1982 r100rs

Greetings
my 82 RS got new pistons & rings about 1000 miles ago. I just changed the oil and filter and now I have an issue. The bike starts up OK, but won't take any throttle and when given throttle in gear and abruptly dies. It will idle fine and was easily warmed up enough that cold start was not the problem. I can't imagine how changing the oil could have this result. The oil light goes right out once the engine starts.

Any ideas what's going on?

I don’t imagine the oil and filter change explains what’s going on. Air, fuel, spark. Since it idles fine, I’d wonder about the carbs. How long since a carb rebuild, or new diaphragms?

When was the last time it ran fine? Any other maintenance since that time?

Check that the carb cables are seated properly.

Has a change in performance recently required a change in carburetor settings?

In the 1000 miles you have ridden since the top end was put back together have you checked the head torque and the valve clearance? It sounds like you could have a valve (or two) close to zero where the engine runs at idle but wont under load. Your description indicates you have fuel/air/spark sufficient for an unremarkable idle and, it was running/accelerating fine before the oil change so the carburetors worked before the oil change. I'm going to guess "Insufficient power from combustion to support forward momentum resulting in a failure to proceed", with a notation to check valve clearance.

Did you turn the fuel petcock(s) on?
Is the fuel level low to the point where you might need to flip the petcock to reserve?

Plot thickens

in response to questions
It ran great before the oil change
The fuel tank is half full and I have opened the reserve and the main petcock with no change
I torqued the heads and reset the valves about 100 miles ago. it ran fine then
I hoped against hope that it was a simple head slapper like Paul's idea that the cables were not seated in the carb - nope

So I fired it up again this evening, after work. it fired right up, warmed up fine, took revs sitting in the garage. so I sit on it and was going to run it up the street, it dies. So I'm just looking at it, sitting on the seat, thinking colorful language and as I lean on the handlebars all the indicator lights ago off.

It is electrical. the least push to the right initiates a short or disconnect in the power. It is too hot in the garage to chase it downright now, but at least I have a track to follow.

I will post as I fuss more.
Bob.

"Coils" is what comes to my mind.

My 78 R100/7 experienced the same issue several years ago. I was somewhat perplexed also. I went out one evening turned the lights out in the garage ground the plugs and cranked the bike over. I noticed the spark at one plug was very weak. Bingo saw the top of the coil was cracked and spark jumping to the frame. The bike would run at an idle but not under a load riding it.

Kill switch problem?

Could it be your kill switch acting up? Is it in the detent for "ON" all the way? Might have gotten bumped out of position. May be a short, or bad switch. St.

So I'm just looking at it, sitting on the seat, thinking colorful language and as I lean on the handlebars all the indicator lights ago off.

It is electrical. the least push to the right initiates a short or disconnect in the power.

You need to poke and prod the wiring bundles that reach the handlebars causing things to turn on and off. Then isolate where in the bundle. Then strip the bundle sheath and isolate which wire(s) are broken. Be suspicious of wire ties too snug.

The last time I ran across an issue like this, it turned out to be an oil soaked air filter. The test is to remove the tubes from the filter chamber to carbs and run the bike with the carbs open to the atmosphere. Some times the last thing you did is the seed of the trouble, but not always.

Bob_M said:

Right next to the zip tie that binds the wire bundle from the starter button to the handlebar there was a break in the sheathing and the green/blue wire had a break in its insulation. Simple fix.

Click to expand...

I'm glad to hear you found and fixed the problem. I had a similar issue on my F650 once.

Thanks for taking the time

Hey, thanks for letting us know what you found. I hate it when people post for advice then don't let us know how it turns out. St.