AMAL carb slide cut-away 1/8 or 1/16 per increment

CAB · Post by **CAB** » Tue Oct 06, 2009 10:18 pm

Hello
I stripped the carb on my 61 G12 CSR at the weekend to find it has been fitted with a re-sleeved slide that is marked as a number 2. According to all my books the carb should have a number 4 slide. Can anyone confirm if the slides go up in 1/8 or 1/16 of an inch? It's possible that the slide could have started off as a number 2 but might have been modified to a number 4 when it was resleeved. If so, what should the total height of the cutaway be if it is put base down on a flat surface? I'm assuming that the datum is zero i.e. a number 1 slide will be at it's highest point an 1/8 or a 1/16 of the flat surface depending on the answer to the above. Of course it's possible that the number 1 slide starts off higher than this and then goes up in 1/16 or 1/8 of an inch. I would be very grateful if someone would take the time to measure the height of a slide cutaway. Apart from the cutaway being incorrect the carb seems to be in good condition with barely any slide wear. All the other jets and settings are as per the book but the plugs look a little sooty but dry. Before I invest in a new carb I'd like to see if I can improve what I have.
Thanks
CAB

Merlin · Post by **Merlin** » Wed Oct 07, 2009 12:00 am

How was the bike running before the strip down?

wilko · Post by **wilko** » Wed Oct 07, 2009 12:50 am

My two 389 no. 4's measure 1/4 inch in cutaway height. That should help! And no evidence of filing.

SPRIDDLER · Post by **SPRIDDLER** » Wed Oct 07, 2009 1:00 am

The difference between each AMAL slide cutaway whole number is 1/16" - as with Wilko's No.4 which is 1/4" (i.e. 4/16ths in old money)

CAB · Post by **CAB** » Wed Oct 07, 2009 9:02 pm

Hello
Thanks for the replies. The bike was running ok but a bit flat, and it would also spit back through the carb just as you were coming to a stop and cutout. The plugs were black and sooty. I stripped the carb to check the jets and slides and apart from the cutaway the carb is correct. I then turned my attention to the ignition. It is fitted with a Boyer Bransden 6 volt system in a mag replacement body and it still runs a dynamo. My dad and I suspected the battery as it had a small capacity as standard and the spitting back/cutting out was noticably worse with the brake light constantly on due to a jammed stop light switch. The dynamo is charging well and I have now replaced the battery with a new larger capacity one, fitted a solid state regulator, low wattage halogen pilot light, head light and an LED stoplight to give the charging and ignition system the best possible chance. I also fitted new plugs and surpressed caps as per the Boyer instructions and checked the valve clearances. The bike was much better but still spat back through the carb and would cut out when coming to a stop. I stripped off the clutch cover and tank and used a dial gauge and timing disc to find TDC and painted a line on crank gear and two on the inside of the timing case for TDC and 35 degrees BTDC. I then timed the Boyer unit to give full advance at 35 degrees BTDC with a strobe. I had to retard the Boyer plate by about 5 degrees (camshaft). The bike starts easier, sounds more lively and has stopped spitting back and cutting out. I didn't get chance to ride it as I had to leave to come back to Bristol (the bike is at my dad's in Cornwall). Hopefully he will give it a run this week if the weather is ok. I think the spitting back/cutting out was due to the amount of advance and not enough power to run the Boyer unit. I also noticed that there is a puff of black smoke when you blip the throttle hence the questioning of the slide cutaway. I'm going to modify the slide.
How far does the cutaway extend around the base diameter? If I file the slide does the new cutaway stay parallel to the old one (in which case the cutaway would extend further around the base diameter) or should it start from the same point on the base diameter (the new cutaway will therefore take the form of a wedge)?
I'll let you know how it goes.
CAB

ebsbury · Post by **ebsbury** » Wed Oct 07, 2009 11:32 pm

There's a picture of a series of slides here that might help.

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=11

CAB · Post by **CAB** » Thu Oct 08, 2009 10:59 pm

Thanks for the link.
The line up of the slides clearly shows the angle of the cutaway getting steeper as the height increases. The start of the cutaway on the base diameter seems to stay in the same place relative to the slot.
CAB

dodger · Post by **dodger** » Sun Oct 11, 2009 8:49 pm

I had the problem of altering a slide and got round it thus. You can pick up an old worn slide at any auto jumble for a few pence. Get one the size you want to end up at, in your case a number 4.Wrap a piece of card tightly round the no 4 slide and hold it in place with a bit of tape. With a sharp craft knife cut the card following the contours of the cut out. Slide out the no 4 slide and insert your No2 in the correct position relative to the cut out. scribe a line on the slide following the curve on the card template. Carefully file to the line.

Hope this helps.

Laurie Long