Looking at a R80/7

[pglaves]

I certainly do not wish to despoil any person's satisfaction with an R80/7. Au contrair, I wish to facilitate your better enjoyment of the creature.

The R80/7, circa 1978, was one of BMW's most problematic engines. This was the first serious year of new air pollution regulations in the US. And many vehicle manufacturers had problems meeting the requirements. (As an aside I had the misfortune of owning a 1978 Dodge Aspen, a totally untunable mess of a car. If it would start cold it ran poorly hot. And if tuned to run well hot it was a bear or impossible to start cold. I solved the issue with a new 4 barrel carburetor.)

So, very careful tuning of the R80/7 is critical. Timing has to be perfect and the carburetor mixture has to be correct. You will discover that re-jetting to a richer jet or a needle position change is probably needed. By design - surprise, surprise, the engine was designed to run too lean. This is also the perfect motor to benefit from double-plugging. Much of Oak Okleshen's writing in this period addressed this issue. I had Oak set Voni's R80 heads up for double plugging and got the whole coil setup from him back in 1980 or 1981.

Double plugging is not essential, but very careful tuning is. And keeping that fine state of tune is equally important which means more attention to carb synch, fuel level in the float bowls, and points timing is critical.

 

[brio]

I certainly do not wish to despoil any person's satisfaction with an R80/7. Au contrair, I wish to facilitate your better enjoyment of the creature.

The R80/7, circa 1978, was one of BMW's most problematic engines. This was the first serious year of new air pollution regulations in the US. And many vehicle manufacturers had problems meeting the requirements. (As an aside I had the misfortune of owning a 1978 Dodge Aspen, a totally untunable mess of a car. If it would start cold it ran poorly hot. And if tuned to run well hot it was a bear or impossible to start cold. I solved the issue with a new 4 barrel carburetor.)

So, very careful tuning of the R80/7 is critical. Timing has to be perfect and the carburetor mixture has to be correct. You will discover that re-jetting to a richer jet or a needle position change is probably needed. By design - surprise, surprise, the engine was designed to run too lean. This is also the perfect motor to benefit from double-plugging. Much of Oak Okleshen's writing in this period addressed this issue. I had Oak set Voni's R80 heads up for double plugging and got the whole coil setup from him back in 1980 or 1981.

Double plugging is not essential, but very careful tuning is. And keeping that fine state of tune is equally important which means more attention to carb synch, fuel level in the float bowls, and points timing is critical.

Besides idle air mixture and syncing what is there to do? The carbs are rebuilt so hopefully air leaks and lean running is minimized that way. What significance does float bowl adjustment have besides keeping an adequate level of fuel in the bowls. How does that change the mixture of the engine?

 

[20774]

Besides idle air mixture and syncing what is there to do? The carbs are rebuilt so hopefully air leaks and lean running is minimized that way. What significance does float bowl adjustment have besides keeping an adequate level of fuel in the bowls. How does that change the mixture of the engine?

The height of the fuel in the bowl can affect the mixture. If the fuel height is low, it takes more "suck" to pull the fuel up from the bowl into the throat of the carb. It's a weight/gravity thing.

I'd say you should start by taking stock of the various settings like jet sizes, etc., and compare that to the standard. More than likely, you will be running in the mid range of the carb performance which is primarily controlled by the needle and its jet. Fine increases in size of that jet will make for richer running. Also, the needle can be raised which represents a coarse change in increasing the fuel mixture.

Go through the basic steps to synch the carbs. One thing to do when setting the idle mixture is to move a small direction to the richer side once you've found the optimum RPM range. Since the CV carb fuel mixture controls a fuel circuit, turning the mixture setting a skoosh counter clockwise will result in slightly more fuel.

Then see how the bike runs and check plugs as time goes by.

 

[brio]

Ok! Before we get that far I have a more pressing issue. Take a look at this:

What could it be?

 

[20774]

First thing I'd do is find another DVM just to be sure there are no issues there. Also, keep the DVM cables away from the spark plug cables. Typically I've had no issues reading an analog voltage with a digital meter, but on my R25/2, I was told to get an analog meter to read the voltage...my DVM was reading strange. Those DVMs has internal sample rates in order to show you the voltage...could be something is incompatible.

 

[1074]

electrics

Shut the bike off and check voltage. Does the meter fluctuate? If it does then use a different meter. If the meter is stable then run it and get someone to hold the probes hard against the terminals and let the meter stabilize.

 

[brio]

Shut the bike off and check voltage. Does the meter fluctuate? If it does then use a different meter. If the meter is stable then run it and get someone to hold the probes hard against the terminals and let the meter stabilize.

It stabilizes when turned off. I wonder if a failed diode board is sending AC through the system...

 

[pglaves]

What significance does float bowl adjustment have besides keeping an adequate level of fuel in the bowls. How does that change the mixture of the engine?

Fuel is pulled out of the bowl by the venturi effect in the carburetor. That is a slight vacuum pulls the fuel through the jets past the tapered jet needle. And the height of the fuel affects the mixture. Too low and the mixture is lean. Too high and the mixture is rich.

 

[brio]

It was the DVM. I Bought an analog and its reading ~ 14v.

Regarding float bowls; it makes sense; Bernouli and column of liquid etc. I’ll run it for a while and pull the plugs after setting idle mixture and synchronization.