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#73729 - 03/01/08 2:44 pm Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
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Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Went out yesterday to run up the bike. Started on the first kick as she ALWAYS does now smile smile smile , ran her on the centerstand for 10 minutes or so. Didn't have time for a ride so I shut her down.

After a couple of minutes, as I was fooling around checking a few things, I opened the twistgrip and felt some "dragging." I closed the grip then opened it again. This time I felt much less than normal return spring pressure...about half as much!

I could hear /feel the right carb slide bottoming in the carb when I released the twist grip but not the left. I tapped the side of the left carb with a screwdriver handle and "CLICK!" the slide popped back down. I opened the twistgrip and the same thing occurred. Tried it a few more times - same thing. I opened it again and, while the slide was stuck, I loosened the outboard nut that holds the carb to the manifold. "CLICK!" the slide dropped back down. Repeated this a few times with the same results...

OK, I have previously read all the info on sticking AMAL slides and here's what I don't understand: These amals have sleeved slides (by the PO). When I rebuilt the carbs, I trued the manifolds/carb flanges, etc with wet or dry paper on plate glass. I was careful not to tighten the carbs excessively. The slides have worked perfectly smoothly until yesterday.

So what "warped" the carb body yesterday in a 10 minute warm up on the centerstand (I do this fairly often if I can't actually ride) that never did it before?

I'll pull that carb today and see what I can determine.

FWIW, I remember that when I overhauled the carbs, I thought there was VEERRRY little clearance between the slides/bodies. I suppose that's a good thing for air/fuel consistency but it seemed to me that there should be a bit more clearance for reliable operation.

I had an almost new 71 750 Commando that I ran for many thousands of miles on the oem Concentrics and it never had any trouble with carbs sticking though I admit that these resleeved carbs idle extremely smoothly compared to those on my 750 which would randomly surge up/down at idle for no apparent reason, sometimes going from 1000 to 2000 RPM occasionally as if I was adding throttle...which I wasn't.

In any case, the thought of sticking slides out on the road makes me think maybe I should reconnect that kill switch that I bypassed! wink

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#73730 - 03/01/08 4:17 pm Re: Amal Concentric Slide sticking...  
Joined: Jul 2005
Posts: 1,919
John RGS Offline
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John RGS  Offline
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Joined: Jul 2005
Posts: 1,919
new jersey usa
I would never by-pass a kill switch if it's there. If you know how to by-pass it, you certainly could trouble shoot it if needed. Ask me why. Have you considered you might just have a bit of foreign matter hanging your slide up?


,_o
_ -\_<,
(*)/'(*)

NOPGS #2
#73731 - 03/01/08 5:13 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
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Joined: Sep 2006
Posts: 609
Mexico City, Mexico
I bypassed the kill switch when I installed the new wiring harness since the switch is the weakest part of the ignition circuit but perhaps I need to rethink that. wink

Re the carb and foreign matter- I suppose it could be but can't think how it would get there - I run an air filter and the carb tops are sealed (choke slides removed and cable fitting hole plugged with a screw). It acts like the slide is binding when it is lifted beyond approximately 1/2 throttle. You can feel the obviously increased drag as it opens. By the time it gets close to WOT it is decidedly hard to open further. But a light tap with the screwdriver handle pops it shut and IF I leave the outboat carb-to-manifold screw loose, it doesn't jam at all.

#73732 - 03/01/08 5:40 pm Re: Amal Concentric Slide sticking...  
Joined: May 2006
Posts: 150
Damon Fever Offline
Life member
Damon Fever  Offline
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Joined: May 2006
Posts: 150
Raleigh NC
Mike, you may have a distorted carb body, most likely as a result of a warped mounting flange. This is common (and a good reason to keep that kill switch); your sleeved carbs are probably even more susceptible to this. You want to flatten your flange, but it's best to de-distort the carb body by applying pressure through it to the flange. In Vintage Bike, John Healy showed a fixture he designed to do this (I made one like it). You can cobble something up. John probably wouldn't mind me sending you a copy of the article if you promise to subscribe to Vintage Bike (which you ought to do anyway). Contact me offline if you want it (10.9MB!).

Cheers
Rick F

#73733 - 03/01/08 5:54 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
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Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Thanks Rick - offline email sent!

#73734 - 03/02/08 12:30 am Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
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Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Yep - the body was distorted. Pulled the carb and disassembled it. Put the slide back in and it would jam rather firmly in any location. If I held the body and pressed with my fingers HARD on both sides where the "AMAL" emblem is located, the slide would freely drop.

So...I took a pair of channel locks, padded the carb body, and squeezed gently at those points with the pliers. released the pressure and tried the slide. Better but still sticking. Repeated the "adjustment" with a bit more pressure. This time the slide would now drop freely. I heated the slide and body in hot water and tried it again-"CLUNK" - a free drop! I put the slide and body in the freezer for 30 minutes and tried it again. The slide jammed slightly though a bit of finger pressure on the slide (much less than the return spring would provide) moved it down. But I did another session with the pliers then repeated the hot/cold test. It falls freely now in both conditions!

I also trued all the carb and manifold mating surfaces with Wet'rDry 220/400 on plate glass. The interesting part about that is that they were NOT true even though I trued them the same way a year ago and they WERE true prior to reassembly...Hmmm. Though I am careful about bolt torque, it appears I applied too much. I think that when I put the carb back on I will just turn the carb/manifold nuts until they compress the Oring and no more - literally finger tight (with loctite blue on the nuts).

IMHO, the sleeved carb slides on my 932s have insufficient clearance for proper, reliable and safe operation. I checked the clearance with a dial indicator against the slide (slide sticking up about 1/8 inch above the top of the body) and the body in a padded vice. In one direction I could get virtually NO movement. 90 degrees from that I managed half-a- thousandth! That's virtually no clearance. Perhaps there are various "opinions" on the proper clearance. Whoever did these has the wrong opinion since the clearance used allows for virtually NO expansion/contraction which occurs in normal operation. Since they were sleeved by the PO, I have no idea who actually performed the resleeving. Otherwise I'd suggest not to use them.

Another contributing factor (to warping) I noticed was that the holes for the screws in the top cap, where the cables plug in, where a bit small. I had noticed this last year but didn't pay any attention to it at the time. The screws actually threaded themselves slightly in that portion instead of dropping through into the threads in the body. I cleaned that up with a drill bit and found the same on the float bowl screw holes. Having no relief around these holes would tend to also cause distortion as the screws were tightened down. I'd bet that the holes weren't this way when new but too much ham-handed tightening of the screws flattened the flanges and forced metal to expand into the holes. This is pot metal, after all! smile

In any case the carb seems perfect now...wonder if it will stay that way? Of course I have to pull the other and do the same truing/hole adjusting. I'll also carefully check the slide though it's working fine. But the other one was working fine too until yesterday.

#73735 - 03/02/08 4:27 am Re: Amal Concentric Slide sticking...  
Joined: Apr 2003
Posts: 239
Stuart SS Offline
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Stuart SS  Offline
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Joined: Apr 2003
Posts: 239
Australia (FNQ)
Mike

I went through the exact same deal `~

In fact I paid a lot of money to have some one who thought he was a bike mechanic screw up mine .
They had stainless inserts fitted to boot ~

Long story . But I made up a hard wood hone block/ rod and a flapper based on the ID measurements of the carb body.

Then gave the carb body a couple of very short hones with <800 grade wet> and dry.

Being stainless inserts they will tolerate some honing .. but I kept it to a very minimum ~

End story . Thye have been flawless every since!


ABSTINENCE;" He neither drank, smoked, nor rode a bike. Living frugally, saving his money, he died early, surrounded by greedy relatives. It was a great lesson to me. "
#73736 - 03/02/08 7:18 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
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Joined: Sep 2006
Posts: 609
Mexico City, Mexico
I want to add more because today I found more things related to this...

This morning, the carbslide that would easily free fall yesterday wouldn't when bolted to the manifold. This despite the fact that I tightened the nuts only to the point where the carb mated firmly with the manifold. I loosened the carb a bit and it was fine. So thought about this for a bit and then disassembled and rechecked the manifold/carb for trueness. It wasn't anymore. So I retrued them.

Then I decided to tighten the nuts NOT based on tightness but based on uniform compression of the Oring between the parts AND specifically not trying to mate the two metal surfaces. It became obvious to me that with the oring in place, if you snug down the nuts to "mate" the metal surfaces, the flanges will warp (and mate) because the O-ring tries to keep the center of the mouting surface apart. You cannot tighten the nuts enough to totally flatten the o-ring without warping the flanges. And, of course, there is really no reason to "flatten" the O-ring.

So I tightened the nuts so that I could see daylight between the mating surface except at the oring joint. There was around .015" clearance between the metal surfaces at that point. I then rather arbitrarily increased the tension so as to end up with .005 clearance between the carb/flange all the way around (blue locktite on the nuts). This was much more accurate from an assembly viewpoint than trying to come up with some sort of torque figure and it compressed the O-ring enough to seal perfectly without warping anything. The slide free fell up or down.

I removed and treated the other carb in the same way. While I was doing this I found another "interesting" thing. The return spring in the carb that was sticking was 3/8 longer than the one in the other carb. At first I thought it was a different version of carb spring. But it wasn't. On close inspection it was obvious that someone had stretched so it would provide more closing pressure. Obviously this sticking slide thing had occurred to the PO! Luckily, I had another slide spring that was the same as the "good" one so I replaced the stretched one.

Every flange on both carbs was damaged by excessive torque on the nuts/screws. All of the holes had metal extruded into them and I cleaned all the flange holes with the proper size drill. The flat washers on the carb-manifold studs were also grooved with metal extruded into their holes due to excess torque. Everything indicates that all the fittings were grossly overtightened in the past - probably many times based on the damage to everything. Fortunately, it was easy enough to clean up and put back to rights.

Looks like the PO was trying to fix leaks/whatever by just tightening fittings instead of correcting the problem with warped surfaces - which may have been factory issued! Additional tightening just compounded the problem since it takes rather little pressure to seal a properly mated joint.

The carbs are back on the bike and running fine. It will take some extensive riding to ensure that the way I tightened the carbs to the manifold will retain the proper seal over the long term. So my method won't be "proven" to me until there is a good bit of mileage with no intake leak. One could always dispense with the Oring and utilize a THIN film of Yamabond or any of the good similar products; this would not produce the warpage because there would be nothing trying to hold the center of the fittings apart while the flanges are trying to clamp them together.

Hmm...Maybe I should have just done that in the first place! wink

#73737 - 03/02/08 9:45 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2002
Posts: 487
ludwig Offline
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ludwig  Offline
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Joined: Sep 2002
Posts: 487
belgium
MM :"One could always dispense with the Oring and utilize a THIN film of Yamabond or any of the good similar products" (quote) .
That is what I do .

#73738 - 03/03/08 1:32 am Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
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MexicoMike  Offline
BritBike Forum member

Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Ludwig - Ever since I put it back together this morning I've been thinking of taking apart and doing just that!

Knowing me, I suspect I will...probably tomorrow! wink

#73739 - 03/03/08 2:49 am Re: Amal Concentric Slide sticking...  
Joined: May 2006
Posts: 150
Damon Fever Offline
Life member
Damon Fever  Offline
Life member

Joined: May 2006
Posts: 150
Raleigh NC
Well done Mike, both diagnosis and treatment. Sounds like the PO was honking down on the nuts to fix a leak, which made it worse, so he tightened more... Looks like you've got it sussed.

Cheers
Rick F (none of whose Amals have O-rings)

#73740 - 03/03/08 4:28 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
BritBike Forum member
MexicoMike  Offline
BritBike Forum member

Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Ok, the carbs/manifolds are apart/back together now without the Orings using Permatex grey!

Sometimes I think I am entirely to ****! wink

#73741 - 03/03/08 4:29 pm Re: Amal Concentric Slide sticking...  
Joined: Sep 2006
Posts: 609
MexicoMike Offline
BritBike Forum member
MexicoMike  Offline
BritBike Forum member

Joined: Sep 2006
Posts: 609
Mexico City, Mexico
Oh.. "too @nal" spelled correctly is bad! I didn't realize...

#73742 - 04/10/08 12:41 am Re: Amal Concentric Slide sticking...  
Joined: Feb 2008
Posts: 338
Alan Prudhomme Offline
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Alan Prudhomme  Offline
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Joined: Feb 2008
Posts: 338
FLORIDA
HEY MIKE....You might just have something there. I have been putting up with Amals for over 40 years.I have had my fill of them.If the slides don't rattle they stick, or the pilot jet will plug, AGAIN, it never ends. I do not like Mikune (you need a dial indicator to set some of their floats)but I might try one. I have been messing with Harley, butterfly type carb's.Have tried a Bendix Zenith 38mm so far but that is a real piece of work ( now I know why the old sportsters were so hard to start). Might try a Keihin or SS super E next? Maybe not.

#73743 - 04/10/08 1:57 am Re: Amal Concentric Slide sticking...  
Joined: Sep 2007
Posts: 107
aceaceca Offline
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aceaceca  Offline
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Joined: Sep 2007
Posts: 107
San Francisco/East Bay Califor...
I make paper gaskets for the carbs and use just a slight smear of silicone seal. Regular shopping paper bags are a Brit bikers friend.

#73744 - 04/23/08 1:50 pm Re: Amal Concentric Slide sticking...  
Joined: Nov 2007
Posts: 251
stu88 Offline
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stu88  Offline
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Joined: Nov 2007
Posts: 251
florida
I had the same problem on my BSA. I put the carb in a vice between two pieces of wood and tightened down hard to flatten the flanges, this solved the sticking issue. I also made a gasket and ditched the O ring.


I am 79, not riding anymore because my knees and balance are shot.lasr bike was a 74 commando.
#73745 - 04/24/08 10:45 am Re: Amal Concentric Slide sticking...  
Joined: Feb 2008
Posts: 190
Fullauto Offline
BritBike Forum member
Fullauto  Offline
BritBike Forum member

Joined: Feb 2008
Posts: 190
Perth Western Australia
Well, I've always referred to them as AMAL Eccentrics. I have a single Mikuni and love it.
The last two tankfuls I have cracked 60 mpg. (Imperial mpg)


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