I have no idea whats going on...

[dreager1327]

I just picked up a 1979 R65 and have a question.  It is excellent shape as far as I can tell but the guy I got it from didnt know much about it or what to do with it.  I come from a Harley background and want to make sure I do the work right.  It seems to do fine until about 40mph then it tops out.  The speedo says 70 but its not even close.  It acts like its governed.  Is this carbs or valves or transmission?  I replaced the fluids and checked over everything.  I am just looking for a starting point.

[Bob_Roller]

Welcome Aaron .

My first guess where to start, is the carbs, these Bing carbs have rubber diaphragms under the domes on top of the carb, they are prone to cracking with age .

A good cleaning and probably replacing the rubber parts and gaskets in the carbs would be good starting point .

There's should be a fine mesh screen over the fuel pickup tubes in the tank, check this to see if it is clogged up, not too uncommon of a problem with bikes that are left idle for long periods of time, as is rust and peeling tank liner .

Seeing as you have no idea about the maintenance history of your newly acquired bike, you've got a bit of work ahead of you .

[Rob Valdez 79 R65]

I second the opinion of the diaphragms.

The two screws holding the top onto the carb body can be a real bear.  Make sure you have a flat-blade screwdriver that fits the slots well.  A small amount of valve grinding compound in the slot can help.  You also might try fitting a screwdriver bit in an appropriate sized socket and using a ratchet, if it is really stuck.

The diaphragm on the '79 is held onto the slide with a large white plastic ring.  It can become stretched over time if it is reused more than a couple of times.

The diaphragm has an indexing tab on both the outside diameter and the inside diameters.  You won't need to worry about the inside tab unless you replace the diaphragms.  The outside tab you need to check every time you open it up.

If the PO installed inline fuel filters, either replace them or ditch them  I have always found the two screens on the petcock to be adequate.  YMMV  
The second screen is on the bottom-most part of the petcock.  

Replace the fuel line, if you don't know how old it is.

Write down everything you do with dates and mileage.

Check the front coil.  The coil mount should have broken by now, taking the wiring harness' main ground wire connection with it.  
Most likely the coil has been remounted somehow, and the ground relocated.  Here is how I did mine.

[drewboid]

See if your carb has a small inset disk in the center of the top - they have been known to leak air around the edges. One fix is to run epoxy around the groove to seal it. Some have epoxied a small BMW emblem there so it looks nice.
The air leak there gives the same effect as a tear in the diaphram.

[Rob Valdez 79 R65]

See if your carb has a small inset disk in the center of the top - they have been known to leak air around the edges. One fix is to run epoxy around the groove to seal it. Some have epoxied a small BMW emblem there so it looks nice.
The air leak there gives the same effect as a tear in the diaphram.

If he has a '79, he probably has "flat-top" carbs, and this does not apply.

This is a problem the "dome-top" carbs had.  There were only about two years that BMW used the flat-top design.

[montmil]

Back in the day, my '81 R65 would begin to stumble and nearly quit when the speedo got to around 60 mph. Grrrr

Inspected the Bing diaphragms but saw nothing evil; no tears, pin holes -those are hard to spot!- and I had already secured the dome discs just in case. So, when I replaced the rubbers, the problem went away. She'll do the ton now.

Do the Bing flat top diaphragms have the "locating tab"? Gotta watch out for the alignment.

Monte

[dreager1327]

Yes they are flat tops on the carbs. So they still have diaphrams right?  I am probably going to tear them down and rebuild them this weekend if I can find the parts locally. I figured on doing a good rebuild on as many soft components as make sense.  Thanks for your help. I'm sure I will have more questions to follow.  

[Lucky_Lou]

Yes they are flat tops on the carbs. So they still have diaphragms right?  I am probably going to tear them down and rebuild them this weekend if I can find the parts locally. I figured on doing a good rebuild on as many soft components as make sense.  Thanks for your help. I'm sure I will have more questions to follow.  

Welcome to the forum Aaron, i have a 79 with the flat tops, diaphragm problems are not uncommon if you strip the carbs and order parts there are replacement screws for the tops stainless steel Allen screws they cost very little and are a good investment if your going to be looking at these on a regular basis.
Dont panic if the Diaphragm "Pops" out when you strip it this is a common fault when people use fuel additives (Dont bother with them).
Replace the diaphragms with "Bing" Originals generic ones are no where near as good and false economy.Do check the tank for debris this too is a common problem, as outlined in previous posts the problem is likely to be fuel/carb related.Keep us posted on progress.
Also are you saying the speedo is reading 70 at much lower speeds?
if so this could be a serious problem on the final drive pull the back wheel off and check the crown wheel splines clean and lube them anyway its not a complicated task Haynes manual may be handy.Put a scissor jack under the frame at the back of the clutch operating lever to take the weight dont rely on the center stand for this.
Lou

[Rob Valdez 79 R65]

Yes - remove your rear wheel this weekend and check those splines.
Check out this article for details: http://w6rec.com/duane/bmw/finaldrive/index.htm

I doubt you will find many parts for your carburetors locally.  Mail-order is the best way to go, and definitely from this company: http://www.bingcarburetor.com/

You should call them on the phone  (1-800-309-2464), and have the 7-digit numbers from your carbs.

 
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[Rob Valdez 79 R65]

Unrelated, but as the new owner of an airhead (pre-'85) with unknown history, you should ready yourself to remove the transmission at some point, to check/clean/lube the splines of the input shaft.

Some will tell you the job can be performed by sliding the transmission back as far as it will go, but I don't recommend it.  Especially for the initial service.

A good grease for both this and the rear wheel splines is Honda Moly 60.  It should be available at a Honda dealership, but call ahead.

Here is a source online: http://www.bernardiparts.com/Honda-Moly-60-Paste__08734-0001.aspx

[dreager1327]

I just want to say "You guys are awesome."  I appreciate the help and I will post my progress.

[dreager1327]

What coils work on the bike? The ones on there now are quite old and worn.  I wanted to put some new ones on while I'm in the midst of straigtening this bike out.  Would any 6v work as long as it has the same output?  

[Bengt_Phorqs]

If you're replacing coils go ahead and buy a Dynacoil from Rick Jones at Motorrad Elektrik.  Money well spent in my opinion and several others on the forum.  Rick is a stand up guy and will take the time to help you sort out any electrical issues you may have.

Also, Motobins in the UK is a great source for Bing carb kits.  Good prices and fast delivery.

[Rob Valdez 79 R65]

Since your's is probably an earlier R65, you may be looking for two coils to replace the ones you have (doesn't really matter).

Here is one, at a VW parts supply:
http://www.vwparts.net/BOS00016.html

And here is a significantly cheaper one from a tractor supply:
http://www.valu-bilt.com/product_info.php?product_id=10599&item_number=A%2025262

And of course, eBay
http://cgi.ebay.com/ebaymotors/PORSCHE-356-6-VOLT-BOSCH-IGNITION-COIL-BOSCH-/200320728073?cmd=ViewItem&pt=Motors_Car_Truck_Parts_Accessories&hash=item2ea40bbc09