the 2H7 advance setup and vac advance if you find you need another

[DGXSER]

The ballast resistor is only there to match up with the early models 1.5 ohm coils. The 81 Special (which where the 4RO engine came from) had 3 ohm coils. So, no need for a ballast resistor.

A simpler, but maybe not as economical solution would be to find a 4RO TCI. Replace it and your system matches.

The pick up coils I believe are the same for all models. It just the elimination of the mechanical advance that changes.

[CodyLane]

Project Update:
So I received the 2H7 advance plate, mechanical advance and timing plate today. The swap was so easy! Instantly my bike's erratic behavior was tamed and the power was back. It's the fastest I've ever had it.
I still need to really tune the timing, tinker with the carbs and check to see which coils I have. If I have the 81 coils I'll probably take out the ballast resistor. I'm anxious to see what the average MPG will end up being now. I'm currently sitting at about 25 MPG.

[windjammergump]

bought my first xs 1100 special for 650

bike had been crashed replaced how front forks guages and turnsignals lights and back tail lights was use to the kz1100 i owned before it and the power wasnt there....rebuilt the carbs still no avail...took to shop number 3 leaked down 40 on a compression test ....now going with boring an 1179 wiseco kit..have a 4 in 1 waiting for later and accel coils and wires now..hope the beast comes alive......we will see shortly
gump...about 1800.00 invested i am hopeing.....dont know the total labor yet