R60/7 on One 1 1/2 Cylinders

[BandAidMan]

I am in the process of restoring a 1977 R60/7 into a reliable runner and I have hit a wall. I have gotten the right cylinder firing just fine but the left bogs immediately off idle. A little background about the bike. It had 36,000 miles when I got it last fall and it arrived without a maintenance history. It had a Dyna electronic ignition, Euro bars, and an S fairing added but was otherwise stock. It was running a little rough and the left side was noticeable weaker.

I have gone through and replaced the coils, plug wires, plugs, and air filter (along with the mouse nets.) I have taken the carbs apart, cleaned them and replaced the jets, choke piston, needle, springs. New clutch and throttle cables when in. I adjusted the valves, lubed the clutch splines, and replaced a blown blinkers relay.

I ran a compression test and both cylinders had nearly identical values (148 & 145 lbs.) The fuel flow is good into the carbs, the coils and spark plug wire are new, and it has a good air cleaner. The left side still has a problem. If I pull the left throttle cable while grounding out the right side's spark (using one of Jeff Trapps little carb syncing extensions) the engine will actually die. At this point I don't know where to go. Of course I could have messed up something along the way, but to start weak on the left and ended up weak, makes me wonders. A bad carb, another mouse nest in the left muffler? Anyone have any ideas for me?

[sumran]

I would check two things in the carbs. Be sure the idle passage in the carb body is open. Sometimes they get something stuck in there. Then check the idle jet. There are several holes in it along the sides and one in the end. The best way to clean it is with soft copper wire. It can break loose scale that resists carb cleaner or air. The copper is softer than the brass, so you won't damage it if you take reasonable care.

Be sure you have the right setting on the idle mixture adjustment. It is a different setting than idle speed. You might also want to check to be sure the enricher is not installed backwards and that it is turning off completely.

[BandAidMan]

I checked the idle jet, which is new, and it is clean. The hole above appears clean but I can't tell for sure so I will see if I can find some fine copper wire. I have been using some bamboo to clean things like that but it is not fine enough.

This is a latter style type 53 slide carb and only has the choke, it does not have a tickler. I can visually see the choke piston close when the carb is removed and I am playing with it. I have messed with both the idle speed and the fuel/air mixture without any luck. I tried to get them working for a 1000 RPM idle with is OK-ish but the off idle circuit is not happy on the left.. The Bing book has been informative but not helpful in my case.

[sumran]

My earlier post was based on CV carbs. I don't know enough about Type 53 to be a help. Others here have lots of experience.

[AnnapolisAirhead]

It may be loud, but to verify all the mouse nests are out, remove both mufflers and run the engine with just straight headers. Sounds obnoxious, etc. but it works DAMHIK (all my bikes sat for a minimum of 8 yearsbefore I bought them).

Does the bike start easily? If not, the plate that holds the throttle cable in place could have slipped out.

I have earlier type 53's on my Toaster but they only have the ticklers, not the enricher circuit. It's difficult to balance my carbs because there is no vacuum port, unlike the CV types Randy mentioned (unless later models have them or you were brave enough to buy and install the Bing kit).

I guess the other obvious things are: did you do a static timing, then did you set the valves on a cold engine? If not, I'd try that first and then move to the carbs. It does smell of a carb issue.

[44006]

"I have taken the carbs apart, cleaned them and replaced the jets, choke piston, needle, springs"

Be sure that the stopper is in the bottom of each "choke piston"
this can be dissolved away by cleaners and will fool you for a long time

[BandAidMan]

Good point on the piston "bumper". The rubber stopper on the choke piston had disintegrated and I had to scrape it out with my sharpened chopstick. The immediate prior owner has mistaken the rubber gunk from some kind of gasket. After cleaning the choke shaft I replaced the piston and the piston spring. It now seats well.

I am going to try the checking the exhaust (for nests), the timing, valve clearance (to make sure I did not mess it up), then swap the carbs, in that order this weekend. Hopefully something will stand out as an issue.

[AnnapolisAirhead]

"I have taken the carbs apart, cleaned them and replaced the jets, choke piston, needle, springs"

Be sure that the stopper is in the bottom of each "choke piston"
this can be dissolved away by cleaners and will fool you for a long time

What's a "choke piston"? And what type of cleaning fluid are you using?

My Bing Type 53 carbs don't have a choke (e.g. enricher), just ticklers but they on a1972 R60/5 so maybe different. I couldn't find anything called a chocke piston on the realoem.com site either.

You obviously replaced something, but which part on your referring to as the "choke piston" and which carb model? I'm curious. Do you mean the tickler? :scratch

BandAidMan, any pictures?

[BandAidMan]

The later Type 53 carbs has an enricher/choke shaft. At the bottom of the shaft there is an air tub and a small brass pipe that goes to the fuel bowel. The lower part of the shaft is open to cylinder’s input behind the main slide. In the shaft is a "piston" that looks like an upside-down "T". The choke cable attaches to piston’s vertical part of the “T” and a sleeve slides over it to keep cable in place and make the piston T into a mini-slide. There is a spring to keep the piston down and sealing the air and fuel inputs until activated.

Pulling the choke cable lifts the piston and allows extra gas/air to flow into the cylinder without regard to the position of the main slide. The bottom of the piston is rubber to seal the air/fuel input and can fall apart with age. The Bing book and the manuals mix the 53 versions and don’t show how it fits in. I had the carbs apart three times before I understood exactly how the choke functioned. If you look up a 1977 R60/7 in RealOEM find the CARBURETOR-PISTON/NOZZLE NEEDLE page. It is item number 1, BMW part 13111335687. I can take some pictures when I have it apart next if you want.

To clean the carbs I removed all the pieces I could and sprayed Gumout carb cleaner into everything. I then went at it with a toothbrush and my trusty chopstick. I repeated this until everything appeared clean and I could blow air through all the little passages. There was rubber from the piston stuck to the bottom of the choke shaft that I had to scrape out. I suspect a PO may have got some car cleaner on to the piston which softens up the rubber but it could just be age.

[AnnapolisAirhead]

Good information to know. I was not aware that any type 53 carbs had such a mechanism. I'd love to have a choke.enricher circuit on my /5. Something to think about.

Thanks for the info. :thumb

[Bill Burke]

Is this the carb that has an "accelerator pump"?

I worked on a Type 53 with a tickler recently and the issue in this case appears to have been crusty deposits in the two tiny orifices in the slide chamber. I would purchase, for about $5 at your local hardware store, a "welder's tip cleaner" kit which consists of graduated wire sized pins designed to clean crud out of orifices - theoretically without deforming or enlarging them. Work great if you don't get overly aggressive and damage the orifices. In any case, the key to success is cleaning out those holes which are effecting adversely your idle and mid-range circuits. Needless to say, focus on the left side carb: that's where your problem clearly sits.

[BandAidMan]

Thanks to everyone for the suggestions. I had another go at it this afternoon. I checked the static timing and valve clearance and they both looked good. I then took the left carb apart once again. I used some copper wire and welders cleaners to have another go a the inner workings. I then blasted the passages with carb cleaner and followed up with compressed air. Some dirt specs appeared in the parts basin so I kicked something loose. I took her for a 15 mile ride and then tried to sync the carbs. This time things were better.

The left carb is now pulling more of its weight and I was able to sync them at idle and 1500 rpm. Things still are not perfect but the left is idling and pulling better. I worked mostly on the choke and idle circuit passages, since they are the smallest but it is better across the board. I am not sure what I did right this time but I learned more than I every wanted to about the passages in the later Type 53s.

Now I just need to figure out what to do about the dents in the tank from dropping it. Note: Don't place your gas tank on top of a flat topped garbage can and mess with the hose. The gas will slosh around and side the tank off the garbage can when you are not looking.

[BandAidMan]

Here is a follow up: I cleaned the carbs once more, synced them at idle and now found I had issues with both carbs off-idle. Opening the throttle from idle cause the RPMs to drop or stumble until it was half open or more. Something was clearly wrong with the mid-range circuit and it felt like an overly rich situation. The needle and needle jet where new and correct. The choke was closing correctly, the new float was adjusted correctly, and all the little passages were clean.

I went back to the books. Studying the Bing chart for the type 53 (which shows three variants) and the BWM shop manual I realized a “reed” was missing from the “cylinder” in the accelerator pump. The reed is a plastic disk about 1/8” in diameter. It slows the fuel flow through the accelerator pump as the cylinder is being moved up and down by the needle. Apparently a PO lost them while cleaning the carbs. BMW does not sell the reed, only the complete accelerator pump for $55, so I called Bing. Bing wanted 96 cents for the reed. I ordered the reeds, springs for the accelerator pump, and some cable adjustors BMW no longer stocks from Bing.

I installed the parts and presto no more mid-range issues. The bike is now harder to start and more cold blooded (before it had in affect a double choke) but once warm it is much smoother. I now know more than I every wanted to about the later Type 53 carbs but putt-putt is running happy. Next it is the suspension . . .

[sumran]

Thanks fot the update!