Power loss question

[Tv]

G'day. My name is Tony and I'm new to the forum.  I have an 84 R65 which i bought in December 08 and I'm trying to fix a power problem. I since purchased a 81 R65 (in probabl;y better shape then my 84) as a donor bike and have been using it's components to try and find a solution using a process of elimination.
I've searched the forum but have been unable to find an answer so maybe someone can help.  BTW - great forum.
My bike seems to lose power at about 4-5k revs.  More when under load such as riding uphill.  Down hill it doesn't seem so bad.  Occaisionally it just flys like I imagine it should go all the time.
When it dies it sort of bogs down, splutters and groans and if I hold the thottle full open it seems to do it more.  Sometimes it'll get through its fit and take off to full revs. It's done this with both sets of carbs and both coils so:- I've overhauled the carbs and set them up as specified in this forums tech hints and links to other technical help (jet needles set on 2nd notch).  I replaced the coil, checked the valve clearance, adjusted the head bolts, relaced the air filter, high tension leads and spark plugs and even blew up the tyres.
I cant seem to find any info on ignition timing adjustment for the electronic ignition so I wonder whether it needs to be done? Do you think ignition timing could be the problem?
Thanks a lot!
REgards
Tv

[goomicoo]

If you hear pinging from the motor the timing is too advanced. If it runs hot and lacks power all the time it retarded. You have intermittent power loss so the timing is probably not it. Unless the advance weights in the bean can are shot ( jerky engine). How's the compression? Does it do it when cold or hot? All the time? Clean fuel screen, filter? Is this fun or what?

[Justin B.]

Did you replace the diaphragms?

[Tv]

The engine is not jerky.  It runs smoothly to 4 or 5k revs then starts to break down.  Sometimes if I tickle the throttle it helps to get it to run at full power but I've tried blipping the choke just a bit to see if a bit of extra fuel will help it lets me know that's not it.  Plenty of power down low. Does it cold and hot. I've renewed the fuel filter,however, the tank did have a lot of crap in it when I cleaned it out.
When I overhauled the carbs I put a full kit thru, including new jets, needles, diaphrams and o-rings.  It does feel like a diaphram issue but couldn't be as the problem exists with both sets of carbs.
I dont have a compression tester

[beemer]

Ignition coils breaking down?

[steve hawkins]

Does it eventually pick up again and go on, or can you accelerate through it on full throttle?

If so, you might find that you are running a little rich at that point in the rev range.  I would try dropping the needle a click or two to lean it out a bit and see if the situation improves.  You can do a spark plug  check at this rpm as well, to see - ride the bike to the appropriate revs and then shut the bike off, coast to a halt and then immediatly check your plugs - if they are dark, then it is running rich at this point.

Is the bike standard otherwise or do you have aftermarket exhaust or air filters?

SteveH

[Tv]

It does eventually pickup and if I get to the 5.5k+ rev range.  I've checked the plugs after my ride and the top of the insulator and electrode seem to look normal but the rest of the plug looks a bit black and furry.  The air filter is standard but I'm not sure about the exhaust.  They look normal but sound bit louder than other bmw's I've heard.  Does it seem odd that I would have the same problem with two sets of carbs?  When I installed the jet needles (they are the twist in type, not the screw in type) I've clicked them in to the second position so are you suggesting I take it back to first poisition to lean the mix?  I tried changing the needle position with the original carbs and that didn't seem to fix the problem so thats why I overhauled my other carbs hoping that would solve it.
AS far as the coils go, it's done the same thing with both coils so that seems unlikely.
Thanks a lot for your help
REgards
Tv

[fastcataz]

Have you checked your fuel filter and petcock?

[donbmw]

How old are your sparkplug wires. I had my 82 R65 act like it had a fuel problem. I turned out to be plug wires.

Don

[Tv]

The plug wires, caps and plugs are all new.  The fuel filter is new.  I checked and cleaned the petcock and the tank filter before I overhauled the carbs.  The tank was full of crap when I cleaned it out so I might check that again.  I'll get another new fuel filter and try the other tank also.  
I once had a 1958 Hillman Minx car that used to die every time I went up a hill so I overhauled most of the engine stuff and it turned out to be rust and rubbish inside the fuel tank.  Once I cleaned it out it went like the clappers.

[Bob_Roller]

A little information on the OEM ignition coils, it's highly unlikely that both would cause the same problem.

But if you have the gray and black coils, they are commonly referred to as the 'crack-o-matic' coil , they are a problematic part, and if they are not giving problems now, they will in the future.

BMW upgraded the coil some time in the early '90's, to a red and black part, I replaced my original gray and black coil with the upgraded part, and it only lasted 10 years before it failed again.

Just a little heads up info.

Have you replaced the fuel lines yet ?

I had a problem of one of the lines would kink on me and restrict fuel to the right carb.

Seeing as how you have a 'donor' bike, if you run out of places to go, you may want to try and swap the ignition canisters ( commonly referred to as the 'bean can') , located under the front cover of the engine.

If by chance the can is the problem area, there is a pictorial guide to taking the unit apart on our FAQ section, under the heading 'Bean Can Overhaul'.

Also there is an ignition control unit under the tank, it has an aluminum heat-sink bolted, or riveted to it, they usually work, or don't work, but it's a quick swap over.

From the looks of your profile, you appear to reside in saltwater coastal area, I don't know if corrosion is an issue with your area, but it would be a good idea to disassemble the electrical connections in the wiring harness, and check for corrosion and security of all of the connectors.

Welcome to the world of 28 year old motorcycles !!!!

[Tv]

Welcome to the world of 28 year old motorcycles !!!!

Thanks - I sold my Harley because I felt I couldn't tinker with it and it was costing me too much to own.  I bought these new (old BMW) bikes for a fraction of the cost and have been fiddling ever since - much more fun, still, I wouln't mind solving this problem.  I'll take the advice given so far and let you know what happens.

[nhmaf]

Is it always RPM related, or does it happen rather intermittently (and you end up revving the engine to try to get it to recover ?  What I am thinking of is that if this is happening with (2) sets of carbs and (2) sets of coils, it is more likely to be something that you haven't changed yet, so what could it be..
1.  What type of fuel filter did you install?  Perhaps you can try flushing out your fuel tank to make sure it is really clean, and run without your aftermarket filter - perhaps it isn't flowing fuel well enough and you are getting a fuel starvation issue - or - you might have a gas tank venting issue.
2.  It could be the"bean can" ignition trigger unit, but it might by the ignition control unit.   I'd take it off and renew the heatsink paste that goes on the metal back of the ICU where the aluminum alloy heatsink plate presses against it - it these get too hot they can misbehave.   You could also try swapping the ICU from the 81 to the 84 to see if the problem follows the part or not.

Best of luck - we'll stick with ya until you get this solved.  So far you've been going about it in the right way !

[Landlubber]

It may just be the fuel cap not venting at high revs, try loosening the fuel cap tp prove me wrong.

[Tv]

Thanks fellows.  I'll try all the suggestions one at a time and let you know the outcome.  

Update - Changed the tank including petcovk and the electronic module and still the same.  I tried the old 'switch the system down when the fault occurs' trick then checked the plugs.  They were blackish and bit furry so looks like the mix is too rich.  I better try moving the jet needles.  Do I need to make them shorter or longer?