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R90s
- Thread starter arptra
- Start date
something fishy going on here
If your motor is static timed to the F (full advance) mark, You should have broken the starter nose cone by now. We might be able to confirm this with forum member "Crazydrummerdude", but he has been absent for quite some time. The need to extend the range of adjustment on the points plate suggests a slack timing chain, and as such, high mileage. I would think that if the motor starts and runs with the timing significantly advanced, that you would hear a distinct pinging noise, especially under load. Of course, I could be completely wrong.
If your motor is static timed to the F (full advance) mark, You should have broken the starter nose cone by now. We might be able to confirm this with forum member "Crazydrummerdude", but he has been absent for quite some time. The need to extend the range of adjustment on the points plate suggests a slack timing chain, and as such, high mileage. I would think that if the motor starts and runs with the timing significantly advanced, that you would hear a distinct pinging noise, especially under load. Of course, I could be completely wrong.
if I take it down any farther retard it doesn't run as well and only has about 1/8 left in that direction,, ordered new points and will check that out, it is sometimes a little slow start but not bad, it is running great now. It isn't a high mile bike very low mile. In the old hotrod days that is how we set timing on cars and trucks, if starter didn't drag a little it didn't run as well. I'll figure it out I thought someone may have had the same issue.
So it starts at idles with the F mark in the window. Have you put a timing light on it to see what happens when advance the throttle? If the F mark moves out of the window, then James' question about pinging really becomes an issue. If it does ping, then seeing the F mark at idle means that is a real observation. If there is no pinging as the ignition advances, then seeing the F mark can't be real. I would think that if the bike were that advanced, the performance would be awful and the pinging can result in real damage to the piston and the big end bearings.
Maybe the advance unit is not working? What about the springs that hold the weights of the advance...are they good? Maybe try shining a timing light on the advance unit with the engine running...see how they operate.
Maybe the advance unit is not working? What about the springs that hold the weights of the advance...are they good? Maybe try shining a timing light on the advance unit with the engine running...see how they operate.
The mark moves down when accelerated, I tried taping in the advance unit and f mark still there, it is a little lower in the hole than before when it was clattering like they do with bad gas. It runs strong now and will cook on the road and is very smooth and starts/idles smooth. I will take this one to a pro after the holidays, it is way to nice to damage. I mostly have and ride airheads with electronic ignition and they are a breeze to time.
I had thought about the flywheel being one bolt off, but for a 5-bolt flywheel, that would mean that it would be 72 degrees off. IIRC, the F-mark is something like 30 degrees before top dead center. I don't see how the flywheel could be 72 degrees off and the piston is at TDC and the OT mark is in the middle of the window. If the flywheel was 72 degrees off, the OT mark could be in the window but the piston wouldn't be at TDC. 
I had thought about the flywheel being one bolt off, but for a 5-bolt flywheel, that would mean that it would be 72 degrees off. IIRC, the F-mark is something like 30 degrees before top dead center. I don't see how the flywheel could be 72 degrees off and the piston is at TDC and the OT mark is in the middle of the window. If the flywheel was 72 degrees off, the OT mark could be in the window but the piston wouldn't be at TDC.
yeah,, I just got the piston exactly at top and looked in the hole and it is perfect,,, I'm thinking it must be points, the advance all look good,, I went ahead and ordered points from Ted, thanks for that info.
Forgot to mention the "S" trannies had different gear ratios than the standards. AFAIK, all "Ss" came with the 3.00 to 1 final drives which could give slightly better gas mileage, and the transmissions had a sport cluster the same as later RS. No biggie, you'd have to ride one and immediately ride the other to feel the difference. Or I could be completely wrong, I'd have to look it up.
Never know what you'll find in an old airhead, but it can all be sorted out. Happy Thanksgiving.
Never know what you'll find in an old airhead, but it can all be sorted out. Happy Thanksgiving.
good to know, I thought they were all the same, I know they seam to run strong
R90/6. 1st-13.60 2nd-8.84 3rd-6.40 4th-5.16 5th-13.60
R90S. 13.20. 8.58. 6.21. 5.01. 13.20
There were other ratios in the R80, lower, and R100S, higher. And of course all of these went through specific geared FD up to 2.91, down to 3.36, to one. Got a spare gearbox?, find out what it came out of. Gear boxes have numbers but I don't think they tell anything except the approximate date of manufacture.
This came from mag road tests and could be wrong, FWIW. A tranny expert might be a better source of info.
R90S. 13.20. 8.58. 6.21. 5.01. 13.20
There were other ratios in the R80, lower, and R100S, higher. And of course all of these went through specific geared FD up to 2.91, down to 3.36, to one. Got a spare gearbox?, find out what it came out of. Gear boxes have numbers but I don't think they tell anything except the approximate date of manufacture.
This came from mag road tests and could be wrong, FWIW. A tranny expert might be a better source of info.
the little tab that holds the point wire was in the way not letting it roll around enough, got it almost on time, mark is a little high to the mark on the hole but advance F mark at 2000-2500 is right on,, it runs terrible set there, you know I had plenty cars/trucks that wouldn't run on time but never an airhead.
shandeland
Club President
Is this bike Dual Plugged? that would make a difference with the timing.
Steve
Steve
it doesn't change over 2500 rpm
mine is the early unit I read 2200RPM, ( bmw motorcycle tech) said they changed the springs later, that sounds about right on mine, it didn't change over low 2000
"Only a bit later than BMW's phasing-in of the noted changes, BMW was finding a lot of pinging (pinking), in countries where the gasoline had a relatively low octane. BMW again changed the automatic advance, so that the prior maximum advance which was obtained at about 2200 rpm, was now 2800, 3000 or 3200 rpm (depending on which literature you are reading). "
...but you consider your R90S and it's advance unit "early"? Have you looked at the number that is stamped on the unit? I'd be interested to know where yours.
