Timing advance springs dilema....

[R65Singh]

Just replaced the  advance springs in the bean can as the older ones were worn out.  The bike idles super nice with no vibrations as compared to before and the timing mark is rock solid where as it was dancing around a bit before.  
Now I am faced with this new problem, bike bogs down and hesitates at low rpms i.e less than 3500, above that it is like a turbo kicked in.  
I know it is coz of springs as I put back the old ones back and the problem went away.
I think the new springs are too strong (bought from Motobins) and there might be causing some sort of timing issue, which is beyond me. Any one else experienced something similar and what you did to rectify it.  Thanks!!

The picture is new(shorter spring) vs new(longer, stretched spring).

[steve hawkins]

Are they supposed to be different lengths?

Just curious - cant recall if I have ever changed mine, and its got more that 100,000 miles on it (1979).

[Barry]

I know that there are at least 2 strengths of spring for the earlier airheads. As far as I know that doesn't apply to the bean can airheads which all use the same springs. Are the springs you bought definitely for a bean can model.

I suppose your original springs might have stretched but it's even more likely that they were not the correct ones in the first place or have bean damaged. I'm guessing there was no or very little tension on the bob weights at the resting position.

Which is the new spring in the pic ?

There's nothing special about advance springs that means you absolutely have to buy them as BMW spares. It would be a bit of a lottery but if you are really stuck I would take the original springs to some place that stocks a wide range of springs and say I want some like this with the same spring rate only a touch shorter and you might just get lucky.

[Bob_Roller]

http://www.euromotoelectrics.com/Euro-MotoElectrics-s/58.htm?searching=Y&sort=13&cat=58&show=20&page=3

If you scroll down to the middle of the page, you'll see there are two different springs for the advance mechanism, this may be your problem .

[nhmaf]

Great Link Bob!!!

That would appear to be a problem - different wire sizes in the springs would make them different in spring rate.  The most ocnfusing bit is that it lists BOTH for Type 247 engines, and for overlapping model years, and claims BOTH to be OEM parts.   I had no idea that BMW used different springs in what I thought were the same beancans.   Perhaps the beancans are more different than we thought?
The thicker springs are claimed for model years 1969 - 1981, and models R50, R60, R75.... I suspect that "1981" is an error, and that these are really for the early /5 models with the early points setups.

The thin wires ones are listed as 1973 - 1984, and for models R60, R75, R80, R90, R100, so I presume these are for the /6, /7, and later twinshock macines with the later points in a can or Hall sensorin a can units.

BMW must have used some heavier bobweights in those early units.

[montmil]

I also ordered new springs from Motobins for no real reason other than I was replacing the Hall sensor and had the ITU completely apart.

The "new" springs just looked and felt wrong so they now reside in my parts boxes. Replaced the original springs and went on.

I did not have a jumping timing mark but that issue can also be related to a worm timing chain and/or sprockets.

Monte

[R65Singh]

Thanks for your valuable suggestions guys.  I should have been more clear about the picture.  The shorter spring is new and the longer one is older,  that came out originally.  The picture was just to show the difference in lengths, new vs old.
Bob, the springs you pointed out are for non bean can models.  I ordered one of those too for my 1970 r60 as well (which I bought a couple of months ago and working on it to restore) .  Those came in two types as u said, regular and stronger (for r60 to help pinging problems).  
The ones in question are from Motobins part no 72620, unless some one made a mistake there and sent me the wrong ones, but i doubt that.  The old ones got stretched overtime and developed gap between coil and if I compress it with my hand, its length is same as the new ones.  
I know my timing chain is good (only 16k Kms on the bike) and did replace the older timing chain tensioner with the new one from Motobins.  I think the springs are stronger than the stock ones.

[Barry]

I have a hard time believing that euromotoelectrics have listed the springs corretly. They are suggesting that pre-bean can and bean can springs are the same which can't be right. And what planet are they on with those prices. Springs of that size cost pence to make !!!!  The implication being made with the price and part number would seem to be that they are "genuine BMW springs" and yet BMW don't sell parts for the Bean can.

Motobins don't look to be much better if Monte had the same problem.

Sounds like the original springs have been stressed if there are gaps in the coils and that can't be fixed. The springs may be too long but the spring rate should still be OK so you could compare spring rates by hanging a suitable weight from each spring and measuring the % extension with calipers. That will tell you roughly by how much one spring is stronger than the other. Then you could go looking for suitable springs and have at least as good a chance of getting it right as either of the suppliers mentioned here.

[R65Singh]

Just a quick update about the situation.  Found the problem which was that, I received  wrong springs from Motobins. The replacement springs arrived a couple of days ago and the bike runs much better.  These replacement springs are a bit smaller in length than the one they sent before and have some air gap in the coils.   Thanks to everyone.

[steve hawkins]

Glad it all worked out in the end.

Rev Light.