New Owner - rattle rattle

Hi guys

I just bought a 81 KZ750e. It was the same model of my very first motorcycle. I have always loved it - and wanted another.

I am kinda mechanically minded - but am not very knowledgeable. I can do things like bolt on new parts - but 'sync carbs' I am going to need to look on Youtube to get that sorted out.

I bought it a few days ago - and here are some things I am not loving:

1 - It seems way more temperamental to get to run. I remember just using the choke and the a minute or two later backing off the choke and away you go. The other day I stalled a couple of times and had to use the choke to restart.

2 - When he's cold - he rattles like crazy. Sounds almost like something is broken in there.

3 - Compression is 52 - 30 - 30 - 60

Advice?

Those compression numbers are way low. Did you either have the carbs off or open the throttle when you checked the compression? You need to do one or the other to get good numbers.

I don't have the right attachment for the compression tester.

Basically - I pulled a plug - started the bike and pushed the pointy rubber tipped tool thing into the spark plug hole. I didn't rev the bike high though.

You need to get a factory service manual. That is not how you do a compression test.

Yeah. You don't do the compression test on a running motor. Some compression might be slipping by your gauge. I doubt an engine would run if those numbers were accurate.

I pull all the plugs, put the compression tester in Cylinder No. 1. I crank the motor with the starter until the pressure stops rising on the gauge. Write your reading down and move on to the next cylinder. Make sure to hold the throttle wide open if the carbs are hooked up.

Where is the rattling coming from, the top end, bottom, tranny?

Give the compression test another shot and post your numbers.

And bike should be warmed up?

I did my check on a cold engine. The cold numbers might be a shade lower than hot numbers, but should still be pretty accurate.

So I haven't had a chance to do the compression test - partially due to my lack of a fitting for my cheap compression tester. It becomes a two man job - but I think the compression might be ok. The bike easily does 70MPH - and I know the carbs are not up to snuff. I might have to google how to rebuild and sync them.

The rattle is still there at low idle. Sometimes it is even a 'thunking' sound. My neighbor is a serious motorcycle guy with a few completely disassembled old Yamaha's in his garage. He thinks it is nothing to worry about and just the gears in the motor banging edges (or something like that). Does that make sense? Is it typical for these bikes to be kinda clanky and noisy when not warm?

Another question - I rode for about 30 minutes - and when I parked I saw smoke coming up from the motor. I had just replaced the gas tank so I was worried it was fuel - but I think it was coming from the engine. Does this typically mean I need to pull the top of the motor and replace the gaskets? I couldn't localize where it was coming from as it was such a sunny day and i had no flashlight.

Suggestions?

The low rpm noise may be the primary chain, not gears. The primary chains are known to make noises as you describe, but that does not mean they are out of spec or need replacing. It is more likely that you need
to sync your carbs; that will normally reduce the noise although it may not eliminate it completely. If you sync the carbs and set the idle at between 1000-1100 rpm the clunking noise will probably stop.

Regarding the engine smoke, I would thoroughly clean the engine then go for a ride and see where oil may be weeping out. Don't even think about pulling the engine apart! Just locate the source of the oil leak, IF there is a leak, and then determine how best to correct it. It could be something as simple as a tachometer drive seal that can be fixed for less than $10 in about 15 minutes. Ed

Ok Excellent - thanks for weighing in. It is pretty clean now - so I will give that a go.

I have a 4-1 Pipe on order and a neat dual headlight that should fit right in. I think it will look pretty good when complete.