New Guy with a Project bike.

[ChuckyShamrok]

Hey, I'm new. For a background, I grew up around airheads, my father had 2 growing up, now he has three. I've been working on cars since I was old enough to hold a wrench, and am currently employed as a fleet mechanic. I just picked up my first airhead, a 74 R90/6 that was a damn near a basket case without being one. So far I've rebuilt the top end of the motor (New Rings, wrist pin clips and gaskets. I've had to rebuild the tranny as the input shaft had teeth sheered off the gear the kicker engages. Any tips on getting the tranny back together? The manual says to heat the case up, but I'm pretty sure I would be murdered if I used the kitchen oven. Another issue I've ran into is the engine doesn't want to start, at all. I've gone over the carbs, and mucked with the timing, ALOT. I'm leaning towards either a weak spark(Much weaker than modern cars at least) or the mechanical timing is off as I get suction at the exhaust pipes.

[PITAPan]

You didn't disturb the cam, timing chain etc. So the base cam timing is still correct. Reset valves. Make double sure you are on TDC compression (spin the pushrods). Use go/no-go feeler gauges. Engine must be cold but seeing as how it isn't running, it is.

Fresh plugs. Check spark with plug laying on head. But even with a weak spark you should get a chuff or something.

Check for fresh (<1 month old)fuel in bowls. No gas = no run. Check fuel height. See snowbum. Measuring fuel depth in bowls is most accurate and if you mark the bowls (as in make a mark x.xx mm down from the bowl lip) It is easy to do, easy to check and you have the mark ever after. Don't remove a bowl with any petcocks open. Don't worry about dribble into the bowls. it is very little. The starter fluid routine diagnoses fuel problems pretty quick.

Set timing with a static light ignition on engine not running. Easy with a points setup. Check points condition and gap. Never hurts to replace points and condenser. Put old one back in after all is running and if they work well then use them up and save the new ones for later. You don't "muck" with timing, you simply set it on what it's supposed to be.

Refer to the the documentation you used to get the transmission apart for info on how to put it back together. If you've been making up your own documentation, you are in trouble. The case temp for assembly after checking the shimming is given in the manual. What temp does water boil at where you are and do you have a bunch of cheap towels?

Edit; I've been thinking slightly not nice thought about you because despite your claimed experience you are asking about the most basic diagnostic procedure you can do on any gas 4 stroke engine---and you are looking at one of the simplest engines on the planet. So I've been trying to think of what might be non-obvious and airhead specific that could trip you up. The spark is going to be a big clue. no spark = no run, but if you get no-spark the WHY could be non-obvious. If you have the tranny out then the neutral switch is disconnected. This should result in the starter not even spinning it. But I don't know if you've rigged the wiring so it will try. Try holding in the clutch and see if you get sparks. There are some other odd causes of no-spark. But you haven't reported the condition so...

[ChuckyShamrok]

Thanks, the Points part is screwing me up, I'm 27, haven't had to really work on cars with points OR carbs. I have a weak spark that will occasionally fire a cylinder off, but more often than not won't. Carb wise I'll check the fuel level in the float bowls. I set timing using a ohmmeter to set the points. I spun the engine to the S mark on the flywheel and than checked the points, which are open at that point. I set the gap at spec. Still have a weak spark. battery voltage at power wire going to the coils. I have a set of points and a condenser on order, as I figured I would rule those out cause they're cheap. What scares me basically is the previous owner has had his hands in various parts of the bike, and it worries me he may have done something weird.

[PITAPan]

Thanks, the Points part is screwing me up, I'm 27, haven't had to really work on cars with points OR carbs. I have a weak spark that will occasionally fire a cylinder off, but more often than not won't. Carb wise I'll check the fuel level in the float bowls. I set timing using a ohmmeter to set the points. I spun the engine to the S mark on the flywheel and than checked the points, which are open at that point. I set the gap at spec. Still have a weak spark. battery voltage at power wire going to the coils. I have a set of points and a condenser on order, as I figured I would rule those out cause they're cheap. What scares me basically is the previous owner has had his hands in various parts of the bike, and it worries me he may have done something weird.

Thot that might be. What I know about magnetos you could engrave on the head of a pin with an axe---but I don't have to deal with one or I'd take a day and learn it. Big upside to that bike is there is a tremendous mount of documentation and the issues are known. one special one for that particular one is if you have old /5 style switchgear or the newer WTF-were-they-thinking? kind. Pretty different wiring diagram with important changes in the starting system. But carbs or FI, pulling a plug to check for some gas on it is all the same. Sparks is sparks be it points and coil or Electronic pickup and HEI. The latter bites harder but a limp yellow spark and it won't run right. Ought to run tho' If it''s very cold in your shop then more trouble. Starter fluid.

The chokes on the carbs may not be overly functional. Diagnose with starter fluid. If it runs on the spray but not on the carbs, you got a fuel problem, right?

if you are serious about keeping and wrenching it, I would buy 3 books. The charging system manual from Mottorad Electrik. $23 or something. The Bing carb manual from Bing Agency International. $11 shipped. And the old VW book from amazon, get a $10 used one, any vintage that deals with the air cooled VWs. http://www.amazon.com/How-Keep-Your-Vol ... agen+alive. It will teach you everything you really do want to know about points and coil ignitions. Unlike Snowbum, it's well written for the everyday hippy mechanic and it's fun. Pics. worth framing. Add a Clymers (beware of errors!) and maybe a Haynes just to waste the money and you are set.

The VW book with do for an intro to carbs but those were downdraft Solexes. You really want the Bing manual to know the Bings work. Good news is they are dead simple.

try a trouble light instead of the ohm meter. Just make one maybe---with micro clips on the wire ends. Goes under the seat nicely too.

Do not turn the engine with the alternator rotor bolt unless you remove the plugs. I avoid turning the motor with that bolt at all. Kickstarter or rear wheel work fine.

yes, you want to time dead on the S mark. But the points gap has to be pretty on or it throws you off---and the dwell won't be right. And you gotta clean them or the new ones burn on you... Read the book. You want to know WHEN the points open. Should be on S set static. if you just check that they are open on S but don't notice WHEN they open, that could be on L, M, N,or Q. No good.

There is a heavy rubber hose between the carb and the head. Any air leakage it its joints will lean out the mix. Makes it hard to start. Starting fluid helps with diagnosis. if those are hardened and cracked, replace. But you can limp them with smears of silicone sealant short term and get up and running. Then add to next parts order or make some. Big leaks will hurt starting. Little leaks not so much but it sure won't run right when you rev it and the vacuum builds.

Tight exhaust valve = very hard to start. Double check.

You want 5k ohm resistance in the spark plug secondary circuits. Resistor plugs and non-resistor cables or vice versa. Never both,. Never carbon core cables, only copper core. It will start and run with no resistance although the sparks are shorter duration.

It's an old bike. Clean every electrical connection. This will be more important sorting the starting and charging systems.

No compression = no start. What do you mean you put the funny wrinkeled ring at the top of the piston? When you get it running, check compression with it warmed up, carbs off.

I assume you have looked at the air filter. Remove it when using starter fluid.

Starters overheat. Bad. Don't crank and crank. If it don't fire after turning over 4-5 times figure Allah don't wuv you and change something or set up a diagnostic. Let that starter cool (as in the brushes and commutator that you can't just put a hand on and check temp) while you put a small charger on the battery.

I pay attention to the heads on fasteners and look for poorly patched in elec accessory circuits. Both say the PO was a hack.

Edit:

You cannot pull the upper plastic air tubes, open the throttle butterfly and just spray starter fluid in the carb. Works poorly. You have to open the throttle butterfly, then reach in with a popsical stick and lift the piston, then spray in the carb. Once running you can spray into the partially opened butterfly. An interesting feature of the CV carb is it is a vacuum slide type. You open the butterfly with the throttle (just like a FI throttle body) but the real throttle is a vacuum operated slide (round cylinder slide). When the vacuum builds in the venturi a diaphragm above the slide raises it opening the real throttle. That slide has a tapered metering needle hanging out the bottom going into a jet (orifice). As the slide raises the needle withdraws from the jet making a bigger and bigger hole for gas. look and see with your popsicle stick but don't bend it. Some are "alloy" and fragile. This setup makes the carbs self adjusting in certain ways, and fuel efficient. But they ain't real responsive. look in your manual and set the carb to the nominal values to begin balancing them. This screw so much open, that one so much closed, throttle cables slack, etc. That will at least get you an idle. if anything open the idle air screw and extra 1/4 to give you a richer starting mix if working in the cold. The o-ring on that screw, or on the idle mix jet feeding it, can be hardened, cracked, broken. This will murder the starting mix. When warm you can get away with it although you can't balance the carbs. In the cold...problems. But this all assumes you have tested for a fuel problem with the starter fluid and confirmed you got one. Then you go after what the carbs are doing. There is a source for cheap kits that will cover the basics. (like $30 for both carbs and includes the expensive diaphragms---from a real dealer no less---avoid eBay crap at all costs)

[Airbear]

G'day Chucky, and welcome aboard.
Along with PP's advice above, I suggest getting one of these -



With the cover on the pointy bit it will wedge nicely between the jug fins. The alligator clip goes on the terminal on the condenser. You want the light to come on as the S mark passes the middle of the window, rotating the engine clockwise.

An important thing to note is that you might have one cylinder correct but the other cylinder might be significantly advanced or retarded, so rotate the engine through another 360 degrees and check again. On my '74 the sync was way out due to a very slack timing chain and a bent cam nose.

Weak yellow spark? 40 year old coils? New coils make a big difference. They are packed full of fat blue sparks. Your BMW uses the same as used on old 6Volt VeeDubs.

http://vwparts.aircooled.net/6V-Bosch-B ... -016us.htm

Also, it is worth reading this, written by Duane Ausherman, a member here -

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

And, if you possess the courage, this article by Snowbum will keep you busy for a while -

http://bmwmotorcycletech.info/ignitionsingleplug.htm

Have fun, and good luck. You will find great satisfaction in solving this issue, and will look forward to the next challenge you bike will throw at you.

[PITAPan]

G'day Chucky, and welcome aboard.
Along with PP's advice above, I suggest getting one of these -

Where'd you get that thing??


Tool lust...

[ChuckyShamrok]

The chokes on the carbs may not be overly functional. Diagnose with starter fluid. If it runs on the spray but not on the carbs, you got a fuel problem, right?

Will occasionally fire, but doesn't run on the spray

yes, you want to time dead on the S mark. But the points gap has to be pretty on or it throws you off---and the dwell won't be right. And you gotta clean them or the new ones burn on you... Read the book. You want to know WHEN the points open. Should be on S set static. if you just check that they are open on S but don't notice WHEN they open, that could be on L, M, N,or Q. No good.

So set the points to begin opening on S. The S mark on my Flywheel looks like "| IsI" Do I set it the line above the S to the mark on the case?

You want 5k ohm resistance in the spark plug secondary circuits. Resistor plugs and non-resistor cables or vice versa. Never both,. Never carbon core cables, only copper core. It will start and run with no resistance although the sparks are shorter duration.

Plug cables have 5K ohms, plugs are non resistor.

I pay attention to the heads on fasteners and look for poorly patched in elec accessory circuits. Both say the PO was a hack.

Yup, alot of the heads are messed up, mismatched with other style bolts in the same place and I've found some weird wiring in the bike; a random push button going to the starter relay, I'm thinking he may of ghetto rigged a kill switch onto the bike.


Thanks for the help, I'll bounce down to the barn tomorrow and freeze my butt of and get some work done. It's funny. I helped swap a LS1 out of a 98 Camaro and put it in a 86 Trans Am, no problems, but something which should be simpler, with less electrics and no computers, is being more difficult for me.

[ChuckyShamrok]

What helped alot putting the engine in the Trans Am was this

It's a Power Probe three. tells you the amount of voltage, and can provide power and ground with it.

[Deleted User 62]

So set the points to begin opening on S. The S mark on my Flywheel looks like "| IsI" Do I set it the line above the S to the mark on the case?

Just to clarify, you need to adjust the points gap first, to as close to .016" as possible. This is done when the points rubbing block is on the high point of the cam under the advance unit; fully open. Timing is accomplished by rotating the whole plate the points are mounted to. See the notch and two nubs at about 2 o clock? This is the adjustment that gets your static timing light to come on when the S is centered in the window while you rotate the engine clockwise. The marks you see above and below S are for too advanced or retarded. Do you have a strobe timing light as well? Once you get it running, you need to make sure the F mark is centered in the window at full advance, usually around 3000 rpm. Hope this helps...

[Airbear]

G'day Chucky, and welcome aboard.
Along with PP's advice above, I suggest getting one of these -

Where'd you get that thing??


Tool lust...

From my local Auto Tool Shoppe. Just bought a new one yesterday for the grandson - OZ$8.50.
Bloody hell, I just googled 'auto test lamp' and found this, for OZ$4.80, free shipping (in OZ).

http://www.ebay.com.au/itm/Auto-Circuit ... 1334502668

ps: Tool lust can be burdensome. Have you thought of joining a support group?