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- Oct 29, 2006
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I posted at length about this on another Norton site but since now being able to access this site again (through a proxy server) - for the first time in a couple of months - I thought I'd mention it here:
A few days ago I went up to the bike and, for no particular reason, twisted the throttle to WOT and let it snap shut. The "snap" sounded odd. I then opened the throttle again and noticed considerably less resistance to opening until about 3/4 open.
Yep, left carb slide stuck at about the 3/4 position when closing.
Now this surprised me considerably because I am extremely careful and precise about rebuilding my Amals. I ensure surfaces are true and am very careful of the torque in re-assembling. I had redone the carbs a few months ago and they were perfect. There was no slide sticking on a short ride just a couple of days prior. But sitting in the garage the slide stuck. I loosened the outer carb-to-manifold screw just enough to barely see it move and the slide snapped back to full closed.
This would indicate that the nut was too tight originally and had warped the body. BUT, per AMAL instructions, I don't tighten those nuts at all - I just turn them down until the mating surfaces just touch - allowing the o-ring to do the job it is there to do.
When I got the bike, the cabs had been sleeved by the PO but they were a disaster. Bodies/all mating surfaces warped from overtightening, etc. Sticking slides even with springs that had been stretched by the PO to 1/3 more than correct length.
So I carefully went through everything, including adjusting the bodies to true them up with the slides and all pertinent new parts/surfacing/drilling tapping for new body screws (old ones partially stripped).
So, as I said, I was a bit surprised at this.
I pulled both carbs. Both (sleeved) slides were quite sticky in the bores. I could not get a sliver of an .001 feeler gauge between the slide/bore in either of them.
So I worked on them both for several hours with wet/dry paper wrapped around a piece of hose so that it was a snug fit and worked it up/down/rotating - sort of like valve grinding. I started with 240 paper and ended up with 1500. The bare slides in both carbs will now fall open/closed by inverting the body. I then reattached the manifolds to the carbs, checking the slides again after tightening the nuts. I did the same with the float bowls.
OK, now to the point of this. One of the replies I received on the other site from John H. noted that the clearance AMAL set up for the carb/slide is .0035" BUT the clearance set up by many of the "sleevers" is sometimes as little as .001. In other words, they are "fixing" something that isn't a problem, creating a possible much bigger problem. This won't work properly, as my carbs clearly demonstrated. It also explains why the PO had stretched the return springs in both carbs to provide enough force to close the slides. Now, I want to make it clear that I am not saying sleeving is bad, but I am convinced that improper sleeving, resulting in less than amal spec clearance is poor work. The .0035 clearance specified by Amal is there to compensate for any possible warping and the fact is that if the .0035 is there, there will be no issue with warping - yes, there may be warping if the fittings are overtightened BUT the warping will have no effect on slide operation. Sleevers will say how they eliminate the "excess" clearance with provides for a better idle. But, as pointed out by John H, any air "leakage" due to the clearance is simply compensated for by adjustment of the idle mixture screw.
Anyway - I totally agree with his view and my carbs do as well!
A few days ago I went up to the bike and, for no particular reason, twisted the throttle to WOT and let it snap shut. The "snap" sounded odd. I then opened the throttle again and noticed considerably less resistance to opening until about 3/4 open.
Yep, left carb slide stuck at about the 3/4 position when closing.
Now this surprised me considerably because I am extremely careful and precise about rebuilding my Amals. I ensure surfaces are true and am very careful of the torque in re-assembling. I had redone the carbs a few months ago and they were perfect. There was no slide sticking on a short ride just a couple of days prior. But sitting in the garage the slide stuck. I loosened the outer carb-to-manifold screw just enough to barely see it move and the slide snapped back to full closed.
This would indicate that the nut was too tight originally and had warped the body. BUT, per AMAL instructions, I don't tighten those nuts at all - I just turn them down until the mating surfaces just touch - allowing the o-ring to do the job it is there to do.
When I got the bike, the cabs had been sleeved by the PO but they were a disaster. Bodies/all mating surfaces warped from overtightening, etc. Sticking slides even with springs that had been stretched by the PO to 1/3 more than correct length.
So I carefully went through everything, including adjusting the bodies to true them up with the slides and all pertinent new parts/surfacing/drilling tapping for new body screws (old ones partially stripped).
So, as I said, I was a bit surprised at this.
I pulled both carbs. Both (sleeved) slides were quite sticky in the bores. I could not get a sliver of an .001 feeler gauge between the slide/bore in either of them.
So I worked on them both for several hours with wet/dry paper wrapped around a piece of hose so that it was a snug fit and worked it up/down/rotating - sort of like valve grinding. I started with 240 paper and ended up with 1500. The bare slides in both carbs will now fall open/closed by inverting the body. I then reattached the manifolds to the carbs, checking the slides again after tightening the nuts. I did the same with the float bowls.
OK, now to the point of this. One of the replies I received on the other site from John H. noted that the clearance AMAL set up for the carb/slide is .0035" BUT the clearance set up by many of the "sleevers" is sometimes as little as .001. In other words, they are "fixing" something that isn't a problem, creating a possible much bigger problem. This won't work properly, as my carbs clearly demonstrated. It also explains why the PO had stretched the return springs in both carbs to provide enough force to close the slides. Now, I want to make it clear that I am not saying sleeving is bad, but I am convinced that improper sleeving, resulting in less than amal spec clearance is poor work. The .0035 clearance specified by Amal is there to compensate for any possible warping and the fact is that if the .0035 is there, there will be no issue with warping - yes, there may be warping if the fittings are overtightened BUT the warping will have no effect on slide operation. Sleevers will say how they eliminate the "excess" clearance with provides for a better idle. But, as pointed out by John H, any air "leakage" due to the clearance is simply compensated for by adjustment of the idle mixture screw.
Anyway - I totally agree with his view and my carbs do as well!
So much more so with the 32 mm carburettors. Carburettors would wear out in 5000 miles. Changing to dissimilar metals stops the galling. Change your needle jet as well as your needle when getting the re-sleeve done and flatten the flange at the carb and both surfaces of the manifolds
