79' KZ750 Twin Right Cylinder Low Exhaust Pressure

I recently got a 1979 kz750 twin that I have been working on....After fiddling with mixtures, I finally got the right cylinder to stop backfiring when cold, but then I went to the back of the bike and put my hands behind the mufflers....The left exhaust was at least 5 times more powerful than the right. So far, I haven't noticed any problems stemming from that while riding; though to be honest I wouldn't know what to look for anyway. My question is whether this is a major problem and what the problem might be...On a side note, I looked under the bike and saw that it looked as though the separate exhaust systems were in fact connected to each other through a tube on the bottom of the bike. In my bike's case, that tube was bent inward on itself as though someone went over a bump and crushed it in. Whether or not this could be a problem or whether it is actually connecting the two system is a mystery to be. I would be happy to hear your ideas and comments!

Welcome aboard.

The cross over pipe does in fact connect the two exhaust pipes. This effectively lets each cylinder use both exhaust pipes and mufflers. This increases performance and allows the use of smaller mufflers than would otherwise be possible. It is a good thing.

The unbalanced pressure could be caused by several things.
First, are you certain that incorrect mixture was the cause of backfiring? Are you sure that fiddling with the mixture screws has not just masked the real problem, like plugged circuits in the carb? Could the mixture now be so far off that the cylinder is not firing? It is best to approach these problems in a systematic way. The factory shop manual lists such procedures, and several board members (MFolks comes to mind) have posted these things in the past. Give the search function a try, and get and follow a factory shop manual. It will save you many times its price in time, money and frustration.

If that cylinder is firing as it is supposed to, then the uneven pressure may be the result of a rodent nest in the muffler, or the internal collapse of the muffler due to rust, or valves that are way out of adjustment, or problems with spark.

When the bike is running, spray a bit of water on each header tube in front of the engine. If the water evaporates at about the same rate from each, then that is an indication that the cylinders are firing about equally and the mixtures are likely in the ballpark. A temperature gun is even better than water. If one pipe is noticeably cooler than the other, then there is a problem. If one of the mufflers is clogged, or if the valves are out of adjustment, or if the ignition system has problems, there is no way to get the mixture right.

Happy hunting.

Thanks for your reply! I do have the factory repair manual, so I'll go dig through that a bit. I had also wondered whether I had set the mixture so the cylinder wouldn't fire but couldn't really tell. After "setting" the mixtures I didn't notice a change in the way the bike ran but, if it was a problem with the bike before I had it, then I wouldn't have anything to compare it to. Again, thanks for your reply

If you're sure that cylinder is firing.

I'm going to suggest the first thing you do is a compression test. This will save you a lot of digging around, and if you can't do one at home a shop wouldn't charge you much since it's a 5 minute job. If it's a bad valve, sticky valve, or bad rings on that cylinder you'll know right off the hop. As that cylinder will likely have low pressure.

If the compression checks out good, then look to the balancing of your carbs for the problem. Balancing them on the bench, or bike, is easy and well described in your manual.

I wouldn't worry about the stupid balancer pipe on your exhaust. It has little to no performance effect on a twin, and most people I know would remove it and cap off the ports it was connected to. It makes trouble shooting much easier once that POS is gone.

I'm unsure on your year(never seen a pre 1980 exhaust still in on piece, LOL), but most likely you can remove the baffling from your mufflers to inspect it for rot or moose's nest.

If you can't remove the baffles, you could remove the balancer pipe, Plug the mufflers, and check the pressure at those ports. If you have even pressure there, then your mufflers are probably screwed.

Let us know how you make out... best of luck to ya!

You plan on keeping this bike and riding it? If so, then do the following, it will save you a lot of time and grief.

Engine:
Check/adjust the valve clearance.
Adjust cam chain tensioner
Compression test
Remove carbs, clean and check/adjust the fuel level in the float bowl.
Bench sync carbs (that's good enough to get it running halfway decent)
Install carbs
Check coil with DMM, ~17k-20k ohms measured between the two spark plug wires, 3-5 ohms measured across the two little wires.
Better idea is trash the coil and get new coil/wires/plug caps.
Check adjust the points.
Better idea, convert to electronic ignition.
Change oil and filter, Shell Rotella T 15w40 works good.

Now the engine ought to start and run decent, vacuum sync will make it run better.

Bike

Check swing arm bushings/bearings
Grease swing arm fitting
Remove rear wheel and check/replace/grease wheel bearings, install
Remove front wheel and check/replace/grease wheel bearings, install
Check/replace chain and sprockets (most of us use 17 tooth front)
Disassemble steering stem and check/replace/grease steering stem ball bearings.
Drain fluid from forks and refill with proper amount and weight
Flush front and rear brakes, and check/replace pads
Check/replace tires
Check for loose spokes.

That's a solid days work, but you'll have a safe bike to ride.

When I get another bike, I do all the above, and I don't have any further problems with it. I have a 79 KZ750B4.

Wire spoke wheels or mags?

I have mag wheels...Thanks for the list! I'll try and do most of that, as well as possibly rebuilding the carbs sometime this winter. For now, it actually runs quite well. For some reason, I started it up today and the difference in pressure was not anywhere near as great as it was the other day. I got the bike when it had 12,700 miles on it which was late last month. I'm now at 13,100 and haven't run into any issues that would cause me to worry about riding the bike in the meantime. I have replacement front pads for the brakes, did and oil and oil filter change, and got a replacement air filter and now it starts, runs, and stops without a problem. Still, I am thinking that would be a good list of things to do in winter.

I am going to do a compression test as soon as I figure out where I put the tester. I know I have one somewhere...

Wow....It's the strangest thing...I went out today and checked the pressure again and they were that same....I have no idea what changed, I have ridden it a little bit but, other than that, I have done nothing. If it acts up again I'll let you guys know, but I just thought it was the strangest thing...