New Member Question and Intro 1975 R90/6

[bandersnatch]

I spent some time last weekend working on the carburetors. I used an unlit propane torch to go around the fittings looking for leaks and was pleased to find that the engine didn't speed up at all so I'm good there. Played around with the mixture and found that by turning the screw out about 1 full turn I was able to get the bike to start well and after a couple of minutes was able to shut off the choke and give it some throttle.

I also adjusted the valves, they didn't seem too far off but the idle seems smoother. Very happy with how it's running now.

The throttle is fairly hard to turn and doesn't return by itself so I have two new throttle cables ordered. I know the left cable is bad but for the price it doesn't make sense to not replace both.

Included with the bike was a spare seat that's in excellent shape except for two really small splits in the leather. I went ahead and installed the replacement seat and started tearing down the original one to see if it's worth reupholstering. Unfortunately, the tin worm has had its way with the seat pan and I'm not sure there's enough left to make it worth it. I'll probably keep my eyes open for a used replacement pan that's in better shape and stick with my spare for now. The spare is nice enough that hate to rip it up but it's not up to snuff for a restoration. Here are some pics.IMG_0141b.jpgIMG_0144b.jpgIMG_0145b.jpgIMG_0025.JPG

[Friedle]

Below the throttle you should find a thumbscrew "friction lock". It is an early form of cruise control. If screwed in too far it will impede the throttle from easily returning. At the other end of the cable there should be a return spring on the carb body to ensure the throttle closes when the grip is released. That spring might be weak or missing. Good luck.

Friedle

PS: Consider joining the Airheads Beemer Club www.airheads.org

[khittner]

If you haven’t already opened it up, the handlebar throttle assembly could probably benefit from some cleaning and new grease.

[8ninety8]

The MG is a very very nice piece of workmanship! The bike will come along nicely. They're not making old stuff these days.

An old friend came over last evening and I showed him my old 900, and fired it up. Normally I never start it unless I'm going some place. He acted as if he'd never seen anything like it before. Old stuff is so much fun. Windy here in the 70's today. Going for a spin. Work out the kinks.

I use a dab of blue locktite on that cam nose nut. FWIW.

[bandersnatch]

Thanks for the suggestions guys. I did open up the handle and cleaned/degreased the insides. I used a dab of white lithium grease on the gears and cam. The carbs were recently rebuilt although i did reuse the springs because they seemed fine with good tension.

I also verified the throttle lock screw was loose and not causing drag. The left cable has a broken sheath at the carburetor end which I think is the reason for the failure to return. New cables are on order.

I have joined the Airheads club and in fact went to my second local airheads meeting a couple of nights ago. Katie, a long-time member sold me a Clymer workshop manual which I will be using in addition to my factory owner's manual and a Haynes manual.

My alteration to the cam nose seems to be working out well, so a dab of Locktite will go on shortly. Sounds like a smart thing to do.

It looks like my seat pan is pretty much shot. really thin metal in several places and all of the screw holes are filled with broken or drilled out screws. It looks like I'm in the market for a replacement pan (I'd like to recover it myself), so if anyone has one they'd like to part with please send me a note.

Also looking for a center stand, mine only has about half of the left leg. One that needs some cleanup or minor repairs would be fine (I have a welder), but I'd like it to be complete. it works okay as long as I put a piece of 2x4 under it but I'd prefer not to haul the 2x4 around in the tool box!

Regards,
Larry

[bandersnatch]

Just an update for folks. I found that even after replacing the throttle cables the throttle still refused to return on its own. I once again disassembled the handle and this time slid the handgrip off the handlebar. Underneath was 30+ years of congealed grease/oil which I cleaned off with some Goo Gone. Squirted on a dab of oil, reassembled and I have a working throttle!

Now the down side. I ended up pulling the tank to make it easier to replace the cables and remove the completely frozen master cylinder and must have knocked something loose because now I have no spark whatsoever. Looks like I'm pulling the tank again to find out what i did.

Two steps forward, one step back. Just like normal . . .

How about some advice on the master cylinder from you, o learned ones? Just chuck it and buy a new one, or try rebuilding it? It's really stuck, I'm not sure I'll even be able to pull the piston rod out. Worth the effort or not?

Larry

Oh, I almost forgot. A special thanks to Chip who is sending me a replacement center stand. He's my new hero! Much appreciated, I do love communities like this that jump right in to help out fellow members.

Reminds me of last summer when my wife and I were returning from a trip in the MG. We both heard an odd knock coming from the left rear of the car, but it didn't repeat so I took the car to the gas station after dropping the better half off at home to see if I could get it to make the noise again. Got all the way to the station and most of the way home when the noise came back with a vengeance. Made it to the house but couldn't get up the really slight incline in the driveway, fortunately a neighbor walking by helped push it into the garage.

Found out that one of the axle bearings had disintegrated and threw ball bearings into the differential gears. Exploded it like a pumpkin. I posted on an MGA forum for a replacement on Saturday, got a call on Sunday from a fellow MGA'er in California who put one in the mail to me on Monday. By Thursday I had a perfectly good used replacement rear end (just the pumpkin, fortunately) and by the next Saturday was back on the road.

[20774]

Larry -

As for the lack of spark, one thing I'd check is that the small black jumper wire is still in place that connects the two coils. Without that, no spark. On the down side, there's power at the coil terminals so if you touched the tank to the power side, it could have fried something. But look for the small black wire first.

RE: the master cylinder...I like keeping original equipment. There is a process to convert to a handlebar master cylinder...there seem to be positive benefits there. But I like the feel and performance of my under-tank master cylinder. I'd use various penetrants like AeroKroil or the best yet is a 50-50 mix of ATF and acetone. Soak things and see if you can free it up. You may find it's beyond saving, but there are companies that can resleeve the bore.

When I recently rebuilt my master cylinder, I followed Brook's blog on this...was very helpful:

https://brook.reams.me/bmw-motorcycl...ster-cylinder/

[bandersnatch]

Thanks Kurt. I do have a can of Kroil (bloody expensive stuff I might add) that I'll squirt it with every day or two. I also like original stuff but I'm wanting the bike to eventually look like it just rolled off the showroom floor so that does mean at least SOME new parts. In this case the brake fluid reservoir as it's quite yellowed. It seems intact for now though so I'll likely hold off on that.

I want to ride the bike for a bit as-is for that 'survivor' look before I tear it all down and start repairing/replacing/repainting.

I was looking at the coils when I had the tank off and maybe even jiggled the wire you're talking about. Sounds like I might not have a good connection any longer so time to clean some contacts.

Larry

[bandersnatch]

Things just go from bad to worse. Last night I pulled the tank off to investigate why I no longer have any spark at the plugs. I did open the points manually with the key on and got a spark there, so the problem seems to be at the coils.

I pulled each coil individually and thoroughly cleaned all contacts on the coils, then reinstalled them making sure I put all the connections back where they came from. I also check the black cross-over wire for continuity and found it good. Both coils show exactly 1.5 ohm across the negative and positive terminals, so it all seems fine there.

Next, I swapped the plug wires across and checked for spark on the left cylinder with the plug laying on the cylinder head to make sure it wasn't a bad plug wire. Still nothing. I put the plug wires back to their original locations and checked the right plug for spark (plug out and laying on the cylinder), no spark there either so it's not the plugs.

Then I pulled the starter relay after making a diagram and carefully labeling each wire. I shined up the relay contacts and scraped out the individual plug wires as best I could with a small screwdriver and reassembled and that's where it all fell apart. Now I get nothing at all when I press the starter button. The headlight and turn signals still work, but nada from the starter.

I have the wiring diagram from the Haynes manual and am looking through it to try to track down the problem but any suggestions on what to check next would be greatly appreciated.

Regards,
Larry

[jagarra]

You may have knocked a wire loose or your points maybe the issue. I would check them to see if you have the correct gap.
As far as your M/C, 14mm come up on e-bay frequently, but if you want to just rebuild it, it may need to be sleeved. I have used a Mark Frappier to do M/C, he sleeves them in stainless, 800-528-5235, cost is about $100.00, great work, items sleeved, honed and returned in about a week.

[1074]

If you are getting a spark when you manually open the points then I would recheck the point gap. The spark the manually tells me that all wiring through the coils and points is in working order.

[bandersnatch]

Thanks for the tip on the MC rebuild Gerard, that price sounds a heck of a lot better than the $350-$400 for a new one.

There is a good chance that my fix on the camshaft nose didn't hold, I'll check the points gap when I get home tonight. I'd love it if that was the issue on the no spark. I do still have to figure out why it's not cranking now after I cleaned the contacts, probably didn't get one of the connections on well enough.

Larry

[20774]

How's your battery? Put your digital voltmeter across the battery terminals and measure voltage before hitting the starter button and while hitting the starter button. Report back the voltages. If the voltage drops well below 10v, the battery is bad.

You can measure for 12v across the coils. 12v comes into the left coil terminal...put your digital meter with one connected to ground and one on the left terminal...you should read 12v. Then do the same thing with the output terminal on the right coil. Should be 12v. If not, you have a supply problem. If you do, then, as pointed out, the points are not working properly.

[bandersnatch]

Hi Kurt,

Just a note, I do have two issues which may or not be related. Initially, I stopped getting spark to the plugs after having it starting up reliable for a month. While attempting to resolve that I made it worse and the starter motor now refuses to even think about turning over. Flat out nothing from pressing the starter button.

The battery is brand new and has been kept on a battery tender. All starting on the bike is with a green (fully charged) light on the tender.

I'll do the voltage test on the coils in the next day or two. I can say that I'm not getting any clicks at all from the starter relay when I press the starter button, so it appears that my cleaning of the terminals may not have gone well. Either that or the starter button had decided to take early retirement on me (after all, the bike is only 44 years old).

Thanks,
Larry

[20774]

I wouldn't rely on the lights on the battery tender. Put your voltmeter across the battery terminals and read the voltage when you hit the starter button. If it shows around 12v when hitting the starter, then the problem is probably the starter relay since it is not latching. If it shows something like 8-9v, then the battery is probably bad.