airhead balancing act

[noz]

ok what am i doing wrong with balancing the carbs.

i'm going for a ride to warm her up, gettting the idle in balance .1000
then once that fine i balancing the throttle at 1500-2000.

She seems fine all nicely in balance.
then nexdt day i go for a ride even when i broght it back after about 20 mins still lumpy idle at 700 odd rpm like it wasnt warm. am i balancing it wrong?

using home made manometer to balance it.

someone help making it hard to ride.

[tres]

I think the problem is that the idle jets are still not balanced. The idle jet is balanced via the screw underneath the exit port of the carb. When balancing at 1.5k - 2k, you're balancing the mains. So you could have an excellent ride as soon as you start opening the throttle, but chortle and die as soon as you take your hand off the throttle.

[noz]

i start out by balancing the idle using the srew adustment underneath with no problem .

then move onto the cable to see the load balance and get that so there no difference.
if i took it for another right there and then it would be fine.

[borg]

The screw "under" the carbs is the idle mixture screw, depending on your model these will be some where between 1 and 2 full turns out from seated to start with. Once the bike is warm you fine tune these by ear until you get the fastest/smoothest idle going on that cylinder. Once both sides are smooth then adjust the idle speed using the screw for that, it's the one you access from the top, you'll see it working on a small lever arm. Once your idle is set then you can work on part/full throttle adjustments which is really a matter of adjusting the amount of freeplay in the cable sheath-to-carb distance until both carbs are coming off idle at the same time.

I highly recommend getting the Bing manual. Also make sure everything else is good, choke is closing all the way, no air leaks etc

Steve

[tres]

Sometimes it's helpful to take nothing for granted. If you haven't taken them apart & verified that the needle positions are correct & that everything is clean enough to function correctly, it might help.

I've heard stories of people who opened up their Bings to find that a PO created mess that would make it impossible to ever balance.

[tres]

I recently had a very similar issue.

I had installed some Bings for an R65 that I had put R100 jets in. I changed the slide out, & changed needle position on the main & changed the idle jet to the same size used on a 100/7. I cleaned everything, installed new o-rings, diaphragms & floats. Pretty much brand new.

The idle would work well during startup, but that's because the Boyer electronic ignition keeps the engine up above 1k for the first few minutes. Once things got warmed up, the Boyer wanted to drop down to 600 - 800 rpm.

And once that happened, there was no way to keep that engine running at idle until it was completely warmed up (and even then, I still had issues sometimes). I really hated trying to finesse that throttle every time I needed to slow or stop for the first 10 miles.

I had recently changed out the flywheel/clutch/transmission to a post 1981 version -- much lighter & so I thought that the Boyer just relied on the heavier flywheel. I changed to another ignition only to find the same problem still existed.

So long story short, I put some carbs intended for an r100 onto the bike & never had that problem again. Now it's like brand new.

Probably not relevant for you or 99% of everyone else out there, but if you do have carbs that weren't intended for your bike, it may be the problem. There are some press-fit parts that just can't be changed out.

[Renner]

some confusion regarding idle mixture vs. idle speed adjustment screws because the year model is not specified.

/5s have idle mix & adjust at the bottom and close together. Later model carbs the idle speed adjustment moved to the top.

What bike is this and are the carbs original equipment for that year?

When making adjustments (I like the manometer too) are you running a sizeable fan in front of the cylinders. Also some slack in the cables at idle?

just checking.

Points ignition?

I find if the idle is set a little high the advance mechanism can come into play, advance increases and idle comes up further increasing advance...

Maybe try 800 rpm idle.

[jtwind]

Here is the rundown of the carb sync procedure. It's the same steps no matter what tool you are using, twinmax, manometer, plug shorting, vaccuum gauges, etc.

http://wisconsin.airheads.org/content/view/33/51/

[noz]

thanks everyone for helping.

Rite the bike is a 76 r75/7 with origional 64/32/13 and 14 carbs
i have rebuilt the carbs including all orings new floats and needles. checked for leaks and the choke systems has been checked for orientation and operation. Also butteryfly marked before dissasemble. reinstalled as good and i can get it for no light around it.

the carbs have the idle adjustment screw underneath aswell as mixture
mixture set at 3/4 out.

i have read the balancing guide and it doesnt say to adjust the mixture any more than setting to spec.

i have retro fitted the later carb springs to stop the slides hanging up.

i could well be getting the slack wrong.

i have been litteraly getting the balance of idle of 1000rpm with the cables not afftecting it them setting the cables. in balance so they dont affect the 1000rpm and balance clean on the manometer with slight slack on the throttle.

have just been out for another ride mid way through there it was fine brought it back and lumpy idle again.

[noz]

hang on maybe it me with the setting of the mixture, and finding the sweet spot for it and not setting it for the sweet spot before setting the idle after that.

would this cause these irregularities?

[Xcuvator]

By any chance, when you have the lumpy idle, do you have the bike in gear with the clutch pulled or is the bike in nuetral? I had a bike that would slow down at idle when warm with the clutch pulled.

[borg]

Originally Posted by noz

hang on maybe it me with the setting of the mixture, and finding the sweet spot for it and not setting it for the sweet spot before setting the idle after that.

would this cause these irregularities?

You do have to chase these two around the block a few times before finding the sweet spot.

Steve

[Prairie Beemer]

Make sure there's a little slack in your throttle and choke cables. Check for any intake leak. Carb floats moving freely? Since you're in there, why not clean the idle jets?

[rufusswan]

Originally Posted by noz

i have read the balancing guide and it doesnt say to adjust the mixture any more than setting to spec.

That is the starting point. You must get the bike to idle and run so you can ride it for 15 minutes. Then you can start to chase mix/idle speed around as borg said until you are happy.

Originally Posted by noz

i have retro fitted the later carb springs to stop the slides hanging up.

I assume you mean throttle return springs which are to make sure the butterfly closes on the idle stop. Your slides should not 'hang up'. When on the bench they should smoothly go from end to end when you turn the carbs over, or suck/blow into the vacuum hole in the carb throat.

[P B G]

Originally Posted by rufusswan

I assume you mean throttle return springs which are to make sure the butterfly closes on the idle stop. Your slides should not 'hang up'. When on the bench they should smoothly go from end to end when you turn the carbs over, or suck/blow into the vacuum hole in the carb throat.

What he means are the springs above the slides, those big loosely coiled things. Some carbs didn't have them oem, others do. They shouldn't hang up, but some might w/o springs sometimes.

Every spring before I do this job I make sure of a few things.

New air filter,
Valve adjustment,
Ignition system check up.

THEN I move onto the carb balancing. Its tempting to put off these things and tune the carbs so you can ride, then later on you decide you'll check the valves and change the air filter and such. Do it first. Its better.