ezridermn
New Member
I am having a problem getting my ’81 Honda 750c to idle below 1500 rpm’s. It will “idle” at 3000 rpm’s but when I dial the idle screw down to reach 1500 rpm’s or so the bike soon sputters and dies.
Other than the idle issue the bike runs great. Full power with no sputters through all rpm’s and gears. If it wasn’t for the idle problem I would say everything from a fuel delivery standpoint is good.
I have searched this site and the rest of the web trying to find an answer to my problem. I found other posts that deal with this same problem and identified a number of things I could try to get the problem solved. However, to this point in time it remains unresolved. (ugh)
Here is some background. I initially decided to clean and rebuild the carbs because the bike would bog down under full throttle. However, if I pushed it pretty hard it would eventually come back to life after several full throttle efforts.
I decided it might be a carb issue so I figured it couldn’t hurt to work the carbs over. Before I took the carbs off the bike it was idling just fine at about 1200 rpm’s.
Please note: I am running K&N pod filters (no airbox) and re-jetted the carbs using the Dynojet Stage 3 kit.
Here is what I have done so far.
• I completely rebuilt the carburetors. Soaked them in Pine Sol and meticulously cleaned every surface and orifice. Used all new K&L components in the rebuild. Note: I did not break the carb bank apart.
• It is at this point I re-jetted using the Dynojet Stage 3 kit.
• I set the pilot screws per the factory manual.
• I dynamically synced the carbs after putting them back on the bike.
• At that point I found the idle problem I described above.
• I checked the throttle to see if it was hanging open. It is not.
• I checked to be sure the choke cable and butterflies were working properly. They are.
• I read a lot about vacuum leaks leading this sort of problem so I bought a new set of carb insulators and installed them. Same idle problem remained after I installed those.
• I tried setting the pilot screws in a number of different positions. From 1 ½ turns out to 3 ½ turns out and adjusted the idle screw each time trying to find the right combination.
• It would idle a little slower (high 2000’s) when I had the pilot screws at 1 ½ turns rather than more turns out which resulted in high rpm’s. The difference was more subtle rather than dramatic.
• I dynamically checked the timing. It is properly timed.
Here are some behaviors that might give you a clue as to what is going on. At cold start I pull the choke fully out and the bike fires right up in just a couple of seconds. However, within 30 seconds or so full choke leads to the engine bogging down and killing.
When cold if I start with the choke fully out and then take the choke off in 30 seconds or so and use the throttle to keep the revs up I can keep it around 1500 rpm’s. After a couple of minutes the bike will idle at 1500 rpm’s without the choke or using the throttle. Everything seems to be as it should be at that time. It will just sit there and idle nicely.
However, if I then take it for a ride by the time I hit the first stop sign the bike is revving over 3000 rpm’s at idle and if I turn the idle screw down to get it to idle at a lower level the engine sputters and dies.
So that’s my story. If you have a suggestion or two on what else I should try to fix this problem I would greatly appreciate hearing it. Thanks in advance for your help!
PS -- Question. What are the symptoms of improperly set pilot screws?
Other than the idle issue the bike runs great. Full power with no sputters through all rpm’s and gears. If it wasn’t for the idle problem I would say everything from a fuel delivery standpoint is good.
I have searched this site and the rest of the web trying to find an answer to my problem. I found other posts that deal with this same problem and identified a number of things I could try to get the problem solved. However, to this point in time it remains unresolved. (ugh)
Here is some background. I initially decided to clean and rebuild the carbs because the bike would bog down under full throttle. However, if I pushed it pretty hard it would eventually come back to life after several full throttle efforts.
I decided it might be a carb issue so I figured it couldn’t hurt to work the carbs over. Before I took the carbs off the bike it was idling just fine at about 1200 rpm’s.
Please note: I am running K&N pod filters (no airbox) and re-jetted the carbs using the Dynojet Stage 3 kit.
Here is what I have done so far.
• I completely rebuilt the carburetors. Soaked them in Pine Sol and meticulously cleaned every surface and orifice. Used all new K&L components in the rebuild. Note: I did not break the carb bank apart.
• It is at this point I re-jetted using the Dynojet Stage 3 kit.
• I set the pilot screws per the factory manual.
• I dynamically synced the carbs after putting them back on the bike.
• At that point I found the idle problem I described above.
• I checked the throttle to see if it was hanging open. It is not.
• I checked to be sure the choke cable and butterflies were working properly. They are.
• I read a lot about vacuum leaks leading this sort of problem so I bought a new set of carb insulators and installed them. Same idle problem remained after I installed those.
• I tried setting the pilot screws in a number of different positions. From 1 ½ turns out to 3 ½ turns out and adjusted the idle screw each time trying to find the right combination.
• It would idle a little slower (high 2000’s) when I had the pilot screws at 1 ½ turns rather than more turns out which resulted in high rpm’s. The difference was more subtle rather than dramatic.
• I dynamically checked the timing. It is properly timed.
Here are some behaviors that might give you a clue as to what is going on. At cold start I pull the choke fully out and the bike fires right up in just a couple of seconds. However, within 30 seconds or so full choke leads to the engine bogging down and killing.
When cold if I start with the choke fully out and then take the choke off in 30 seconds or so and use the throttle to keep the revs up I can keep it around 1500 rpm’s. After a couple of minutes the bike will idle at 1500 rpm’s without the choke or using the throttle. Everything seems to be as it should be at that time. It will just sit there and idle nicely.
However, if I then take it for a ride by the time I hit the first stop sign the bike is revving over 3000 rpm’s at idle and if I turn the idle screw down to get it to idle at a lower level the engine sputters and dies.
So that’s my story. If you have a suggestion or two on what else I should try to fix this problem I would greatly appreciate hearing it. Thanks in advance for your help!
PS -- Question. What are the symptoms of improperly set pilot screws?
