Got a pair of Concentric 930's on my '66 A65L. Can't stop them from sticking when approaching W.O.T. (ie, going too damn fast). I use the rubber intake mounting gaskets, self-locking nuts (barely past finger tight), have rolled the slides across a mirror to check roundness, and checked the upper part of the bore as best as possible to check for out of round. Has anyone used emery cloth or some other method to remove a bit of metal from the slide to reduce this problem or is there another way to eliminate banging on the side of the carb when approaching a "ton" to slow 'er down!
I had a sticking slide on one of the carbs on my T120R that I messed around with for quite awhile without success. I finally sent it to this guy http://www.tritonmachining.com and had it resleeved. It hasn't given me any touble since and the price was pretty reasonable. He was very good to deal with.
Yeah, Bruce does good work. If you're not ready to get them resleeved here's an alternative:
take the carbs off. with the slide in, wrap a shop rag around the body at the top and give it a squeeze with a large pair of channellock pliers. Use just enough force so the slide will move freely all the way up and down.
A local brit bike mechanic showed me that trick. I did it to my carbs and they've been fine ever since!
It does require a delicate touch. Not recommended for the hamfisted...
Here are some other tips. Make sure the top of the carb body is flat where the cover fits on. A nice flat surface and some emery cloth do wonders. Don't get crazy tightening the screws on the cover to body. It does localized warpage of the top of the carb. Put a buff wheel on your grinder and LIGHTLY buff the slide with compound (brown - Tripoli if I remember right) Sheesh hijack my own thread, this memory loss thing is getting bad....I hate it. But back to teh subject, a lightly buffed slide works nicely in the carby. Actually not a bad idea to do both, makes the throttle a bit lighter.
Verify it is the carb. Sometimes old cables will have a bad spot that gets tight in certain positions. Also verify you don't have a tight spot on the throttle to bar fit and throttle to throttle body fit. I have seen problem in this area cause sticking.
But what ever you do, fix it. It sucks to be stuck wide open.
I ran into this with some monoblocks. I took the carbs off, diassembled them, coated the slides with white polishing compound (the kind you use on dull paint), reassembled the slide and pushed the slide up and down reapplying fresh compound as required. Towards the end I reassembled the cap and spring and just pushed it up letting the spring push down until it was free and smooth. The orange rubbing compound is more agressive and may work better but I'd try the white first.
You are beating a dead horse if you try to salvage your worn out carbs. Many will say that they have had success with resleeving but others have not. The sleeving works OK but the carb body may be distorted and the slide will still stick when mounted to the bike.
The problem is too fold. First, the slide and the carb body are both made of pot metal. In this case the two parts gall rather than slide against each other and in time and the slide clearances get too big too quickly (air leaks around slide and causes irratic idle). The worn out slide can also bind in the bore by getting canted. Secondly, people overtighten the hold down nuts on the intake manifold's studs. This warps the body of the carb also making the slides want to stick because it is a round slide in an oblong hole.This can also lead to an air leak at the carb to manifold juction and an irratic idle.
The REAL cure is new carbs. Use the special O-ring supplied with the carbs, then only tighten the special manifold to carb hold down nuts to the point where you can still just move the carb (rotate it on the studs). Any tighter and the carb body distorts permanently. The O-ring will do the sealing just fine.
This is a SAFETY issue. Stuck throttles at full throttle can hurt. One friend had one stick, crashed, and spent years on crutches during many operations to fix the broken leg bones. It is not worth the risk! 35 years is long enough for the original equipment carbs. New ones are required, at least in my mind.
I sure agree with LD on the sticky slide issue. It can be a killer. Pain hurts. Being Dead lasts a long time! What really bothers me are the many Brit Bikes out and around Without a Kill Button under the riders thumb on the handle bar. Arrgh! Personally I wouldn't ride down the driveway without a kill button. Whatever ...
Anyhow .. I too hear about the carb 'resleeving' issue. Are you gents aware there are new AMAL carb bodies and chrome plated slides available at reasonable prices? I notice one of my suppliers lists quite an assortment. Sure seems the way to go to me..
I couldn't agree more with LD and Dave. Bite the bullet and spend the money. The bike will run great and be much, much safer. Once you're out on the road with the bike running great and with a big smile on your face, you'll soon forget about the pain in the wallet. I have new carbs with chrome slides on my Brit bikes. Combined with a complete head overhaul both bikes probably never ran as well from the factory. I had one carb re-sleeved, and the guy did a super job, but the bike still didn't run as well as I thought it should until I bought a new carb.
Before laying out the $$$ to resleeve/re-carb...I tried the Rubbing/polishing compound trick and wa-la....no more sticking slides. Checked them staticly numerous times then hit the road. No problem at W.O.T...the carbs repond smooth cranking it in & chopping it back. I was ready to kill the ignition just in case. Thanks for the suggestions/ideas.
Well I agree with Dave & LD about saftey, and the kill switch, but that's where it ends.Most the new Amals have sloppier slides than the ones I'm trying to fix. I have salvaged more Amals than most and it's not that hard and they run fine.
First inspect the slides, you'll find gauling of the sides. Use wet & dry sand paper in 600 grit or high WET to smooth the marks, Stay away from the alighnment tang, it's required. You can then go to 0000 steel wool and then clean thoroughly to get any grit or steel fibers off. Now polish with buffing wheel.
You can do the same with the bore but not till you true the body. I use a milling machine vice since it has large flat jaws. First I flaten the flange that bolts to the manifold. Test the slide for binding. If you still have a tight spot, you can gently pinch the slide bore in the vice to round it up. Once you get the binding to a minimum polish up the bore. This takes a bit of trial and fit, but eventually you get it.
You aren't done. Yes the top cap has to fit flat or you will torque the slide bore again.
The next two things will keep it from repeating the binding and keep you from being an unwanted crash dummy.
Depending on how much you want to go, I do two different things to help the slide seal or keep it lubed. First the cheap way. I use a silicone grease called Super lube, it very thick and sticks well. But it won't stay on the slide unless you keep the vacuum from sucking it up the throat.You can do this by sealing the top cap, including the cable entries. I use a thin urethane sheet to make a gasket seal for the cap and either Asian cable boots or you can buy thread protectors for bolts at your local hardware store and fit them over the cable by cutting the end for the cable to pass through. I rub graphite into the slide and bore, grease the slide, insert it and add grease above the slide.
The second is more time consuming and requires machining. There are pump and cylinder seals sold at bearing shops made of teflon and nylon derivatives. They are very thin and are made like a split ring key ring. You find a size close to your slide bore, cut a groove near the bottom of the slide where the most meat is. Fit the ring and sand it to fit the bore. This forms an air seal for the slide and gives a friction glide. I have also drilled and tapped the upper part of the slide and used nylon screws cut off near flush as glides. They can't come out and get sucked in. This keeps a loose slide from rattling around and repeating the damage.
There is also a spray can of molybdemum sulfide in a carrier that can be baked on and forms a low friction coating. But this stuff is hard to find anymore.
I actually have slightly larger 'O' rings I use since most of the new ones seem to be undersize in cross section. I don't like the paper insulators, they aren't flat and compress and cause warpping. I use high temp silicone on the gaskets, wipe a thin film on the gaskets and insulators, let it skin, then assemble.
I have no problem with idle or air leaks and the set on my Firebird has worked flawless for 5 years.
I'll volanteer now to dispose of you old Amals and any Smith's clocks you want to replace.
If you don't like change, you're going to hate extinction... 75' Commando 71' Bonneville 71' BSA Firebird 71' B50 Street tracker 62' BSA A10 Super rocket 60' BSA DBD Goldstar roller 97' Buell S3T 09' KTM 990 Adventure 00' Sherco 2.5
Hmm, I broke a collerbone crashing an 850 trident with stuck re-sleeved 30mm concentrics. AMAL give them quite a bit of bore clearance, I doubt the guy doing the re-sleeve gave them the same, I had done maybe 100 miles with them the day before and they were shutting fine but I think maybe they distorted a little on cooling down. We don't usually shut off for a corner before we need to, it takes more time than you want to spend working out 'I shut the throttle but the thing's still going flat out, kill button is broken off flat with the switch block even if you have 1/2 a second to think of it, don't want to pull the clutch,(very bad decission not to, revs just as well on its side)looking at the key, front brake twin discs, tyre smoke, road/ sky/road /sky /road/sky/trees, bikes on its side one million rpm, run round tank side and turn it off, watch TV for 2 weeks waiting for bone to knit. I personally prefere how the carbs that start with an 'M" work, and I recommend if anyone finds themselves in the above situation without some straight road in front of them, don't worry about the motor pull the clutch use the brakes and when you are safe turn it off. Unless you usually turn it off with the killswitch you likely won't have time to think of it.
Having slides stick after they have been sleeved seems to be a common thread. The specification for clearance on a Concentric slide is .0035" to .004." Because there seems to be some belief that you improve the carburetor by using less clearance many people who sleeve Concentrics use less. The only thing using less clearance does is increase the chances that the slide will stick when they are over tightened on installation and make the instrument run richer.
AMAL has compensated for the air that goes around the slide in how they prepared the parts that control the mixture. Barry Johnston and Jeff Binks, the two engineers that designed the Concentric, did understand how this carburetor worked when they specified the .0035" to .004" clearance. They also knew the consequences of using less. In my opinion you run an AMAL slide at less than .0035" clearance at your own risk.
In my mind the usefullness of the chrome slide is debatable. Like you, I am searching for something other than than the zinc material for a slide. Grosvenor Works, previous manufacturer of the carbs, spent a lot of time and money trying to make a brass slide that would have the provisions for the choke. What they finally came up with is the chromed zinc one we find available today.
AMR in Tuscon has been fitting chrome brass Mikuni slides to Concentrics for quite a few years. It is actually a pretty straight forward process. There is no provision for a choke slide.
I do know that I would never use a chromed AMAL zinc slide in a worn Concentric mounted to a large single.It doesn't take a brain surgeon to see what will happen when the slide bangs back and forth in the body with the pulses of the intake. It takes a pretty good size chunk off the slide in the area of the cutaway and presents it into the cylinder. Although this can happen as a normal course with a big single, nitrogen imbrittlement from the chroming doesn't make it any better. john
One of you seemed to know the AMAL designers. I have a question about their designs. My BSA Monobloc slide has the cable connection in the exact center of the slide top. But the concentrics on my Commando have the cable connections in the tops of the slides off-center, meaning that the slides will automatically try to cock in the bores when pulled up. This was evident when I took them apart and found the engine-side of the slides at bottom worn to almost paper thin and galling in the bores (the like-material slides and body problem). Why on Gods green earth are those cable connections off-center? Disaster in the making! Bruce at Triton did his magic and now they have brass or bronze liners in the bodies and new slides. I polished the slides with Simichrome, and just some silicone spray in the bores. Then made damn sure the cables were in good shape and carefully routed to avoid kinks- even put some bent copper tubing over them at the very difficult bend at the point where they enter the carb tops to keep the curve graceful. So far- smooth as silk, but I look at the bottom front of the slides yearly to see if they're wearing. Smart to learn to use that kill-switch every time you shut down- keeps it from corroding, and hands on the controls, and your hand knows where it is. Joetc5
Joe posted: My BSA Monobloc slide has the cable connection in the exact center of the slide top. But the concentrics on my Commando have the cable connections in the tops of the slides off-center, meaning that the slides will automatically try to cock in the bores when pulled up. -------------------- The needle sits in the middle of the slide on both of these carburetors which precludes the cable being placed in the middle. john
I noticed that when I tightened the nuts of the flange af my (brand new from the box!) Concentric with gentle fingers and normal force, the carburettor housing deformated and the slide seized. The flange gasket however was very thick, almost 3 milimetres. For the position of the carb in relation to the rubber sleeve of the air filter, something had to be there, so I made an aluminium spacer - the shape of the gasket - and use this with two thin gaskets on each side of it. Now there is no deformation when tightening the nuts. I wonder how long it takes before it starts to seize anyway, because also here in Holland everybody complains.
Just a thought, but has any one ever tried making stainless steel slides. Ideally they won't corrode and and should be heavy enough, hence no need for "double springs and lead fishing weights", to fall back down again without too much bother. Maybe in the new year I'll experiment with machining a couple out of some bar stock and see how they perform.
Weight is not the issue here, Cariboo, and not the solution. Also, the weight difference between a hollow piece of aluminium and a hollow piece of stainless steel is very small in relation to the size of the near death experience you have when both air slide and clutch do not respond simultaniously when you approach a red traffic light in dense traffic . The area where I live, near Rotterdam, is among the crowdiest in the world. However, surfing the different sites mentioned in relation to this topic, I found that different materials are used for slides. But the initial problem is deformation of the housing.