R69S hesitation, crackling sound, uneven power at 40mph

[rsolin]

Hi All,

This is a weird one that I'm hoping someone can help with...please. My '68 R69S exhibits a hesitation, crackling sound (almost like a leak in exhaust) and non-smooth power transition at about 40 mph. When i get above about 50 mph it "goes away", or quite possibly it's being covered over at higher speeds. I'm wondering if it might be due to a bad crankcase breather valve, in which case i'm hoping someone can point me to instruction, photos, etc to diagnose and repair (i've found very little online, in shop manuals, in C. Betjemann's bible on how to diagnose, inspect, repair). I've ruled out (the hard way) pretty much everything else I know of -- please see breadcrumbs below.

- 3rd over done; broken-in (it's not compression)
- valves, seats rebuilt (done right by Ted Porter)
- carbs rebuilt; no leaks. Floats levels adjusted to spec. Fuel is not restricted (flows evenly on both sides).
- spark wires, boots, plugs replaced
- PowerDynamo installed, so it shouldn't be timing (yes, i know the purists do not like these things

Supplemental:

The left side push rod snapped a few years ago under strain going up a hill. After replacing the pushrod and adjusting valves, it ran but with limited power. Also, the hesitation and crackling sound then occurred between 20 and 60 mph. After 2nd-over and valve job, power is good (it will do 90 mph), yet the symptoms above are presenting. Note that the speed band at which the hesitation, crackling sound is occurring is different than before, i.e. it now occurs between 40-50 mph.

I would be most grateful for ideas, recommendations, pointers, exorcisms, prayers!

thanks in advance,
Roger

[Daves79x]

These pushrods are pretty robust. To snap one, I'd say your valve lash was miss-adjusted, possibly not adjusted on the compression stroke? I'd also be checking to be sure other pushrods are not bent, since you broke one.

Dave

[rsolin]

Thanks, Dave. The pushrods are confirmed straight. Valves, related are no longer an issue.

[malmac]

The crackling noise may be un-burnt fuel igniting in your exhaust - an air leak between muffler and head pipe may contribute to this.

How do your plugs look. Is the bike running rich?
Have you checked your main jet size and your needle height.

You may be running rich in that mid range because your needle jet is too high.
Once you are running on the straight main jet with the needle not playing a part, the problem goes away.

Also your needle jet might be worn in the mid range area - so it is not the height but the wear.

Just a thought but worth a look.
Enjoy the journey of finding the solution.

Mal

[rsolin]

Hey Mal,.

Thank you! Yes, it's running rich (on purpose, as I was breaking in new top end). Needles and jets are new and should be correct for R69S. I will adjust needles and see if that does the trick.

Again, thank you!

Best
Roger

[rsolin]

Circling back after leaning out mixture (adjusting needle jet height), it now runs great. After all the remediations, this was the "last" one to make it run great again.

[malmac]

Glad you have things working to your satisfaction.

Not many bikes that are better than an R69s when running at it's best, when it comes to classic bikes.
Yes I am biased, and happy to be so.

Mal