Adjusting Engine Idle

[montmil]

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...

Gonna have to call you on that statement, Barry.

My $5.00 yardstick manometer filled with BMW 7.5 fork oil is quite sensitive to the positions of the Idle Mixture screws. I use the bottom screws to get my vacuum balance and idle set correctly before doing anything else.

US-sold Airheads are set leaner and do require the greater turns out of the mix screw that the Euro bikes. Using the tighter settings will have 'murican owners chasing their tail.

[Luke D.]

Good day Berry, thank you for your quick response.  Sorry if I am not understanding but are you and Montmil saying the opposite thing?  You are saying to adjust the mixture screw (bottom) to the book setting and then hook up the meter and equal them out with the idle "speed" screw (top).  Correct?  And I think Montmil is saying to set the mixture screw (bottom) first, back the idle "speed" screw (top) all of the way out.  Hook up the meter and equal them out with the mixture screw (bottom).  Then adjust the idle after that.  I think I am missing something :-/.  Sorry if you guys are saying the same thing and im just not getting it.  This carb stuff is waaaaaaaay over my head.    I understand what they do and how they do it but I have never really worked with them.  Thank you both/all for your help with my bike.  Have a great day everyone.

[Barry]

Luke,  I was trying not to make this more complicated than it needs to be. I agree with Monte that ideally idle mixture should be set first but to do that you have to have the engine running reasonably well with the idle reasonably balanced otherwise it's simply not going to work. You inevitably end up doing the whole thing several times in order to home in on the best settings. That's why I suggested setting the mixture screws to the book setting and doing the idle and throttle cable balance first before going back to fine tune the idle mixture.  If this fine tuning results in the need for an idle speed correction then you have to do the vacuum balance again with the throttle stop screws and cable adjusters.  

If I'm reading Monte correctly, where we differ is that a manometer can be used to set the idle mixture because within normal limits the mixture screws have no impact or at best very little impact on engine vacuum.

Short of using a proper gas analyser setting the idle mixtures spot on is very difficult and that is good reason to not differ wildly from the book settings. I find the shorting method works well for me as an additional check that the idle mixtures are the same side to side but we are getting too complicated before you have the engine running reasonably well.

How does everyone else set their idle mixture ?

[Luke D.]

Good day everyone.  I know you guys wanted an update on my carb syncing and stuff so here is the dealio.  On Tuesday nights we have a get together of bikes at one of the pubs here in Duluth.  So I toddled over there to see what I could see.  Sure enough there were a couple of Beemer guys there, perfect.  I talked to a couple of them and told them my issues, well my motorcycle issues.    So the older gent went to his bike pulled out a couple of tools and started syncing the carbs.  He had me hold the bike at idle and he adjusted the mixture screw (bottom) and them he tightened up the throttle cables because they were a tab uneven.  Then he messed with the idle speed (top) and got it to purr like a kitten.  It did not hop around and it sat there and idled just about perfectly.  I stayed the for a while and bought both gents a drink (root beer) for their help and talked for a while.  When it was time to leave I fired the bike up and it would not stay running(idling).  Both gents were gone so I headed home and let the bike be.  I headed down to the cities this weekend with it, made some idle speed adjustments (to try and get it to idle) and it wont work.  My left (sitting on the bike) carb was not flat (angled to the side a bit) so I fixed that thinking that may be part of the issue but it did not help.  Once the bike warms up it will idle (most of the time).  when I first bring it out to ride it wont.  Now maybe you are thinking that the bike is cold and therefor wont idle without the choke.  It is stored in my room (basement) every night.  So I am still at a loss with this but will continue to work on it till she works, and of course will keep all you lovely folks  updated as I chug along.  Thanks again for everyone's help and hope you have a great day.

[montmil]

My Airheads live in a Texas garage where indoor temps can get rather toasty. Even so, the bikes require a few minutes running on the enrichener circuit before they'll idle properly. A couple minutes riding and gradually pulling off the "choke" gets both of us happy.

[donbmw]

My bikes are like Monte's. Need enrichment on for a couple of minutes before they will idle. After carb work set everything to the basic settings then go for a ride about 30 minutes then set carbs.

Don

[Luke D.]

Hey everyone!  Thank you Montmil and donbmw for the help/input.  I have some new stuff going on.  Once the bike warms up it will idle kind of fine but it was starting to die so I gave it some gas and it started popping.  Now last week when the gent adjusted my carbs and got them sync'd my left (sitting on bike) carb was not level.  This weekend I leveled the carb.  Could that have mess up the sync because the carbs were set for a not so correct carb?  I hope this makes sence because I know im not the best at explaining things.  Thanks for all of your help.  Have a great night/day.

[Barry]

Now last week when the gent adjusted my carbs and got them sync'd my left (sitting on bike) carb was not level.This weekend I leveled the carb.Could that have mess up the sync because the carbs were set for a not so correct carb?  

No, a slight imclination of the carb won't have any materiall effect on the carb tuning. Folks are divided on whether the carbs should be dead level or inclined in at the top slightly to provide a smoother throttle cable run.

If it idles ok when fully warm then there is not much amiss.  At any time before it's fully warmed up you can't necessarily expect it to idle or run smoothyly at very low revs without holding it on the throttle. Even in the middle of summer mine won't idle unassted until it's done 3 miles and then it idles at 800 RPM instead of 1000 RPM. That is as it should be if the idle mixture is set correctly i.e. not too rich.

If you change the carbs settings so that it does idle nicely before it's fully warmed up it will then idle too fast when it is fully warm.

[Luke D.]

Good day all, I know its been awhile.  I am still having issues with my bike idleing but I had an idea.  Since the US models had the that funky air stuff that comes out the front of the jugs and goes into the air box.  So our (US) bikes have one jet (size wise).  The European bikes do not have this air system so they must have a different size jets.  If I take the extra air stuff off my bike (US) do I need to change the jet sizes?  The bike is idleing at first start up just fine but once she warms up it will idle and die.  I have to keep the clutch in and the throttle on.  I did hook up a colortune spark plug.  It is kinda clear so you can see what color the spark is.  My left side is the correct blue (with alittle throttle)  the right side however, I cant seem to get the right color.  Also the spark is on the outside of the plug instead of inside the cylider.  Still trying to figure that one out.  I thought you guys would like to know my (slow slow slow) progress.  My real question is about the jets?  Thanks all, have a great day/night.

[Barry]

No experience with emissions plumbing but if I had it on my bike I'd remove it without question. Don't know if it requires a jetting change but I doubt it will. In any case that would have no impact on the ability to set a good idle mixture.

If you are still experiencing the idle speed falling away when hot then I'd go back to the first basic step in carb tuning which is to ensure the float levels are correct as everything else is a waste of time until that is confirmed. Bing floats are known to be sinkers when they get old so it might be worth weighing both of them to make sure they are the same weight and not too heavy.  Last time I had the same symptoms of idle speed falling off  it was one float that was 15 or 16 grams and close to a sinker.

[montmil]

Removing the Pulse Air Injection System will not require a jetting change. This entire POS plumbing came about due to California enacting their oft times bizzare enviro laws. As an example, one spin off is that lawnmower manufacturers have to produce special Cali units that are sold out there. To avoid the possibility of some of their motorcycles running into legal issues if being resold in California, BMW Motoradd made ALL their products with the bathroom plumbing.

Both my R65s have been through rehab treatments. Your exhaust valves and seats will thank you. Here's a DIY article with a list of the bits needed:

http://www.ibmwr.org/r-tech/airheads/plug_fresh_air.shtml

[Luke D.]

Good day all,  Thank you Berry and Montmil for the information and help.  Montmil, I took off the pulse air system and plugged all of the holes with the correct items that were in the link you sent me earlier in this thread.  I was super excited to get it out but must not have tightened everything down enough because about a mile from my house one of the exhaust plugs fell out.    I had bought the two oil drain plugs for it and they looked great.  Lost the darn plug.   found the crush washer though.  I ended up taking the part that originally went in there and found a bolt that fit the hole and welded the bolt in and then tightened that on with the crush washer.  Works great and it has not fallen out.  Berry, thank you for your input too.  I will open up the carbs and check them out.  I did notice that when I opened them earlier this year one of them was brownish looking.  I had the carbs gone though a couple of years ago by the BMW mechanic that worked on it when my uncle bought it back in 82  Pretty cool.  It ran flawless after that and now..... not so much.  I will check that out the floats though.  I'll have to find something to weigh them with though.  Do you by chance know how much a float is supposed to weigh?  I will check my books when I get home.  Thanks again for all your help.  Have a great day eh.

[Barry]

Last year I installed new float sourced from Motobins and  weighed them on super accurate lab scales at 12.495 Grams.  Call it 12.5 grams. That was lighter than I expected as 13 grams is reckoned to be the standard weight.

You can run floats at 13 grams 14 grams 15 grams or even  in a pinch at 16 grams but you are definitely on the slippery slope beyond 15 grams. Allowances have to be made for the extra weight because The method of setting floats parallel or setting fuel level measured in a float bowl at 24mm is fundamentally flawed for anything other than new floats or floats known to weigh the same as new.

The actual operational fuel level which has an impact on the mixture is close to the top front edge of the bowl due to displacement of the fuel by the submerged part of the floats, castings and jets. Because of differences in buoyancy,  setting float levels by depth of fuel in the bowl will give different  operational fuel levels depending on float weight just like old Archimedes in the bath.

To give a specific  example:

You have one new float weighing 12.5 grams adjusted to give 24mm of fuel in the float bowl.

You have another old float weighing 15 Grams adjusted to give 24mm of fuel in the float bowl.

Place the new float in the float bowl and it will displace the 24mm of fuel increasing the level to within a few mm of the top edge of the bowl.

Place the old float in the other bowl and because of it's reduced buoyancy it will displace more fuel increasing the operational level by several mm beyond the level that the new float did. When the bowl is then offered up to the carb the difference is increased even further and  that difference in fuel level will have a big impact on mixture strength .

I’m not saying you can’t use old floats that weigh more than new ones. Even at 16 grams they do not sink and produce an incontinent carb (at 17+ Grams  they do). What I am saying is you can’t judge the operational fuel level by measuring the depth of fuel in the bowl at the normal figure. The 24mm often quoted is only valid for new floats and would need to be substantially reduced for heavier floats. If using the parallel method then old floats have to ne set lower than parallel by several mm.

To set up old floats by the depth of fuel in the bowl method, as an approximation I reduce the 24mm figure by 1mm for every additional gram that the float weighed above new ones.  So I would adjust a 16 gram float to give to 19.5mmmm in the bowl.

What I concluded after a fair bit of  experimentation with floats is that to stand a chance of getting them right you either have to fit new floats or you have to accurately weigh them and then make allowances in setting them up. I really don't see any other option particularly as a pair of old floats are not likely to weigh the same as each other.

[tunnelrider]

I had that same high rev in neutral idle problem too when I bought it but it came right pretty quick by adjusting the idle stop screws so the cylinders are firing equally, often noticed by listening to the exhausts from behind the bike.  There's a great article in the FAQ section on this forum titled Carb Tuning By Ear I think
If you haven't already, have a play around with the idle mixture screws too and you'll learn how to balance your carbs after doing a tune up. I found that 1100rpm suits my high mileage '85 R65 to get a steady idle...