Adjusting Engine Idle

[Luke D.]

Good day all.  After working on the bike during the winter, she does not want to stay running.  All I did over the winter was change the valve cover gaskets, take off the air pulse system, and pull the bowls off to make sure everything down there was okay.  I got it fired up no problemo, went and throw some race gas in it and when I got to the station she died.  Got home no problem and tried to adjust the idle a little bit.  Will run for a short time then idle down and die.  Could you help me with the procedure as to how to adjust the idle up and make it run synced up?  Thank you all for your time.  Have a great day.

[Bob_Roller]

Sounds like you may have debris in the carb causing problems .
The first thing  would do, is to remove the float bowls and blow through the small metering jet, that feeds the cavity that the small diameter brass tube fits into .
You may want to remove the carbs and use carb cleaner to clear the drilled passageways in the carb body .
I had numerous problems with my '82 LS, clogging the ports and passageways, the auto parts store sold me vacuum hose, instead of fuel line, it was mismarked by the manufacturer .
If your fuel line is old, may be a good time to replace it .

[Luke D.]

Thank you Bob Roller for your input.  If some of the ports are clogged would the bike run fine when using the throttle and just not stay running?

[montmil]

The Bing CV carbs can be a bit tricky, especially getting the idle to where you want it. BTW, to keep oil pumping to the timing chain chest, idle speed should be between 800-1100 rpm.

Here's an easy suggestion: Take the bike for a good warm-up ride. Maybe 20+ miles depending on ambient air temps.

Back off the Idle Adjust Screws to where they are just off the lever. Note the position of the Idle Mixture Screws. Mark that screw slot position with a pencil so you can always return to your original location.

Adjust both screws to where the idle is to your specification. Turn no more than a screwdriver's blade thickness. Blip the throttle and allow the engine speed to settle. Too high? Go the other direction. Shoot for that 800 number, minimum.

Go for another ride and take along your screwdriver. If the idle needs to be a bit higher, use the Idle Adjust Screws to adjust.

This is all dependent on your carbs being clean and free flowing.

Be advised that the valve lash, bean can advance weights and timing also play a part in getting your idle to its happy place.

[Luke D.]

Montmil, thank you for you help.  What about the little brass screw on the bottom of the carb?  Its next to the little (brown on mine) vaccum hose.  At the beamer meet up here at the Minnesota State Fair, on of the really smart air head guy helped me even out the carbs and made it run right(right rpm and not dieing).  He adjusted the top (idle screw?) and then the bottom brass screw.  Thanks again.

[nhmaf]

It is also important to know that your valve clearance is correct before you go about synching the carbs and setting the idle speed.   It is possible / likely that you have some debris clogging the idle jet, which would cause the engine to not idle and stay running unless you keep twisting the throttle to pump some gas in to the intake stream.   If you removed the carb(s) it might be that you didn't get the carb back onto the rubber boot securely and/or you have an air leak between the carb and the cylinder head.

[Barry]

The adjustment screw on the bottom of the carb is the idle mixture screw which weakens the mixture when you turn it in and richens the mixture when you turn it out. There is a base setting which is usually 1/2 turn out from being turned in until it gently seats.  Besides making sure the carbs are clean you should check the float levels are correct.

[Luca]

There is a base setting which is usually 1/2 turn out from being turned in until it gently seats

small detail, but on the US bikes the base setting is further out.  Something like 1 to 1-1/2 turns.

I remember wondering why my bike idled like crap at the base setting and required so much extra juice... it was because we're jetted leaner than the European bikes.

[Luke D.]

Sorry its taken awhile to say thanks to all of your help.  I finally had a chance to get the carbs apart and cleaned up.  It idles just fine now (once I got it to the right setting)  But now once it warms up and I go above 3000 RPMs and pull the clutch (shift/slowing down) it will stay at 3000.  I read that it may be the bean can stuck on advance, or the carbs are not synced up, a couple other things.  My grandpa let me borrow his carb sync tool and that is my next step.  I have a question about when you are syncing the carbs what do you adjust to make the sync up?  The idle screw, air/fuel mixture screw?  I did put the air/fuel mixture screw to about 1- 1 1/4 turns from bottom. (Thank you Luca)  Also after the engine has been rev'd up for awhile (freeway/highway) when I put the clutch in it goes down to the idle set and sometimes dies, but when I am at lower speeds (in town) it idles just fine. Could that be because the carbs are not synced?  Thank you all again for your help with my issues.  You are all a great help.  Have a great day.

[montmil]

The initial step in syncing the twin Bings, and a very important one, is to have the engine at full operating temperature. With the temps in MN right now, that could mean a ride of 20-25 miles depending on ambient temps.

Best to have your garage prepped for the syncing drill prior to your warm up ride. The engine must be at normal op temps. Have a fan handy to blow some cooling air across the engine if you spend more than 5-7 minutes doing the manometer work. Avoid overheating. Stop if you must to allow a short cool down.

Carb cables should have about 2mm of freeplay at the carb's cable adjust screws and lock nuts. This is important. The idle adjust screws -those on the top of the carbs- should be just off the throttle levers. Not touching but just clear.

With the manometer lines attached to the vacuum take off points on the bottom of the carbs, adjust the idle air mixture screws -those on the bottom of the carb body- to equal readings on the manometer. Get the idle up to a minimum, balanced rpm -where the engine is not stumbling- using only the idle air screws. You want to keep oil squirting -and that's exactly what it does- on the timing chain and gears. Blip the throttle occasionally after each adjustment and permit the idle to re-establish itself.

After vacuum levels are equal, you can use the idle speed screws up top to set a slightly faster idle, if desired.

Balancing the throttle cables is another step but only after you have balanced the Bings.

Keep us posted on your efforts and success.

[Barry]

I have a question about when you are syncing the carbs what do you adjust to make the sync up?The idle screw, air/fuel mixture screw?I did put the air/fuel mixture screw to about 1- 1 1/4 turns from bottom. (Thank you Luca)Also after the engine has been rev'd up for awhile (freeway/highway) when I put the clutch in it goes down to the idle set and sometimes dies, but when I am at lower speeds (in town) it idles just fine. Could that be because the carbs are not synced?  

Your sync tool generally won't respond to changes in idle mixture screws and they should be set separately. The base setting for turns out will depend on what size idle jets are fitted. Euro bikes have 45's and US bikes I think have 40's so that would explain the need for more turns out but I'm surprised it's as much as 1 - 1 1/4 turns.  

As far as the idle hang up is concerned it's nearly always carb related rather than a sticking advance so eliminate carbs as the cause first before diving in to the bean can.

If the mixture screws happen to be set grossly too rich or grossly too weak it will reduce the idle speed and the throttle stops then have to be screwed further in to compensate and bring the idle speed back up. These are the conditions that cause carb related idle hang up because the throttle plate is now open further than it should be at idle which starts to flow mixture from the transition ports. Therefore in tuning the carbs the object is always to achieve the correct idle speed using the minimum possible idle stop screw setting.  And that means you should always set the mixture screws first.  From 1 1/4 turns out I'd be inclined to try turning them in until the idle speed starts to fall or stumble and then out again only as far as is needed to restore a smooth idle. Any further out will be richer than necessary at least when the engine is fully warmed up.

[Luke D.]

Good day all, hope you are all having great days.  Alrighty here is the scoop, I have an old Manometer (grandpas tools  ) so I took my bike for about a 10-15 mile ride on the way home from work. Temp was about 60ish maybe a little more.  I got back and hooked up the manometer and the carbs a tad bit off (inch or so on the meter).  Well first I checked to make sure there was a little bit of play in the throttle cables (Montmil) that was good.  I adjusted the idle screws (on top) so they were just off the throttle piece.  It would not start.  I turned the idle screws down a bit (enough to get the bike to idle).  Then I hooked up the meter and they were kind of close, the right side (sitting on bike) was at 4 and the left side was at 6.  I made the low side richer but the meter did not show any change.  I believe Berry said that the meter would not change based on the idle mixture being changed.  ( I could be mistaken)  So I put the mixture screws (bottom) back to the book setting (3/4 turn from bottomed) and that did not work so I put them up to 1 turn from bottom.  Now I am just lost on how this is supposed to work.  Do I set the idle mixture (bottom) to the book/ 1-1.5 turns first or do I set the idle (top) first and then adjust the mixture (bottom)?  I am really confused on all of this stuff.  Thank you guys for all your help, and im sure if I knew anything about carbs it would help but Im at a loss.  Again thank you guys lots and lots.  Have a great evening.

[montmil]

Hey, Luke-  The Idle Air Mixture screws are the first item of business. Also, the US-sold Airheads were jetted leaner than the Euro models due to US Bubmint's clean air regs; so try 1,25-1,50 turns out on the Idle Air screws. Also, take them out and make sure they are clear n' clean. Rubber o-rings can be problematic if they are buggered up.

I'm wondering about Grandpa's "old" manometer. Can you confirm it is functional? You should definitely see changes in vacuum readings on the manometer with even the slightest movement of the Idle Air screws.

Leave the Idle Adjust screws off the butterfly arms until the mixture adjustments match.

There may be some carb disassembly and cleaning in your future...

[Luke D.]

Morning all, thank you Montmil for responding so quick.  Frist off no I can not tell if the manometer is working.  The silver stuff goes up and down very rapidly (vacuum from the cylinder firing, I think) and it seemed to do little changes when adjusting the idle mixture screw(bottom) but  they would not equal out.  The closer I got to equal the crappier the bike ran.  I might be doing something wrong though (most likely).  So the next thing are the idle adjust screws (top).  If I don't have some kind of preset if you will on the butterflies it wont run.  By the way why do they call them butterflies :-?? I will try and take the mixture screws out to see if they are clean before I try this next and then I will adjust them out to 1.25-1.5 turns. Thank you again for all of your help.  Have a great day.

[Barry]

As I said above your sync tool won't respond properly to changes in idle mixture screws. It will however respond to the smallest adjustment of the throttle stop screws.

To begin with I would put the mixture screws back to the book setting. I have to say I've never seen as much as 1.5 turns out for an R65 regardless of the size of the idle jet but do whatever the book says.  Then use the sync tool to balance the carbs using the throttle stop screws at idle. Once you have them balanced at idle do them again with a small throttle opening of  2-3000 RPM using the cable adjusters on the top of the carbs to make sure both carbs are opening up together.

That should give you a reasonably smooth running engine and you can then go back and fine tune the mixture screws by ear if necessary. I generally turn the mixture screws in from the book setting until you hear the first indication of the revs dropping off and then turn them back out again only enough to restore the idle speed.
The other method is to turn them in until the revs drop and the  out again until the revs drop noting the mixture screw settings for each position so that you can then set them in the middle of the two extremes.