Trouble w/ idle that works for hot and cold motor

[Mucci]

I’ve had this ‘83 R65 for a while now and I’ve never been able to get the idle perfected.

I just gave the carbs an ultrasonic clean and rebuild, sync’d them up, and set all the cable slack to spec.

When tuning the mixture screws I set the idle to 800 and it’s very clear where each screw is happy. A 1/4 turn in either direction of this happy area and the idle drops. I’ll then set the idle speed to 1000.

The problem is the bike wants a higher idle to stay running from cold start. The bike will die if the choke is pulled unless it’s below freezing. I use the cruise control knob with the throttle slightly cracked to warm the bike up. At this same idle speed setting the bike will increase to 1400ish after a run on the highway when the motor is its hottest.

So I’m stuck somewhere in the middle or having to adjust the idle speed up then down every time I ride it.

I’ve checked for vacuum leaks multiple times and found nothing. Recently set valve clearance and rocker arm lash. The bike fires right up and runs great otherwise. Any ideas?

[Barry]

The problem is the bike wants a higher idle to stay running from cold start.

I think your carb tuning is fine, this is perfectly normal behavior.  You are crediting a 40 year old design with a level of sophistication that it simply doesn't have. In the absence of a throttle lock, I hold it on the throttle and don't attempt an unattended warm up but just ride off.  The enricher is relatively crude device, some say it can be used to set a cold idle and some say it won't. One thing for certain is you can't expect it to influence idle speed once it's shut off.  Then with the drag of cold oil and lack of enrichment, the idle speed is bound to be lower until the engine warms up.  Mine will idle reliably after 1/2 a mile but at lower than normal RPM.

[Mucci]

The problem is the bike wants a higher idle to stay running from cold start.

I think your carb tuning is fine, this is perfectly normal behavior.  You are crediting a 40 year old design with a level of sophistication that it simply doesn't have. In the absence of a throttle lock, I hold it on the throttle and don't attempt an unattended warm up but just ride off.  The enricher is relatively crude device, some say it can be used to set a cold idle and some say it won't. One thing for certain is you can't expect it to influence idle speed once it's shut off.  Then with the drag of cold oil and lack of enrichment, the idle speed is bound to be lower until the engine warms up.  Mine will idle reliably after 1/2 a mile but at lower than normal RPM.

Sorry but I can’t accept that BMW designed these bikes in a way where they don’t start up and idle without having to hold the throttle open. I’ve had plenty of other older bikes that do this just fine. Usually I can use the choke to do this on other bikes but for some reason the choke kills this one.

I would think that means it’s already on the rich side but the mixture screw feedback tells me it’s right on.

[Barry]

I can understand you not wanting to accept it but it's the nature of the enrichers on Bing carbs.  BMW wrench gave you a similar response on ADVR and he has endless years experience servicing airheads.

In my opinion the enrichers are not tuned to work properly for different airhead engines. One size shouldn't fit all. For example the exact same enricher is fitted to the R45 and the R65. It works even less well on the R45.  If you want to resolve it then take the enrichers apart, understand how they work and re-design them to do what you want.  I'm being serious, I improved mine no end by drilling an extra fuel hole in the disc although that was the subject of a service bulletin.  If you think the enricher is producing too rich a mixture then block up the fuel holes and re-drill them a smaller size.

[Mucci]

I can understand you not wanting to accept it but it's the nature of the enrichers on Bing carbs.  BMW wrench gave you a similar response on ADVR and he has endless years experience servicing airheads.

In my opinion the enrichers are not tuned to work properly for different airhead engines. One size shouldn't fit all. For example the exact same enricher is fitted to the R45 and the R65. It works even less well on the R45.  If you want to resolve it then take the enrichers apart, understand how they work and re-design them to do what you want.  I'm being serious, I improved mine no end by drilling an extra fuel hole in the disc although that was the subject of a service bulletin.  If you think the enricher is producing too rich a mixture then block up the fuel holes and re-drill them a smaller size.

Is the redrilling for a smaller size what's covered in the service bulletin? Do you have that?

The reason I want to track this down is because it idled fine 5 or so years ago, so I know it's possible! I've cleaned and rebuilt the carbs a few times since then trying to perfect it but have yet to solve it.

[Barry]

The service bulletin was to drill a hole that was blank from the factory and to enlarge the counter bores.  it only applied to early models but  attached for interest.

[donbmw]

I have never needed to use a throttle lock to get a higher idle on start up with any of my bikes. When I start mine it’s full choke on, start, will idle 2000 RPM,s, while putting on helmet and gloves idle will go up, choke goes to half way open position. As I roll down the driveway choke goes to off. When I come to as stop about 1/8 of a mile. Is idling just fine. I think you are having a induction system issue. Check the your enrichment valves. They can be put together wrong and could be installed on the wrong carbs.

[georgesgiralt]

hello Mucci,
I've an '82 R65. identical bike but the carbs jetting is slightly different. I bought her new in 1984... So came to know her a little ;-) ....
First, check that you have new return springs on the gas and choke on the Bing.
Then here is what I does to set the carbs and idle :
I set the mixture screw per factory spec (assuming they are in good shape).
I triple check that the choke is totally closed (hence the new springs...) And don't ask me why I triple check...
I sync the bike cold to have a good idle and do NOT touch the mixture screw. Idle is set per spec at 800~1100 RPM.
I go for a ride to warm the bike up.
Once back in the shop, idle is waaaaay too high so I set it back to spec 800~1100 RPM. I adjust the sync both at idle and at 2000 RPM then at 3500~4000 RPM depending of the time of the day to ease the relationship with the neighbor .... I do not touch idle mixture or adjust it so slightly to perfect engine noise and it is often less than 1/8 turn. So nothing really. If you have access to an exhaust gas analyzer, you can play with it.
Doing this, when cold, the idle is too low for her to run without choke nor by itself. So I start the bike full choke. After a few seconds she start to splutter so I reduce choke to the mid position and finish to prepare myself with gloves and helmet and close the garage door.
I go with the bike and close the choke. (remember why I asked for the return springs ?) And at the first traffic light 500 m away, the idle is fine and holds be it winter or summer.
Trick : When you adjust idle with the bike hot aim for 1100 RPM or 1200. This way when the bike is cold you have a chance to attain 800 and have the bike running properly. When you adjust the bike cold, aim for 800 RPM or lower if she want/can run that low. This way you will have a chance to have hot engine idle below 3000 RPM ;-)
Frankly, those bikes are crude but very well engineered and will work flawlessly be it cold or hot (I ride all year long between -10°C and 40°C ). Idle won't go to the roof unless the bike overheat in traffic jams in very hot summer. But then you know it is wrong for her and for you...
Hope this helps.

[Mucci]

hello Mucci,
I've an '82 R65. identical bike but the carbs jetting is slightly different. I bought her new in 1984... So came to know her a little ;-) ....
First, check that you have new return springs on the gas and choke on the Bing.
Then here is what I does to set the carbs and idle :
I set the mixture screw per factory spec (assuming they are in good shape).
I triple check that the choke is totally closed (hence the new springs...) And don't ask me why I triple check...
I sync the bike cold to have a good idle and do NOT touch the mixture screw. Idle is set per spec at 800~1100 RPM.
I go for a ride to warm the bike up.
Once back in the shop, idle is waaaaay too high so I set it back to spec 800~1100 RPM. I adjust the sync both at idle and at 2000 RPM then at 3500~4000 RPM depending of the time of the day to ease the relationship with the neighbor .... I do not touch idle mixture or adjust it so slightly to perfect engine noise and it is often less than 1/8 turn. So nothing really. If you have access to an exhaust gas analyzer, you can play with it.
Doing this, when cold, the idle is too low for her to run without choke nor by itself. So I start the bike full choke. After a few seconds she start to splutter so I reduce choke to the mid position and finish to prepare myself with gloves and helmet and close the garage door.
I go with the bike and close the choke. (remember why I asked for the return springs ?) And at the first traffic light 500 m away, the idle is fine and holds be it winter or summer.
Trick : When you adjust idle with the bike hot aim for 1100 RPM or 1200. This way when the bike is cold you have a chance to attain 800 and have the bike running properly. When you adjust the bike cold, aim for 800 RPM or lower if she want/can run that low. This way you will have a chance to have hot engine idle below 3000 RPM ;-)
Frankly, those bikes are crude but very well engineered and will work flawlessly be it cold or hot (I ride all year long between -10°C and 40°C ). Idle won't go to the roof unless the bike overheat in traffic jams in very hot summer. But then you know it is wrong for her and for you...
Hope this helps.

Great info, thanks George.

After someone mentioned the choke plates could be on the wrong sides I have a feeling that could be the issue. Even cracking the choke kills it... as if it’s starting on the richest setting.

How are you doing the sync? Do you have the machine the manual references?

[Barry]

Checking the enricher discs is simple, the pear shaped slots should be at the top of the disc with the narrow end pointing towards the cylinder head. They can't be wrong when aligned like that.

[Luca]

It's hard to compare your results to someone else's without at least discussing ambient temperature. What works at 70F definitely doesn't work at 35F.  Especially in the shoulder seasons, your bike in the garage is much colder in the morning than the ambient air that is warming up from solar radiation.

Morning temps are still in the 30's/40's here and I need to ride a few miles before it will hold a steady idle.  I can improve engine warm up by running a little richer and/or going up a heat range on the plugs, but then I open myself up to a high idle coming off a highway run.  If you ride all winter you should try running a 10w40 oil for the colder weather, it will provide better startup lubrication and cause less drag inside the engine.

Barry is right, it's a 40 year old design that was a bit old fashioned when it came out, but the trade off is the ease of serviceability and reliability.  Also, the air cooled boxer engine lends itself to great hot weather performance (think German  R75's in Africa during WWII), but that can result in over-cooling/long warmups in colder temps.

[Bob_Roller]

When you rebuilt the carbs, did you remove the throttle shaft to replace the o-ring ??
The throttle plates go on in a specific way, the bevel on the plates are different and can be put in wrong .
There is something wrong with the way the engine is behaving given the description you have posted, as Barry posted, check the enrichment assemblies, there is a left and a right they can't be swapped .
As Georges Giralt posted carb adjustments need to be accomplished on an engine that is up to normal operating temperature, use two fans to blow cooling air over the cylinders during the procedure .
Use a manometer, or vacuum gauges I've had my '81 R65 coming up on 40 years and I've never had a starting issue due to carbs, this is from 19 F, -7 C, up to 128 F, 53 C.

Do you have  a black and gray ignition coil ??
If you do, I would suggest replacing it . It's a known problematic part, the case cracks and causing starting issues, not the issues you have .

[Mucci]

Well, I was really hoping I’d find the choke plates were installed incorrectly and that would be the fix but unfortunately I am a somewhat competent mechanic it turns out.

I also gave the plates a quick facing with 400 grit on a surface plate and installed new clutch return springs. They operate nice and smooth now. Unfortunately the issue still prevails.

While the bike was still cold I tried turning the mixture screw in and out, checking if it would hold idle but neither direction helped. Bike still dies with even a slight pull of choke. 

I’m going to do some on-road tweaking once the rain clears up.

Doing all this in 65F weather at sea level currently.

[Barry]

Out of curiosity how many fuel holes in the enricher discs ?

I was just wondering if the first holes was blank like mine.  It shouldn't be for that model year but you never know.

[Mucci]

All four were drilled out.