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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Amal 289 Throttle Slide Cutaways
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<blockquote data-quote="greg brillus" data-source="post: 81353" data-attributes="member: 597"><p>There are two (2) parts to the equation, the first deals with the idle slow running circuit which is within the brass jet block, and the second affects the off idle to normal running which is in the size of the slide cutaway. This applies to the type 29 carb's not so much the 276 found on Rapides as they seem quite good straight out of the box. The 289 carb's once installed can suffer the following running condition......Once started it is found that the mixture screw does very little even when wound fully in (rich) upon opening the throttle the engine spits back constantly out the carb unless the choke (air slide) is dropped near closed and then the engine behaves better. However this takes too long and if you attempt to ride the bike, the engine stumbles because it is too rich, open the chokes and the carbs spit badly again. The real easy fix for the slides is to buy a pair of number 3 1/2 slides from the VOC spares co, as they are not available from Burlen's themselves. Though the slides are quite expensive, this is what prompted me to simply modify either a number 3 or 4 slide to fix the problem. On the number 4 you need to machine off 25 to 30 thou off the flat base of the slide, this will lower the slide within the carb body. On 3 slide you need to machine the cutaway taller at the front by half the amount, use a black texter pen to draw a reference line and use drill bits on a flat bench to check how much you are removing. It sounds all experimental and it basically is.......But it works.......do not get carried away and take too much. The fix for the idle circuit is a bit detailed and I will discuss it if you feel it is causing a problem. It is common for a cold engine to spit back through the carbs as it warms up, but it should not do it all the time, this means it is running lean on that cylinder. If you do decide to machine the base of the number 4 slide, you are best off doing it in a lathe, and we made up an alloy solid slug that slides neatly into the inner bore of the slide so that the sides to not collapse in as the jaws of the chuck grip the slide. They are generally plated brass and machine quite well, just debur the edges carefully afterward and you are good to go. When I modify a slide like in Tom's picture above I use a surface plate and linish the cutaway by hand, it is not that hard to do, but you need to take care that you only remove the metal from the shaded area and not past the bottom arrow point, this is why I mark above the original cutaway with a black texter pen so I can see how I am progressing, then check the heights on a flat surface using number drills as an accurate guide. This has worked many times for me and not just on Vincent's either. Cheers......Greg.</p></blockquote><p></p>
[QUOTE="greg brillus, post: 81353, member: 597"] There are two (2) parts to the equation, the first deals with the idle slow running circuit which is within the brass jet block, and the second affects the off idle to normal running which is in the size of the slide cutaway. This applies to the type 29 carb's not so much the 276 found on Rapides as they seem quite good straight out of the box. The 289 carb's once installed can suffer the following running condition......Once started it is found that the mixture screw does very little even when wound fully in (rich) upon opening the throttle the engine spits back constantly out the carb unless the choke (air slide) is dropped near closed and then the engine behaves better. However this takes too long and if you attempt to ride the bike, the engine stumbles because it is too rich, open the chokes and the carbs spit badly again. The real easy fix for the slides is to buy a pair of number 3 1/2 slides from the VOC spares co, as they are not available from Burlen's themselves. Though the slides are quite expensive, this is what prompted me to simply modify either a number 3 or 4 slide to fix the problem. On the number 4 you need to machine off 25 to 30 thou off the flat base of the slide, this will lower the slide within the carb body. On 3 slide you need to machine the cutaway taller at the front by half the amount, use a black texter pen to draw a reference line and use drill bits on a flat bench to check how much you are removing. It sounds all experimental and it basically is.......But it works.......do not get carried away and take too much. The fix for the idle circuit is a bit detailed and I will discuss it if you feel it is causing a problem. It is common for a cold engine to spit back through the carbs as it warms up, but it should not do it all the time, this means it is running lean on that cylinder. If you do decide to machine the base of the number 4 slide, you are best off doing it in a lathe, and we made up an alloy solid slug that slides neatly into the inner bore of the slide so that the sides to not collapse in as the jaws of the chuck grip the slide. They are generally plated brass and machine quite well, just debur the edges carefully afterward and you are good to go. When I modify a slide like in Tom's picture above I use a surface plate and linish the cutaway by hand, it is not that hard to do, but you need to take care that you only remove the metal from the shaded area and not past the bottom arrow point, this is why I mark above the original cutaway with a black texter pen so I can see how I am progressing, then check the heights on a flat surface using number drills as an accurate guide. This has worked many times for me and not just on Vincent's either. Cheers......Greg. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Amal 289 Throttle Slide Cutaways
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