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.

 

why don't my Hatachi carbs have brass pistons ? either set

 

I think some of the Pistons are Teflon Coated.

I'm not too sure about what the coating is ... but, they are coated.
There is also some texture to the coating. A fine texture; but there.
I think that helps them glide when everything is working perfectly.

 

Nev-R-Dull is COOL STUFF it's been around since the 50's my Grandma used to use it on silver. I thought it was long gone but then discovered it at the auto parts. It's a NON-abrasive polish, and it does work quite well. Be aware that part of its "magic" is an oily wax that it leaves behind, great for some things (like chrome) not so good for others...

 

maybe yours are brass but mine are anodized aluminum and you for sure don't want to take the anodize off

 

ok you got me I just happen to have my carbs apart for larger mains and new shaft seals so I did the clunk test all 4 sound good and the bores look almost new but not polishedso I know what I'm doing tomarow
-excelent write up Rick I think I may go buy stock in polishing compounds now :lol:

 

If you do the work and bring the Bores to a brilliant polish ... when you wrist-on the power ... the Diaphragms are going to OPEN and get you moving on Main Jet Fuel ... right-quick!

Shut the Throttles and they Slam Shut ... braking line a Fuel Injected mill.

 

Thanks for the info Rick. I'll be doing my carbs this winter.

 

Since that article was published, here, I have found a MUCH easier way to deal with Diaphragm Piston Bores.

Dremel Tool.
Flexible Wand Extension.
Sanding Barrel Bit.

I remove the Rubber Barrel and substitute seven (7) ScotchBrite Pad 19mm Discs.

I make the Discs myself.
Using a 19mm Socket which I have GRINDED both the Inside and Outside Diameter of its opening to a Cutting Edge, ... I used the 19mm Socket "Cookie Cutter" to fabricate perfect 19mm Shining Discs.

I mount 7 circular Discs on the Bit using additional hardware to keep the Discs from freewheeling.
I arrange the Discs on the Nit like this:

Bit Shaft>Flat Washer>External Star Washer> 7 Discs > External Star Washer>Flat Washer>End Securing Screw.

Its a tight fit.
The Discs look like a Ball once fitted.
ScotchBrite GRAY will remove the glaze and shine the Cylinder.
ScotchBrite WHITE will apply a crude finished surface.

Dremel Buffing Pads and No.'s 5 & 6 Jewelers Rouge's will put a Mirror Finish on the Bore and will get you writin' home to momma!

 

does this "maintenance" work on all carbs? on all bikes?

 

On ALL Bikes having Constant Velocity-type Diaphragm Piston Carbs.

Either Hitachi -or- Mikuni

The Bore gets Oxidized after the passage of time and particularly if the Bike "Sat" for an extended period.

Routinely done by Racers as an element of "Special Tuning"

 

more specific then...a '76 GL1000

 

The Carbs on that Honda have two areas that need to have as fine a finish on them as you can apply.

The Bore:
Where the Vacuum Piston travels within the Body of the Carb.

The Upper Body Outer:
The Outside surface of the Vacuum Pistons "Moving Part"

The Dashpot Inner:
The Inside Diameter of the Dome that fits over the Vacuum Piston Assy.

You have to be able to reach in the Carb and lift the Piston and feel for smooth and free movement up and down.

 

Only one of of my 4 close like a slammed in the wind door ... the other 3 close like a creaky coffin lid!

Just had the carbs off several times, but this sounds a worthwhile reason to take 'em off again as the sticking means the revs stay up too long when you throttle down.

Cheers for another inspirational thread Rick

 

I've got mine all apart right now and thought they were good. I started reassembling them last night and realized that two of the four were falling like a rock, until about the last quarter inch or so of the bore. Looks like I get to polish those again. My bike hasn't run in over 6 years, I've only had it for about 5 months piecing it back together so I want to make sure this thing is running to it's full potential when I get back on the road.

 

Hi Rick,
I was rereading your posts and have a question to throw out there. The pistons on my 82 xj650 have a micro etching on them like very small rings running around the outside. I think these rings help hold a small amount of fuel between the piston and the carb bore for the purpose of lubricating the piston. Would polishing the piston not remove those etchings and cause the piston to stop retaining the nessesary fuel between it and the bore?

Thanks,
James

 

Don't Polish the Poston.
Re-finish and Polish the Carb Body Bore.

The Diaphragm Pistons for some Bikes have Pistons that have something like a Teflon Coating.
That you just clean.

The Pistons which are NOT coated can be Cleaned and Polished.
But, I have not found a product to use on them that will remove the "Smile" on the Piston where it it exposed to the Throttle Plate opening.

 

Can you post a photo of the polishing tool you used to polish the bores?

 

Dremel
Flex Extention Wand Attachment
Dremel Buffing Wheel

http://cgi.ebay.com/ROTARY-GRINDER-TOOL ... 3a5924547a

 

Can you effectively gauge the clunk if the carbs are fully assembled? Or do you need to pop the hat, remove the springe, and unseat the diaphragm?

 

Hey guys
Was just looking at stuff on the Maximum Suzuki forum and found this little piece on cleaning carbs with Pine Sol. Here's the link: http://www.cb750c.com/modules.php?name= ... 66&start=0
I've seen the posts about using Ultra Sonic equipment, but unless you have the money for a big unit the carbs have to be seperated . This way all you need to do is get a big plastic tub, fill it with Pine Sol and you're good to go. One guy uses an orbital sander as a poor mans Ultra Sonic but he's not sure if it helped.

 

That's an interesting idea. Anyone have their own two cents on it?

 

I did mine tonight. None of them were falling very well.

I used 1500 grit WETorDRY using WD40 as my wet compound. I used a new little strip of the paper for each carb, and went at it. Up and down only, evenly around the bore. I spent about 10 minutes on each carb, wiped it down, cleaned the piston itself with a little carb cleaner and they all dropped like an important call on AT&T.

I didn't do the 800-1000-1200-1500 paper route, nor did I super-polish the bore with a Dremel I don't have, but what I did took them from barely falling to free falling like Tom Petty.

Pretty painless! Can't wait to forget all about my brakes and let the engine do all the work.

 

Nice!

 

Well lets hope these bloody fingers made a difference! Just got done polishing!

 

CLUNK!

 

best part was i thought they needed to go clunk with the diaphragm and hat on. So I did 800-1000-2000-polish.. If i'd remembered it was with the all that off I'd been done at 800!

 

I'm a total noob on this stuff too. Just so I'm clear:

*The pistons only need to go 'clunk' when the diaphram and such is off?*

I'm asking because they clunk perfectly when the rubber boot and spring isn't connected. But when everything is put back together, they don't clunk. And also they don't all spring at exactly the same rate. One may spit out a little slower or faster than another. But I've cleaned them all pretty well. I have a black coated piston, so I only wipe it down well with a cloth.

-KJ

 

Right.
When you are cleaning the Carbs ...
The Diaphragm Piston needs to be lifted and Clunk-down shut.
Hesitation, delay, drag, sticking or vibrating = No Good.

Once assembled.
They react to air pressure.

 

I used jewerler rouge to polish my aluminum on my Peterbilt so I can imagine how good it will do for polishing deep down into the bores. I have all the Dremel stuff and rouge needed. thanks for the info. my 750 does back off when twisting back on the wick however not as fast as a race bike. nice winter project, along with other winter projects

 

damn it i just read this after instalin the carbs. can sticking cause the idle to race to 5k as well?