Couple of nebie questions: hard starting, popping, ect..

[schrader7032]

Peter -

Hard starting might be associated with magneto timing. The magneto must be positioned to provide the hottest spark when the engine is turning the slowest, when trying to kick start it. This is known as the abrisz (sp?) point. Once you set the magneto at this point, you then must set the timing to have the points open at the S-mark. Vech has an explanation of this process at http://www.benchmarkworks.com/. Go to FAQ Tech and look into the various articles...you want the "Magneto Blues"...rather you don't want the Magneto Blues! Read what Vech has to say...

Popping on deceleration...I'm thinking that's too rich and unburned gases are getting into the exhaust and burning then. Try adjusting the air mixture screw a bit CCW. You might also want to be sure the valves are set properly.

Header color...you might need to be sure the carbs are synched. You want them to each contribute the same amount to the idle speed and have the proper mixture. A way to do that is to get the bike started and then turn the air mixture screws CW and CCW until you find the point where that given cylinder runs at the highest RPM, then turn it slightly CW maybe 1/16 of a turn. Since it's an air screw, closing it down restricts the air or makes it slightly richer. Then you should see how the idle speeds are. One at a time, pull the spark plug lead and determine at what speed the bike will run on one cylinder or how many revolutions it goes until it stops. If one is runs better than the other, increase the idle speed of the cylinder that doesn't do too well.

The above work needs to be done with about 1mm of slack in the throttle cables. There's a ferrule nut where the cable that enters the carb that is used to adjust this gap. The last step is to have a little bit of tension in the cables, meaning turn the throttle so the engine runs about 1500 RPM or thereabouts. Then, similar to the idle speed, pull the spark plug cables and note the engine speed. For the cylinder that runs slower, increase the cable tension slightly until the idle speed on a single cylinder is the same.

What you really need, rather than pulling the caps is spark plug extenders. Allan has some good pictures of these:

http://www.flickr.com/photos/roundel/18516219/
http://www.flickr.com/photos/roundel/18516221/

This allows you to use a screwdriver to quickly short out the spark and kill a cylinder. In the long run, this is really the better way to go rather than pull the cap. Alternate back and forth between adjustments. Give the engine time to readjust after you short a cylinder out and let the unburned gas clear out.

The transmissions are clunky. It might be something you have to get use to and time the shifts better and when you ease on the gas. You might also need to consider lubing the input splines to the transmission. Normally a sticking clutch disk results in jerky engagements. You're talking about clunks which may more technique than anything. Plus, these trannys do better in higher gears...less clunking.

HTH...Kurt in S.A.

[Bruce Frey]

Hard starting may also be something as simple as establishing the right "starting drill" for your bike, i.e., how long to tickle the carbs, how much thottlee, etc.

On my prewar machines, I generally tickle each carb for 3 seconds, kick it through twice without the ignition and with the throttle just barely cracked open, turn on ignition (with the throttle sitll barely cracked) and they will usually start on the first kick or second kick. The prewar bikes also have a manual spark adjustment that must be retarded for starting. After the bike starts, I advance the timing a bit which makes the idle speed increase slightly while it warms up. After about 2 minutes for warm up, my old bikes will happily run, even in cold weather. My R90S is balkier than the old machines when cold.

Each bike may have different preferences, so some experimentation may help.

Bruce

[schrader7032]

+1 Bruce is right...try simple first...I keep forgetting that each bike requires something a little different. I find I have to tickle my carbs about 4-5 counts, kick through a couple of times with the key off, then finally turn it on, crack the throttle about 1/4 of the way and she'll usually fire up in 1-2 kicks.

Kurt in S.A.

[Bruce Frey]

With respect to the other issues, you should check the timing as Kurt suggests. Check both cylinders to see if there is differential timing. The automatic advance mechanisms can also be a pain.

It would be worthwhile to check the compression to make sure both cylinders are about equal.

BMW transmission are a bit clunky (compared to new Japanese bikes) and you can't speed shift them. I "preload" the shift lever a bit with a bit of pressure, close the throttle, pull in the clutch and let the shift lever move. It will clunk a bit, but it should be a smooth process. My R6 shares the same basic transmission as your bike and I have always been quite happy with how it shifts. Think of it as how a proper gentleman would shift.....slowly and gently.

If you have had the carbs apart, I assume both sides are jetted the same and the needles are in the same positions.

Finally, check the carb flanges. They are notorious for warping and you may have a leak. Spray some carb cleaner around the flanges with the engine running to see if the speed changes.

Bruce

[Allan.Atherton]

... the bike pops a lot on deceleration. Not obnoxious but always present, anytime I roll off the throttle. Is this normal?...
The soft continuous popping normally happens under those conditions when the idle mix is too lean. If you richen the idle mix, the popping will go away. You may also notice that this will reduce any tendency to hesitate when giving throttle and starting off from a stop.

Turn the idle air screws inward 1/4 turn to reduce the amount of air admitted, take a ride and check for the popping, and turn them out another 1/4 turn if needed.

Note that when adjusting the idle mix, the point at which the motor idles the best (fastest) is too lean and may cause popping and hesitation when ridden. From the point of fastest idle, the screws should be screwed in 1/4 turn to richen the mix before locking them.

[c.d.iesel]

your exhaust popping - back-firing is a leaking exhaust system

look for loose - ill fitting pipes and muffler joints

Welcome to the Art Of BMW Shifting !

..........and the oil used in the gearbox matters.
put 1-finger into the filler hole and see if it appears
to be like thick maple surup ? a lighter oil like SAE30, SAE40
will help all the cogs engage a little quicker at cold temps.
BUT - all 'early' BMW gearboxes need a delicate touch,
Patience, and practice for non-clunk-bang shifting

[VBMWMO]

Love to get some help so that I understand what is normal and what needs attention as I am new to early BMW's.

The bike is a 1953 r51/3. It was restored, probably 5 years ago and I believe it has been sitting acting as garage-art for some time. The main problem I am having is starting. It starts after 5+ kicks cold, maybe 3 or 4 kicks when warm. I took the idle jets out and made sure they weren't gunked up and all looked fine. Took the plugs out and held my finger over the hole and slowly turned the engine over. Decent "thumb compression". Once started is is quite quick. I am actually surprised how well it pulls.

Another issue: the bike pops a lot on deceleration. Not obnoxious but always present, anytime I roll off the throttle. Is this normal?

Another (possibly related) issue is that the right hand exhaust header is not as golden as the left. I guess that cylinder is running rich, how could that be? Do I need to start messing with the jets or is this indicative of another problem?

Lastly, the trans clunks pretty alarmingly when going into second and less so into third. If I am putt-putting around, not so much. Any technique I need to learn here?

Any help or information appreciated..

Thanks, Peter Z
Bay Area - California