82 XJ750 Seca - Performance degrading

Do they make a 275?? I looked up a kit to see what was originally made and don't think I saw it...

And with #3 being low it should do nothing but increase as it wears?

 

Chacal sells them in increments of .005, so yes there's a 275.

And no, they tighten over time, they don't wear.

 

Well the shim and lobe wear but I guess you are saying the valve / seat interface wears more

Makes sense...

 

I have noticed that after market shims do not make all the sizes

oem run from 2.00 to 3.15
aftermarket 2.00 to 3.10
as the valve pounds down deeper into the valve seat your valve clearances get smaller. you are putting the shim directly on top of the valve stem with the bucket sitting in between. the cam and shim do not wear enough to cause the replacement of the shim it is the valve into the valve seat.

 

The shim and lobe must wear a little, but even very old/high mileage shims are still pretty accurate.

I measured each of mine in my Maxim,(80k kms) when doing my valves, and each was within 0.001mm of it's labeled spec.

 

Plus there is the manufacturing tolerance on the new shims, grab a couple of 270's measure them with a micrometer and they won't be the same... but now we are splitting hairs and for the application we are using the resolution of precision measuring can be relaxed.

 

are you sure ? .001mm is thinner than a fairy fart

 

Posted in APRIL..........Tim wrote: "Rode it a couple times a month over the winter..."

Nothing wrong with keeping the valve clearances squared away but.....I would have drained the gas and refilled with fresh fuel...........

jeff

 

the shim and lobe have a constant coating of oil which keeps wear minimal if you have a lobe or shim that has worn you may have an oil flow problem.
valves on the other hand have constant high heat and pounding at the seats with out the benefit of oil. to cool and lube them

 

As sure as equipment quality and measurement methodology could allow.

I measured with a pair of calipers that go down to hundredths of a millimeter, and every one measured exactly what it said on the shim. I'm pretty confident that they're what they're supposed to be (at least within reasonable error) given every one measured consistently what it said.

I measured them specifically because I was concerned about wear - all three of my motors are pretty high mileage after all, but all of them measured bang on.



Oh.

Oh. I'm embarrassed now. 0.01mm, not 0.001mm. Sorry, my bad; mental conversion from "275" to .275 instead of 2.75.

What's an order of magnitude between fairy farts anyways

 

This makes a lot of sense, thanks.

 

depends on if they had beans for dinner

 

To recap... bike was running away as if it had a vacuum leak.

So now my carbs have been to church thanks to Dave...
I've installed the shim needed after doing my valve checks...
I have a new valve cover gasket, will install that tonight (Old one leaked a little). And going to do an RTV job on the intake boots and new gaskets there as well.
Tomorrow is install boots and carb rack. I also have installed a new petcock to eliminate what might have been spotty flow witnessed from the old one.
Pick up vacuum gauge tonight to do sync.
I don't have a colortune but at least new plugs and color check planned after 10 minute ride to see about any mixture tweeks... I'll get a colortune eventually.

What am I forgetting?

 

Did you wet-set the floats?

 

Ah yes.... will do before mounting. What's your experience? Much adjustment?

 

got done:
Valve cover gasket
New intake boots
mounted carbs and got her running...
ran OK but I can tell the sync and colortune will be important.

I've still got this issue where at 55mph (4K rpm) and only when nice and warmed up, sounds like con rod bearing noise. But goes away once you throttle off a little. From what I've read it could just be small exhaust leak or missing muffler baffle(s). But how do you know as you can't get off and listen at 55 mph? Also, no noise when rev to 4.5K in neutral so I'm hoping that's a good sign...

 

If it were rod knock, you'd hear it all the time.

 

This is a XJ650 turbo exh valve ......he lost compression gradually as the cracks developed. Had it fragmented, his engine would have likely been good for little more than scrap metal but this was caught & replaced....for the grand total of a half day of labor and the cost of a head gasket.

Maybe take it to a Dyno station.....they will induce a load on the engine, giving you or the tech a chance to locate the sound.

erad

 

Does it make the noise if you rev it to 4k in the driveway? That could help you find the source, and if it's a loose part on the exhaust, you can ignore, or stuff a piece of leather in there to silence it.

 

Thanks Jeff
Think it might show up in a compression test?

 

So I've been playing around a little and think almost all my noise issues are exhaust related. I cleaned up the front of the engine real good and then took note of some carbon build up above pipe 1 and 2 after a few rides... took apart those pipes and checked gaskets / seats as they were new last time installed about 4-6 mos. ago. Nothing obvious when disassembled.

When I swapped the header pipes I used new gaskets at the head but left the old ones at the collector and mufflers.

After reassembly noise is still there but noticeably reduced so I think I need to just replace exhaust gaskets from one end to the other and be meticulous about the line-up...

Also noticed decent carbon build-up in the exhaust ports so think I'm running a little rich... the plugs looked pretty good though.

 

are the header pipes in the right order?

 

Hope so... checked going in and 1&2 just checked OK...

 

pretty sure my maxim had #'s on the pipes for the cylinder number
could one of our parts guys confirm this

 

The stock headers should have the cylinder numbers stamped in them.

 

Tim, that might be something to check. they fit in any cylinder but they fit a lot better in the right one.
i fooled around a long time with mine until i realized that number meant something

 

The numbers are in the right place

 

synced my carbs today and it definitely made an improvement. Even though it's smoother... still getting the knocking (or popping if you will) at speed and load increases. Convinced more than ever it's exhaust gaskets and will be swapping them all as time and money allows.

 

Time to change the original fuse block...

Had my first random engine just dying... thankfully restarted a minute later.

 

Might be a sticky sidestand switch. Bad fuseboxes usually don't fix themselves, but sidestand switches do pop back out and make contact again.

 

I'm just guessing as I did move the switch multiple times and it didn't make a difference and I kind of beat up the fuse block when I last installed my carbs / airbox boots.

 

To protect my carbs and seals, etc., I never run gasohol. Locally I can buy alcohol free 87 octane. When in doubt I buy premium alcohol free. I don't notice any improvement in performance with higher octane.

My experience - these bike operate as a 'system' - cumulative maintenance builds toward a smooth running bike. Sometimes it isn't any one thing causing certain symptoms. One problem can mimic another, or mask another, problem.

 

Checked it out this morning and I can make the ignition circuit open and close by pressing the fuse clips around with my finger... so new block it is...