Points/Odd Noise

My '75 R75/6 has been running "rough" as of late. Not being mechanically inclined, I thought I would come here in hopes of getting a clue of what to look for.

Over the last few months I noticed the bike would falter/run roughly on rare ocassion as I was accelerating around 4500-5000 rpm. It would only be a 1-2 second hesitation and then the bike seemed to run fine from then on.

The last couple of days I've noticed these same symptoms appearing more frequently, and have noticed the engine producing a different, muffled-like sound, which seems to be coming from the front of the bike. I only notice this sound when manipulating the throttle and/or when at higher rpm's and I release the throttle to slow down.

I noticed yesterday that my throttle cable connection was very loose on one of my carburators. After tightening the cable, the bike is running smoother, although the bike still has this muffled sound to it.

The bike idles fine, so I'm assuming (maybe incorrectly) that the carbs are synchronized. I plan to check this later tonight. I did notice some cracking at the end of one of the plastic tubes that runs from my right carburator to the air box and plan to order a new one today. Thought this may be the cause as well?

I am unfamiliar with the points and how to or how often they need to be adjusted. It's been awhile since I had that done (40,000 miles or thereabout) and wondered if this may be my problem as well.

Any feedback would be appreciated.

When was the last time you had a full tune up? Valve adjustment, points, plugs, the whole works?

Dave

If your throttle cable was out of whack, chances are your carbs are, too. I don't know anything about points. I'd follow Dave's advice: adjust the valves, replace (or clean) and gap the plugs, synch the carbs.

I adjusted the valves a little over a 1000 miles ago. Points haven't been adjusted for around 40,000. I plan on replacing the plugs tomorrow, which are about a year old, when I replace the cracked air tube I mentioned earlier. I'm heading out of town the following day, but should have the chance to synch the carbs beforehand. If the problem still persists, I'll be back on here.

What type of symptoms would I experience from the bike if the points needed adjusting/replacement?

You don't want to go so long between setting the points and timing. The rubbing block of the points will wear down and cause the point gap to close up. The timing will be retarded which will affect performance and gas mileage. There is a greater chance that the point surfaces will burn and pit which will further degrade ingnition performance and spark. If the point rubing block completely wears away you may have metal to metal contact between the point arm and the ignition cam on the advance assembly. You may also find that the ignition advance will experience considerable wear without regular cleaning and lubing a the recommended service intervals.

Based upon my experience with a 1973 1/2 R75/5, I wouldn't think that the bike would run with 40K on the ignition points. Is it possible that the previous owner replaced the point ignition with a Dyna III Electronic Ignition? That was the single best modification I ever made to my R75.

The bike still has the old points system. Since my last post I changed the spark plugs, replaced the cracked air tube, and synchronized the carbs. The bike is running much better now. However, based on your recommendation I think I will take the bike in sometime over the winter to have the points/timing adjusted if needed.

FWIW, if you can handle a valve adjustment, you can swap the points out and time them yourself pretty easily.

I used to swap them on my VW in about ten minutes. You'll need a light bulb with a couple alligator clamps to set the timing, but that's about it. I assume you've already got feeler gauges since you did the valves.

dave

Well, then I may just give it a shot this winter when I mostly rely on the wind protection on my K1100LT. I actually looked at my maintanence records and saw that I did have the points adjusted about 11,000 miles ago when I had the bike serviced a few years back. With the addition of two newer bikes over the last couple of years the R75/6 has seen less road time and therefore I apparently cannot rely on memory alone regarding maintanence. Even so, I still am very fond of the bike and enjoy using it primarily as a commuter and for shorter rides. This was my first bike (boutht it back in 1997) and I plan on keeping it. I've heard too many people tell stories about regret for selling their first bike. I guess I'm just a sentimental push-over.