R69 not running right

niall4473 · Post by **niall4473** » Thu Dec 06, 2007 11:58 am

Sorry if I'm stating the obvious here, but how did you know there was fuel in the tank? You looked inside, right?
And then the bike ran ok for 5 minutes again, right?

If the bike has stood for a while this happens and the reason is SO obvious no-one checks this, they start ripping the bike to bits and get really frustrated because the problem just won't go away.

What happens is the rubber (or cork) seal in the fuel cap dries out and shrinks a bit, then you fill the tank up with petrol, (right to the top), and it swells up again. Only now it is bigger and softer than it was before and when you yark the cap tight it spreads out and masks the little annular breather holes around the periphery of the cap, just enough to create a partial vacuum, which restricts the fuel flow enough to make the engine run rough. When a sufficient negative pressure is reached either the motor stops and you look in the tank to see where all that petrol went and break the vacuum, or the seal breaks a little and some air gets in and the bike picks up until the vacuum is created again, (you can test this, undo your fuel line at the carb end and run it into a jerry can, it takes longer to build a vacuum the less fuel is in the tank, but you won't get a gallon (UK or US) out before the flow starts to peter out, sometimes you hear a little farty noise as air gets in and the flow will pick up again, or loosen the cap and listen for a hiss as the seal breaks and the flow will increase). But when you examine the cap often it looks fine because with no pressure on it the rubber (or cork) goes back to shape.
Solution: either very carefully trim the seal right round its outer circumference (not easy, often they disintegrate when taken of the cap), or drill a 3/64 hole in the top of the cap and periodically rod it through with a wire.
Once again sorry if I'm telling my Grandmother how to suck eggs but I've had this problem and its infuriating. If you haven't already, have a look, it might save a lot of needless expense and effort.
Good Luck!

R50Bill · Post by **R50Bill** » Thu Dec 06, 2007 12:35 pm

This sounds so much like my problem ("Newbie") and now I can't even get it started.

Hmmmm, my cap is so loose it just spins around loosely, the bike sat outside unstarted (not by me!) for over 2 years. The reference to creating a vacuum makes sense, since in modern cars you get a CEL if the fuel cap is loose. Do I need a whole new cap?

niall4473 · Post by **niall4473** » Thu Dec 06, 2007 1:11 pm

To R50Bill,

This sounds so much like my problem ("Newbie") and now I can't even get it started.

Hmmmm, my cap is so loose it just spins around loosely, the bike sat outside unstarted (not by me!) for over 2 years. The reference to creating a vacuum makes sense, since in modern cars you get a CEL if the fuel cap is loose. Do I need a whole new cap?

I don't know mate, I see you have a locking cap, if its the sort which turns when its locked up I suppose so, possibly, just try doing what I put in the post to redavide and you'll soon see if its vacuum locking. Locking caps can be prone to this, but whats a CEL?

redavide · Post by **redavide** » Thu Dec 06, 2007 1:18 pm

Niall,

Thanks for your input. A friend of mine suggested the same thing and it makes good sense because the cap is very tight and it could easily have sealed the tank, and as you point out, it makes sense in light of the symptons (vacuum build up, release, vacuum build up release, etc) which would explain the 5 minute intervals of apparent fuel starvation. When I take it out for a test run next week, if the problem recurs I can visually check the transparent fuel filters to see if fuel is or isn't arriving from the tank. If it isn't flowing and then starts to flow when I unscrew the cap, I guess I'll know that you're right.

Thanks again.

R50Bill · Post by **R50Bill** » Thu Dec 06, 2007 1:22 pm

Yeah, my cap is loose as a goose m8, you can tilt it up and down and it doesn't even lock anymore, the key turns, but the 2 'fingers' on the inside don't move. I don't think there's much pressure being created in the tank. Is there a repair kit or at least a universal cap that will fit temporarily?

CEL? "Check Engine Light". If you have a German car, you'll know what I mean.

niall4473 · Post by **niall4473** » Thu Dec 06, 2007 3:42 pm

R50Bill
If your cap as is loose as that then the root of your trouble lies
elsewhere, as for a replacement, if you have a shop in your area that specialises in old VWs they should have one that fits (Beetles had the same cap in the 50s , although some had the WV rune on them),
Also many older European (not British) vans have an 80mm cap that will fit, I don't know how common they might be over there.
If its loose enough to spill fuel when you rock the bike, definitely change it ASAP.
As for a repair kit, again try aircooled VW dealers, I've seen a repair kit for the Blau caps.

R50Bill · Post by **R50Bill** » Thu Dec 06, 2007 4:02 pm

I'll get a new one from BlueMoon I guess, saw one on e-bay today, but no cork left, too bad.

Check this out:

On Dec 6, 2007, at 2:02 PM, Bill Squire wrote:

Hi John,

I took it out after you left, but it still runs very poorly, and I haven't been able to get it started since then. It acts like it has no gas. BMW forums say it may be a clogged petcock filter, residue at the bottom of the carbs under the floats, a bad coil and even a poorly sealing gas cap (not enuf pressure). Any ideas?

I've just purchased a bunch of new replacement stuff, it would be great if it ran.

Bill

From: John Long [mailto:4long@mindspring.com]
Sent: Thursday, December 06, 2007 2:07 PM

Bill,
It's probably two fouled spark plugs after all the flooding carb
problems."

John

On Dec 6, 2007, at 2:24 PM, Bill Squire wrote:

Are they new plugs John? If new, do I just clean 'em up with some steel wool? If not, what is the part number, I'll get some, and do they need gapping?

Bill

From: John Long [mailto:4long@mindspring.com]
Sent: Thursday, December 06, 2007 3:44 PM

The plug is a NGK BP6HS and the gap is .020" Once they get fouled they are NG.

John

R50Bill · Post by **R50Bill** » Fri Dec 07, 2007 2:32 pm

If its loose enough to spill fuel when you rock the bike, definitely change it ASAP. As for a repair kit, again try aircooled VW dealers, I've seen a repair kit for the Blau caps.

Thx! I grabbed this in the meantime, seemed like a good deal: http://cgi.ebay.com/ebaymotors/ws/eBayI ... Y.m311.lVI

This seller has lot of stuff, ne1 have any feedback on him/them?

schrader7032 · Post by **schrader7032** » Fri Dec 07, 2007 4:48 pm

S. Meyer is a very well known supplier of vintage parts. They're in Germany, as well as other suppliers from that side of the pond. Mark Huggett is another supplier (Switzerland) who is a distributer of BMW Mobile Tradition, basically an arm of BMW. There are suppliers here in the US; one is Vech at Bench Mark Works who also has close ties with BMW Mobile Tradition. Check here for other parts and service suppliers:

http://www.vintagebmw.org/version6/index.php?q=node/75

Kurt in S.A.

EuroIron · Post by **EuroIron** » Sat Dec 08, 2007 11:21 pm

well he is telling you right about fouled plugs and today's fuel

often getting a troubled bike up and going good will require a few sets of new plugs before getting everything dialed in

sometimes blasting them will recuperate them though

I've not found it to be consistent and new plugs are cheap, sorta still anyhow

not a bad idea to even set the gap down a bit to see if that helps

if it does, you do have a weakness in your ignition and even though, the old timers here may not believe the tales about being able to determine coil vs condenser by looking at metal transfer on the points contacts

it's very true and the first logical place to look once it has been determined there is an ignition issue, cheap and easy just to keep an eye on anyhow