Your Carbs NEED to go CLUNK!!!

There have loads of Posts, recently, concerning performance and mixture settings. Generally speaking, the mixture settings of the carbs won't un-set themselves and cause your bike to start running poorly. Other factors, unrelated to Jets, floats, sync and pilot screw settings will. The Number-1 cause of a decline in performance -- "Related" -- to carburetors is "Slide Piston Stiction." The brass piston part of the diaphragm assembly needs to have 100% absolutely FREE travel in the carb body cylinder bore. No. A tiny bit of drag IS NOT OK. There needs to NO drag. NO friction. NO binding. NO 'Nuthin!!! When you get done CLEANING a set of carbs; you need to do "CLEAN-TUNING" too. You do this by conducting a "CLUNK TEST."
With the top off ... spring out ... and diaphragm un-seated to its locating channel -- LIFT the brass piston to the top of its travel and let it fall. It needs to FALL! It absolutely MUST drop ... from being raised-up and let-go ... like a safe out a second-story window! If it chatters down, hesitates, acts like it being hydraulically controlled, is slow, stops and goes ... or, does anything, other than drop ... like a wet bag of cement ... you got a performance problem. SLIDE PISTON STICTION. Get rid of it. It's easy enough to do.
Polish the brass piston. It should be a shining brass object a Marine Corp Recruit would be proud to show his Drill Instructor. You can polish the needle, too! BUT -- DON'T bend it!
The carb body bore is usually where the problem is. A film of oxidation forms on the Inside Diameter of the cylinder bore surfaces. This film reduces the inside diameter's already close tolerance to make the brass piston's travel become impaired. Elbow grease and finishing papers will restore the original shine to the alloy.
Use # - 800 Wet-'O-Dry to clean the surface. Vertical motion only. Refinish the bore with 800 using WD-40 as the wetting agent. Using sections of 800 about the size of a pack of matches ripped in half ... refinish the inside diameter of the bore. Throw-away the 800 section as it becomes fouled. Refinish UP and DOWN ... moving ALL AROUND. Don't do anyplace where you think its sticking. Keep the bore round.
Feel like doing another 15-minutes of work that will give you a stage closer to RACE-PREPPED??? OK ... after you clean-up the bore with the 800 Wet ... Hit the bores, AGAIN, with 1000 - 1200 and 1500 !! WD-40 is your wetting agent. When you are done, there should ZERO drag. Nothing preventing the diaphragm from raising the piston when vacuum is present. And, NOTHING from preventing that SPRING and NO VACUUM from allowing those slides to slam-shut for some ABSOLUTELY wonderfully controlled engine braking.
I know you! You're a sneaky little devil ! You ride like an accountant all the time, huh? Until the "Ride-Hard" bug bites you in the butt and you want to twist-again ... like you did last summer. We'll ... now you get to appreciate having sore fingers and elbows for a little while, doin'-up your carbs.
You'll be coming into a nice sweeper or a really sweet decreasing radius turn ... you tach-up for gear-change and the bike sounds like Formula-1 ... right-up to where you need to match RPM for the downshift -- immediately. No farting-around with the throttle -- "Asking Scotty for a few more revs. You're there ... on the hairy edge of sweetness. You matched your revs and now want to loose some speed ... close the throttle and you have On-The-Track engine braking. You're power goes back on without a hitch as you start looking like the guy in the commercials and sales brochures ... leaning over in the turn.
You exit the corner and wrist-open for the straight.
Hang on tight, brother ... you'll be going fast in a second!

Editors Note:
Since this article first appeared, I have experimented with Bore Refurbishing and Polishing.
Now, what I do is:
• Scrub. Using ScotchBrite Pad Strips. (Medium Gray ~ 3/4" Wide)
Scrub the Bore to bare aluminum.
• Polish. Using ScotchBrite Pad Strips. (White Extra Fine ~ 3/4" Wide)
Prep the Bore for Polishing.
* Polishing. Using Jewelers Rouge's No.-5 & No.-6 and a Dremel Polishing Wheel ... Polish the Bore to a Mirror Finish.

 

Nice post.
Those slides, slide diaphrams, and needles work an amazing amount of the usuable powerband, and are often overlooked.
A simple pinhole, in one slide diaphram, can cause unexpected problems, and something as small as a sticking slide can be easily overlooked.

Thumbs up for the post.

 

Hmm... sounds like another winter project for me.

 

Rick, a very excellent write up!!
You in sales by the way?
I just rebuilt my carbs (and they work sweetly) but you've just about got me ready to yank em off and polish those slide ports.
I don't want to loose a minuite of ride time though, so I'll wait till winter too.
Thanks for the inspiration.

 

Thanks RickCoMatic, great post

Just been down to the garage and checked my carbs. One slide come down like a guillotine on the neck of a hapless french aristo and one come's down a little less violently. The other two really need Zimmer frames to travel anywhere. I can't understand how I missed this after all I have stripped the carbs down twice now.

Mick Faighaigh.

 

Don't worry Mick, I've stripped mine ten times before I did anything with the slides. Rick's on the money, it makes a lot of difference.


Top write up Rick, but when there little fingers are bleeding and sore with only 1 carb done and three to go I'm sure they'll have a new name for you. :wink:

 

Very useful post, have been trying to get my 81 XJ650 to throttle down correctly and now know how to fix the problem. Thanks.

 

Now that's what I call a post.

Someone asked whether you're in sales - forget that, you should be doing motivational speaking ! Right, where did I put that 800... ?

Nice one Rick.

 

here's a bump and a quick question:
Rather than using a 'vertical motion only', can you use a Dremel with the right attachment?

 

^^ What he said... I'm lazy.

 

DREMEL, ruining fine equipment for thirty years.

Cheers,

Phil

 

I have expanded to using a Dremel with a Polishing Wheel. After I sand down the Bore ... I use the Dremel with some Polishing Jewelers Rouge to put a Mirror Finish on the Bores.

They have exceptionally good movement after a Buffing and Polishing.
Number 5 and Number 6 Jewelers Rouges. Available at Lowes.

 

Oh, you wacky expatriate Brits...

(pondering) "zimmer frames"? (rummages around for his English-to-English translator)

So am I, but I'm not *that* lazy. Went and sanded mine down a while ago, but I've still got them apart. Just the 600 and the WD40 did wonders. Following that up with 1000/WD40 didn't seem to do much more. I plan on hitting them up with the polishing compound and the dremel when time permits.

Bitter much?

NOW you farking tell me. After I went out and bought the polishing compound blocks from freaking Sears...

 

Sears ... Lowes ... Ames ... It's the same stuff. Jeweler's Rouge. The trick is in the High-Speed Buffing. You need the Buffing Attachment and the "Wand" attachment that goes on the Dremel.

Then you can reach down in the Bore and get the Bore surfaces that are on either side of the Intake Port.

 

'taint got numbers on this stuff. The package refers to it as "buffing wheel compound", and it's got Emery Cake/Black, Tripoli/Brown, White Rouge and Red Rouge. I even went and got the Blue Rouge as well for the sake of completeness. I'm guessing start with brown and then white, and perhaps blue for gits and shiggles?

Funny how the people who work in the jewlery stores have no idea what this stuff is.

Mrmph. Back to Home Despot, then...

 

They aren't the artists who create the Jewelery ... they are the Sales people who sell what the Jeweler creates.

Google the stuff ... you got the right idea anyway.

 

Zimmer frames=what we call a "walker" here...remember: Biscuits=crackers; Crackers=insane...

 

Try 'T' cut instead of Jeweler's Rouge, this is a very mild abrasive, guaranteed to do no harm.

 

Whats the best thing to use to get the piston Sparkling??

 

You won't get-out the "Smile" whare it has been exposed to the elements for 25-years.

I tried a Product called "NeverDull" ... It worked pretty good.

You really need to Polish the Bore more than worrying about the Piston.