Throttle cable adjustment

[fermin]

I  am having a hard time adjustying throttle cables while attempting to synchonize the carburetors on the '84 R65.  The main problem is that in order to get the recommended free play at each of the carburetors I need to have slack at the throttle side.  This leaves 'free play' at the throttle wich I dont particularly like.  If I take up this free play at the cable adjuster then by default it removes the slack at the carburetor side.

The other issue is that once I get about 1/16" free play at the carburetors at idle, there is no way I can get it at 1500 rpm,unless I increase the free play substantially at idle and this leaves a very 'loose' throttle.

It may be the first cable (throttle to cable adjuster) is worn as this cable has not been replaced during the restoration process.

Any suggestions??

[Mike V]

fermin,

If I understand you correctly...first make sure your throttle gears at the handle perch are lined-up at the index marks and are in good shape and your cable splitters and cables are in proper order and condition.  No kinks, frazzles, or binds. A little lubrication at the cable barrels where they attach to the carb may help things in the long run for consistency.

On a completely warmed-up bike (±10-15 mile ride) get your idle circuit adjusted first in both mixture and rpm with plenty of slack in the throttle cable sheath at the carb attachment.  Make sure your throttle cables are not affecting the rpm's setting.  This should only be done with the idle speed screws at the carb and shaft flange - not with the cable.  Once you get the idle settings (speed & mixture) set where you like them, adjust the cable sheaths so there is >1/16" of free play or slack.  The cables should not affect your idle settings.  Then adjust your carb balance at the cables.  Takes a little fiddling.  If I want less cable free play, I will turn the cable adjusters at the carb "up" or counterclockwise to lesson the cable slack during the balance process.  You should always have a slight amount of free play in the cables for many reasons.  It's pretty difficult to adjust all the free play out of the cables and not have it affect your idle and/or operation - but you can limit it with some work.  My suggestion would be to leave a small amount of free play in your cables.

[Bob_Roller]

There is an adjustment at the 'input' side of the cable splitter under the fuel tank, with the two cables at the carbs slack, turn the  aduster at the splitter, to get just about 1/32nd to 1/16th inches free play on the outer conduit of the cable going to the throttle grip, tighten the lock nut .

Adjust the cables at each carb the same way, the swaged end of the cable conduit should just move at best 1/32nd to 1/16th inches, about 2 mm .

You may have to adjust the cables after doing a carb synchronization .

The usual method is to have the engine running, open the throttle to  say around 3500 rpm, then adjust the cables to get proper synchronization at about half throttle, tighten the lock nuts .

Hope this helped you out, instead of confusing you any more  !!!!

[montmil]

When adjusting the idle rpm using the mixture screws, the idle screw must be off the idle screw stop. Otherwise, the mixture screw tweaking will be a nightmare as any idle screw pressure on the idle stop contact will prevent correctly setting idle rpms.

As mentioned, throttle cables should be well slackened during mixture then idle screw adjustments.

It's back n' forth, back n' forth, ad infinitum.

A manometer is very helpful. Synchronizing the throttle cables at approx 3500 rpm will require turning one throttle cable adjuster out while the other turns in. You're looking for a small amount of slack in the cables with the engine at idle revs of 900-1100 rpm.

Here's what I consider to be one of the best carb synchro articles ever written.
http://www.airheads.org/content/view/183/98/

Monte

[fermin]

Thanks for the comments.  I think I can see what I was doing wrong, no problem adjusting the idle , its the cable synchronizing that I was messing up.  Will try this tomorrow armed with a $1 manometer and a $300 digital vac gauge I borrowed from work.

Once its warmed up it behaves, but until that point I get consistent stalls with a muffled "pop" noise.  This is especially true upon starting.  Any other items I should be checking?

[montmil]

Try returning the $1.00 manometer and keeping the three C-note tool. Think they'll notice?

"Any other items I should be checking?"  I dunno. Maybe the diaphragms? Check 'em for pin holes or small tears. If you've been inside the Bings, you've probably done this already.

Monte

[Ed Miller]

"The other issue is that once I get about 1/16" free play at the carburetors at idle, there is no way I can get it at 1500 rpm,unless I increase the free play substantially at idle and this leaves a very 'loose' throttle."

There isn't supposed to be any free play in the throttle cables at 1500 rpms, if I understand you right.  Just at idle.  Or am I confused?

[Barry]

Will try this tomorrow armed with a $1 manometer and a $300 digital vac gauge I borrowed from work.
 

It will be interesting to hear which is the best tool for the job.

Few tools are as sensitive and well damped as the home made manometer filled with auto transmission fluid.



Many guides to carb balancing suggest having lots of extra free play in the cables when setting the idle balance. I don't subscribe to this and have never done it. I think it creates work, disturbs the cable balance of a bike that is probably already very close and it confuses people unnecessarily.

Yes there should be some minimal free play in both cables 1/16" or 1/8" whatever seems comfortable in use. If everything is lubricated and in good order no additional free play is needed to set the idle balance and anyway what's the point when your going to adjust back to 1/16" or whatever in actual use.
If the idle vacuum won't balance nicely with the amount of free play that you are going to have when actually riding the bike then something needs fixing and it's a futile exercise trying to set them up with more free play.

Does the logic of that make sense at least when doing the tiny fractions of a turn adjustments needed for a routine balance of a bike that is already running reasonably well ?

[montmil]

...There isn't supposed to be any free play in the throttle cables at 1500 rpms, if I understand you right.  Just at idle.  Or am I confused?

No free play other than at idle revs. The slack at idle takes cable adjustment out of the carb tuning process while setting idle mixture screw and the idle stop screw.

Monte