The Airheads Beemer Club is a non-profit club reclaiming the 'Legendary Motorcycles of Germany'

Topic-icon 1973 R75/5 right carb running far too rich

  • cynispin
  • cynispin's Avatar Topic Author
  • Offline
  • R100 Level
  • R100 Level
More
2 months 3 weeks ago #4073 by cynispin
Apologies in advance, as I'm sure you guys are tired of the incessant carb issue threads!

The distillation of my problems is this: right carb is running so rich that within 5 miles of riding the right plug is completely covered in black soot (dry). Obviously there is stuttering, imbalance, and surging both at idle and low rpm (especially coming from a stop). The most telling symptom is that my idle mixture screw has to be turned ALL THE WAY IN to get a high-idle. Anything less and it really bogs down. I know, this is obviously telling me that something is wrong...

Here's a not-so-brief history for this year:

- Started out the year okay (this is when I acquired the bike), but I really only ride on the weekends for an hour or so. After about 200 miles or so, I had trouble with surging and the engine bogging down, and noticed the plugs were fouled. Checked valve clearances, left side were tight, so adjusted them accordingly. After having to adjust the left side again, took it into the shop to have them check it out, balance carbs, and fix an issue with charging system.

- Shop finds stripped threads in the block on the left side, and used to a timesert to repair it, and replaced gaskets and pushrod tube seals. Replaced diode board and alternator rotor (both were bad), did the yearly fluid and filter service, and finally did the basic carb rebuild (new floats, o-rings, and gaskets).

- Went to pick up the bike, but it wouldn't start due to a dead battery. None in stock, so they dropped the bike off at my house and put in an order for one. Installed a few days later.

- Take the bike out for a drive (needed to go about 40 miles away for work). Bike is idling incredibly low, and I'm blipping the throttle to keep it running at stops. No big deal, just needs to warm up and wear in, I think. Hesitates a little on takeoff, but overall running decently. A few days later I leave to return home. The bike is hesitating more, surging quite a bit (at all RPMs, it seems), and I basically limp the final few miles to the house. Have to pull off and restart the bike several times.

- Replace spark plugs, run for 10 miles (bike is still running awfully after the first several miles), and try to adjust throttle stop and idle mixture. Order a set of spark plug adapters to conduct "shorting method". Play around each Saturday for a month or two futilely. Right side carb has to be turned all the way in (leanest) to get the highest idle.

-Yesterday, checked valve clearances, and both sides were good. Left spark plug has some fouling, but it's not awful, and the center of electrode is actually clean. Right is thoroughly covered in soot as usual. Clean both up with a brush and carb cleaner. Check float bowls, and both have the same amount of fuel. Fuel is a little low (about 20mm), but that shouldn't be cause for it run RICH. Check float float needle, and fuel cuts off when float is parallel to carb body as expected. Pull right side carb to check needle, jets, diaphragm, float. Spray carb cleaner all around and through apertures. O-rings seem to be fine. Jets appear to be fine (no distortion of shape), and mixture screw end looks like it's supposed to. Hard to tell which position needle is in, so I take it out and set it to 3rd position (as per manual), but that was the position it was in before. Diaphragm and o-rings are all fine. Jets are clear. I can blow through the little tube and aperture on the float bowl (can't remember the name), which is a moot point since the carb is getting too much fuel from the sound of it. Check enrichment/auxiliary carb installation, and it is on correctly. I actually thought this was the main culprit, as others had posted similar issues to mine on forums.

No improvements. I try the carb balancing act again, but it's a useless effort considering the fundamental issues with the right side. My first choice would be to go back to the shop and have them take a second look. Since the bike wasn't actually running when they gave it back, they probably never got to run a full diagnostic on the thing, and certainly couldn't balance the carbs. Unfortunately, Richard Brown (the technician working on my bike) has since retired! My luck just gets better and better.

In any event, what would the sage advice be for me to check next? If I am out of my beyond what I can probably diagnose on my front porch, are there any airhead friendly mechanics near Pensacola? Richard Brown was the only one I saw on the capable shops list :ohmy: If it comes to it, I can find a way to further away, but I'd really rather not...

Please Log in to join the conversation.

More
2 months 2 weeks ago - 2 months 2 weeks ago #4079 by Wobbly
Replied by Wobbly on topic 1973 R75/5 right carb running far too rich
I can appreciate that you tried to research a qualified mechanic, but you should have never removed the bike from the shop without it running correctly. Now you have the bill, but are still left with a non-runner. In other words, you don't have a baseline to work from.

This should be the tip-off for you... How many 1973 cars did you pass on the road today ? How many in all of last month ? Probably the same goose egg numeral. I say that to point out that your bike is no longer merely "used", or "old", but it has now moved into "vintage" status. As such, it deserves the attention of a dedicated mechanic who is keeping notes on all maintenance and compiling and growing in knowledge about your specific bike. That person is YOU ! (Read ABC club cannon #6 again !)

It's going to go slowly at first becasue you'll be learning. But if you want to ride a vintage bike, then you're simply going to need to get directly involved. Otherwise it's going to cost you a fortune, and you still won't get to ride the bike.


Suffice it to say, Jay Leno is about the only guy rich enough to ride old motorcycles and not work on them himself. But even he doesn't take his bikes to random shops ! :P

Don't hide 'em, Ride 'em !!
#15150
Last edit: 2 months 2 weeks ago by Wobbly.

Please Log in to join the conversation.

More
2 months 2 weeks ago #4080 by Wobbly
Replied by Wobbly on topic 1973 R75/5 right carb running far too rich
Actions for YOU to take....

• Compression test both sides with carbs removed.
• Replacement of plugs, plug caps and plug wires if over 10 years old.
• Carb repair as detailed in this response.... www.airheads.org/forum/my-airhead-needs-...ments-have-no-affect

Don't hide 'em, Ride 'em !!
#15150

Please Log in to join the conversation.

  • cynispin
  • cynispin's Avatar Topic Author
  • Offline
  • R100 Level
  • R100 Level
More
2 months 2 weeks ago #4081 by cynispin
Replied by cynispin on topic 1973 R75/5 right carb running far too rich
Hey, Wobbly, thanks so much for the replies! I really appreciate you taking the time to offer sage advice and some direction. I'm going to chase some of those gremlins you mentioned (compression test, replacing plug wires and caps), and check out the thread you mentioned again. I have done several of the things you mentioned, but could stand to replace jets, needle, etc.

Just to clarify my original post, which I know was pretty long, the last mechanic I went to was on "the list". It's just that he's retired, and so is no longer working at the shop I took it to. It's funny you mention baseline, because that was PRECISELY the reason I wanted to get it into the shop! I hope my post doesn't give the impression that I don't want to work on the bike, I'm just trying to get some experienced advice (which you have so kindly provided).

Thanks again!

Please Log in to join the conversation.

More
2 months 2 weeks ago - 2 months 2 weeks ago #4084 by Wobbly
Replied by Wobbly on topic 1973 R75/5 right carb running far too rich

cynispin wrote: Just to clarify my original post, which I know was pretty long, the last mechanic I went to was on "the list". It's just that he's retired, and so is no longer working at the shop I took it to. It's funny you mention baseline, because that was PRECISELY the reason I wanted to get it into the shop! I hope my post doesn't give the impression that I don't want to work on the bike, I'm just trying to get some experienced advice (which you have so kindly provided).


And allow me to clarify, becasue it's very hard for me to convey concern (and yet still be technical) through the written word....

• Having just retired (for the second or third time) from the motorcycle trade, I feel qualified to say that maybe the biggest concern facing the Club is the shrinking number of qualified mechanics. Each brand and type has it's own quirks and foibles, which can really only be learned over time. Guys who worked on these bikes in the 1970's are now nearing 75 or simply dying. The knowledge base is simply disappearing before our very eyes. So I don't envy your position at all.

• It's obviously much easier to keep any motorcycle running once you get it to that state. Then you have that "base line" to work from, and it's understood that anything that happens was probably the result of some sort of misstep within the last few days. In those instances, you can simply backup "one square" and find the cure. It's all based on having the personal knowledge of the repair history. So, with no "finger pointing" at you or your mechanic, it's truly a shame the machine was not in running condition when it was returned, especially in light of the mechanic's retirement.

• All that said, your next best solution is going to be a local Tech Day. But you're going to need to take with you a pile of new parts, becasue it's not really clear to me where your issue lies. So you'll need to take complete carburetor rebuild supplies, and the same for the ignition system, etc, etc.


I used to be a whiz at getting bikes running again. It was like I could walk up to the machine, lay my hands on it, and the bike would tell me what the problem was ! Although it had that appearance, I realize now I was subconsciously reading a host of visual clues. If there were cobwebs, then the bike had been stored indoors and the issues were probably dirty points and gummed up carbs. If the bike was covered with rust, then it had sat outside and had compression issues due to equal amounts of internal rust. If there were fingerprints all over the carbs, they had simply been reassembled incorrectly.

Sadly, there are no visual clues when working over the internet. And that's why you must get the bike to someone who can see it, who knows what they're looking at, and can go right to the problem. Otherwise, you'll end up rebuilding the entire engine (and spending millions) all to find something unbelievably simple.

All the best, and keep us informed of your progress.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 2 months 2 weeks ago by Wobbly.

Please Log in to join the conversation.

  • cynispin
  • cynispin's Avatar Topic Author
  • Offline
  • R100 Level
  • R100 Level
More
2 months 2 weeks ago #4087 by cynispin
Replied by cynispin on topic 1973 R75/5 right carb running far too rich
Thanks, Wobbly!

I'll put in an order for carb rebuild kits, wires, caps, and plugs. In the meantime, I should be able to check compression this weekend. Don't have the tools to do a leakdown check, but I can still check for air leaks around the hoses.

Will probably pull those wires this weekend and check them with a multimeter as well, but regardless it's probably time to change them out. At least I can know whether or not it's part of the problem!

Will definitely update.

Please Log in to join the conversation.

Moderators: 8166Wobbly
Time to create page: 0.973 seconds