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R75/5 Idling High
- Thread starter sloane
- Start date
pglaves
#13338
Recheck the carb adjustments. Then find the air leak.
stevenrankin
Active member
list
What prompted you to change the advance springs?
Check point gap, and if proper, check timing. If timing is correct, then go to carbs.
Did you do any work on them lately? If so, did the problem start afterwards? If you did adjust or work on the carbs, recheck your work.
Check for a vacuum leak as suggested.
Are your throttle cables loose enough to allow the carbs to the idle position? Look online or in a repair manual for starting recommendations as to number of turns for idle mixture screw and other adjustments.
There are a lot of things which can cause a high idle. For tune ups, always remember valves first, points if you have them, timing, second, carbs last.
I must admit, it has been a long time since I had to adjust points and mess with timing on an airhead, but I do remember timing too far advanced at idle can cause a higher rpm. Points opening and closing up from wear, also changes timing advance or retardation.
I don't remember if incorrect timing or improper point gap (leading to improper timing) could cause the idle rpm to reach as high as you are seeing.
Best thing BMW did on the airheads was get rid of the points. St.
What prompted you to change the advance springs?
Check point gap, and if proper, check timing. If timing is correct, then go to carbs.
Did you do any work on them lately? If so, did the problem start afterwards? If you did adjust or work on the carbs, recheck your work.
Check for a vacuum leak as suggested.
Are your throttle cables loose enough to allow the carbs to the idle position? Look online or in a repair manual for starting recommendations as to number of turns for idle mixture screw and other adjustments.
There are a lot of things which can cause a high idle. For tune ups, always remember valves first, points if you have them, timing, second, carbs last.
I must admit, it has been a long time since I had to adjust points and mess with timing on an airhead, but I do remember timing too far advanced at idle can cause a higher rpm. Points opening and closing up from wear, also changes timing advance or retardation.
I don't remember if incorrect timing or improper point gap (leading to improper timing) could cause the idle rpm to reach as high as you are seeing.
Best thing BMW did on the airheads was get rid of the points. St.
pglaves
#13338
My rule of thumb for Airhead high idle is usually correct. Nothing is 100%, but:
If the idle is high and you pull it down by lightly loading the engine in gear, and it stays down it is almost always the advance mechanism sticking, but;
If the idle is high and you pull it down by lightly loading the engine in gear, and it goes right back up it is almost always an air leak.
If the idle is high and you pull it down by lightly loading the engine in gear, and it stays down it is almost always the advance mechanism sticking, but;
If the idle is high and you pull it down by lightly loading the engine in gear, and it goes right back up it is almost always an air leak.
A good way to find air leaks is to use an UNLIT propane bottle that you'd use for plumbing repairs etc. Just open the valve and pass it around the carbs/intake slowly. If the idle speeds up you have found your leak.
Another area on the bings is the choke/enrichner not coming off all the way.
Another area on the bings is the choke/enrichner not coming off all the way.
