7 replies [Last post]
312Icarus
312Icarus's picture
 Offline
Joined: 07/15/2016
Posts: 355

‘68/2 US

Recent engine rebuild ~500 miles ago. Timing static and dynamic is spot on, carbs are well adjusted, starts on first gentle kick. I do have mismatched main jets however. The plugs look good, one just a touch rich, the other perfect (new plugs).

When I accelerate hard to near redline in second for example, I get a couple of back fire pops only on the right cylinder. Any thoughts? My best guess is a jet issue.

Icarus

Twocams
Twocams's picture
 Offline
VBMWMO #8750
Joined: 03/16/2014
Posts: 699
Any thoughts? Only one, why

Any thoughts? Only one, why would you push an old push rod engine to the limit anyway? OK, its rebuilt with 500 whole miles on the engine.
Guess Im just old fashion, I like to see how long things will last.

__________________

Twocams
69 R69S 03 K1200GT
92 R100RT

312Icarus
312Icarus's picture
 Offline
Joined: 07/15/2016
Posts: 355
Well, I don’t really push it

Well, I don’t really push it to the red line, but “My redline” some where around 35 mph in second just for a second, trying to vary the speed to break in the rings. I don’t fire wall the throttle, just run it up a bit.

Icarus

malmac
malmac's picture
 Offline
VBMWMO #8751
Toowoomba, Australia
Joined: 06/29/2014
Posts: 288
un burnt fuel in muffler

If there is a "popping" in the muffler, would that be unburnt fuel vapour being pumped out of the right cylinder?

I can only think of three possible reasons - there may well be more.

1. The fuel mixture is so rich on the right cylinder that not all the fuel is burnt during the combustion process.

2. Raw fuel, could escape through the exhaust valve on the compression stroke if the exhaust valve is leaking.

3. Exhaust header pipe may not be sealing properly (or header to muffler - more likely), allowing oxygen rich air into the right exhaust pipe, one of the above conditions would also have to be true - however with these rather unsophisticated engines I expect total fuel burning is probably unlikely even in a perfect engine.

Always interesting little mysteries to ponder on.

Mal

__________________

mal - R69s
Toowoomba- Australia

johnpst
johnpst's picture
 Offline
Hawaii
Joined: 03/22/2016
Posts: 73
SORRY MAL, GOTTA DISAGREE

Aloha,

Popping during deceleration, like you describe, is generally a lean mixture. Believe it or not. The mixture in the cylinder is too lean to burn under the compression and fairly weak temperature of the spark plug source. The exhaust system may be hot enough along with the new air/fuel environment to cause it to pop. Rich mixture generally results in a backfire.

Check your plugs. If they are running close to normal, light-ish brown, then look for an air leak.

Now, to Mal's defense, we need to define popping. Some peoples pop is another's backfire.

Good luck,
John

__________________

John
55 - R50, 06-R1200RT, 96-M900, 10-TU250x

312Icarus
312Icarus's picture
 Offline
Joined: 07/15/2016
Posts: 355
Problem solved...Turns out to

Problem solved...Turns out to be a loose exhaust nut on the right hand side. No backfiring now. Still have a chirp/squeal/squeak at mid rpms that I can’t find however!

Thanks for the help,

Icarus

Daves79x
Daves79x's picture
 Offline
VBMWMO #9030
Joined: 08/09/2015
Posts: 326
Gotta Say

I must say, about the idea of running these things hard, why would you not if everything's right? They are very under-stressed at designed max rpms. I have 600 miles on my complete R50 rebuild, ran varied and gently at first, changed the oil and cleaned the sump twice. I now feel quite confident running the bike out in each gear occasionally. I know others that flog the daylights out of these things and they keep coming back for more!

Dave

__________________

Dave

Slash2
Slash2's picture
 Offline
VBMWMO #9015
Joined: 10/17/2015
Posts: 269
I'll second that one Dave!

This guy isn't blowing smoke either! Dave came out to my farm last fall to go for a nice leisurely ride on some of our mutual favorite country roads. I on my 1964 R60/2, Dave on his newly restored to perfection 1956? R50. (Forgive me if I got the year wrong Dave, as I think I'm pretty close) At any rate, this was the first time I'd ridden with Dave and his bike is beyond perfect, so I expected a rather stodgy ride punctuated by frequent stops to polish his flawless Dover white paint. To be perfectly honest, I was somewhat surprised he was even willing to ascend my rather long and rustic driveway.

Well, I had no idea what I was getting myself into. But soon I came to find that Dave likes to punch it off the line with gusto and run that R50 like he stole it! (And maybe he did?) Just kidding Dave! But what followed was a spirited ride that was an absolute hoot and had me wishing I'd brought my 1968 R69US out for the flogging instead! Next time Dave I'll be ready!

__________________

64' R60/2 - 66' R27 - 51' R67 - 68' R69S
88' R100RS - 06' K12R

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.