Carburator Rebuilding

When I took my 1970 Rokon to the show at Metropolis, Illinois we (Dad and I) realized something was wrong with it. The bike ran fine at high speed but it wouldn’t idle. We tried running carburetor cleaner through it but it didn’t work. Finally my dad decided something was wrong with the low speed idle bypass valve. He decided that we needed to completely rebuild the carburetor.

First off this two-stroke carburetor was easy to take off since it is gravity fed and no other accessories like pollution control stuff. I removed the throttle cable, two bolts, and the gas line and it came right off. Next I had to take it apart. I built a box to take it apart in so I wouldn’t lose any of the little screws or pieces. I also had to make sure to put on older clothes so I didn’t get gas on us. First thing I had to do was take the air cleaner off of the carburetor. The screws that held the air cleaner on had safety wire on them so they wouldn’t fall off and down into the engine, the safety wire was also hard to remove. Next I removed the gas line from the carburetor making sure to wipe off excess gas. When I took the carburetor off of the motorcycle, I took it off, intake manifold and all because it was easier. So next I took the intake manifold off. The next thing to come off was the needle jet adjustment screws. First, before removed them I checked to see how they were set. The high speed was set at 1.5 turns and rounded on the end. The low speed was set at 1.25 turns and pointed on the end. So from here on out basically all I did was remove every single screw in the carburetor to dismantle it completely and separate all the metal parts from the non-metal parts for cleaning. Once I separated then, I put all the metal parts into the strainer and had dad put them into a can of carburetor cleaner. This cleaner is very strong and if we would have tried to clean the carburetor assembled the cleaner would have eaten all the rubber and gaskets out of the carburetor.

We purchased a carburetor rebuild kit that included new rubber parts and gaskets. I left the parts in the cleaner over night, took them out the next morning and rinsed them off. The screws and bolts were not completely clean so I put them in a tumbler to finish the cleaning. When I was finally done with the cleaning I got all the parts and set them around me. With all the little parts and screws it was a little overwhelming, but if you look at it one piece then the next it wasn’t too bad. There were no real directions for putting it back together but I did have a diagram to help me. Following the diagram was a little tricky but soon it got easier when the parts got fewer. We got out the new gaskets and things out of the rebuild kit and set the old ones aside. Sometimes it was hard to remember what went where but the diagram helped a lot. I had to remember not to tighten any screws until I was completely done with that section otherwise it might not be set right. Also, if the screws were in a circle I had to screw them down in a star pattern so it was even. Some things the diagram didn’t help you with and you had to try and remember. Like whether the needle with the point went in the high or low speed. Luckily, I wrote it down before I took it apart. Once the carburetor was back together we had to add the gas line and the air cleaner back. I had to take it back to the bike at least once to make sure it was on straight. Another tricky thing I had to do was replace the safety wire on the air cleaner. So there it was back together now all I had to do was put it back on the bike.

When we put the carburetor back on the bike wouldn’t run at all. If we sprayed carb cleaner in the carb it would run on the cleaner, but it wasn’t getting gas. I took the carb apart again and made sure everything was in the right spot and they were. I disassemble the carburetor 2 more times under Dad’s close scrutiny and we couldn’t find anything wrong, except there was no gas getting to the top of the carburetor. Finally we went on the Internet and found a diagram of how the carburetor works. We realized that the carburetor has a built in fuel pump. After the fourth time we figured out there was something wrong with the vacuum in the intake manifold. There was a hole that shouldn’t be there. Evidently when we soaked the intake manifold in carburetor cleaner, what ever they had used as a plug dissolved and opened a hole from the pulse tube into the intake so there was no pulse vacuum to operate the fuel pump in the carburetor, so NO pump NO gas,. NO run. After Dad welded up the hole we smoothed it with a Drimel tool, we put it back on, and it worked great! It started second pull. So my first carburetor rebuild was successful, but we caused another problem, only because there was something wrong with the intake before we started. Dad said that is one problem with working on old vehicles you never know what someone else who worked on it before you did. He said he has wasted lots of time working on old cars when the person before him put it together wrong.

BACK	My First Time Rebuilding a Carburetor By Haley, Junior AACA member


When I took my 1970 Rokon to the show at Metropolis, Illinois we (Dad and I) realized something was wrong with it. The bike ran fine at high speed but it wouldn’t idle. We tried running carburetor cleaner through it but it didn’t work. Finally my dad decided something was wrong with the low speed idle bypass valve. He decided that we needed to completely rebuild the carburetor. First off this two-stroke carburetor was easy to take off since it is gravity fed and no other accessories like pollution control stuff. I removed the throttle cable, two bolts, and the gas line and it came right off. Next I had to take it apart. I built a box to take it apart in so I wouldn’t lose any of the little screws or pieces. I also had to make sure to put on older clothes so I didn’t get gas on us. First thing I had to do was take the air cleaner off of the carburetor. The screws that held the air cleaner on had safety wire on them so they wouldn’t fall off and down into the engine, the safety wire was also hard to remove. Next I removed the gas line from the carburetor making sure to wipe off excess gas. When I took the carburetor off of the motorcycle, I took it off, intake manifold and all because it was easier. So next I took the intake manifold off. The next thing to come off was the needle jet adjustment screws. First, before removed them I checked to see how they were set. The high speed was set at 1.5 turns and rounded on the end. The low speed was set at 1.25 turns and pointed on the end. So from here on out basically all I did was remove every single screw in the carburetor to dismantle it completely and separate all the metal parts from the non-metal parts for cleaning. Once I separated then, I put all the metal parts into the strainer and had dad put them into a can of carburetor cleaner. This cleaner is very strong and if we would have tried to clean the carburetor assembled the cleaner would have eaten all the rubber and gaskets out of the carburetor. We purchased a carburetor rebuild kit that included new rubber parts and gaskets. I left the parts in the cleaner over night, took them out the next morning and rinsed them off. The screws and bolts were not completely clean so I put them in a tumbler to finish the cleaning. When I was finally done with the cleaning I got all the parts and set them around me. With all the little parts and screws it was a little overwhelming, but if you look at it one piece then the next it wasn’t too bad. There were no real directions for putting it back together but I did have a diagram to help me. Following the diagram was a little tricky but soon it got easier when the parts got fewer. We got out the new gaskets and things out of the rebuild kit and set the old ones aside. Sometimes it was hard to remember what went where but the diagram helped a lot. I had to remember not to tighten any screws until I was completely done with that section otherwise it might not be set right. Also, if the screws were in a circle I had to screw them down in a star pattern so it was even. Some things the diagram didn’t help you with and you had to try and remember. Like whether the needle with the point went in the high or low speed. Luckily, I wrote it down before I took it apart. Once the carburetor was back together we had to add the gas line and the air cleaner back. I had to take it back to the bike at least once to make sure it was on straight. Another tricky thing I had to do was replace the safety wire on the air cleaner. So there it was back together now all I had to do was put it back on the bike. When we put the carburetor back on the bike wouldn’t run at all. If we sprayed carb cleaner in the carb it would run on the cleaner, but it wasn’t getting gas. I took the carb apart again and made sure everything was in the right spot and they were. I disassemble the carburetor 2 more times under Dad’s close scrutiny and we couldn’t find anything wrong, except there was no gas getting to the top of the carburetor. Finally we went on the Internet and found a diagram of how the carburetor works. We realized that the carburetor has a built in fuel pump. After the fourth time we figured out there was something wrong with the vacuum in the intake manifold. There was a hole that shouldn’t be there. Evidently when we soaked the intake manifold in carburetor cleaner, what ever they had used as a plug dissolved and opened a hole from the pulse tube into the intake so there was no pulse vacuum to operate the fuel pump in the carburetor, so NO pump NO gas,. NO run. After Dad welded up the hole we smoothed it with a Drimel tool, we put it back on, and it worked great! It started second pull. So my first carburetor rebuild was successful, but we caused another problem, only because there was something wrong with the intake before we started. Dad said that is one problem with working on old vehicles you never know what someone else who worked on it before you did. He said he has wasted lots of time working on old cars when the person before him put it together wrong.