The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: DadsR65 on May 06, 2018, 04:22:42 AM
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I have a recently restored 1980 R65. I've spent the last couple of weeks (~250 miles) getting the carbs tuned and synced. All is well except for a couple of issues:
1 - Doesn't like to be cold. I think this may just be a "feature" of airheads.
2 - Drop-off in power at wide-open throttle.
Regarding #2: it happens when I'm in higher gears, trying to accelerated up hill at high speed (i.e. when I need max throttle). I twist the throttle, but power doesn't increase, and actually drops a little. If I back off throttle to ~3/4, I feel a noticeable power increase. I'm wondering if this is a main jet issue. Background: timing is set, points gap good, float level 24mm, carbs tuned and balanced, new plugs, new plug leads.
Has anyone had success with slightly bigger main jets?
Thanks!
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Regarding #2: it happens when I'm in higher gears, trying to accelerated up hill at high speed (i.e. when I need max throttle). I twist the throttle, but power doesn't increase, and actually drops a little. If I back off throttle to ~3/4, I feel a noticeable power increase.
While it would be unusual for the stock main jets to be too small, what you describe is a classic symptom that they are. There seems to be two main jet sizes for an 80 model year R65 up to 1/80 was a 140 main jet and for the rest of the model year a 145
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Regarding #2: it happens when I'm in higher gears, trying to accelerated up hill at high speed (i.e. when I need max throttle). I twist the throttle, but power doesn't increase, and actually drops a little. If I back off throttle to ~3/4, I feel a noticeable power increase.
While it would be unusual for the stock main jets to be too small, what you describe is a classic symptom that they are. There seems to be two main jet sizes for an 80 model year R65 up to 1/80 was a 140 main jet and for the rest of the model year a 145
My current jets are 145. I know they're OEM, since my Dad bought the bike new. I certainly wouldn't expect to have a lean jet issue on a completely stock bike. The designers are smarter than that, but the evidence sure feels like it's too lean at WOT.
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Took a short ride this morning. Max speed in 5th gear is ~60mph, which can't be right. Low and mid-range power seem fine.
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Have you checked the rubber diaphragms under the top covers on the carbs, sounds like they may have holes in them .
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Have you checked the rubber diaphragms under the top covers on the carbs, sounds like they may have holes in them .
Good thought, but those are brand-new. As are all the o-rings. Other than max power, everything runs great.
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Have you first checked the valve lash ? And checked that the advance mechanism is apt to go up to the "Z" mark at above 4000 RPM ?
If both statements are true, try increasing the size of your main jet 'till you have full power at WOT.
Just my 2¢
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needles in the prescribed notches? Both the same?
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The diaphragms, are they Bing parts, or aftermarket pattern parts ??
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Have you first checked the valve lash ? And checked that the advance mechanism is apt to go up to the "Z" mark at above 4000 RPM ?
If both statements are true, try increasing the size of your main jet 'till you have full power at WOT.
Just my 2¢
Reset valve clearances last week (this is a reasonably fresh rebuild). 0.006" intake, 0.011" exhaust (per Snowbum). Oddly, my feeler gauge set doesn't have a 0.010". Timing was set so S is at idle and Z above ~3500rpm.
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needles in the prescribed notches? Both the same?
Both should be at 3rd from top, but the carb rebuild was a couple of months ago, so it's probably worth rechecking. Good call.
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The diaphragms, are they Bing parts, or aftermarket pattern parts ??
Hmmmm...interesting question. This one took a bit of digging, but here's what I used:
https://www.eubmw.com/collections/carburetor-kits/products/bing-carburetor-kit
I can't tell if it's OEM Bing or not.
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Were the new diaphragms the same thickness as the old ones ??
There were some in the past, that were thicker and stiffer than the OEM Bing part .
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Have you first checked the valve lash ? And checked that the advance mechanism is apt to go up to the "Z" mark at above 4000 RPM ?
If both statements are true, try increasing the size of your main jet 'till you have full power at WOT.
Just my 2¢
Reset valve clearances last week (this is a reasonably fresh rebuild). 0.006" intake, 0.011" exhaust (per Snowbum). Oddly, my feeler gauge set doesn't have a 0.010". Timing was set so S is at idle and Z above ~3500rpm.
Also, it runs great in lower gears all the way up to redline (or at least as close as I've gotten). This makes me think timing, points, valves, etc. are probably OK. Issue is isolated to nearly max throttle at high speed, which makes me think about a fuel issue.
Also, I did a fuel flow test. Measured about 500mL in one minute. Seems OK.
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Were the new diaphragms the same thickness as the old ones ??
There were some in the past, that were thicker and stiffer than the OEM Bing part .
The bike hadn't run in 25 years. The old diaphragms were just black goo that I scraped off.
Diaphragms aren't expensive. Might be worth it to just replace them and see. It's always possible I accidentally damaged one during rebuild.
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The diaphragms, are they Bing parts, or aftermarket pattern parts ??
Hmmmm...interesting question. This one took a bit of digging, but here's what I used:
https://www.eubmw.com/collections/carburetor-kits/products/bing-carburetor-kit
I can't tell if it's OEM Bing or not.
And it doesn't matter a damn if they are or are not OEM. providing of course that they are good quality and seal correctly.
The "non-OEM" diaphragm thing started a few years back when some one had difficulties after rebuilding their carbs and assembling them wrong. They tore down and rebuilt, but with OEM diaphragms and wonders of wonders the bike ran correctly - obviously it was the diaphragm's fault.
The myth persists.......
Thing is, if you look at the vacuum system in a Bing carb it is immensely powerful (relatively speaking) a "stiff" diaphragm (within any rational meaning of the term) can do nothing more than slow the rate of change, it cannot alter the amount the slide will rise because vacuum is vacuum.
I have been using non-OEM diaphragms since 1980, and I have never had a problem. Initially Stromberg diaphragms, but more recently whatever Moto-Bins is flogging as the OEM alternative.
I have miss-assembled carbs on occasions and I have sucked up the fact that I made a mistake and fault diagnosed till I found and eliminated my own mistake.
In no particular order I set out below a list of things that can cause your problem (or similar) for you to check.
Diaphragms seated correctly in both carb body and slide.
Dome seating correctly and no leak at the top (if there is the 'approved" fix is the BMW badge that is the same diameter and epoxy - if you are in the USA you can send the dome to Bing USA for removal of the metal "bung" fittment of a new one and re-crimping, but be aware that the price is pretty much the same as just buying a new dome.
Slides have full, free and correct movement available, all airways (vacuum ways I suppose) not clogged
Start enrichment circuit assembled correctly and all screws tight
Emulsion tubes clean and correctly mounted to jet assembly
Funny looking flat washer fitted to mainjet - you would be amazed how many people remove this and either do not replace it, or replace it with a much smaller one - the odd looking oversized washer is the correct one and does an important job.
Float valve, needle and seat and floats not binding and flowing fuel freely. It is possible to miss-assemble these so that they can "hang up", but usually the lack of fuel in the bowls is a dead giveaway.
Intake trunk rubbers on the cylinder heads in good condition and snug tight to both head and carb
Check plastic intake trumpets and make sure any rags you stuffed in there on disassembly were removed when you put it back together (don't ask me why this one is included).
Airfilter, clean and good quality (which includes not being an oiled fabric piece of rubbish) - sometimes OEM, or a good copy, is best.
If you had the throttle plates out are you absolutely sure they went back in the right way round?
Fuel tap in god condition and flowing correctly? There is a filter built into the tap, it is known to clog.
Fuel lines in good condition and not kinked anywhere? My personal trick was to trap the cross feed pipe on an early model R65 with clam shell aircleaner - it flowed enough to trick me for some time, except that the RHS carb would run dry quite quickly at WOT or thereabouts. I felt a 1st class dill when I eventually found it.
Recheck every jet, a minute piece of lint will change the flow characteristics for the worse.
Once you are absolutely sure that your carbs are OK, start checking ignition components - on the well established principle that if you *think* it is fuel it will be electrical - and vice versa.
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The EUBMW parts aren't Bing but I've seen good reviews of those and other parts they provide.
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And it doesn't matter a damn if they are or are not OEM.
I just ordered and received kits for my carbs(O-rings, gaskets and diaphragms) for about $20 so I don't think I got the OEM parts.
I felt the diaphragms and my sensitive lil pinkies could not discern ant difference from the ones on the bike now. and as Tony said, the difference in material would have to be huge to make any difference at all, considering the amount of vacuum power acting on them.
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hahah ! got exactly the same problem for the same job... :-) does not like the cold.. and lost of power at full open throttle...
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The diaphragms, are they Bing parts, or aftermarket pattern parts ??
Hmmmm...interesting question. This one took a bit of digging, but here's what I used:
https://www.eubmw.com/collections/carburetor-kits/products/bing-carburetor-kit
I can't tell if it's OEM Bing or not.
And it doesn't matter a damn if they are or are not OEM. providing of course that they are good quality and seal correctly.
The "non-OEM" diaphragm thing started a few years back when some one had difficulties after rebuilding their carbs and assembling them wrong. They tore down and rebuilt, but with OEM diaphragms and wonders of wonders the bike ran correctly - obviously it was the diaphragm's fault.
The myth persists.......
Thing is, if you look at the vacuum system in a Bing carb it is immensely powerful (relatively speaking) a "stiff" diaphragm (within any rational meaning of the term) can do nothing more than slow the rate of change, it cannot alter the amount the slide will rise because vacuum is vacuum.
I have been using non-OEM diaphragms since 1980, and I have never had a problem. Initially Stromberg diaphragms, but more recently whatever Moto-Bins is flogging as the OEM alternative.
I have miss-assembled carbs on occasions and I have sucked up the fact that I made a mistake and fault diagnosed till I found and eliminated my own mistake.
In no particular order I set out below a list of things that can cause your problem (or similar) for you to check.
Diaphragms seated correctly in both carb body and slide. Verified
Dome seating correctly and no leak at the top (if there is the 'approved" fix is the BMW badge that is the same diameter and epoxy - if you are in the USA you can send the dome to Bing USA for removal of the metal "bung" fittment of a new one and re-crimping, but be aware that the price is pretty much the same as just buying a new dome.Inspected, looks ok
Slides have full, free and correct movement available, all airways (vacuum ways I suppose) not cloggedVerified
Start enrichment circuit assembled correctly and all screws tightVerified
Emulsion tubes clean and correctly mounted to jet assembly Verified
Funny looking flat washer fitted to mainjet - you would be amazed how many people remove this and either do not replace it, or replace it with a much smaller one - the odd looking oversized washer is the correct one and does an important job.Verified
Float valve, needle and seat and floats not binding and flowing fuel freely. It is possible to miss-assemble these so that they can "hang up", but usually the lack of fuel in the bowls is a dead giveaway.Verified
Intake trunk rubbers on the cylinder heads in good condition and snug tight to both head and carbVerified
Check plastic intake trumpets and make sure any rags you stuffed in there on disassembly were removed when you put it back together (don't ask me why this one is included).Verified
Airfilter, clean and good quality (which includes not being an oiled fabric piece of rubbish) - sometimes OEM, or a good copy, is best.200 miles on new filter (not K&N)
If you had the throttle plates out are you absolutely sure they went back in the right way round?Verified
Fuel tap in god condition and flowing correctly? There is a filter built into the tap, it is known to clog.Did a flow test: ~500mL in 1 minute. Then disassembled petcock. Removed filter (kept in-line filter) as a test.
Fuel lines in good condition and not kinked anywhere? My personal trick was to trap the cross feed pipe on an early model R65 with clam shell aircleaner - it flowed enough to trick me for some time, except that the RHS carb would run dry quite quickly at WOT or thereabouts. I felt a 1st class dill when I eventually found it.Verified
Recheck every jet, a minute piece of lint will change the flow characteristics for the worse.Verified, all disassembled and sprayed with carb cleaner
Once you are absolutely sure that your carbs are OK, start checking ignition components - on the well established principle that if you *think* it is fuel it will be electrical - and vice versa.
Took the carbs off and completely disassembled, cleaned, and reassembled. Same for petcock. Did a quick tune last night, need to ride it tonight then do a real tune, then we'll see if I've made any improvement to the top end.
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AhAh !
I see that you have in line filters.
In France they suffer a very very bad reputation giving bikes not apt to attain top speed or top power.
May I suggest that you remove them and test again ?
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AhAh !
I see that you have in line filters.
In France they suffer a very very bad reputation giving bikes not apt to attain top speed or top power.
May I suggest that you remove them and test again ?
Exactly the same thought I had. Might be that two filters in series is too much pressure drop. I removed the filter in the petcock and left the inline filter in place. I like to see fuel flow, helps with diagnostics.
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I removed the filter in the petcock and left the inline filter in place. .
In my considerably less than humble opinion, you removed the wrong one.
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The filter that you still have installed, is it a sintered element filter, the filter is granulated bass like material that's pressed into a conical shape ??
Another not too common issue, is that the fuel cap is the vent for the tank, my '84 LS sat for 17 years with fuel in the tank, the fuel cap was clogged with fuel varnish, had issues when I got over 50 mph .
Loosened the cap and my power issue went away, soaked the cap in carb cleaner and eventually got it unclogged .
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I removed the filter in the petcock and left the inline filter in place. .
In my considerably less than humble opinion, you removed the wrong one.
In the long run, I agree. During the diagnostic phase, I find it useful to see fuel flow (my inline filter is clear). Once everything is sorted, I'll likely go back to the petcock filter.
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The filter that you still have installed, is it a sintered element filter, the filter is granulated bass like material that's pressed into a conical shape ??
Another not too common issue, is that the fuel cap is the vent for the tank, my '84 LS sat for 17 years with fuel in the tank, the fuel cap was clogged with fuel varnish, had issues when I got over 50 mph .
Loosened the cap and my power issue went away, soaked the cap in carb cleaner and eventually got it unclogged .
I've had the issue with the tank cap loosened, so I don't think it's a venting issue.
Inline filter is this:
http://www.euromotoelectrics.com/product-p/ff-451e.htm
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Update: disassembled, checked, and cleaned both carbs. Everything looked fine, but I cleaned just to be safe. Set fuel bowl levels at 24mm. Removed filter in petcock since I also have an inline filter. Tuned carbs, rode, then tuned and balanced with manometer.
Bike starts, idles, and runs great. There is still an odd behavior at high speed. Two observations:
1 - at high speed, not much power at 4000rpm. If I want to go faster than about 60mph, I need to wind it up in 4th so that I’m about 5000rpm in 5th. Then I can get to 80+mph (faster than I want to go). Is this typical?
2 - There’s a flat spot in the power band around 4000rpm at any speed. I’ll shift, then hold throttle about half open. Not much power (but enough to show the engine is still running ok), then after a second or two at constant throttle it comes into its own and starts pulling harder. Maybe needle jet? Maybe ignition/points/advance related?
Also, finally got it registered. Took a couple hours at DMV. Although the website says they only require a VIN check, they made me start it and demo all the lights. Good thing I had put the carbs back on! Nice surprise: no sales tax for immediate family members. DMV lady was excited to see another BMW and showed me the papers from earlier that morning for a guy with a mid-70’s R75. Original title was from Idaho. She even asked to see a pic of my bike.
(Full disclosure: also posted on advrider.)
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Could you please test it without the in line filter and report back ?
Also, you set the fuel level in an unorthodox way. The blessed method is to have the flow stopped when the float is parallel to the carburetor base.
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Could you please test it without the in line filter and report back ?
Also, you set the fuel level in an unorthodox way. The blessed method is to have the flow stopped when the float is parallel to the carburetor base.
I suppose. With the filter out of the petcock, it will be unfiltered.
I'm surprised to hear that the 24mm rule is unorthodox. Seems pretty common, but I can try the "set them level" approach. Thanks for the suggestions!
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Update: seems that points gap was too tight. I corrected it and re-timed and bike pulls like a champ now!
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Fantastic!
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Update: seems that points gap was too tight. I corrected it and re-timed and bike pulls like a champ now!
I am VERY glad that you have fixed the problem.
You are also now entitled to be a card carrying member of the "When you think it is carbs, it will be Ignition and when you think it is ignition it will be carbs" society.
Oh....And it was nothing to do with those "evil" non-OEM diaphragms!
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"Once you are absolutely sure that your carbs are OK, start checking ignition components - on the well established principle that if you *think* it is fuel it will be electrical - and vice versa"
........as Tony Smith said!
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Thanks to all for the help!
Next issues are bouncy speedo and inability to get idle low enough.
On the idle, I can get it down to ~1200rpm and balanced, but no lower. If I continue to back out the left side idle speed screw, it no longer touches the throttle lever. I can push on the throttle lever with a long screwdriver and idle will drop. This tells me it's a mechanical issue. I ordered new throttle return springs as step 1. If that doesn't work, then new throttle cables.
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Next issues are bouncy speedo and inability to get idle low enough.
Bouncy speedo could be the cable. You could try driving the speedo using something like an electrical screw driver or variable speed drill to see if the speedo unit itself is OK. If not OK then generally a faulty speedo is best repaired sooner rather than later before more expensive internal damage is done.
On the idle, I can get it down to ~1200rpm and balanced, but no lower. If I continue to back out the left side idle speed screw, it no longer touches the throttle lever. I can push on the throttle lever with a long screwdriver and idle will drop. This tells me it's a mechanical issue. I ordered new throttle return springs as step 1. If that doesn't work, then new throttle cables.
It could be cables but it would be unusual if stock return springs were at fault as they are actually a fair bit stronger than they need to be. It's more likely an issue with the butterfly spindle or alignment. Has the butterfly been detached from the spindle and if so did it go back the right way up. Was it correctly centred in the venturi before tightening the screws.
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Next issues are bouncy speedo and inability to get idle low enough.
Bouncy speedo could be the cable. You could try driving the speedo using something like an electrical screw driver or variable speed drill to see if the speedo unit itself is OK. If not OK then generally a faulty speedo is best repaired sooner rather than later before more expensive internal damage is done.
On the idle, I can get it down to ~1200rpm and balanced, but no lower. If I continue to back out the left side idle speed screw, it no longer touches the throttle lever. I can push on the throttle lever with a long screwdriver and idle will drop. This tells me it's a mechanical issue. I ordered new throttle return springs as step 1. If that doesn't work, then new throttle cables.
It could be cables but it would be unusual if stock return springs were at fault as they are actually a fair bit stronger than they need to be. It's more likely an issue with the butterfly spindle or alignment. Has the butterfly been detached from the spindle and if so did it go back the right way up. Was it correctly centred in the venturi before tightening the screws.
The butterfly on both carbs did come out during rebuild. Shafts, o-rings, and tiny screws are new. I've double checked them and they appear to be correctly installed. Also no light coming through any gaps. The fact that I can push on the throttle lever at the carb and get the revs to drop still makes me think cable and/or spring.