R75/5 w/Mikuni question

[Airbear]

Welcome, 8 Gauge. It sounds like you are about to discover a whole lot of stuff about your fortunate inheritance. No Mikuni experience here, but I urge you to become familiar with your ignition system after you've checked valve clearances. Assuming your bike has points you will have periodic maintenance to do, and probably 'side of the road' adjustments to make along the way. It's good to carry a little test light to do static timing - this one cost $7 -



A 16 thou feeler gauge with a bend in the end and a points file, plus a spare set of points, should be part of your kit. Points get burnt over time and the little block that runs on the cam wears, with the result that the timing alters. Synchronisation between the cylinders can be affected by a bent points cam or slack in the timing chain. As Motorhead suggests, ensuring that your valves have the proper clearance and that the static timing is correct (for both cylinders) is the first port of call before you start fiddling with carbs.

Duane's and Snowbum's sites have good info on procedures, and feel free to ask here. Good luck, have fun, and please keep us up to date.

[8 Gauge]

Thanks for all the info! Will update as I find out more. Wish I had more wrenching time but work, grad school and keeping the girl happy are kicking my butt. For some reason she doesn't believe that hanging out in the garage is "quality time."

Here's a pic of what I'm working with. Shes in unrestored and unmolested original condition with about 9k miles on her. She is dusty and dirty, but should clean up very nicely. I made a pact to spend more time riding than cleaning so the restore will have to wait till after I get some miles under my belt. Strangely everything works and seems to be tight except the tach. I also have an original fairing laying around somewhere but I've never liked the looks of them.

This is the only bike that i have ridden with a drive shaft instead of a chain. It is slightly "clunky" feeling when you change gears and initially whines slightly. I thought i had a problem, at first, then came to the conclusion that this was normal. Sometimes I forget that this thing is more than 40 years old.


Looking at this pic i kinda wish I didn't bead blast the air cleaner covers as they stand out now.......



By travisc3

[Mal S7]

Hi 8,

good to see your posts and pics. I wish I had that R75/5 with 9K in my shed. That would indeed be quality time.

" Bike starts easily (kick starter) ..."

No one else picked you up on this, but I have read many times that use of the kick start is a really bad idea. Somehow it can cause early gearbox failure. Others know about this, my 1977 R100/7 is far too plastic and modern to carry one.

Hope you get your mikunis sorted and get out riding soon.

cheers

Mal

[twist]

I have mukuni's on my R100 but they are the flat slide variety. Still, mikuni's are easy to tune and they hold a setting well. Like the beemer, they are easy to work on. Duane, the best part of Mikuni's is the throttle response! They are much like having del-orto's. I had a similar problem and it turned out to be a burnt valve. Have a leakdown test done and good luck!

[8 Gauge]

Had more time to play around than I was expecting this weekend which was a nice surprise!

3/4 valves were within spec. Only the exhaust valve on the left cylinder (the one thats running nicely) was slightly out of spec on the open side. Now that I know this I can hear a faint ticking coming out of that cylinder. My awesome sense of logic advised me that it is unlikely that the exhaust valve on the left cylinder is making the right side run lean so I carried on to the ignition system.

Took a visual inspection on the points and ignition system. It is pretty obvious that that the points were recently replaced. They look brand new and the business end of them had no wear that I could distinguish. Everything else in there looked much better than expected. I have worked on enough bikes to know that you don't always get lucky finding things in nice shape when you get to wrenching.

After a little more than an hour of wrenching, the only thing I adjusted was the throttle assembly because I did a hasty job of adjusting the throttle cables. After I finished inspecting the ignition system, I remembered something that I noticed in the picture I posted above. If you look at the fuel filter in the picture it is VERY yellow. The filters are brand new and clearish. The actual filter element is a bit yellow but not bright like in the picture.

I know the gas in the tank isn't ancient and I regularly use fuel stabilizer before I put things away for the winter but I don't think there was much gas in there at all. To make a long story short, I added a gallon and a half of fresh gas, swished it around a bit and VROOM VROOM!!

Wow! She's now making a totally different tune. It is apparent that both cylinders are firing nicely. No popping from right side carb and no fuel/air mix shooting out the wrong way. Both cylinders are running much cooler as well.

My problem must have been a combination of crappy fuel and the throttle being slightly open due to a tight throttle cable.

Put a few miles on her and adjusted the idle, let her cool off and checked the plugs which were both a very nice shade of brown. After she was cooled down completely, I started her again with kickstarter. I cannot believe how little effort this thing starts with the kick starter. Its amazing. Someone mentioned that use of the kickstarter isnt a good idea and I agree but my my battery is shot (or my charger for that matter)

Still needs a tuneup (I'm going to richen up the needle jet in short order)

Any maintenance/safety things that I should check before putting some miles on her? (specific to an old air head as I've already checked the non specific stuff)

Thanks!

[Motorhead]

The Usual rubber bits

Forks with no stiction working brakes and lights and tires and legal stuff other wise have fun

[Airbear]

Well done, 8. Maybe get that battery checked before you go too far from the Big Toolbox. A battery retail outlet should be able to quickly do a 'load test'.

And when you are headin' down a nice curvy road well out of town with a grin on your face and everything feeling right - that would be a good time to thank your grandpappy for the fine inheritance.

[8 Gauge]

And when you are headin' down a nice curvy road well out of town with a grin on your face and everything feeling right - that would be a good time to thank your grandpappy for the fine inheritance.

I have a grin on my face just thinking about it!

Good call on getting the battery checked out. I wonder if they can test the charger in the same way? My tractor battery didn't seem to take a charge and then i put it on for a third round of charging and its fully juiced up.

Thanks!