Rookie needing assistance

Hi Everyone,

I have a 1972 Norton fresh off a total rebuild. 100 miles driven so far. It was running perfectly until 2 weeks ago.

Symptoms: Right cylinder not firing properly. Popping and back firing. Idles fine, but dies when I give throttle.

Carbs: New Amals (not premier)
Ignition: Tri-spark


What I tried:
-I swapped sparkplug leads and problem was still isolated to right side
-Installed new plugs
-I removed the right carb three times, soaked it in pine sol, shot it with air gun and carb cleaner, and air passage is clear (you can suck air through it with your mouth and hear the air when you put your finger over the hole).
-Needle appears to be seating fine.
-Floats / pins are in proper place and the gasket is not interfering
-I noticed some rust in the fuel line filter, so I removed the tank and got rid of the rust while I had it off the bike. I also installed fuel filters.
-there is gas in the bike and in the fuel lines

Any thoughts?

Cheers,
Gatsby

Dual coils? Try swapping coils.

Slick

EDIT:

Re read your post. When you swapped the spark plug leads did you swap the complete wire or did you take it off the plugs and swap to the other leaving the coil end attached?

gatsby said:

Hi Everyone,

I have a 1972 Norton fresh off a total rebuild. 100 miles driven so far. It was running perfectly until 2 weeks ago.

Symptoms: Right cylinder not firing properly. Popping and back firing. Idles fine, but dies when I give throttle.

Carbs: New Amals (not premier)
Ignition: Tri-spark


What I tried:
-I swapped sparkplug leads and problem was still isolated to right side
-Installed new plugs
-I removed the right carb three times, soaked it in pine sol, shot it with air gun and carb cleaner, and air passage is clear (you can suck air through it with your mouth and hear the air when you put your finger over the hole).
-Needle appears to be seating fine.
-Floats / pins are in proper place and the gasket is not interfering
-I noticed some rust in the fuel line filter, so I removed the tank and got rid of the rust while I had it off the bike. I also installed fuel filters.
-there is gas in the bike and in the fuel lines

Any thoughts?

Cheers,
Gatsby

Click to expand...

New engine? Start with the basics:
Throw a timing light on both plug wires to remove any doubt about the ignition firing. Since you already eliminated plugs and wires, try the coils.
Remove the air filter and check for even slide movement, as in, are the carbs properly synced? Not likely since it was running fine before, but it's possible the right-hand side cable let go.
Gently pull the cables at the carb tops one at a time to verify that only the left cylinder is the one running.
Puff a bit of WD-40 or similar aerosol into the carb mouths to see if it won't momentarily light off the offending cylinder.
Also, check this out for greater insight: http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html Note the first cut-away and following pencil drawing show two holes in the green zone. These must both be clear to give good transition from idle to part-throttle operation. You may need to go back a forth time to verify liquid shoots out of both orifices.

Make sure the valve clearances haven't gone tight during the break-in period. I know a tight valve is more likely to kill the idle first, but you never know with these bikes.
Compare compression left to right.

It sounds like carbs based on your description, but, as we all know, 90% of carby issues are ignition related, and vise-versa...

Nathan

Thanks for the quick responses.

Jim and slick – I forgot to mention I am running a CNW single coil conversion, so I can’t swap the coils.

Nathan – I will check for ignition with the Tri Spark test button. I puffed aerosol carb cleaner into the carb and did not get a flame, but the motor sputtered. I also get a light mist of fuel on my air box from the carb when it runs with the carb boot off. This is apparent as the new paint on the air box cover is deteriorating. I will also swap out the carb bodies with one that my friend gave me.

Cheers,
Gatsby

Sometimes we all overlook the most obvious ..... try swapping spark plugs.

Slick

Hi Slick, unfortunately I tried that already. I would welcome an obvious fix though Thanks for your input!

Cheers,
Gatsby

gatsby said:

Symptoms: Right cylinder not firing properly. Popping and back firing. Idles fine, but dies when I give throttle.

Gatsby

Click to expand...

Re-sync the slides? It's not uncommon to have to do this a couple time. Adjusters move and cables slip.

Like Nathan said, make sure all 3 ports on each carb are open, not just 2 ports. Carb cleaner in one port should come out the other 2. Try them all.

I'll bet dollars to donuts one or more valve lash adjusters have loosened or tightened up...

Compression check?

Gatsby, if you read my latest "pop, fart, sneeze" thread, you will see that I had a very similar problem with a very similar ignition set up as you and went through the entire bike from valve gaps, valve lift, changed numerous ignition parts, swapped coils, and pretty much rechecked all the wiring...

I took the carbs off proabably 4 or 5 times. blew them out a few times, Poked them with a guitar string a few times, and generally flooded them with carb cleaner every time... None of this worked, but I was on the right track because it was the carb. This should make sense since my misfire was only on the right side,... so it shouldn't have been ignition because a boyer and a dual coil are a "lost spark" application which either fires both or neither, not just one or the other.

As it turned out, it was the idle jet that was clogged shut. It seemed to me that the bike was idling somehow on both cylinders, and the misfire started when I raised the throttle, after the throttle was about half open, the right cylinder would kick in and the bike would run at high RPM's. This should make sense in hindsight because the idle circuit is not in play at greater throttle opening... (I guess it took me a while to observe this and have it sink into my brain)

After searching the forum with the search function at the top right of the page with my symptoms many times, I found many threads about the idle circuit being blocked and causing misfires at the lower RPM ranges. I had poked that idle jet 1000 times, but I was certain it had to be the culprit because of all the other things I eliminated by substitution. I looked for a screw and tap that would fit in the casting if I drilled the back side of the idle jet port and found that I had something very close to the right size, so I drilled it.

The guitar string was doing nothing all the times that I poked the jet from the idle air screw side. The jet was plugged completely. It took a sewing needle that I gripped in a visegrip to poke the crap out of the jet. At the point I found the clog I couldn't see through the jet to daylight past the idle air screw port. Once I cleared the pilot jet with the sewing needle, I knew I had fixed the carb because I could see daylight through the pilot jet with the idle air screw removed from the other side! Now, I just had to thread the hole that I drilled and seal it up with a set screw, which was pretty simple.

The bike fired first kick, No pop, fart, sneeze. running strong like it has all summer.. before it developed the misfire.

Edited to add: I see your original post says the carbs are new, so a plugged pilot jet would be less likely, but the symptoms match up to mine which was a misfire in the low RPM range. Perhaps your missfire is a result of a misplaced throttle body needle... but I would bet it's your carb.

fresh rebuild? Try checking the head gasket torque.

Hi Everyone,
Thank you for all of the replies. I have been running through all above recommendations, as well a the "pop and sneeze" thread. I am happy to report that my carb has clear passage, and my Fender acoustic is current need of a "b" string. I also purchased a compression tester today, and slapped it on the head. The left side was around 154, and the right side was 0. I realize this is not good. I have yet to start my research on what to do next, but this is an update of where I am.
Cheers,
Gatsby

gatsby said:

The left side was around 154, and the right side was 0.

Click to expand...

Ouch!! Do you have access to a leak-down tester? With one of those, you can pressurize the cylinder and listen for hissing/gurgling from intake/exhaust/oil breather. As said earlier, check valve lash. I'm guessing you have a tight exhaust valve.

Best of luck,
Nathan

you do know that the throttle must be held fully open while kicking for the compression test?

Nater_Potater said:

gatsby said:

The left side was around 154, and the right side was 0.

Click to expand...

Ouch!! Do you have access to a leak-down tester? With one of those, you can pressurize the cylinder and listen for hissing/gurgling from intake/exhaust/oil breather. As said earlier, check valve lash. I'm guessing you have a tight exhaust valve.

Best of luck,
Nathan

Click to expand...

I would agree with Nathan's tight valve lash assessment, or perhaps a bent valve caused by something such as a screw that might have gotten into the cylinder. Even a burned valve will yield some compression. Back off on the lash adjuster, rotate the engine thru a cycle, and ensure the valve has nothing holding it off the seat, then do the compression check. If you still come up zero, you might pull the exhaust header off and have a look at the valve.

Good luck,

Slick

PS: Did you or builder prelude with STP? Comnoz has shown this can cause valves to stick.

Annnnnddd...the winner of the "0" compression diagnosis contest goes to......Slick! I have a bent valve, caused by a bum piston. I owe a big thanks to a fellow forum member who came over to my house to help me and made the job look easy.



You can see daylight under the valve



Very dissipointing, but at least I know what the problem is, and there is an end in sight.

Thanks everyone!
Gatsby

Take a careful look at the valve guide. It might have suffered as well.

"Bum" piston? What is/was problem? I see a nick on the valve pocket of the piston. If wrong pistons were fitted, then other side is a potential problem as well. Was the head milled? Thin head gasket? You need to identify source of problem, or it may re-occur.

Slick

Hi Gatsby.
Seems odd that a piston would smack a valve after 100 mile and not at initial start-up after rebuild.
Perhaps delve further for a cause to your problem e.g. cam chain set-up, tension, etc.
Ta.