R60/6 '75 backfiring issues.

[Lasse]

I am being told it might be a burned valve, lets not hope so Eagerly avaiting a "timingpistol", but I guess it's kind of hard timing when its hard to reach 3000 RPM.

[Lasse]

I just borrowed a timing light.

At idle I could see two centre dots, one smaller than the other. Smallest to the right. When I could finally get it to 3000 RPM I had nothing, nada, zero in the window.

So can I assume my advancing unit needs to be looked after? Should I try taking off the whole pointsplate and go from there? Whats a good starting point?

[Kurt in S.A.]

Does sound like your timing has shifted big time. The dots are supposed to be the marks at full advance...you shouldn't see them at idle.

The good starting point is to time the bike statically, using a volt-ohm meter or light bulb for testing continuity across the points. You also need to be sure the points gap is near the proper range...about 0.016".

Once you've done that, then come back and recheck for full advance around 3K RPM. Those dots should come into the window and remain there from 3K and up.

Kurt in S.A.

[enigmaT120]

Have you checked valve clearances yet on a cold engine? Points gap, and timing? Those are just good things to check before messing with the carbs. If you have a compression gauge you can check for that too. It would be spectacularly bad luck to burn a valve 2 days after buying the bike, though. I don't know what the initial setting for your mixture screws should be.

Oh: I don't think you need to remove the seat to pull off the gas tank, you should be able to do that with the seat in the raised position.

Here's a useful site (if you're a fast reader...) for several procedures on your bike, including carb rebuilding and tuning and balancing:

http://bmwmotorcycletech.info/techindex.htm

Edit: dang, I didn't notice the second page before I posted. Sorry.


Good luck,

[Lasse]

I think I have solved it, turns out that the points didn't really open.

Turned the engine several times by hand and couldn't see any movement, I tried with 0.15mm at various place to see if it was just my eyes.

Turned the engine to approx. TDC as I knew the points would have to open around there, no difference. So I set them to 0.4mm turned the engine over again to check that it was in fact the point of highest lift. Happy days.

Started the engine, sounded smooth, revs freshly up through the range.

Tomorrow I will try the timing light again as I now have a better starting point.

[dwerbil]

Good going, Lasse!
Would be prudent to do a valve lash check with engine cold, then you'd know the valve settings are ok.
Then proceed with timing, etc. Sounds like you found the culprit, though.
You're on your way down the highway!

[Lasse]

I think I know why it happened. The felt pad was completely dried out. Couldn't that have been the cause of the fast changing gap change?

[Kurt in S.A.]

The felt pad that drags grease around for the points rubbing block? I don't think that's the cause of this. Unless there was absolutely no grease and had been that way for years...the rubbing block would have worn down causing the points gap to close. A small gap would result in the timing being more retarded...the points would open later and later.

Your points plate could have rotated. You really need to establish a baseline for timing by redoing the static timing and going from there.

Kurt in S.A.

[Lasse]

The felt pad that drags grease around for the points rubbing block? I don't think that's the cause of this. Unless there was absolutely no grease and had been that way for years...the rubbing block would have worn down causing the points gap to close. A small gap would result in the timing being more retarded...the points would open later and later.

Your points plate could have rotated. You really need to establish a baseline for timing by redoing the static timing and going from there.

Kurt in S.A.

Any info on static timing? I have requested milimeters before TDC on another site, but to no avail. Haven't found any info besides "use a timing light". My german workshop manual doesn't list anything either.

[Major Softie]

I believe Duane has a page on static timing. If not, he still has a ton of stuff you'll want to know.

http://w6rec.com/duane/bmw/index.htm