Exhaust pressure uneven

So I finally received my Colortune and was able successfully dial in my mixtures and vacuum sync the carbs (had already synced previously). I was worried about it being difficult to use the colortune but it was very easy to notice color changes and I set all 4 to be just off yellow and into the blue.

The bike appears to run fantastically and pulls harder and smoother than ever before, but I noticed a significant difference in exhaust pressure between the left and right exhausts. This seems odd considering that as far as I can tell the mixtures and sync is dead on. From the older Honda twin I also work on I know that the old school way to sync the carbs is to match the exhaust pressures so it worries me that they wouldn't be even.

Should I be concerned about this and if so, what would be the first thing to look into? I can't find any sort of exhaust leak around the headers.

Valves clearances were checked and adjusted recently and carbs have been rebuilt and cleaned - floats wet set.

 

Check your compression, and ignition.
The sync just adjust's the individual cylinder to it's best efficiency, and if the compression is low, the volume of gases emitted will be less. If the ignition is impaired, the gases will not be as voluminous as a cylinder with strong ignition.
The reason the old school used exhaust pressure is that it was quick and "good enough". Now that you have the test equipment, do as the old time pilots say, and "trust your gauges".

CZ

 

Well, actually the synch process adjusts the engine to it's best possible efficiency (but not necessarily the highest power output)............the purpose of synch is to get the power output of each individual cylinder the same (equal) as all the others, this is how you get the "sewing machine" effect and how the engine produces the max output possible without introducing excessive wear and tear......note that since the synch equalizes the power output of each cylinder, then by implication each cylinder is "tuned down" to the output of the LEAST powerful cylinder (that's the only way to get them all equal).

 

Your bike has a full "collector box" exhaust system. ALL of the exhaust goes into "the box" gets crossed and all scrambled up and then goes out the mufflers. You're not feeling any difference between the cylinders in the motor, there is NO correlation there. Any output from either muffler is from all 4 cylinders.

More likely one of the dividers inside your collector box has partially rusted away. I wouldn't worry about it.

 

That sounds like most likely Fitz. The exhaust collector is not in the greatest shape and is on my long term to-do list of things to address. I guess I should stop fretting about the little things and get on with riding.

I have checked the compression (end of last season) and it was good and even across all 4.

 

While I have this thread going, what should I expect my idle RPM to be when using the enrichment circuit?

I've noticed that no matter how much I give it it'll never idle higher than about 1400 rpm, but I've seen in videos of other XJ's that the choke easily gets the bike in the 2k-2.5k range and that increases as it warms up.

The enricher has a clearly noticeable effect and I know for sure the jets are clear as can be, but starting off even on a warm day I'd be in poor shape without a good bit of enrichment to keep the RPM above 1k.