Engine bogs right when I get to 55-60 mph

Early this August I picked up a wonderful KZ550 LTD Shaft bike with only 1200 miles on the clock for $800. It's in pretty good condition too!





When I rode the bike home for the first time, I had a ton of oil leak out of the air filter since the guy apparently put a whole quart of extra oil in the bike. No big deal, I removed the oil and refilled it with the correct amount and the bike worked fine.

Cut to a month ago, I'm getting started on a 400 mile journey when I realize the bike won't let me climb past 70 miles an hour. Whichever gear I'm in, I can't get the thing to gain any speed. Eventually it gets worse till I'm stuck going 55 miles an hour on the highway while being passed by cars going 80 mph!

I played with the petcock and adjusted the crankcase breather hose, and the bike suddenly worked fine... till Friday. I decided to adjust the crankcase breather hoses since they were sort of cracked and I had a suspicion that they were part of my performance issues. However, now I can't get my bike past 60 mph again!

I'm really lost as to what it could be. I've played with the petcock a good amount to no result. The crankcase breather hoses are really suspect looking, and seem to be the main culprit.

Anybody have similar experiences?

you say crankcase breather hoses?
there is only one hose and that comes out of motor case round looking thing then goes to elbow then bottom of air cleaner box.

4-carbs
4- vacuum nipples
2-of them should go to (1-4)carb this is for the clean air set-up.
1-is capped off (3)carb
1-is vacuum petcock (2)carb

this all seen from sitting on the bike (left to right) (carb 1-2-3-4)
firing order should (1-4) (2-3)

oh by the way nice ride

On my bike there's one hose on each side of the engine. I'm talking about parts number 7 on this picture:

Let's do some simple checks:

1. Make sure the gas tank cap's venting is good, some are built into the cap, so remove the screws looking for something blocking the vent.

2. Remove the sparkplug caps(they unscrew from the sparkplug wires) and test them with a multimeter, they should have 5000 ohms for each one. Before re-installing them, trim about 1/4" off the end of the sparkplug wires and screw the caps back on.

3. How's the sparkplugs look? Black is too rich, White too lean,but a light tan is about right. Using the correct sparkplugs and heat range?

4. Airfilter clean? not clogged with dust/dirt?

5. Using a fuel filter? Is it restricted? Using some of the E-gas(Ethanol)?

6. Compression good? A new/rebuilt engine might have 180-200 PSI, put some years/miles and it might be 160 PSI or so. An engine will run at 100 PSI, but produce low power. Any compression test should be done with the throttle wide open for best results.

7. How's the spark look? It should be a hot,fat spark, not weak and orange.

Spark plugs were the first thing I replaced, and they were all a very pretty light tan. I'll check the rest of the items when I get back from work today.

What's the best way to check the air filter?

You described the "Smog Gear" Kawasaki designed and built to reduce the exhaust emissions. Most riders here have bought block off plates & plugged the vacuum lines. This system neither added nor subtracted horsepower from the engine.

Here's a company that makes the block off plates, see if they make one for your bike:
www.kzzone.com/billet.html

If not,two pieces of 1/8th to 3/16th Aluminum cut to fit the reed valve cover will work.

If your bike has the stock air filter, it was made of paper, designed to catch small dust/dirt particles. A shop vacuum might be used to clean it. Most riders changed to a K & N gauze type filter, that was treated to a light coating of the K & N air filter oil. Usually cleaning & re-oiling once a year was about all it needed.

Spent a lot of time on the bike last night.

Air filter is very clean. Spotless, almost. This bike really must have only had 1,200 miles on it.

Gas cap seems to be in good shape and venting normally, and there's no fuel filter.

I've noticed that even at lower speed, the engine is very responsive right up to around 4k-5k rpms, when it really starts bog terribly. However, if I'm in neutral, I can rev it up to redline without an issue.

Also, last night was relatively cold and I had a lot of trouble getting the bike going this morning... Probably just a symptom of any carbureted bike.

Lddemi wrote: However, if I'm in neutral, I can rev it up to redline without an issue....

Yikes! That is not a good thing to do with no load. Ed

Drain your carb float bowls into a clear container and look at the fuel, see if it has debris. Check that with the drain screws loose and the petcock on "Prime" that fuel flows out the tubes freely. After bikes sit, they usually have carbs that are plugged up, much worse these days with the Deathanol fuels.



Also look at the vacuum system you posted, check the small vacuum lines, running from the two outside carbs into the Tee, going to the Air Valve. You can disconnect it, and plug off the small ports on the manifolds with caps. Then check the Line from #2, thats the one on the Left side one in, the line goes to the Vacuum petcock, make sure it is good.
then there could be either a mechanical Ignition Advancer or a fixed CDI style of ignition in your year. You can pull the 6" or so sized cover on the right hand end of the crank shaft and look which you have. If it still has the mechanical type, it may be sticking. So if so it needs removing and cleaning/ lubing.



Then that bike even though the low miles, is due for a Valve adjustment check.
If you don't have the Kawasaki Manual, member Loudhvx has the older one in his signature, but it won't be exactly the same. Carbs, and electrical would have changed, especially if you have the CDI ignition.

So it's too early to declare victory since I haven't taken it up on 95 yet, but the bike is running SIGNIFICANTLY better.

I drained a couple ounces out of each of the carbs. The fuel was very clear. All of the carbs let loose a solid stream of fuel when I opened the drain EXCEPT for the far left (1st) carburetor which only dripped at a two drops per second speed. I played with the vacuum tubes for that side of the carburetor as well but the speed of fuel from that drain did not increase.

Also, I added a few ounces of B12 Chemtool to the tank earlier in the day. That may have also contributed to the renewed performance.

When you tell me I can cap off the vacuum lines, you're saying I would cap off them off directly from the carburetor? The picture below is where I'd assume I'd be capping off.