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Inconsistent idle

C

crouthier

Member
Hi, morning, my '72 R75/5 is suddenly experiencing an inconsistent idle after running great...

Carbs were rebuilt by Phill Cheney at MAX several years ago, I adjusted valves last season (all okay) and I just upgraded to new coils, plugs and plug wires and it was idling consistently and evenly - the past two days, not so much. It DOES run great at speed, fyi. And it will idle ok when warm, then 5-10 seconds after stopping - slowly slow down where I have to goose the throttle to keep it going, then it will be fine...but at times not hold a decent idle...bad gas? I put some dry gas in tank...no difference. Thoughts?

Thanks for reading, Chuck
 
Maybe try a new tank of gas first. Then probably should do a carb synch first after a good ride to warm up the engine. Tough idling is a symptom of closing valve clearances...worth a quick recheck. What about the condenser? Maybe check the timing gap.
 
Thanks for advice Kurt, I'll do those checks. It did seem to start with a fill up, but can't be 100% sure abut that.
regards, Chuck
 
Miles

So, depending on how many miles you put on since the valves were last adjusted, it may be a good time to check them again, they should be regularly done about 15K miles or so.

Same goes with the posts, since I don't know how many miles you have ridden, I can't say much more than they may need adjustment. For what it is worth, I would ditch them and go to one of the systems out now on the market. it is nice not to have to fiddle with them. I did it on my 78 RS. Since then, I haven't had to adjust timing of course no points in 30K miles.

If you don't ride a lot of miles, then perhaps the problem could be gas, of course even a new tank of gas can sometimes have problems, depends on the station's tanks and quality.

Valves first, points and timing second carbs last, Good luck. St.
 
Thanks ST. I've been riding it almost every day (when not expecting thunderstorms) - I checked valves last year so will do so in the next day or so. I tend to ride about 2k miles a season...not much.

"I would ditch them and go to one of the systems out now on the market." I have been trying to get an Alpha 3 but has not avail due to an issue with the module I believe...I did some research and not sure I want the Dyna III, I may reconsider as I really want to convert my points - I'll check those and timing as well.

I'll report back,

Best Chuck
 
Have the valves been upgraded for unleaded fuel? How many valve adjustments have you done? Is there a pattern of them closing?
 
Looks like

Well, Chuck, it looks like you are on the right path. Most likely it will be something simple.

I have looked at the Alpha system as a possible replacement system for my RS if the Dyna ever craps out. The Alpha system is almost identical to the system BMW went with in 81 and is on my 84 RT, Very easy to install, and trouble shoot if any problems. Only difference between the system for the 84 and your bike would be there is no bean can, the Hall effect plate takes the place of the points. St.
 
Hi I'm the second owner - I've had it for over 5 years. I've done several valve adjustments and I don't believe they change much, but I will make more detailed notes going forward. I don't think the valves have been upgraded...

St. - reviewing all the electronic ignition options (three I guess? Boyer, Dyna and Alpha), I really want to hold out for the Alpha...

thanks, Chuck
 
Reporting in: I checked the valves and timing. The timing was spot on, but valves on the right side were off: the intake was essentially closed and the exhaust was a bit loose - the other side was spot on. Yes, I'll watch this and check again after some rides. I did take it for a test ride and it was better!

What causes the valves to close like that?

thanks for your input.

Best Chuck
 
Chuck -

It wouldn't be the first time...or the last!...but it's important to be sure and rotate the engine 360 degrees after setting (or checking) valve clearances on one side. Once done if you don't rotate the engine, then the other side will be tight.

If you didn't do any of that, yeah about all you can do is keep an eye on things. Make note of the ticking sound side-to-side...put your head down the left side then over to the right...if that sound changes, then the clearances are changing.
 
Thanks Kurt, yes I did turn the engine over several times and checked the valves each time. I'll pay close attention going forward.

Regards,
Chuck
 
Why?

It is a good question for the engineers on the forum, why is it the valves have to be adjusted every 15K miles? LOL, I post this as a lark but if you think about it, what does in fact make the valves loosen or tighten? Oh sure, there is with a good oil a minuscule amount of wear on the cam, push rod and lifters. But, the valve adjusters are tight, I have yet to find one of mine loose, so, why do the valves get so far out of adjustment?

Points I can see getting out because of the plastic wear block wearing. I can see carbs getting out of adjustment due to cable stretch and minor erosion of the needles and jets.

Glad to hear things are running better, have fun riding. St.
 
Final report in:

So the idle had gotten better after a valve adjust - as mentioned in an early post, but I ended up getting a Boyer electronic ignition - super easy to instal and time. Made a big difference in idle, very stable (after it was fully warmed) and was very smooth at speed! Glad i did it - thanks for encouragement.

Regards,
Chuck
 
Happy

You will be very happy to get rid of points. Once you get the Boyer set up and the timing set, it is pretty much one less thing to have to constantly adjust. Best thing you could do for smooth running. performance and maintenance.

Glad the bike is running well, enjoy. St.
 
STEVENRANKIN said:
It is a good question for the engineers on the forum, why is it the valves have to be adjusted every 15K miles? LOL, I post this as a lark but if you think about it, what does in fact make the valves loosen or tighten? Oh sure, there is with a good oil a minuscule amount of wear on the cam, push rod and lifters. But, the valve adjusters are tight, I have yet to find one of mine loose, so, why do the valves get so far out of adjustment?

Points I can see getting out because of the plastic wear block wearing. I can see carbs getting out of adjustment due to cable stretch and minor erosion of the needles and jets.

Glad to hear things are running better, have fun riding. St.
Click to expand...

The metallurgy in 1972 was designed for leaded fuel. A side-benefit of lead is lubrication of the valves and seats. With unleaded fuel, the valves will eventually beat the seats down and the symptom is closed valve lash. Apparently, once it really gets going, the beat-down accelerates.
However, there are examples of engines from that era not showing much in the way of closed valve lash.
The solution is upgraded metallurgy of valves and seats. Several shops offer this such as Porter.
 
The metallurgy for the '81-84 models was a poor upgrade for the unleaded fuel. The valve seats were a tool steel that didn't transmit heat well away from the valve face into the head, so the heat generated was retained in the valve face. The valve faces ended up warping or tuliping and the result was the same issue with valve lash closing up. They got the metallurgy right for 1985-on. Ted Porter is top notch with Airhead head work!!
 
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