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1980 KZ550 Power issue + other

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If I'm posting to the wrong section let me know. It's been a while since I used TT.

I have a 1980 KZ550. My problem is that she bogs down when I throttle her up quickly (as in, I have to take a few seconds to bring in power). She was also backfiring at higher RPM'S. I was wondering if the carbs were out of sync so I bought a set of vacuum gauges and balanced them out. When I was balancing the carbs I found the cylinder that was backfiring and checked the lead. It was heavily corroded and the tip of the wire broke off when I was cleaning it. The backfiring seems to have stopped now that I've cleaned the contact.

The power problem did not stop after the sync though.

When I throttle the bike up with the choke on, she seems to do pretty good keeping up.

Does this mean I need to increase the fuel flow?... that means enlarging the jets right?

Also, when I was doing the synchronizing, the right three cylinders (2,3, & 4?) registered at about 8 o'clock or 200 mm vacuum when I went to idle, but the left most cylinder (1?) went to about 10 o'clock. or approx. 10 mm vacuum.

Running at 4k rpm the carbs were registering at 100 mm vacuum.

The owners manual says to check that "the vacuum difference

between the cylinders is less than 0.80 in. Hg

(20 mm Hg)".

Why am I reading where I am?

The last possible clue I can give is that there is a slight rattling sound coming from the middle portion of the left most cylinder (1?).

Is my left cylinder needing a valve adjustment, and the other three are having to pull it along?

Sorry for being so wordy. I hope you someone can figure out what I'm saying and help me out. Thanks


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Well, not that this bears any importance on much of anything, but I was just perusing the owners manual again and ran across a little section labeled "Fuel and Exhaust Systems - Air Suction System". Before starting the bike up and after cleaning the lead contact to the ignition coil, I took the time to cut the splitting end off of some rubber hose running to the the top of the engine from the carburetors. Turns out that leads into the suction valve in the engine... which I think was keeping the suction valve from closing, thus sucking extra fuel into the system on deceleration and resulted in backfiring.

How am I doing boys?

I have much to learn sen-say.

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Rich? I thought by opening the throttle too fast I was leaning it out too quickly. Dang working on motors is like proving bigfoot.

Should I check the air port on the carbs?

welcome to my world friend. first thing to do is check the colour on the spark plugs,are they at least similar? what colour are they?white means lean,not good.colour changes with mixture all the way through grey to tan to brown to dark brown into black meaning too rich, not as bad as white but she still wont run right. if they arent the same colour this gives clues to isolate maby one unhappy cylinder or some primate has been all over your carbs bending up the fioats. iv seen this often. if the bike is nice and stock the haynes or clymer manuals are invaluable. check float heights,jet sises, pilot screw settings,air filter and ignition timing, this can cause bogging also. definatly check any vacume hoses and inlet rubbers.

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I felt like being positive about my synchronization job so I did it again. This time I noticed that the 1st carb was varying more than seemed appropriate. Then I noticed the needle actuator arm wiggled while the others didn't. It turns out some retard in the past didn't see it fit to keep track of his parts, and lost the counter suck screw. He must have also thought it was a good idea to replace it with a flush screw that didn't screw all the way down.

I replaced that with the correct screw, which nestled the arm in place nicely, and had a much easier job of syncing the carbs.

After that I took it out for a run around the block. She does have more power, but it's still bogging down until I open the throttle up to full.

Does anyone know how or where to identify what type of mikuni tk carburetors I have? I want to see if they match the bike.

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Someone mentioned I might have an after market exhaust on my bike. Does anyone know how to figure this out?

I also went through the carbs and found the floats were not equal. I fixed that. I also noticed someone wrapped one of my needle jets in teflon to seal it where the o-ring used to be. Special people.

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