exhaust back pressure, or lack of.
#22
05-09-2010, 07:28 PM
Join Date: Apr 2010
Location: West Central Indiana
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#23
05-09-2010, 08:03 PM
It is most likely the original carb for the bike. It is a Keihin butterfly carb, not a CV carb.
CV means Constant Vacuum or Constant Vekocity. It is a more modern and better performing carb. I prefer to stay with the original carb for my bike. Changing is not just a bolt on change - the CV does not fit at either end so adapters are required.
You probably do not need a rebuild kit. Dismantle the carb, clean, inspect; you may need a new float bowl o-ring but if you are careful the one that is in there will still be good. Likewise for the float needle - the old one may very well be better than a new one in a kit.
Here are my carb cleaning notes ...
1. Removing it from the bike should be straight forward. First thing when it is out is to check the pilot screw setting. Turn it all the way in until gently seated counting the number of 1/4 turns; then write this number down; then reset it.
2. I put mine in a vice to remove the screws, and for much of the following work. Wrap in a shop towel; close the vice gently taking extra care with the choke and throttle linkages. The vice is a needed extra pair of hands.
3. You must be very careful handling the float so as to not change the level. You must have the official specs for setting the level as in the FM, and check it, every time you dismantle the carb, as the last thing before putting it back together.
4. The jets are made of brass, a soft metal that is easily damaged. Use an exact correct size screwdriver. I ground a medium flat blade screwdriver down to exact size on my bench grinder to access the slow jet.
5. The general appearance of the inside of the carb is not necessarily a good indication of its condition. It can look spotless and have clogged jets, or look cruddy and have clear jets.
6. Ignore any advice that says to soak or boil the whole carb in carb cleaner. Rather, clean each individual part. Do not allow any solvents to contact any rubber parts [tip of needle, o-ring seal for bowl]
7. Make a list of all of the jets and passages for your carb using the carb manual or the FM for the bike. Then ensure that you can blow either compressed air or carb cleaner thru each one.
8. Remove the pilot screw and clean the parts and the passage. The passage contains in this sequence: pilot screw, spring, washer, o-ring. These are very small parts, especially the washer and o-ring. Usually the spring will easily fall out. One time i thought the spring was not in there because it would not fall out; i obtained a new spring and could not get it in! The technique for removing the washer and o-ring is to use a pipe cleaner: stick it in the hole, twist it around, remove it - you should see the washer and o-ring on the end of the pipe cleaner.
EDIT: the washer and o-ring are part of the pilot screw assembly for 1979 on. They are not in the 1978 and earlier Keihin carbs.
Remember that the purpose of the washer is to protect the o-ring from the spring and you will always get them back in in the correct sequence.
9. Dismantle the accelerator pump assembly noting carefully the sequence and orientation of the parts. Clean and inspect the parts. Replace the diaphragm if it is cracked.
10. Check the float level then carefully put it back together. I personally find it very confusing trying to decide which way to bend the tang if it is not correct. If the fuel level is low is the float high or low? Do i need to bend the tang up or down? On the bench the carb is usually upside down, adding to the confusion. Sort all this out before making an adjustment.
Best to replace the original Phillips screws for the bowl with stainless steel socket head screws.
CV means Constant Vacuum or Constant Vekocity. It is a more modern and better performing carb. I prefer to stay with the original carb for my bike. Changing is not just a bolt on change - the CV does not fit at either end so adapters are required.
You probably do not need a rebuild kit. Dismantle the carb, clean, inspect; you may need a new float bowl o-ring but if you are careful the one that is in there will still be good. Likewise for the float needle - the old one may very well be better than a new one in a kit.
Here are my carb cleaning notes ...
1. Removing it from the bike should be straight forward. First thing when it is out is to check the pilot screw setting. Turn it all the way in until gently seated counting the number of 1/4 turns; then write this number down; then reset it.
2. I put mine in a vice to remove the screws, and for much of the following work. Wrap in a shop towel; close the vice gently taking extra care with the choke and throttle linkages. The vice is a needed extra pair of hands.
3. You must be very careful handling the float so as to not change the level. You must have the official specs for setting the level as in the FM, and check it, every time you dismantle the carb, as the last thing before putting it back together.
4. The jets are made of brass, a soft metal that is easily damaged. Use an exact correct size screwdriver. I ground a medium flat blade screwdriver down to exact size on my bench grinder to access the slow jet.
5. The general appearance of the inside of the carb is not necessarily a good indication of its condition. It can look spotless and have clogged jets, or look cruddy and have clear jets.
6. Ignore any advice that says to soak or boil the whole carb in carb cleaner. Rather, clean each individual part. Do not allow any solvents to contact any rubber parts [tip of needle, o-ring seal for bowl]
7. Make a list of all of the jets and passages for your carb using the carb manual or the FM for the bike. Then ensure that you can blow either compressed air or carb cleaner thru each one.
8. Remove the pilot screw and clean the parts and the passage. The passage contains in this sequence: pilot screw, spring, washer, o-ring. These are very small parts, especially the washer and o-ring. Usually the spring will easily fall out. One time i thought the spring was not in there because it would not fall out; i obtained a new spring and could not get it in! The technique for removing the washer and o-ring is to use a pipe cleaner: stick it in the hole, twist it around, remove it - you should see the washer and o-ring on the end of the pipe cleaner.
EDIT: the washer and o-ring are part of the pilot screw assembly for 1979 on. They are not in the 1978 and earlier Keihin carbs.
Remember that the purpose of the washer is to protect the o-ring from the spring and you will always get them back in in the correct sequence.
9. Dismantle the accelerator pump assembly noting carefully the sequence and orientation of the parts. Clean and inspect the parts. Replace the diaphragm if it is cracked.
10. Check the float level then carefully put it back together. I personally find it very confusing trying to decide which way to bend the tang if it is not correct. If the fuel level is low is the float high or low? Do i need to bend the tang up or down? On the bench the carb is usually upside down, adding to the confusion. Sort all this out before making an adjustment.
Best to replace the original Phillips screws for the bowl with stainless steel socket head screws.
#24
05-09-2010, 10:36 PM
Join Date: Apr 2010
Location: West Central Indiana
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I wanted to get a rebuild kit mainly because the whole kit is just a few dollars more than buying only the accelerator pump kit and then I have everything on hand just in case. I still can't help but feel that accelerator pump isn't working up to snuff. That will be the first thing to replace after I check the timing and the other carb setting that you recommended before.
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