1982 XJ750 Seca - Ongoing

28$ https://www.ebay.com/itm/1982-Yamah...321961926910?_trksid=p2385738.m4383.l4275.c10

here is one mounted to final drive 50$




https://www.ebay.com/itm/1981-YAMAH...ash=item4403506e60:g:EqIAAOSwjDZYdqNO&vxp=mtr

 

i have to think you've never heard the real "can of rocks". i have and if i heard it while going down the road, i'd jump off

 

True that... don't think I have.

 

Checked U-Joint by just peeling back boot, inspecting, and trying to get movement relative to final drive... everything seems tight and no metal shavings or anything so I'm going to assume not an issue for now, but will be dropping the rear end for full inspection sometime in the future.

On another note, finally found the first pinhole in my exhaust... just after the collector in the first 2-3" of the muffler. Might just this one pinhole be the "knock" I'm hearing when warmed up and above 4K RPM? Have a feeling there is probably more than one hole as I continue to look...

 

So this "rod knock" noise that's driving me nuts...

Noticed on my way home from work that it's still worse in warmer weather (72 today), and that when cruising at 55 mph (4K rpm) it is pronounced, but when either rolling off throttle, or giving it gas and accelerating (punching it pretty good), the noise goes away.

Crawled all over it when I got home and can not find any more exhaust leaks...

Any more ideas?

 

Doesn't seem like anyone is interested... but in researching this I found a decent article. Guess I better get around to trying that colortune I picked up... might explain why worse in warm weather (Leaner) and only at certain RPM (4k-5K)

http://www.mikuni.com/tg_detonation.html

 

I can tell you that my bike has never run better after the colortune. I'm having to get used to it starting, running, and operating the way it should instead of adapting to it's quirks.

 

Very, very, angry....

Finally got a little time for colortune and just cross threaded number 2.... Are there taps at the auto store?

 

Standard plug thread, so, yes, there are normally taps and thread repair kits at any decent parts store.

Not sure what tricks people have to avoid getting chips and shavings into the cylinder... maybe a bit of tubing and a shop vac?

 

That's what I was thinking on the vac... yes. Thanks

It's only the first couple threads but I don't want to mess with it any more without the right tap or I think I'll just make it worse...

 

grease the thread chaser or tap. grease will capture most of the chips

if you really f it up heli coils to repair threads

 

Got it tapped out last night and think I got most chips

Hopefully the one or two go out the exhaust

Started her up and all seems fine for the moment...

For comic relief here's a pic of the awesome test setup

 

Finished colortune all cylinders last night... running sync in between each adjustment.

Seems to me I was running quite lean before compared to where I ended up. And this morning the bike was definitely quieter and smoother than it has been, but it was also about 52F and she makes more "knock" when it's hot out.

Now being richer, I felt like the low end was same or very slightly more sluggish, but the high end (50mph+) was way more responsive. So much so that I was coming into some corners too hot as the sound and vibration was less than usual so it "felt" like I was going slower than I actually was. I usually drive 55 on my way to work but I'd randomly look down to a 65+ speedo for no reason.

My 50 Mph+ knock was gone but there were hints of it on the way home when the temp was 75F+. My theory is that I had some detination at that speed before and piled on top of rusted out collector and muffler baffles, the sounds compounded and made me obsess over them.

I'm pretty confident now there is no rod knock... but I did notice that when there were hints of the sound return my right knee / leg had a warm breeze compared to my left. Anyone think I could have an intermittent exhaust leak? It always did sound like it was coming from that side, but I've gone crazy trying to find a leak and can not.

Also, at the end of each ride, it seemed like the engine was generally running cooler than before.

 

If it was infact running lean that would lend to the engine being hotter

 

Just updating my 'log" here...

• Changed exhaust 3 and intake 4 shims
• Exhaust 3 was really tight
• #1 plug looked rich after 120 miles, closed 1/8 turn
  
• Resynched

The popping or knocking I was hearing for so long and driving me crazy was just about gone after getting #3 exhaust right. What little I can hear goes away when I lean forward so assuming it's just my very old mufflers letting a little by...

Running really well as of tonight's test ride.

 

running lean will give you a popping sound it is fuel burning in the exhaust

 

So will running rich, especially when idle jets are oversized or pilot screws are too far open. A bent valve will, too. The former usually on engine braking, the latter just sitting at idle.

 

well, it's pretty much gone now so not too worried.

Of course, now that I'm reveling in how great the bike is running, I missed a shift leaving work and slammed it into 2nd at high revs and thinking I'm hearing every little sound that something has changed because of it....

God doesn't want me to be comfortable with my bike I guess....

I really was crazy happy with how smooth she was today up until that point....

 

It needs to be entirely gone. Valves can be burnt. Pistons can end up with holes in them.
You are very close to having her running right.

 

Last night disassembled, clean, inspect, never seize, right front caliper because the metal holder was rubbing the brake disc some.
When I got it lined up correctly, surprised how there is play in the fork to move the pinch point on the axle... I'm used to my mountain bike and it's a fixed position ad you have to shim the caliper itself if there's a lineup problem.