R65GS 1991 issue

[dannydk]

Hello all, I have surfed around a lot on this informative page. I drive quite satisfied a R65GS 1991.

But in recent days not so satisfied, the lady has started running unstable. lacks traction when accelerating. Or to explain it another way-it will not take full throttle and is not accelerating properly. However, I can get it to take throttle if I give full choke. Example, I run in third gear and pull full throttle, the engine does not set out, but sounds soaking or somewhat and pulls really bad, turn on the choke and it begins to run fine. To begin with, I could run with the choke on step one, but now I have to run at full choke before it will draw properly out the gear. I have run some test rides on the 20km so it should be warm and not need choke at all after 15-20 min, correct?
I have no experience with troubleshooting a Boxer MC and need help to solve this sudden problem. I've only had the machine for 14 days. Today purchased new spark plugs, engine oil, oil filter and new throttle cable when the old is part threaded. I've looked at carburator throttle/choke valves for proper working if they travel the same and have the same setpoint. it looks in my eyes fine.

Thanks

[Kurt in S.A.]

Welcome! Adding choke to make it run better sure suggests a carb problem!! Sounds like you'll need to consider a carb overhaul since you have no maintenance history. I'd suspect carb diaphragms right off the bat...they're probably holed and not adjusting the carb slide as needed.

Generally, though, you probably need to step back and perform a complete basic tune up, which is ensure proper head bolt torque, set the valves, check the timing (should be OK with the electronic ignition), new air filter, put those new plugs in.

But I'm thinking you've got something wrong with the carbs. On these carbs, your hand doesn't directly control the slides in the carb...you only open/close the butterflies. That creates the vacuum which raises or lowers the slides. You could see if the slides are working by opening the throttle up in your driveway to see if the slides are moving around as they should.

Kurt in S.A.

[dannydk]

Hi Kurt, Thank you very much for your answer. It seems to me that I nedd speed up my knowledge of big carburetors, there are several technical terms in your explanation that says nothing to me.

But most important for me is to know where I need to focus. I want to surf and find some documentation about the service of carburetor and separate them by, sure it makes much more sense when I have the parts between my hands dirty.

Can I go on with the same, or is it necessary to buy spare parts before I start?

Another problem I did not get mentioned in my first post. If I run with choker at step 1 or 2 and heavy braking, then go engine out. Is it normal?

I also have a problem with turn signal on the left handlebar only works by I activate high beam.So either I can give signal and blind another in the traffic, or does not blink. I create another thread with this problem

[SteveD]

Hi Danny. Welcommen.
Here's a quick video introducing you to BING's. https://youtu.be/Q__LkgoaGGk
and as they say, mantling is the reverse of dismantling. https://youtu.be/4TiI18uNjR4

[Kurt in S.A.]

Another problem I did not get mentioned in my first post. If I run with choker at step 1 or 2 and heavy braking, then go engine out. Is it normal?

Yes, BMW designed it this way. No, that shouldn't happen. I wonder if the issue might be as simple as the float set such that it shuts fuel filling into the bowl early...that is, a small amount of fuel in the bowl. If the fuel level were too low, you'd also run out of fuel at high draws such as near wide open throttle. Plus, it's harder for the carb to draw fuel up from a low fuel level, so under high demands like you describe, the bike could sputter.

If you drop the bowl and turning off the petcock, you should probably see something like an inch of fuel level when measured in the center of the bowl. That is an easy check and costs no money. Be careful with the bowl gaskets that mate with the carb body. If they tear or don't seat properly, you'll have leaks.

Kurt in S.A.

[SteveD]

Sounds like an overhaul is the way to start. Check the diaphragms whilst doing that.

Danny, the usual starting technique using the choke from cold would be:
Sit on the bike and be ready to ride, no need for 5 minute warm up on these bikes.
1. Taps on.
2. Full choke.
3. With free play on the throttle taken up, start the engine, open throttle only when the engine starts.
4. Ride off, turn to half choke within 200 metres. It will want to stumble to off when throttling off unless you do this.
5. Ride sensibly until you turn off choke at 2kms. That's the warm up period.

Idle might not hold up unassisted until it's adequately warm, but choke really should be well off within 3 minutes in my experience.
So, choke off earlyish but if you need to stop and idle in the first 10kms the idle might want some help. My bike will idle ok after 3kms. A mates 75/5 takes a bit longer, but his needs some carb tweak maybe.