- Joined
- Apr 7, 2004
- Messages
- 1,691
I thought this might help people setting up Mark two’s on their Norton’s
The set up on my Norton Commando for Mark 2’s follow, the carburetors on mine are 34mm. Jetting is fairly typical. Needle jet is a 106, needle is 2A1. Main jet 250, Slide # 3 cutaways, pilot jet 25.
It’s all the other things that make them run right. Other things; the slides are 2 cycle parts, brass with chrome plating. The floats are also 2 cycle parts much larger than four cycle floats. I elected to blend the 34mm size down into the head but it will work if you just blend the size difference in the manifolds. The aluminum bushings at the air entrance of the carb are removed to defeat this circuit. The air cleaners are huge K&N's this requires a notching of the oil tank for clearance but since this mod is at the top of the tank one doesn't loose much oil capacity. . Also these carburetors do not clear one another and require grinding were they touch at the unused idle screw bosses in the casting. This set up needs dampening support without it the carbs will not stay on the rubber spigots but that’s not the worst part. The needles and their jets will wear very soon without dampening. The mark 2 carburetors have a semi flat spot above the intake throat in the casting that must be machined flat. There are two tapped holes on this flat spot. One just makes a piece out of aluminum 3/8 thick by1/2 tall by 1and 3/4 long. Than drill clearance holes to line up with the tapped holes that are already in the body. Than drill and tap 10-24 hole in the middle of the aluminum key for 1/4 shoulder bolt 3/8 long shoulder on the same plane as the mounting screws. Now just install hardware hooks in the frame above the shoulder bolts and use O-rings to suspend and dampen the carb assembly. On a Commando these holes are in the slanted sheet metal gussets that are mid frame use the threaded hooks with nuts and washers. Custom made very light gage throttle and choke cables need to be used. Also use straight cable fittings at the top of the carburetors. I use an after market throttle mechanism for dirt bikes that has the cable coming out parallel to the handle bars and the cable adjusters are underneath the tank near the splitter boxes. Don’t put the adjusters out in the air. Cable routes are very important so take extra time to get this right or you will be constantly fiddling at adjusting later as the system wears in. Start rich and work to lean till she's nice and snappy mine gets 50 MPH and no dead spots or sick rich out of the plugs. Starting needs half choke most of the time with a two block warm up. I had to buy some of the knurled idle adjustment screws and than add small springs to get it to hold idle. All my other bikes will be single carbs don't care about 120 MPH so much any more. Most of these modifications were necessary because my bike has a some what higher compression ratio and a higher balance factor and a Winy Eads’s rose joint head steady. You can't win, you can't brake even, and you can't quit. Norbsa48503
The set up on my Norton Commando for Mark 2’s follow, the carburetors on mine are 34mm. Jetting is fairly typical. Needle jet is a 106, needle is 2A1. Main jet 250, Slide # 3 cutaways, pilot jet 25.
It’s all the other things that make them run right. Other things; the slides are 2 cycle parts, brass with chrome plating. The floats are also 2 cycle parts much larger than four cycle floats. I elected to blend the 34mm size down into the head but it will work if you just blend the size difference in the manifolds. The aluminum bushings at the air entrance of the carb are removed to defeat this circuit. The air cleaners are huge K&N's this requires a notching of the oil tank for clearance but since this mod is at the top of the tank one doesn't loose much oil capacity. . Also these carburetors do not clear one another and require grinding were they touch at the unused idle screw bosses in the casting. This set up needs dampening support without it the carbs will not stay on the rubber spigots but that’s not the worst part. The needles and their jets will wear very soon without dampening. The mark 2 carburetors have a semi flat spot above the intake throat in the casting that must be machined flat. There are two tapped holes on this flat spot. One just makes a piece out of aluminum 3/8 thick by1/2 tall by 1and 3/4 long. Than drill clearance holes to line up with the tapped holes that are already in the body. Than drill and tap 10-24 hole in the middle of the aluminum key for 1/4 shoulder bolt 3/8 long shoulder on the same plane as the mounting screws. Now just install hardware hooks in the frame above the shoulder bolts and use O-rings to suspend and dampen the carb assembly. On a Commando these holes are in the slanted sheet metal gussets that are mid frame use the threaded hooks with nuts and washers. Custom made very light gage throttle and choke cables need to be used. Also use straight cable fittings at the top of the carburetors. I use an after market throttle mechanism for dirt bikes that has the cable coming out parallel to the handle bars and the cable adjusters are underneath the tank near the splitter boxes. Don’t put the adjusters out in the air. Cable routes are very important so take extra time to get this right or you will be constantly fiddling at adjusting later as the system wears in. Start rich and work to lean till she's nice and snappy mine gets 50 MPH and no dead spots or sick rich out of the plugs. Starting needs half choke most of the time with a two block warm up. I had to buy some of the knurled idle adjustment screws and than add small springs to get it to hold idle. All my other bikes will be single carbs don't care about 120 MPH so much any more. Most of these modifications were necessary because my bike has a some what higher compression ratio and a higher balance factor and a Winy Eads’s rose joint head steady. You can't win, you can't brake even, and you can't quit. Norbsa48503
