Need advice 81 KZ550 LTD

I bought this bike not to long ago and it didn't run. I've got it running but it is hard to start and is fouling #4 plug. I is very hard to start takes a lot cranking and sometimes I have to hook up the battery charger to start it. It tends to backfire at idle once warmed up but runs good up to 5500 rpm. Also it will not run over 5500 rpm. I've pulled the carbs and cleaned them but I think they need to be cleaned a little more thorough especially on the choke circuit. Also I did the WG upgrade with the relay to the coils previous voltage was 9 volts now getting a full 12.

My question is what sort of tests should I run to diagnose the problem. Compression test? Anything else? Also I plan on ordering a carb rebuild kit this week.

Any suggestions at all. Bueller.....Bueller........

the backfiring could have to do with the air injection system on top of the valve cover you could try plugging it of, also you need to run a compression test first thing so you can tell what is going on, the hard starting could be low compresion due to tight valves, also low compression could effect it everywhere quite a bit

If points, first clean, then gap. Next would assure correct ignition timing and proper operation of advancer unit, using strobe-type timing light.

Should run way over 5500 rpm even with one cylinder missing.

Good luck with diagnosis and repair.

When doing compression test, remember to hold throttle wide open.

I've checked valve clearance and all were in spec I will pull the cover and check again just to be on the safe side. And it doesn't have points but I've pulled the plate and pickups off and cleaned what looked like some oil residue inside the cover. Also I pulled the advancer unit and greased it according to the manual. Also I have capped all vacuum lines in an attempt to reduce possible problems. I started thinking that maybe the diapram form the petcok was leaking gas into #4 carb causing to foul the plug. So for now I turn the tank to PRI for a second or two then to ON after the bike starts I turn it back to PRI since the vac line for ON is disconnected.

I will do test tonight also I'll check the valves again. Thanks for the replies.

When you take the carbs off have them cleaned in an ultrasonic cleaning tank , check with your local auto carb specialist . Remove the jets floats and adjustment screws prior to ultrasonic . I have had good luck cleaning the jets in paintbrush cleaner . Sounds like you may have a clogged pilot jet(common on bikes that sit for long periods) causing hard start/bad idle . Choke mechanism on your carbs is interconnected with an idle speed increaser , which is adjustable . I have a few 550's with the same carbs as you .

OK checked valves again and one is tight and a couple are close to tolerance. The acceptable tolerances that I found said int.004in-.008in and ext.006in-.010in.
1 2 3 4
int .006 .004 .005 .004
ext .005 .008 .007 .008

So I figured that I will go up on shim for #1 ext. Should I go up on 2 and 4 int or not.

Oh and I figured that I would do the compression test with the carbs off.

Your specs look good enough to me they should not be the problem.What color are the plugs? What does your comression look like?

Well I didn't get to do the compression test last night due to part place didn't have a 245 shim so that it can get a little more space on #1 ext. And they won't get one untill next week. So I will put it back together today after work and run a compression test then.
Plugs are on week old and don't look to bad except for #4 which is black. I will take pics of plugs for all to see later as well.

Well I been very busy the past week. Sister-in-law in town with 3 year old nephew and they are staying at my house so time working on the bike has been limited. But I did get the carbs rebuilt and comp test done. In order from 1-4 results are 150, 160, 150, and 170. Also still waiting on a 245 shim to increase my clearance on #1 exhaust.

After putting everything back together it still doesn't want to pull over 6k on the tach. I also had to adjust the mixture screws almost all the way in, only about 3/4 turn out. If I turn them out more or lean the mixture then I get backfire through the carbs and a very rough idle. I chekced for vacuum leaks with WD40 spraying around the carbs and got no noticable change. I will try agian later. Anyone have any suggestions?

Other than the low rpms it runs very well and I actually drove it around the block.

Also I'm thinking that maybe I should move the clip on the needle down to try and richen the mixture. My theory is this might help pull more RPMs. Also the carb holders look old with few cracks around the mounting ears. But the cracks do not appear to be very deep.