project r90/6 wont start -- help needed

[montmil]

Well said, Ken.

[montmil]

I have a good friend that lives within the Dallas-Fort Worth MetroMess and owns five BMWs. Friend is having a very similar problem with his "new to him" neglected R90/6. Two of us are attempting to assist him but we're rapidly running out of ideas. Both of us have encouraged him multiple times to post up here on Boxerworks and/or the AirList with info on what he has done and what the symptoms and issues continue to be. Perhaps he's a bit overly sensitive, but he tells us that he doesn't want to be made to look foolish, ignorant or unwashed.

Well, heck... I get that here at home!

We now return you to our regularly scheduled topic.

Monte

[pleather717]

no worries i'm not too proud to ask, been googling this issue for weeks and although i have made mild progress i am still waiting for the "AHA" moment. i am planning on buying a new coil this week to see if it improves the sparks. that and go through the carbs again.

paul

[steve]

here is what i have done:
new starter relay. new plugs/wires. fresh oil. fresh gas. new points, new condenser. timing adjusted statically to "s" mark. points properly gapped.

Did you try to start it before replacing the starter relay, points, plugs, wires and condenser? The reason I'm asking is sometimes it's best to limit the number of things you change or replace before that first startup attempt. When I am trying to start a long-stored bike that I just bought, I typically do only a very few things:

1. I look in the float bowls. Are they dirty or clean? I don't make any carb adjustments, or do any carb disassembly/cleaning, unless the carb is clearly dirty/varnished/messed up.

2. I quickly look at the points to see if they open and close, and have approximately the correct gap. I don't adjust or replace the points "just because". I only replace or adjust them if they obviously appear to be damaged or way too far out of spec to allow the bike to start.

3. I gently turn the motor over by hand to see if the innards feel right and make no bad noises.

4. I do a preliminary inspection of the ignition circuit (wiring, relays, and so forth) to make sure everything at least superficially appears to be in place. No replacing condensors, spark plugs, relays, and so forth before initial start up attempt.

5. Replace oil and fuel.

Then I try to start it. If the bike starts after I do only these few things, great, I've just found out that the critical parts are functional. I can then replace them (or not), whenever I like. I also now have the advantage of a running bike, allowing me to then go through the entire ignition circuit with my multitester, to see if all of the parts are operating within spec. And I have minimized the possibility of me making an error (when disconnecting and reconnecting wires, say, or installing the wrong condenser, or setting the timing wrong, or some other blunder). That is important in my case, seeing as how I am not an expert mechanic, and each part I replace comes with a real chance for error.

I think of the initial startup as a kind of scientific experiment. I change variables only when necessary (and change only one variable at a time), until I get the data I am looking for.

None of the above may be helpful to the OP (sorry!). I suppose it's more like a philosophical lecture than helpful advice. I just wanted to throw it in here for those less-experienced folks, like me, who need to follow practices that minimize the potential for screw-ups and maximize the chance of starting the bike.

[Airbear]

Paul, with your static timing procedure, did you rotate the engine a couple of times to check that the S mark appears in the central position for both sides? The cam nose can be slightly bent and it takes very little deflection to have wildly different sparking for each cylinder. This occurred with mine and there was almost 30 degrees difference. One cylinder was correctly timed and the other was grossly advanced (or retarded - I don't remember which). When it did run (badly) I attempted to check dynamic timing with a strobe. Only a single image in the little window but shining the strobe on the advance mechanism showed this:



It's worth checking. With a weak spark and one cylinder badly timed, starting will be very difficult.

[pleather717]

airbear, yes i rotated it a few times and got what seems to be "s" in the central position for both sides. i will take another look, it never hurts to become more familiar with the process and what used to take an hour now takes about 10 minutes to check and set. my test light comes on at the correct time and i gapped points per manual

the under tank mc was leaking badly and ruined the starter relay so i have been reconstructing as i go , the points were worn and the condenser was a fairly cheap part so i bought one.

bike was last registered in in '96 so its been a while

i have a new coil on the way and plan on rechecking each carb to make sure every tiny hole and orifice is clean and clear.

thanks for the help everyone

[Airbear]

It's the passage that runs from the idle mixture screw into the throat that is difficult to clear, being a bit of a tortuous path. Took me a while to find that. I simply could not get one carb to be tunable at idle when my bike was new to me. Haven't had any trouble since and I'm very fond of the Bing, generally speaking.

Do you have any idea of the compression? A bike that hasn't run since the previous millennium may have a non-seating valve or stuck rings. It would be good to discount that.

[chasbmw]

A couple of squirts of engine oil into the cylinders can help restore compression on a long neglected bike.

I would also think seriously about a long neglected carb.....As Airbear has mentioned the idle circuit gets blocked, float bowl corks harden, choke may not be operating properly.......

And this may be teaching Granny to suck eggs, but I find on CV carbed bmws, it helps to keep the throttle closed when starting the bbike, you then pick it up on the throttle as it starts to fire.

[Duane Ausherman]

We would never replace points and condenser unless we proved that they were needed, which was very seldom. Between my shop and customers who replaced condensers, several were found to be defective. Some didn't work at all, but usually they worked for a short time and then failed. We considered a "new" condenser to be a critical element to suspect.

The whole thing about points and condensers can be read on my website.
http://www.w6rec.com/duane/bmw/points/index.htm

A more general article (list of articles) is here. http://w6rec.com/duane/bmw/electric.htm

[daz]

Since you say you have gone through the carbs, have you looked at the petcocks and fuel line. If you pull a line going to carb is it gushing out or??? Sitting that long no telling what has sunk to bottom of tank, and to petcocks. The filters inside on the input to the petcocks could be blocked.

I heard that sixty per cent of all carburetor problems are in the ignition system.