r75/5 idle adjustment

[TURK]

1973 R75/5 w/ bing 64/32/9 & 10.

When I try to adj idle on the carbs, one at a time to 1000 rpm per Clymers.(pull opposite plug wire and ground extra spark plug ,adj idle to 1000 rpm leaving spark plug in head.)

I put both wires back on and the idle rpm goes to 2500.

This happened before I rebuilt the carbs.

I rebuilt carbs,happens with pulled off throttle cables and cables back on,checked choke position.

Adjusted idle air mix,readjust idle back and forth.

I did this after my first ride 20 miles after rebuild and the bike ran great,smooth all rpm ranges!!

Used fans to cool bike while idling.

valves adj.,timing done.

What am I doing wrong?

Thanks.....Al

 

[mneblett]

What am I doing wrong?

Trying to set a single cylinder to 1000 rpm.

Try setting each to 600-700 rpm as a first shot, then run both cylinders together -- you should be much closer to 1000-1100 idle. Repeat as necessary (lowering the single-cylinder speed a tiny bit each time) to get the idle down to 1000 rpm with both cylinders firing.

Or, do as I (and others) do: Don't use the spark shorting method.

Vacuum balancing (short version): Ensure there's enough slack in the throttle cables that they can't influence the idle, then use a vacuum gauge to adjust the throttle stop screws and idle jet screws to obtain balance at the desired idle rpm. A few back-and-forth iterations to get all four screws set for a balanced idle at teh desired rpm, and you're done.

Be sure to (i) have the bike fully warm (from a road ride, not just sitting in neutral idling -- need to get engine heat back to the carbs, which are quite temperature senstuve); (ii) run a fan in front of the bike while doing this to prevent overheating, and (iii) don't take forever -- if the bike is getting too hot after a couple minutes, shut down, let it cool a bit (back to normal operating temp) and start again.

 

[bikerfish1100]

your starting idle is way too high.
my method is to do adjust side with the grounded plug on the other. set idle high, and then adjust idle air mix to get fastest/smoothest idle (i'm old school, and just do that by ear). once i have that, i turn idle down to where it will just barely run on that one cylinder, shut it down, and then do the same on the other. each cylinder is probably running at ~500-600 rpm when solo.

 

[ebeeby]

trying to set a single cylinder to 1000 rpm.

Try setting each to 600-700 rpm as a first shot, then run both cylinders together -- you should be much closer to 1000-1100 idle. Repeat as necessary (lowering the single-cylinder speed a tiny bit each time) to get the idle down to 1000 rpm with both cylinders firing.

Or, do as i (and others) do: Don't use the spark shorting method.

Vacuum balancing (short version): Ensure there's enough slack in the throttle cables that they can't influence the idle, then use a vacuum gauge to adjust the throttle stop screws and idle jet screws to obtain balance at the desired idle rpm. A few back-and-forth iterations to get all four screws set for a balanced idle at teh desired rpm, and you're done.

Be sure to (i) have the bike fully warm (from a road ride, not just sitting in neutral idling -- need to get engine heat back to the carbs, which are quite temperature senstuve); (ii) run a fan in front of the bike while doing this to prevent overheating, and (iii) don't take forever -- if the bike is getting too hot after a couple minutes, shut down, let it cool a bit (back to normal operating temp) and start again.

+1

 

[20774]

There's a difference in pulling the spark plug cap and shorting the plug. While they accomplish the same thing...letting one cylinder run on its own...pulling the cap and not allowing the spark energy to find its way to ground can be bad for your ignition. More so for a bike with electronic ignition, even aftermarket, but it can also have detrimental effects on a points ignition set up. It has to with possible damage to the coils. So, don't pull the plugs again...read Snowbum's description for plug shorting or go to something like the TwinMax or the $4 manometer.

 

[bikerfish1100]

i pull plug wire, install a spare sparkyplug into the cap, and ground that plug to the cylinder. works like a charm on my points ignition system bike(s).

 

[20774]

i pull plug wire, install a spare sparky plug into the cap, and ground that plug to the cylinder. works like a charm on my points ignition system bike(s).

True...a little hard to do during the dynamic process of carb synch where you're going back and forth between cylinders making tweaks to the settings.

 

[HP1BMW]

Carbs

Check to be sure that you put the carb choke assembly back on properly, they can easily be installed 180 degrees out. The small dimple on the choke goes toward the nozzel on the choke cover. I have seen these reversed more than once.

1973 R75/5 w/ bing 64/32/9 & 10.

When I try to adj idle on the carbs, one at a time to 1000 rpm per Clymers.(pull opposite plug wire and ground extra spark plug ,adj idle to 1000 rpm leaving spark plug in head.)

I put both wires back on and the idle rpm goes to 2500.

This happened before I rebuilt the carbs.

I rebuilt carbs,happens with pulled off throttle cables and cables back on,checked choke position.

Adjusted idle air mix,readjust idle back and forth.

I did this after my first ride 20 miles after rebuild and the bike ran great,smooth all rpm ranges!!

Used fans to cool bike while idling.

valves adj.,timing done.

What am I doing wrong?

Thanks.....Al