1982 XJ750 Seca - Ongoing

I'd like to start a thread for my bike and not have to keep going to the thread of "Performance Degrading" as she's running fairly well now...

And I'll stick with this thread from now on so people can see what's been done so far:

• Bought at 9900 miles
• Currently 12000 miles
• A few oil changes
• Played with the carb levels a lot until hogfiddles did a complete rebuild for me.
• Already has SS brake lines
• New (to me) headers and collector and all exhaust gaskets
• Valves checked and one shim changed
• Synched all carbs
• New valve cover gasket
• New carb-engine intake boots and gaskets, vacuum port covers.
• New Petcock
• New plugs of course
• Rebuilt starter
• Drain and fill final drive
• Fixed a few fuses and have a blade type block I'm looking for time to install.
• New rear tire, front looks pretty new from PO
• Inspected rear brake shoes / mechs when wheel off for tire.

Planned next

• Got my colortune and going to play with that and resync in coming weeks

So on to my first question:

1. When doing the exhaust I'm still not to my happy place and I still hear just a little bit pop-pop at high speeds. When replacing gaskets I got a fair amount of rusty pieces of baffle / screen / whatever falling out of and rattling around in the mufflers so I don't think she'll ever sound as smooth as I want. Is there an aftermarket muffler for the Seca 750 that's as close as possible to the original?

Thanks a bunch....

 

emgo shortys or sportster mufflers are a common choice

http://www.ebay.com/bhp/emgo-muffler

 

Any tips on mounting them? Doesn't look like they have a tab on there....

 

I put Harley slip on muffler on my Seca. I got a 2 inch wide steel and drilled the holes and connect it to the rear foot peg mount. You can buy proper hangers but being this is a temporary measure I went this route.

 

Add to this bike:

Replaced fuse box

 

Hearing a "clunk" or "click" depressing front brake... no performance change and no leaks, nothing appears loose.

Thinking calipers freed up on slide from regular use? Or brake shoe almost gone?

Guess I'll have to open it....

 

I have been having that happen recently please let us know when you find it. i havent got time to rip it apart to check just yet

 

Did you tear down the forks for inspection?

 

I have not.... but I hear it when stopped too so it's not play in the forks.

It sounds like either the shoes hitting the disc, or the caliper piston hitting the back of the shoe... do the shoes clip into the pistons like on a car? Maybe the tang(s) have broken off.

 

As far as I know they do not clip into the caliper piston like you're thinking

 

The pads have anti-rattle springs that clip to them, but the pads run on a retaining pin.
Each caliper is made of two parts, that slide against each other, and there are pins that the halves run on.
My suggestion is to dissasemble the calipers and check for worn pins, as well as replace the piston seals if you have not already done so.

 

+1
The amount of stuff you will find in those brake will surprise you. Spiders, bugs ect... in there. I used a heavy duty rag in between the pistons and then put air pressure to the open banjo hole. Just take your time and watch your fingers, once the piston lets lose it could pinch a finger. Some us a grease gun as that would do the same but slower and more controlled.

 

Yet another noise:

I'm hoping to do an oil change this afternoon and finally get a look at those front brakes... but in the meantime I'm starting to get another mystery noise.

It used to only be after I was riding for a good hour or more, but now occurring almost all the time. It's when decelerating or more like when you are still in gear but going slow for that gear so no load on the drivetrain... think 20-30 mph.

It's a rattle sounds like in the drive shaft area or maybe even more forward in the gearbox / starter clutch area. I mention the starter clutch as it sounds like the rocks in a can sound people describe but it's not when starting the bike... it's gliding on the road. I'm thinking check and grease driveshaft but thought I would ask...

Thoughts?

 

check your u joint

 

Mmmmm...sounds probable... thanks

 

currently a used one on ebay 28$

 

I had to replace a final drive gear on a goldwing when the teeth got warn. After I replaced it the clunking stopped.
Don't most shaft bikes have similar final drives ?

 

Well, I drained oil and checked front brakes last night... plenty of pad left, all clips are there, and pistons and pads are free to move in holder and on slides... so I think it was correct to say the free pad (The one not on the piston) had free'd up from finally getting frequent use. I could cause the same "clunk" I was hearing by tapping on the free pad to seat it against it's holder.

Output drive check out next....

 

yes

 

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.

 

Drove into work today and have been all week... no issues (and a lot of fun) 22 miles each way through windy horse country. I have been riding her a little hard the last month as the number of 30 mph Prius' around here seems to be going through the roof. I blew by a few people this morning and the bike was up to 75 mph or so maybe twice. The rest of the ride is 50-65 mph

About 2 miles out from work bike started feeling rumbly, exhaust sound throaty and rumbly... hesitation on acceleration and general running as well. Like I was losing / lost combustion in a cylinder...

Got to work and all pipes hot and can't isolate to one side or the other by listening to engine or exhaust outlets.

Gas tank a little less than 1/2 full and put two gallons in yesterday at a hole in the wall sandwich shop that I wouldn't normally consider fueling at as I never see anyone else getting gas there either... think analog pump that's been there for 30 years and the place is now a sandwich shop that coincidentally used to be a gas station. I was trying to save time and get back to work and I was on reserve. But I put a good 40 miles on it since putting that gas in so I'm not thinking it's that...

Right now she's on the center stand and cooling down so when I go out at lunch can check oil level again and maybe take samples out of the carb bowls...

Don't know if I can / should ride it home. Going to check oil, plugs, carb bowls, fill it with good hi octane (what she normally runs), and when I start it try and find if it's one cylinder in particular by monitoring temps as it warms up in the lot.

Any other suggestions appreciated. Thanks

 

Was it raining? Any possibility of water getting into the spark plug cap?

 

I was thinking it was acting like that... but no, it hasn't been wet in weeks and operated great all this week.

 

I think what I am going to state is very unlikely as your bike was running fine but my first bike had a fuel starvation problem. What was happening is that fuel could not leave the tank properly because the offset holes in the tank fuel cap were blocked creating a partial vaccum above the fuel. I slackened the cap on the tank and the engine started running properly so I got a pin and cleaned the offset holes in the cap.

Take the fuel pipe off the tank and put tap on prime to make sure fuel is flowing well.

When you check your plugs and caps grab the high tension lead and twist the cap clockwise to make sure you have a good connection on each. If I think of anything else I will let you know, hope this helps.

 

Gas tank cap vent, exhaust internal baffles broken, muffler has blown a hole on the inside that you can’t see at first glance, valves have tightened up, dirty gas with crap in it, water in gas that builds up in bowls. Coil is starting to fail from heat, plug caps failing.....etc
The list can be long enough to make you crazy with worry.

 

well, I took it to the gas station at lunch after checking plug wires, fuel, gas cap, oil level, and warm up... all cylinders same except #1 maybe just a bit lagging.

Filled with high octane, 2 gal.

Not sure if I could sense the condition or not... I'm sure I'm very paranoid about it now. So I'm thinking either a plug wire connection that I moved and made better, or my crappy aftermarket petcock is clogged around the base or some other fuel obstruction. I was going to do an oil change, colortune, and sync this weekend anyway, so I'll pull the petcock while I have the tank off and check the carb bowls, etc.

If it's an obstruction that takes time to run a carb empty or vacuum the tank, I'm sure I'll se it 80% of the way home like I saw it 80% of the way here this morning . I almost hope I do so I can pop the gas cap and see if that was it.

 

If you have a auxilliary tank for the carburetor sync it may run well with that on it. But as it is a waste spark system when one is on compression four is on exhaust both plugs fire the exhaust stroke one on cylinder four spark is wasted. Try a new plug in the affected cylinder too to eliminate fouling etc. Be interested to know what has caused the problem. Or switch plugs one and four to see if the problem moves with them.

 

Made it home... seemed OK until a stop a few miles from my house. Thought I heard something a few times...
Stayed there about 50 min, then started home.

At one point on the way from there really gunned it for 10-15 seconds, up to 75+ mph and then the problem started kicking in again. Stopped, popped gas cap, let sit for a minute or two, restarted, problem still there so not the gas cap. Also still a full tank so probably not the petcock.

As I recall when this happened this morning it was also after passing a couple people and really getting the revs up. So thinking it's temperature dependent?

Will start from scratch tomorrow when doing oil change and also measure valve clearances, change plugs (It's been 4500 miles), then colortune and sync...

 

how old is your vacuum line?

are you using a fuel filter? what kind?

 

Plugs is where I'd start