Valves and Center Stud

After reading more on setting the valves, I decided to redo them. I did not take up the vertical slack on the rocker arms the first time, and each rocker arm had slack. I also reviewed the Owners manual which recommends setting the valves:

• Intake .15mm
• Exhaust .20mm
  

The BMW MOA July ON magazine Keep them Flying article had a article just on setting valves on airheads, and they do recommend the same valve settings.

I had .10/.20, and had vertical slack, so I felt it was worth redoing them.

I also installed the center stud on the right side head which had come loose. The threads seem ok, but I used blue loctite on the stud, I will hand tighten after 24 hours.

A good Sunday

As Ron knows I do not give up easily on these BMW bikes. I decided this morning, to go back under Paul's suggestion and take a second look at the timing under full advance.

I pulled the front cover off (after disconnecting the battery), and decided to lube the advance unit, and clean it up. I then went for a 10 mile ride, at this point came back and did realize that under full advance my timing was around 2800 rpm. I rotated the base plate, and got the advance to hit 3000-3100 at full advance. After doing this idle was a bit low, I carefully adjusted the idle stop screws, and put the gauge on the vacuum ports. It is now running at 1K dead on, after full warm up.

I put the bike back together, and went for another ride, WOW, my power is back, takes off like a banshee, not stumbling, no pinging. My needle jets are set to position three. I got the Bing book, and will check jet and needle sizes during next carb sync, but for now, the bike is running good. When I got back I adjusted the throttle cable just a smidgen, under the gauge, and went for a five mile ride, the bike got even smoother.

At this point with old cables, and carbs that probably need work, I think my R75 is tuned as good as I can get it without more help. She is running good, I will see what kind of gas mileage I get under this setup.

I started to sand and prep the side covers I received from Ebay. I will have to get me some bungys My stock air filter is on order along with the missing valve cover stud/special nut.

State of condition

In summary

• I modified carbs, good idle, but poor acceleration (Tech Day at Pauls)
• I modified timing, good idle, still poor acceleration (was on OT, now on S with line above)
• I modified needle position from 2 to 3, good idle, poor acceleration, and pinging at higher rpm's, speed, loss of power
• Check valves, re-adjusted head bolts to 35nm, but valves read .10 and .20, so no modification.
  

Next Steps
Stock Air Filter
Re-Check timing (operating temperature)
Install new stud bolt and nut/washer

Advance Unit

After reading about the advance unit more online, I thought it would not hurt to check the lubrication of the advance unit. After what Paul told me in an email about re-check timing, I noticed that the advance unit was full advance around 2900-3000 rpm, and it should be around 3000-3200 rpms. This could be causing the pinging.

Check the valves

Today I wanted to verify the valves. It is warm outside but the bike has been sitting for a day, and the temp on the heads reads 88 so we should be ok.

Proceeded to to loosen and re-tighten the cylinder head nuts to 35nm of torque, and checked both left and right valves. Believe it or not they were all spot on, intake .10mm and .20mm for the exhaust. I was really surprised to see both side dead on.

Now I will change the air filter and proceed to re-sync the carbs.

Pins and Needles

Today after thinking more about the carb issue, I decided to check the position of the carb needles. Now the bing book according to Paul suggest setting the needles at position three which is clicking the needle all the way up the diaphragm tube.

I removed the carb tops but left the cable sin tact, diaphragms look ok at a macro level. The needle positions were the same, but they were set to position two in the middle. Given this bike has a K&N filter someone might have set these to "rich", I think.

Anyway I went ahead and put the needles back to position three, and we will see how the bike runs for awhile in that position, will check plugs in a couple of weeks for color, etc.

It is all in the Timing

After yesterday's carb sync, I realized I should have checked the basics first before doing the final tuning procedure, doing it backwards in my mind only creates undo frustration. I decided today that I would check the timing of the ignition to make sure we were not fighting a timing issue. I proceeded to check timing after a short garage warm up.

The timing mark OT was appearing in the window during idle which indicates it is not in timing. The S mark with the line above it needed to appear in the window for dead on timing. I loosened the base plate of the electronic ignition, and adjusted it back and forth until I got the line to appear right at the middle mark in the timing window.

After I test ride I re checked the setting, and it remained right on mark. The hesitation did not go away but the bike did seem to run a bit better on a 10 mike test ride. The idle is still a little high at stops, around 1100, needs to be adjusted,

Carb Sync

Today, Ron, Paul, Doug and myself got together for a kinda of a half day Tech Day at Paul's House. I rode my Bike with some breakfast, Doug brought fresh coffee and Ron brought beer which never broke into.

Upon arrival I noticed some brake fluid seeping down the left alternator cover. So before we dove into cars, I pulled the tank to discover the cable connection to the master cylinder has vibrated loose and was dripping every time I squeezed the lever. Paul was gracious to offer DOT3 brake fluid, and Doug and I proceed to tighten the suspect cable, and bleed the brakes given the lose of fluid. After a quick road test front brake working great. I ntoiced now the front wheel is dragging a bit, so the caliper will most likely need looking at.

After this we discovered some loose wiring under the tank and the left coil plug wire was loose. We cleaned and put dielectric grease on most of the wire connections, zipped tied the loose cabling up, and generally inspected all items under the tank.

We proceed to look into the carbs.
Paul demonstrated the shorting method, of plugging spark plug adapters into the top of each spark plug them attached to the coil wires. While bike running, you short each cylinder to see which is one is pulling to indicate where the adjustments needed to be made. This was great learning from me, because I had never seen this done correctly.

Paul's order of operation was to loosen the throttle cables and set idle first by adjusting the idle stop screws first to reach correct idle speed, then he proceed to adjust idle mixture screws one by one u until it was set just after each cylinder would die out. He did all this by ear and watching the RPM's. We got idel running pretty smooth.

After doing this by ear we stuck Paul's carb stick on to make final adjustments. The bike was idling very smooth but we detected a new problem. Right off idle the machine coughs and acts as if it is going to stall, almost like the idle mixture is too lean. Paul suggested it might bu need position of carbs needing a good overhaul. Even though we created a new problem with suspect carbs, the sync procedure was a good learning experience, and I will not hestiate to try this by ear first.

New Rubber

Today I received my original BMW owners manual, a blank key, and the new rubber sleeves for the carb to head, and carb to airbox tube connection. The old rubber sleeves were hard and cracked and might have been leaking, before a good carb sync I thought I would swap them out, can not hurt. The new ones went on with out a hitch.

Thanks Hans from Hucky's for getting the parts to me so quickly.